Aspects of the rationale for the Women's Health Trial

The effect of diet and nutrition on T cell function in cancer

Cancer can be considered one of the most threatening diseases to human health, and immunotherapy, especially T-cell immunotherapy, is the most promising treatment for cancers. Diet therapy is widely concerned in cancer because of its safety and fewer side effects. Many studies have shown that both the function of T cells and the progression of cancer can be affected by nutrients in the diet. In fact, it is challenging for T cells to infiltrate and eliminate cancer cells in tumor microenvironment, because of the harsh metabolic condition. The intake of different nutrients has a great influence on the proliferation, activation, differentiation and exhaustion of T cells. In this review, we summarize the effects of typical amino acids, lipids, carbohydrates and other nutritional factors on T cell functions and provide future perspectives for dietary treatment of cancer based on modifications of T cell functions.

Reduction in saturated fat intake for cardiovascular disease

BACKGROUND

Reducing saturated fat reduces serum cholesterol, but effects on other intermediate outcomes may be less clear. Additionally, it is unclear whether the energy from saturated fats eliminated from the diet are more helpfully replaced by polyunsaturated fats, monounsaturated fats, carbohydrate or protein.

OBJECTIVES

To assess the effect of reducing saturated fat intake and replacing it with carbohydrate (CHO), polyunsaturated (PUFA), monounsaturated fat (MUFA) and/or protein on mortality and cardiovascular morbidity, using all available randomised clinical trials.

SEARCH METHODS

We updated our searches of the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (Ovid) and Embase (Ovid) on 15 October 2019, and searched Clinicaltrials.gov and WHO International Clinical Trials Registry Platform (ICTRP) on 17 October 2019.

SELECTION CRITERIA

Included trials fulfilled the following criteria: 1) randomised; 2) intention to reduce saturated fat intake OR intention to alter dietary fats and achieving a reduction in saturated fat; 3) compared with higher saturated fat intake or usual diet; 4) not multifactorial; 5) in adult humans with or without cardiovascular disease (but not acutely ill, pregnant or breastfeeding); 6) intervention duration at least 24 months; 7) mortality or cardiovascular morbidity data available.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed inclusion, extracted study data and assessed risk of bias. We performed random-effects meta-analyses, meta-regression, subgrouping, sensitivity analyses, funnel plots and GRADE assessment.

MAIN RESULTS

We included 15 randomised controlled trials (RCTs) (16 comparisons, 56,675 participants), that used a variety of interventions from providing all food to advice on reducing saturated fat. The included long-term trials suggested that reducing dietary saturated fat reduced the risk of combined cardiovascular events by 17% (risk ratio (RR) 0.83; 95% confidence interval (CI) 0.70 to 0.98, 12 trials, 53,758 participants of whom 8% had a cardiovascular event, I² = 67%, GRADE moderate-quality evidence). Meta-regression suggested that greater reductions in saturated fat (reflected in greater reductions in serum cholesterol) resulted in greater reductions in risk of CVD events, explaining most heterogeneity between trials. The number needed to treat for an additional beneficial outcome (NNTB) was 56 in primary prevention trials, so 56 people need to reduce their saturated fat intake for ~four years for one person to avoid experiencing a CVD event. In secondary prevention trials, the NNTB was 53. Subgrouping did not suggest significant differences between replacement of saturated fat calories with polyunsaturated fat or carbohydrate, and data on replacement with monounsaturated fat and protein was very limited. We found little or no effect of reducing saturated fat on all-cause mortality (RR 0.96; 95% CI 0.90 to 1.03; 11 trials, 55,858 participants) or cardiovascular mortality (RR 0.95; 95% CI 0.80 to 1.12, 10 trials, 53,421 participants), both with GRADE moderate-quality evidence. There was little or no effect of reducing saturated fats on non-fatal myocardial infarction (RR 0.97, 95% CI 0.87 to 1.07) or CHD mortality (RR 0.97, 95% CI 0.82 to 1.16, both low-quality evidence), but effects on total (fatal or non-fatal) myocardial infarction, stroke and CHD events (fatal or non-fatal) were all unclear as the evidence was of very low quality. There was little or no effect on cancer mortality, cancer diagnoses, diabetes diagnosis, HDL cholesterol, serum triglycerides or blood pressure, and small reductions in weight, serum total cholesterol, LDL cholesterol and BMI. There was no evidence of harmful effects of reducing saturated fat intakes.

AUTHORS' CONCLUSIONS

The findings of this updated review suggest that reducing saturated fat intake for at least two years causes a potentially important reduction in combined cardiovascular events. Replacing the energy from saturated fat with polyunsaturated fat or carbohydrate appear to be useful strategies, while effects of replacement with monounsaturated fat are unclear. The reduction in combined cardiovascular events resulting from reducing saturated fat did not alter by study duration, sex or baseline level of cardiovascular risk, but greater reduction in saturated fat caused greater reductions in cardiovascular events.

Effects of total fat intake on body fatness in adults

BACKGROUND

The ideal proportion of energy from fat in our food and its relation to body weight is not clear. In order to prevent overweight and obesity in the general population, we need to understand the relationship between the proportion of energy from fat and resulting weight and body fatness in the general population.

OBJECTIVES

To assess the effects of proportion of energy intake from fat on measures of body fatness (including body weight, waist circumference, percentage body fat and body mass index) in people not aiming to lose weight, using all appropriate randomised controlled trials (RCTs) of at least six months duration.

SEARCH METHODS

We searched CENTRAL, MEDLINE, Embase, Clinicaltrials.gov and the WHO International Clinical Trials Registry Platform (ICTRP) to October 2019. We did not limit the search by language.

SELECTION CRITERIA

Trials fulfilled the following criteria: 1) randomised intervention trial, 2) included adults aged at least 18 years, 3) randomised to a lower fat versus higher fat diet, without the intention to reduce weight in any participants, 4) not multifactorial and 5) assessed a measure of weight or body fatness after at least six months. We duplicated inclusion decisions and resolved disagreement by discussion or referral to a third party.

DATA COLLECTION AND ANALYSIS

We extracted data on the population, intervention, control and outcome measures in duplicate. We extracted measures of body fatness (body weight, BMI, percentage body fat and waist circumference) independently in duplicate at all available time points. We performed random-effects meta-analyses, meta-regression, subgrouping, sensitivity, funnel plot analyses and GRADE assessment.

MAIN RESULTS

We included 37 RCTs (57,079 participants). There is consistent high-quality evidence from RCTs that reducing total fat intake results in small reductions in body fatness; this was seen in almost all included studies and was highly resistant to sensitivity analyses (GRADE high-consistency evidence, not downgraded). The effect of eating less fat (compared with higher fat intake) is a mean body weight reduction of 1.4 kg (95% confidence interval (CI) -1.7 to -1.1 kg, in 53,875 participants from 26 RCTs, I² = 75%). The heterogeneity was explained in subgrouping and meta-regression. These suggested that greater weight loss results from greater fat reductions in people with lower fat intake at baseline, and people with higher body mass index (BMI) at baseline. The size of the effect on weight does not alter over time and is mirrored by reductions in BMI (MD -0.5 kg/m², 95% CI -0.6 to -0.3, 46,539 participants in 14 trials, I² = 21%), waist circumference (MD -0.5 cm, 95% CI -0.7 to -0.2, 16,620 participants in 3 trials; I² = 21%), and percentage body fat (MD -0.3% body fat, 95% CI -0.6 to 0.00, P = 0.05, in 2350 participants in 2 trials; I² = 0%). There was no suggestion of harms associated with low fat diets that might mitigate any benefits on body fatness. The reduction in body weight was reflected in small reductions in LDL (-0.13 mmol/L, 95% CI -0.21 to -0.05), and total cholesterol (-0.23 mmol/L, 95% CI -0.32 to -0.14), with little or no effect on HDL cholesterol (-0.02 mmol/L, 95% CI -0.03 to 0.00), triglycerides (0.01 mmol/L, 95% CI -0.05 to 0.07), systolic (-0.75 mmHg, 95% CI -1.42 to -0.07) or diastolic blood pressure(-0.52 mmHg, 95% CI -0.95 to -0.09), all GRADE high-consistency evidence or quality of life (0.04, 95% CI 0.01 to 0.07, on a scale of 0 to 10, GRADE low-consistency evidence).

AUTHORS' CONCLUSIONS

Trials where participants were randomised to a lower fat intake versus a higher fat intake, but with no intention to reduce weight, showed a consistent, stable but small effect of low fat intake on body fatness: slightly lower weight, BMI, waist circumference and percentage body fat compared with higher fat arms. Greater fat reduction, lower baseline fat intake and higher baseline BMI were all associated with greater reductions in weight. There was no evidence of harm to serum lipids, blood pressure or quality of life, but rather of small benefits or no effect.

Reduction in saturated fat intake for cardiovascular disease

BACKGROUND

Reducing saturated fat reduces serum cholesterol, but effects on other intermediate outcomes may be less clear. Additionally, it is unclear whether the energy from saturated fats eliminated from the diet are more helpfully replaced by polyunsaturated fats, monounsaturated fats, carbohydrate or protein.

OBJECTIVES

To assess the effect of reducing saturated fat intake and replacing it with carbohydrate (CHO), polyunsaturated (PUFA), monounsaturated fat (MUFA) and/or protein on mortality and cardiovascular morbidity, using all available randomised clinical trials.

SEARCH METHODS

We updated our searches of the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (Ovid) and Embase (Ovid) on 15 October 2019, and searched Clinicaltrials.gov and WHO International Clinical Trials Registry Platform (ICTRP) on 17 October 2019.

SELECTION CRITERIA

Included trials fulfilled the following criteria: 1) randomised; 2) intention to reduce saturated fat intake OR intention to alter dietary fats and achieving a reduction in saturated fat; 3) compared with higher saturated fat intake or usual diet; 4) not multifactorial; 5) in adult humans with or without cardiovascular disease (but not acutely ill, pregnant or breastfeeding); 6) intervention duration at least 24 months; 7) mortality or cardiovascular morbidity data available.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed inclusion, extracted study data and assessed risk of bias. We performed random-effects meta-analyses, meta-regression, subgrouping, sensitivity analyses, funnel plots and GRADE assessment.

MAIN RESULTS

We included 15 randomised controlled trials (RCTs) (16 comparisons, ~59,000 participants), that used a variety of interventions from providing all food to advice on reducing saturated fat. The included long-term trials suggested that reducing dietary saturated fat reduced the risk of combined cardiovascular events by 21% (risk ratio (RR) 0.79; 95% confidence interval (CI) 0.66 to 0.93, 11 trials, 53,300 participants of whom 8% had a cardiovascular event, I² = 65%, GRADE moderate-quality evidence). Meta-regression suggested that greater reductions in saturated fat (reflected in greater reductions in serum cholesterol) resulted in greater reductions in risk of CVD events, explaining most heterogeneity between trials. The number needed to treat for an additional beneficial outcome (NNTB) was 56 in primary prevention trials, so 56 people need to reduce their saturated fat intake for ~four years for one person to avoid experiencing a CVD event. In secondary prevention trials, the NNTB was 32. Subgrouping did not suggest significant differences between replacement of saturated fat calories with polyunsaturated fat or carbohydrate, and data on replacement with monounsaturated fat and protein was very limited. We found little or no effect of reducing saturated fat on all-cause mortality (RR 0.96; 95% CI 0.90 to 1.03; 11 trials, 55,858 participants) or cardiovascular mortality (RR 0.95; 95% CI 0.80 to 1.12, 10 trials, 53,421 participants), both with GRADE moderate-quality evidence. There was little or no effect of reducing saturated fats on non-fatal myocardial infarction (RR 0.97, 95% CI 0.87 to 1.07) or CHD mortality (RR 0.97, 95% CI 0.82 to 1.16, both low-quality evidence), but effects on total (fatal or non-fatal) myocardial infarction, stroke and CHD events (fatal or non-fatal) were all unclear as the evidence was of very low quality. There was little or no effect on cancer mortality, cancer diagnoses, diabetes diagnosis, HDL cholesterol, serum triglycerides or blood pressure, and small reductions in weight, serum total cholesterol, LDL cholesterol and BMI. There was no evidence of harmful effects of reducing saturated fat intakes.

AUTHORS' CONCLUSIONS

The findings of this updated review suggest that reducing saturated fat intake for at least two years causes a potentially important reduction in combined cardiovascular events. Replacing the energy from saturated fat with polyunsaturated fat or carbohydrate appear to be useful strategies, while effects of replacement with monounsaturated fat are unclear. The reduction in combined cardiovascular events resulting from reducing saturated fat did not alter by study duration, sex or baseline level of cardiovascular risk, but greater reduction in saturated fat caused greater reductions in cardiovascular events.

Clinical research study designs: The essentials

In clinical research, our aim is to design a study which would be able to derive a valid and meaningful scientific conclusion using appropriate statistical methods. The conclusions derived from a research study can either improve health care or result in inadvertent harm to patients. Hence, this requires a well-designed clinical research study that rests on a strong foundation of a detailed methodology and governed by ethical clinical principles. The purpose of this review is to provide the readers an overview of the basic study designs and its applicability in clinical research.

Evaluating Public Health Interventions: 4. The Nurses' Health Study and Methods for Eliminating Bias Attributable to Measurement Error and Misclassification

The Nurses' Health Study and many other large longitudinal cohorts around the world use the food frequency questionnaire to assess dietary intake over time, and to relate diet to health. Controversies concerning this questionnaire's ability to adequately measure diet have led to a flurry of methods for evaluating the magnitude of measurement error and misclassification in exposure assessment, and for correcting the point and interval estimates of effect on the basis of these assessment methods for this error. Nurses' Health Study investigators have been in the forefront of these developments and their applications, although hundreds of other investigators have also used them. This commentary provides an overview of the methods and their uses, and concludes with remarks on their potential applications in the evaluation of public health interventions.

Methodology Series Module 7: Ecologic Studies and Natural Experiments

In this module, we have discussed study designs that have not been covered in the previous modules - ecologic studies and natural experiments. In an ecologic study, the unit of analysis is a group or aggregate rather than the individual. It may be the characteristics of districts, states, or countries. For example, per capita income across countries, income quintiles across districts, and proportion of college graduates in states. If the data already exist (such as global measures and prevalence of diseases, data sets such as the National Family Health Survey, census data), then ecologic studies are cheap and data are easy to collect. However, one needs to be aware of the "ecologic fallacy." The researcher should not interpret ecologic level results at the individual level. In "natural experiments," the researcher does not assign the exposure (as is the case in interventional studies) to the groups in the study. The exposure is assigned by a natural process. This may be due to existing policies or services (example, one city has laws against specific vehicles and the other city does not); changes in services or policies; or introduction of new laws (such helmet for bikers and seat-belts for cars). We would like to encourage researchers to explore the possibility of using these study designs to conduct studies.

Diet and risk of breast cancer

Diet may play a role in both promoting and inhibiting human breast cancer development. In this review, nutritional risk factors such as consumption of dietary fat, meat, fiber, and alcohol, and intake of phytoestrogen, vitamin D, iron, and folate associated with breast cancer are reviewed. These nutritional factors have a variety of associations with breast cancer risk. Type of fat consumed has different effects on risk of breast cancer: consumption of meat is associated with heterocyclic amine (HCA) exposure; different types of plant fiber have various effects on breast cancer risk; alcohol consumption may increase the risk of breast cancer by producing acetaldehyde and reactive oxygen species (ROS); intake of phytoestrogen may reduce risk of breast cancer through genomic and non-genomic action; vitamin D can reduce the risk of breast cancer by inhibiting the process of cancer invasion and metastasis; intake of dietary iron may lead to oxidative stress, DNA damage, and lipid peroxidation; and lower intake of folate may be linked to a higher risk of breast cancer.

Effects of total fat intake on body weight

BACKGROUND

In order to prevent overweight and obesity in the general population we need to understand the relationship between the proportion of energy from fat and resulting weight and body fatness in the general population.

OBJECTIVES

To assess the effects of proportion of energy intake from fat on measures of weight and body fatness (including obesity, waist circumference and body mass index) in people not aiming to lose weight, using all appropriate randomised controlled trials (RCTs) and cohort studies in adults, children and young people

SEARCH METHODS

We searched CENTRAL to March 2014 and MEDLINE, EMBASE and CINAHL to November 2014. We did not limit the search by language. We also checked the references of relevant reviews.

SELECTION CRITERIA

Trials fulfilled the following criteria: 1) randomised intervention trial, 2) included children (aged ≥ 24 months), young people or adults, 3) randomised to a lower fat versus usual or moderate fat diet, without the intention to reduce weight in any participants, 4) not multifactorial and 5) assessed a measure of weight or body fatness after at least six months. We also included cohort studies in children, young people and adults that assessed the proportion of energy from fat at baseline and assessed the relationship with body weight or fatness after at least one year. We duplicated inclusion decisions and resolved disagreement by discussion or referral to a third party.

DATA COLLECTION AND ANALYSIS

We extracted data on the population, intervention, control and outcome measures in duplicate. We extracted measures of weight and body fatness independently in duplicate at all available time points. We performed random-effects meta-analyses, meta-regression, subgrouping, sensitivity and funnel plot analyses.

MAIN RESULTS

We included 32 RCTs (approximately 54,000 participants) and 30 sets of analyses of 25 cohorts. There is consistent evidence from RCTs in adults of a small weight-reducing effect of eating a smaller proportion of energy from fat; this was seen in almost all included studies and was highly resistant to sensitivity analyses. The effect of eating less fat (compared with usual diet) is a mean weight reduction of 1.5 kg (95% confidence interval (CI) -2.0 to -1.1 kg), but greater weight loss results from greater fat reductions. The size of the effect on weight does not alter over time and is mirrored by reductions in body mass index (BMI) (-0.5 kg/m(2), 95% CI -0.7 to -0.3) and waist circumference (-0.3 cm, 95% CI -0.6 to -0.02). Included cohort studies in children and adults most often do not suggest any relationship between total fat intake and later measures of weight, body fatness or change in body fatness. However, there was a suggestion that lower fat intake was associated with smaller increases in weight in middle-aged but not elderly adults, and in change in BMI in the highest validity child cohort.

AUTHORS' CONCLUSIONS

Trials where participants were randomised to a lower fat intake versus usual or moderate fat intake, but with no intention to reduce weight, showed a consistent, stable but small effect of low fat intake on body fatness: slightly lower weight, BMI and waist circumference compared with controls. Greater fat reduction and lower baseline fat intake were both associated with greater reductions in weight. This effect of reducing total fat was not consistently reflected in cohort studies assessing the relationship between total fat intake and later measures of body fatness or change in body fatness in studies of children, young people or adults.

Reduction in saturated fat intake for cardiovascular disease

BACKGROUND

Reducing saturated fat reduces serum cholesterol, but effects on other intermediate outcomes may be less clear. Additionally it is unclear whether the energy from saturated fats that are lost in the diet are more helpfully replaced by polyunsaturated fats, monounsaturated fats, carbohydrate or protein. This review is part of a series split from and updating an overarching review.

OBJECTIVES

To assess the effect of reducing saturated fat intake and replacing it with carbohydrate (CHO), polyunsaturated (PUFA) or monounsaturated fat (MUFA) and/or protein on mortality and cardiovascular morbidity, using all available randomised clinical trials.

SEARCH METHODS

We updated our searches of the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (Ovid) and EMBASE (Ovid) on 5 March 2014. We also checked references of included studies and reviews.

SELECTION CRITERIA

Trials fulfilled the following criteria: 1) randomised with appropriate control group; 2) intention to reduce saturated fat intake OR intention to alter dietary fats and achieving a reduction in saturated fat; 3) not multifactorial; 4) adult humans with or without cardiovascular disease (but not acutely ill, pregnant or breastfeeding); 5) intervention at least 24 months; 6) mortality or cardiovascular morbidity data available.

DATA COLLECTION AND ANALYSIS

Two review authors working independently extracted participant numbers experiencing health outcomes in each arm, and we performed random-effects meta-analyses, meta-regression, subgrouping, sensitivity analyses and funnel plots.

MAIN RESULTS

We include 15 randomised controlled trials (RCTs) (17 comparisons, ˜59,000 participants), which used a variety of interventions from providing all food to advice on how to reduce saturated fat. The included long-term trials suggested that reducing dietary saturated fat reduced the risk of cardiovascular events by 17% (risk ratio (RR) 0.83; 95% confidence interval (CI) 0.72 to 0.96, 13 comparisons, 53,300 participants of whom 8% had a cardiovascular event, I² 65%, GRADE moderate quality of evidence), but effects on all-cause mortality (RR 0.97; 95% CI 0.90 to 1.05; 12 trials, 55,858 participants) and cardiovascular mortality (RR 0.95; 95% CI 0.80 to 1.12, 12 trials, 53,421 participants) were less clear (both GRADE moderate quality of evidence). There was some evidence that reducing saturated fats reduced the risk of myocardial infarction (fatal and non-fatal, RR 0.90; 95% CI 0.80 to 1.01; 11 trials, 53,167 participants), but evidence for non-fatal myocardial infarction (RR 0.95; 95% CI 0.80 to 1.13; 9 trials, 52,834 participants) was unclear and there were no clear effects on stroke (any stroke, RR 1.00; 95% CI 0.89 to 1.12; 8 trials, 50,952 participants). These relationships did not alter with sensitivity analysis. Subgrouping suggested that the reduction in cardiovascular events was seen in studies that primarily replaced saturated fat calories with polyunsaturated fat, and no effects were seen in studies replacing saturated fat with carbohydrate or protein, but effects in studies replacing with monounsaturated fats were unclear (as we located only one small trial). Subgrouping and meta-regression suggested that the degree of reduction in cardiovascular events was related to the degree of reduction of serum total cholesterol, and there were suggestions of greater protection with greater saturated fat reduction or greater increase in polyunsaturated and monounsaturated fats. There was no evidence of harmful effects of reducing saturated fat intakes on cancer mortality, cancer diagnoses or blood pressure, while there was some evidence of improvements in weight and BMI.

AUTHORS' CONCLUSIONS

The findings of this updated review are suggestive of a small but potentially important reduction in cardiovascular risk on reduction of saturated fat intake. Replacing the energy from saturated fat with polyunsaturated fat appears to be a useful strategy, and replacement with carbohydrate appears less useful, but effects of replacement with monounsaturated fat were unclear due to inclusion of only one small trial. This effect did not appear to alter by study duration, sex or baseline level of cardiovascular risk. Lifestyle advice to all those at risk of cardiovascular disease and to lower risk population groups should continue to include permanent reduction of dietary saturated fat and partial replacement by unsaturated fats. The ideal type of unsaturated fat is unclear.

Scientific decision making, policy decisions, and the obesity pandemic

Rising and epidemic rates of obesity in many parts of the world are leading to increased suffering and economic stress from diverting health care resources to treating a variety of serious, but preventable, chronic diseases etiologically linked to obesity, particularly type 2 diabetes mellitus and cardiovascular diseases. Despite decades of research into the causes of the obesity pandemic, we seem to be no nearer to a solution now than when the rise in body weights was first chronicled decades ago. The case is made that impediments to a clear understanding of the nature of the problem occur at many levels. These obstacles begin with defining obesity and include lax application of scientific standards of review, tenuous assumption making, flawed measurement and other methods, constrained discourse limiting examination of alternative explanations of cause, and policies that determine funding priorities. These issues constrain creativity and stifle expansive thinking that could otherwise advance the field in preventing and treating obesity and its complications. Suggestions are made to create a climate of open exchange of ideas and redirection of policies that can remove the barriers that prevent us from making material progress in solving a pressing major public health problem of the early 21st century.

Reduced or modified dietary fat for preventing cardiovascular disease

BACKGROUND

Reduction and modification of dietary fats have differing effects on cardiovascular risk factors (such as serum cholesterol), but their effects on important health outcomes are less clear.

OBJECTIVES

To assess the effect of reduction and/or modification of dietary fats on mortality, cardiovascular mortality, cardiovascular morbidity and individual outcomes including myocardial infarction, stroke and cancer diagnoses in randomised clinical trials of at least 6 months duration.

SEARCH METHODS

For this review update, the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE and EMBASE, were searched through to June 2010. References of Included studies and reviews were also checked.

SELECTION CRITERIA

Trials fulfilled the following criteria: 1) randomised with appropriate control group, 2) intention to reduce or modify fat or cholesterol intake (excluding exclusively omega-3 fat interventions), 3) not multi factorial, 4) adult humans with or without cardiovascular disease, 5) intervention at least six months, 6) mortality or cardiovascular morbidity data available.

DATA COLLECTION AND ANALYSIS

Participant numbers experiencing health outcomes in each arm were extracted independently in duplicate and random effects meta-analyses, meta-regression, sub-grouping, sensitivity analyses and funnel plots were performed.

MAIN RESULTS

This updated review suggested that reducing saturated fat by reducing and/or modifying dietary fat reduced the risk of cardiovascular events by 14% (RR 0.86, 95% CI 0.77 to 0.96, 24 comparisons, 65,508 participants of whom 7% had a cardiovascular event, I(2) 50%). Subgrouping suggested that this reduction in cardiovascular events was seen in studies of fat modification (not reduction - which related directly to the degree of effect on serum total and LDL cholesterol and triglycerides), of at least two years duration and in studies of men (not of women). There were no clear effects of dietary fat changes on total mortality (RR 0.98, 95% CI 0.93 to 1.04, 71,790 participants) or cardiovascular mortality (RR 0.94, 95% CI 0.85 to 1.04, 65,978 participants). This did not alter with sub-grouping or sensitivity analysis.Few studies compared reduced with modified fat diets, so direct comparison was not possible.

AUTHORS' CONCLUSIONS

The findings are suggestive of a small but potentially important reduction in cardiovascular risk on modification of dietary fat, but not reduction of total fat, in longer trials. Lifestyle advice to all those at risk of cardiovascular disease and to lower risk population groups, should continue to include permanent reduction of dietary saturated fat and partial replacement by unsaturates. The ideal type of unsaturated fat is unclear.

Reduced or modified dietary fat for preventing cardiovascular disease

BACKGROUND

Reduction and modification of dietary fats have differing effects on cardiovascular risk factors (such as serum cholesterol), but their effects on important health outcomes are less clear.

OBJECTIVES

To assess the effect of reduction and/or modification of dietary fats on mortality, cardiovascular mortality, cardiovascular morbidity and individual outcomes including myocardial infarction, stroke and cancer diagnoses in randomised clinical trials of at least 6 months duration.

SEARCH STRATEGY

For this review update, the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE and EMBASE, were searched through to June 2010. References of Included studies and reviews were also checked.

SELECTION CRITERIA

Trials fulfilled the following criteria: 1) randomised with appropriate control group, 2) intention to reduce or modify fat or cholesterol intake (excluding exclusively omega-3 fat interventions), 3) not multi factorial, 4) adult humans with or without cardiovascular disease, 5) intervention at least six months, 6) mortality or cardiovascular morbidity data available.

DATA COLLECTION AND ANALYSIS

Participant numbers experiencing health outcomes in each arm were extracted independently in duplicate and random effects meta-analyses, meta-regression, sub-grouping, sensitivity analyses and funnel plots were performed.

MAIN RESULTS

This updated review suggested that reducing saturated fat by reducing and/or modifying dietary fat reduced the risk of cardiovascular events by 14% (RR 0.86, 95% CI 0.77 to 0.96, 24 comparisons, 65,508 participants of whom 7% had a cardiovascular event, I(2) 50%). Subgrouping suggested that this reduction in cardiovascular events was seen in studies of fat modification (not reduction - which related directly to the degree of effect on serum total and LDL cholesterol and triglycerides), of at least two years duration and in studies of men (not of women). There were no clear effects of dietary fat changes on total mortality (RR 0.98, 95% CI 0.93 to 1.04, 71,790 participants) or cardiovascular mortality (RR 0.94, 95% CI 0.85 to 1.04, 65,978 participants). This did not alter with sub-grouping or sensitivity analysis.Few studies compared reduced with modified fat diets, so direct comparison was not possible.

AUTHORS' CONCLUSIONS

The findings are suggestive of a small but potentially important reduction in cardiovascular risk on modification of dietary fat, but not reduction of total fat, in longer trials. Lifestyle advice to all those at risk of cardiovascular disease and to lower risk population groups, should continue to include permanent reduction of dietary saturated fat and partial replacement by unsaturates. The ideal type of unsaturated fat is unclear.

Calcium intake increases risk of prostate cancer among Singapore Chinese

Consumption of dairy products, the primary source of calcium in Western diets, has been found to be positively associated with prostate cancer. In an Asian diet, nondairy foods are the major contributors of calcium. Thus, a study of dietary calcium and prostate cancer in Asians can better inform on whether calcium, as opposed to other dairy components, is responsible for the dairy foods-prostate cancer association. We examined calcium intake and prostate cancer risk among 27,293 men in the Singapore Chinese Health Study that was established between 1993 and 1998. As of December 31, 2007, 298 incident prostate cancer cases had been diagnosed among the cohort members. Diet was assessed at baseline with a validated 165-item food-frequency questionnaire. It is hypothesized that there is greater net absorption of calcium in smaller individuals. Therefore, the calcium-prostate cancer association was also assessed in stratified analyses by median body mass index. Vegetables were the largest contributor of daily calcium intake in the study population. Overall, we observed a modest, statistically nonsignificant 25% increase in prostate cancer risk for the 4th (median = 659 mg/d) versus 1st (median = 211 mg/d) quartiles of calcium intake after adjustment for potential confounders. The association became considerably stronger and achieved statistical significance (hazard ratio, 2.03; 95% confidence interval, 1.23-3.34; P for trend = 0.01) for men with a below median body mass index (22.9 kg/m(2)). Dietary calcium might be a risk factor for prostate cancer even at relatively low intake.

Electric light causes cancer? Surely you're joking, Mr. Stevens

Night is no longer dark in the modern world, and the Milky Way has disappeared. Electric light has benefits but there are also a few detriments. These are (1) loss of the night sky, (2) wasted energy, (3) harm to animal and plant life, (4) and perhaps increases in some severe human maladies such as cancers of breast and prostate. The science on phototransduction for the circadian system and on clock gene function is evolving rapidly, and it provides a rationale for the idea that circadian disruption from light at night could cause disease. Direct evidence from humans and rodent models has also accumulated to the point where the idea is no longer fanciful. Although it may seem logical now, the journey on the path from electric light to breast cancer has been a tortuous one, at least for me.

Dietary fat and breast cancer risk in the European Prospective Investigation into Cancer and Nutrition

BACKGROUND

Epidemiologic studies have produced conflicting results with respect to an association of dietary fat with breast cancer.

OBJECTIVE

We aimed to investigate the association between fat consumption and breast cancer.

DESIGN

We prospectively investigated fat consumption in a large (n = 319,826), geographically and culturally heterogeneous cohort of European women enrolled in the European Prospective Investigation into Cancer and Nutrition who completed a dietary questionnaire. After a mean of 8.8 y of follow-up, 7119 women developed breast cancer. Cox proportional hazard models, stratified by age and center and adjusted for energy intake and confounders, were used to estimate hazard ratios (HRs) for breast cancer.

RESULTS

An association between high saturated fat intake and greater breast cancer risk was found [HR = 1.13 (95% CI: 1.00, 1.27; P for trend = 0.038) for the highest quintile of saturated fat intake compared with the lowest quintile: 1.02 (1.00, 1.04) for a 20% increase in saturated fat consumption (continuous variable)]. No significant association of breast cancer with total, monounsaturated, or polyunsaturated fat was found, although trends were for a direct association of risk with monounsaturated fat and an inverse association with polyunsaturated fat. In menopausal women, the positive association with saturated fat was confined to nonusers of hormone therapy at baseline [1.21 (0.99, 1.48) for the highest quintile compared with the lowest quintile; P for trend = 0.044; and 1.03 (1.00, 1.07) for a 20% increase in saturated fat as a continuous variable].

CONCLUSIONS

Evidence indicates a weak positive association between saturated fat intake and breast cancer risk. This association was more pronounced for postmenopausal women who never used hormone therapy.

The role of dietary measurement error in investigating the hypothesized link between dietary fat intake and breast cancer--a story with twists and turns

The association between dietary fat and breast cancer is one of the most controversial hypotheses in nutritional epidemiology. In this editorial, the authors review the evidence from animal and human studies, including international correlation, case-control, cohort studies, intervention trials, and studies comparing dietary assessment instruments. The authors emphasize the importance of the role played by measurement error arising from assessing dietary habits using self-reported questionnaires, as it can distort estimated associations, not necessarily towards the absence of an association. They describe the twists and turns of the dietary fat and breast cancer debate that have revolved around this issue.

Dietary fat, coronary heart disease, and cancer: a historical review

OBJECTIVES

This report describes the historical development of medical theories and research concerning the relationship between dietary fat intake and breast and colorectal cancer and coronary heart disease (CHD).

METHOD

The historical and medical literature on this topic was analyzed with special reference to the Woman's Health Initiative (WHI) studies.

RESULTS

After 1900, changes in clothing fashions and life insurance mortality studies created strong preferences for slimness and emphasized reduced dietary fat intake as the preferred method of weight control. After midcentury, ecological correlations of countries found that national average dietary fat intake was related to national breast cancer and CHD rates. These relationships were not found in longitudinal studies of the same countries or in studies of dietary fat intake of individuals, including the WHI study. Dietary fat intake was found to affect colorectal cancer in some studies of individuals, although not the WHI. The WHI, like other intervention studies of dietary fat reduction, used unrepresentative samples and costly lifestyle change techniques that are not economically feasible in the community.

CONCLUSION

The WHI concurred with many other studies in finding that dietary fat intake is not a significant risk factor for CHD or breast cancer.

Cytomorphology as a risk predictor: experience with fine needle aspiration biopsy, nipple fluid aspiration, and ductal lavage

Primary prevention of breast cancer requires identification and elimination of cancer-causing agents, which is an incredibly difficult task to follow. Secondary prevention involves screening individuals who are at increased risk for breast cancer in hopes that early intervention will affect survival. In the 1980s, chemoprevention received serious attention. This approach was aimed at reducing cancer risk by administration of natural or synthetic clinical compounds that prevent, reverse, or suppress carcinogenesis in individuals at increased risk for cancer. It was not until 1998, however, when the first report from the National Surgical Adjunct Breast and Bowel Project (Breast Cancer Prevention Trial BCPT; P-1) randomized clinical trial appeared in the literature supporting the hypothesis that breast can-cer can be prevented. This study showed that administration of tamoxifen reduced the risk for invasive and noninvasive breast cancer by almost 50% in all age groups. With the current availability of tamoxifen as a chemopreventive agent and with the increasing emphasis on early breast cancer detection and prevention, more women seek consultation to determine their risk for breast cancer. However, in the absence of any detectable breast lesion, clinically and mammographically, only a few women may volunteer to have their breasts sampled by surgical biopsy for risk assessment. Other non-surgical procedures include fine needle aspiration biopsy (FNAB), nipple aspirate fluid (NAF), and the recently introduced procedure, ductal lavage. These techniques may provide better alternatives. These minimally invasive procedures are capable of recruiting cellular material for cytomorphologic interpretation and biomarker studies.

Dietary intakes of fat and fatty acids and risk of breast cancer: a prospective study in Japan

To examine the possible association of dietary fat and fatty acids with breast cancer risk in a population with a low total fat intake and a high consumption of fish, we analyzed data from the Japan Collaborative Cohort (JACC) Study. From 1988 to 1990, 26 291 women aged 40-79 years completed a questionnaire on dietary and other factors. Intakes of fat or fatty acids were estimated by using a food frequency questionnaire. Rate ratios (RR) were computed by fitting proportional hazards models. During the mean follow-up of 7.6 years, 129 breast cancer cases were documented. We found no clear association of total fat intake with breast cancer risk; the multivariate-adjusted RR across quartiles were 1.00, 1.29, 0.95, and 0.80 (95% confidence interval [CI] 0.46-1.38). A significant decrease in the risk was detected for the highest quartile of intake compared with the lowest for fish fat and long-chain n-3 fatty acids; the RR were 0.56 (95% CI 0.33-0.94) and 0.50 (0.30-0.85), respectively. A decreasing trend in risk was also suggested with an increasing intake of saturated fatty acids (trend P = 0.066). Among postmenopausal women at baseline, the highest quartile of vegetable fat intake was associated with a 2.08-fold increase in risk (95% CI 1.05-4.13). This prospective study did not support any increase in the risk of breast cancer associated with total or saturated fat intake, but it suggested the protective effects of the long-chain n-3 fatty acids that are abundant in fish.

Effects of exercise and diet on chronic disease

Currently, modern chronic diseases, including cardiovascular diseases, Type 2 diabetes, metabolic syndrome, and cancer, are the leading killers in Westernized society and are increasing rampantly in developing nations. In fact, obesity, diabetes, and hypertension are now even commonplace in children. Clearly, however, there is a solution to this epidemic of metabolic disease that is inundating today's societies worldwide: exercise and diet. Overwhelming evidence from a variety of sources, including epidemiological, prospective cohort, and intervention studies, links most chronic diseases seen in the world today to physical inactivity and inappropriate diet consumption. The purpose of this review is to 1) discuss the effects of exercise and diet in the prevention of chronic disease, 2) highlight the effects of lifestyle modification for both mitigating disease progression and reversing existing disease, and 3) suggest potential mechanisms for beneficial effects.

Dietary fat and breast cancer risk revisited: a meta-analysis of the published literature

Animal experiments and human ecological studies suggest that dietary fat intake is associated with a risk of breast cancer, but individual-based studies have given contradictory results. We have carried out a meta-analysis of this association to include all papers published up to July 2003. Case–control and cohort studies that examined the association of dietary fat, or fat-containing foods, with risk of breast cancer were identified. A total of 45 risk estimates for total fat intake were obtained. Descriptive data from each study were extracted with an estimate of relative risk and its associated 95% confidence interval (CI), and were analysed using the random effects model of DerSimonian and Laird. The summary relative risk, comparing the highest and lowest levels of intake of total fat, was 1.13 (95% CI: 1.03–1.25). Cohort studies (N=14) had a summary relative risk of 1.11 (95% CI: 0.99–1.25) and case–control studies (N=31) had a relative risk of 1.14 (95% CI 0.99–1.32). Significant summary relative risks were also found for saturated fat (RR, 1.19; 95% CI: 1.06–1.35) and meat intake (RR, 1.17; 95% CI 1.06–1.29). Combined estimates of risk for total and saturated fat intake, and for meat intake, all indicate an association between higher intakes and an increased risk of breast cancer. Case–control and cohort studies gave similar results.

Behavioral risk factors in breast cancer: can risk be modified?

The International Agency for Research on Cancer estimates that 25% of breast cancer cases worldwide are due to overweight/obesity and a sedentary lifestyle. The preponderance of epidemiologic studies indicates that women who engage in 3-4 hours per week of moderate to vigorous levels of exercise have a 30%-40% lower risk for breast cancer than sedentary women. Women who are overweight or obese have a 50%-250% greater risk for postmenopausal breast cancer. Alcohol use, even at moderate levels (two drinks per day) increases risk for both premenopausal and postmenopausal breast cancer. Certain dietary patterns, such as high fat, low vegetables/fruits, low fiber, and high simple carbohydrates, may increase risk, but definitive data are lacking. These lifestyle factors are likely associated with breast cancer etiology through hormonal mechanisms. The worldwide trends of increasing overweight and obesity and decreasing physical activity may lead to an increasing incidence of breast cancer unless other means of risk reduction counteract these effects. Thus, adoption of lifestyle changes by individuals and populations may have a large impact on the future incidence of this disease.

Fat and protein intake and subsequent breast cancer risk in postmenopausal women

The role of diet in the etiology of breast cancer has been extensively evaluated. Case-control studies generally support an association, while cohort studies have produced inconsistent results. This study, carried out on the ORDET cohort, is the first prospective Italian study to address the relation between diet and breast cancer. Female volunteers were recruited from 1987 to 1992 among residents of Varese Province, Northern Italy, an area covered by a cancer registry. A semiquantitative self-administered food questionnaire was completed by participants. After a mean 5.5 yr of follow-up, 56 cases of invasive breast cancer were identified among the 3,367 postmenopausal members; 214 controls were randomly chosen from the cohort, matched to cases for age, menopausal status at recruitment, recruitment center, and recruitment period. The adjusted odds ratios for the highest tertile of intake vs. the lowest were 3.47 [95% confidence interval (CI) = 1.43-8.44] for total fat, 3.78 (95% CI = 0.95-15.0) for animal protein, and 0.42 (95% CI = 0.18-0.95) for total carbohydrates. These findings indicate a significant positive association between total fat and animal protein and risk of breast cancer and an inverse association with carbohydrates and constitute new evidence for a role of diet in the etiology of breast cancer.

Dietary fat reduction to reduce prostate cancer risk: controlled enthusiasm, learning a lesson from breast or other cancers, and the big picture

Breast and prostate cancer share similar intrinsic and extrinsic risk factors. Based on laboratory, ecologic/international comparison, and case-control studies, the impact of dietary fat or other fat subtypes has been suggested as a potential route to reduce risk. Recent large-scale prospective studies have failed to find an association between fat and breast cancer risk. These studies may provide some insight for researchers examining the relation between fat and prostate cancer. Prospective studies to date have also failed to find a consistent association between prostate cancer and fat intake. Some fat subtypes (eg, saturated fat) or other lifestyle changes (eg, obesity, physical activity) may affect risk and progression of these cancers when examining the sum total of the research, but more precise and specific investigations in humans are needed to address these issues. Other concerns, such as the impact of excess energy or overall caloric consumption on carcinogenesis, still need to be addressed, as well as other methodologic limitations of past investigations. Large gaps exist in environmental (eg, diet, lifestyle) and heritable causes of these diseases. Regardless, until more extensive research is completed, lifestyle changes should be recommended based on reducing morbidity and mortality from cardiovascular disease-the number 1 cause of death in the United States. Additionally, cardiovascular disease remains the number 1 or 2 cause of death in patients diagnosed with breast or prostate cancer. Practical and simple dietary changes should be encouraged by health professionals because they could improve the overall longevity and quality of patients' lives. Numerous ongoing prospective studies of diet and cancer should provide researchers and the public with much-needed answers in this area.

Asian breast cancer survival in the US: a comparison between Asian immigrants, US-born Asian Americans and Caucasians

BACKGROUND

This study examines whether acculturation of Asian American women, assessed by place of birth, is associated with survival after diagnosis of breast cancer. We hypothesized that environmental factors associated with acculturation, such as a high-fat diet, would result in a pattern of better survival for first-generation Asians compared with subsequent-generation Asian Americans.

METHODS

Analyses compare survival among women of four ethnic groups (Chinese [n = 1842], Japanese [n = 3319], Filipino [n = 1598] and a random sample of Caucasians [n = 10,000]) who were diagnosed with primary invasive breast carcinoma in three Surveillance, Epidemiology, and End Results Program (SEER) regions (San Francisco/Oakland, Hawaii, Seattle/Puget Sound) between 1973 and 1994. Analyses by birthplace compare first-generation Asian immigrants with subsequent-generation Asian Americans of the same ethnicity. Analyses were based on the Cox proportional hazards model and adjusted for age at diagnosis, stage of disease, year of diagnosis, type of treatment, marital status, and SEER region.

RESULTS

Japanese women had significantly better survival than all other races, but there were no significant differences in survival between Chinese, Filipino, and Caucasian women. There were no significant differences in survival by place of birth within each Asian ethnic group, after adjustment for demographic characteristics, stage of disease, and treatment.

CONCLUSION

The findings do not support the hypothesis that acculturation of Asian American women is associated with decreased breast cancer survival.

Reduced or modified dietary fat for preventing cardiovascular disease

BACKGROUND

Reduction or modification of dietary fat can improve total cholesterol levels, but may also have a variety of effects, both positive and negative, on other cardiovascular risk factors.

OBJECTIVES

The aim of this systematic review was to assess the effect of reduction or modification of dietary fats on total and cardiovascular mortality and cardiovascular morbidity over at least 6 months, using all available randomized clinical trials.

SEARCH STRATEGY

The Cochrane Library, MEDLINE, EMBASE, CAB Abstracts, CVRCT registry and related Cochrane Groups' trial registers were searched through spring 1998, SIGLE to January 1999. Trials known to experts in the field and biographies were included through May 1999.

SELECTION CRITERIA

Trials fulfilled the following criteria: 1) randomized with appropriate control group, 2) intention to reduce or modify fat or cholesterol intake (excluding exclusively omega-3 fat interventions), 3) not multi factorial, 4) healthy adult humans, 5) intervention at least six months, 6) mortality or cardiovascular morbidity data available. Inclusion decisions were duplicated, disagreement resolved by discussion or a third party.

DATA COLLECTION AND ANALYSIS

Rate data were extracted by two independent reviewers and meta-analysis performed using random effects methodology. Meta-regression and funnel plots were used.

MAIN RESULTS

Twenty seven studies were included (40 intervention arms, 30,901 person-years). There was no significant effect on total mortality (rate ratio 0.98, 95% CI 0.86 to 1.12), a trend towards protection form cardiovascular mortality (rate ratio 0.91, 95% CI 0.77 to 1.07), and significant protection from cardiovascular events (rate ratio 0.84, 95% CI 0.72 to 0.99). The latter became non-significant on sensitivity analysis. Trials where participants were involved for more than 2 years showed significant reductions in the rate of cardiovascular events and a suggestion of protection from total mortality. The degree of protection from cardiovascular events appeared similar in high and low risk groups, but was statistically significant only in the former.

REVIEWER'S CONCLUSIONS

The findings are suggestive of a small but potentially important reduction in cardiovascular risk in trials longer than two years. Lifestyle advice to all those at high risk of cardiovascular disease (especially where statins are unavailable or rationed), and to lower risk population groups, should continue to include permanent reduction of dietary saturated fat and partial replacement by unsaturates.

Dietary fat intake and endogenous sex steroid hormone levels in postmenopausal women

PURPOSE

To examine the relationship between plasma levels of reproductive sex steroid hormones in postmenopausal women and their reported fat intake.

METHODS

We measured plasma sex steroid hormones levels in plasma collected in 1989 and 1990 from 381 healthy postmenopausal women. For each woman, we measured fat intake in 1986 and 1990 by a food-frequency questionnaire. The cross-sectional associations between the percentage of energy from total and specific types of dietary fat intake and plasma hormone levels were assessed by linear regression, controlling for energy intake, obesity, and protein intake.

RESULTS

The plasma estradiol level was 4.3% lower (95% confidence limits, -8.3%, -0.2%) for a substitution of 5% of energy from fat intake for an equivalent amount of energy from carbohydrate when adjusted for obesity and other covariates. Estradiol was also inversely associated with all other fat types except trans fat; the inverse associations with vegetable fat and marine omega-3 fats were statistically significant.

CONCLUSION

We observed an inverse association between total fat intake averaged over 4 to 5 years and estradiol levels. This result is inconsistent with the hypothesis that fat intake predisposes to breast cancer risk by raising endogenous estrogen levels.

Associations between community income and cancer incidence in Canada and the United States

BACKGROUND

Associations between socioeconomic status (SES) and the incidence of cancer have been reported previously in the U.S. Canada has more comprehensive health care and social programs than the U.S. The purpose of this study was to compare the strength of associations between SES and cancer incidence in Canada and the U.S.

METHODS

The regions studied were the Canadian province of Ontario and the areas of the U.S. covered by the Surveillance, Epidemiology, and End Results (SEER) program. The populations at risk were defined using the 1991 Canadian Census and the 1990 U.S. Census. The populations of Ontario and of the SEER areas of the U.S. were each divided into deciles on the basis of median household income. Population-based cancer registries were used to identify incident cases. Age-standardized incidence rates for all major groups of malignant diseases were calculated for each SES decile in Ontario and in the U.S. Income-associated incidence gradients observed in Ontario and the U.S. were compared.

RESULTS

The incidence of most types of cancer was similar in Ontario and the U.S. In both countries, there were moderately strong, inverse associations between income level and the incidence of carcinomas of the cervix, the head and neck region, the lung, and the gastrointestinal tract. In both Ontario and the U.S., several of these diseases were twice as common in the bottom income decile than they were in the top decile. In contrast, carcinoma of the female breast and carcinoma of the prostate were more common among higher income communities in both countries, but the observed associations were weaker in Ontario.

CONCLUSIONS

Despite Canada's universal health insurance and more comprehensive social security system, the association between lower socioeconomic status and the incidence of many common cancers is just as strong in Ontario as it is in the U.S. The mechanisms responsible for these associations require further investigation.

Dietary fat, fat subtypes, and breast cancer in postmenopausal women: a prospective cohort study

BACKGROUND

The intake of total dietary fat and of certain fat subtypes has been shown to be strongly associated with breast cancer in international comparisons and in animal experiments. However, observational epidemiologic studies have generally reported either weak positive or no associations. To extend the prospective epidemiologic evidence on this question, we examined the association between adult dietary intake of fat, fat subtypes, and breast cancer in a large, prospective cohort of postmenopausal women.

METHODS

Participants were selected from a national breast cancer mammography screening program conducted from 1973 through 1981 at 29 centers throughout the United States. From 1987 through 1989, 40022 postmenopausal women satisfactorily completed a mailed, self-administered questionnaire that included a 60-item National Cancer Institute/Block food-frequency questionnaire. Women were then followed for an average of 5.3 years; 996 women developed breast cancer. Risk was assessed by use of Cox proportional hazard regression, with age as the underlying time metric. All statistical tests were two-sided.

RESULTS

Compared with women in the lowest quintile (Q1) of percentage of energy from total fat, the adjusted risk ratio (RR) and 95% confidence interval (CI) for women in the highest quintile (Q5) was 1.07 (95% CI = 0.86-1.32). In analyses stratified by history of benign breast disease (BBD), a positive association was observed among only women with no history of BBD (RR (Q5 versus Q1) = 2.20; 95% CI = 1.41-3.42; test for trend, P =.0003). The increased risk in these women appeared to be attributable to unsaturated fat intake and oleic acid in particular.

CONCLUSIONS

In this study, there was no overall association between fat intake during adulthood and breast cancer risk; however, among women with no history of BBD, there appeared to be a positive association between total and unsaturated fat intake and breast cancer risk.

Migration bias in ecologic studies

Differential migration may provoke bias in an epidemiological assessment of the public health risks from exposure to environmental agents, particularly in ecologic studies of health outcomes with a long latency or induction period. The potential impact of migration bias on epidemiological research is complex, and it depends not only on the direction of the factor-related migration, but also on its extent. This study shows that even a small amount of differential migration can bias the assessment of the exposure outcome relationship. Migration bias may result from a number of circumstances that are related to the way in which 'populations' are defined and ascertained. It is important to understand and minimise this type of bias in epidemiological research.

Fat intake and breast cancer risk in an area where fat intake is low: a case-control study in Indonesia

BACKGROUND

Associations of fat and other macronutrients with breast cancer risk are not clear in areas where fat intake is low.

METHODS

We conducted a hospital-based case-control study from 1992 to 1995 in Jakarta, Indonesia.

RESULTS

The study, based on 226 cases and 452 age and socioeconomic status matched controls, provided the following findings. (a) In the pre-marriage period, the greater the fat or protein consumption, the larger the risk, whereas decreasing risk with increasing carbohydrate intake was detected. The odds ratio (OR) for the highest quartile of intake relative to the lowest was 8.47 (95% CI: 4.03-17.8) for fat, 2.19 (95% CI: 1.30-3.69) for protein, and 0.16 (95% CI: 0.08-0.31) for carbohydrate. A positive association with fat and a negative one with carbohydrate were also observed for the post-marriage period, but of weaker magnitude compared to the pre-marriage period. (b) The effects of macronutrient intakes were stronger among premenopausal than among postmenopausal women. (c) Most of the associations of protein and carbohydrate were insignificant after adjustment for fat intake.

CONCLUSIONS

These findings suggest that fat intake might be an important determinant of breast cancer among populations with a low fat diet in Indonesia.

Dietary fat and carcinogenesis

Epidemiologic investigations have suggested a relationship between dietary fat intake and various types of cancer incidences. Furthermore, epidemiologic studies as well as studies with animal models have demonstrated that not only the amount but also the type of fat consumed is important. At present, the mechanism by which dietary fat modulates carcinogenesis has not been elucidated. The effects of dietary fat on the development of tumours have been summarized in the present review with emphasis on colorectal, pancreas, breast and prostate cancer. It is concluded that influence on synthesis of prostaglandins and leukotrienes may be the universal mechanism by which dietary fats modulate carcinogenesis.

Meta-analysis: dietary fat intake, serum estrogen levels, and the risk of breast cancer

BACKGROUND

There is compelling evidence that estrogens influence breast cancer risk. Since the mid-1980s, dietary fat intervention studies have been conducted to investigate the effect of fat intake on endogenous estrogen levels. To further our understanding of the possible relationship between dietary fat and breast cancer, we conducted a meta-analysis of dietary fat intervention studies that investigated serum estradiol levels, and we reviewed the nature of the evidence provided by prospective analytic studies of fat consumption and breast cancer risk.

METHODS

A computerized search of the English language literature on estrogen/estradiol and dietary fat intervention studies published from January 1966 through June 1998 was conducted using the MEDLINE database. Pooled estimates were derived from the change in estradiol levels associated with fat reduction from 13 studies. Analyses were conducted separately for premenopausal and postmenopausal women and in both groups combined.

RESULTS AND CONCLUSIONS

Statistically significant reductions in serum estradiol levels of -7.4% (95% confidence interval [CI] = -11.7% to -2.9%) among premenopausal women and -23.0% (95% CI = -27.7% to -18.1%) among postmenopausal women were observed, with an overall -13.4% (95% CI = -16.6% to -10.1%) reduction observed. The greatest reductions occurred in two studies in which dietary fat was reduced to 10%-12% of calories compared with 18%-25% of calories in the other studies. A statistically significant reduction in estradiol levels of -6.6% (95% CI = -10.3% to -2.7%) remained after exclusion of these two studies. Review of prospective analytic epidemiologic studies that allowed for dietary measurement error suggests that the possibility that reducing fat consumption below 20% of calories will reduce breast cancer risk cannot be excluded.

IMPLICATIONS

Dietary fat reduction can result in a lowering of serum estradiol levels and such dietary modification may still offer an approach to breast cancer prevention.

Tamoxifen for prevention of breast cancer: report of the National Surgical Adjuvant Breast and Bowel Project P-1 Study

BACKGROUND

The finding of a decrease in contralateral breast cancer incidence following tamoxifen administration for adjuvant therapy led to the concept that the drug might play a role in breast cancer prevention. To test this hypothesis, the National Surgical Adjuvant Breast and Bowel Project initiated the Breast Cancer Prevention Trial (P-1) in 1992.

METHODS

Women (N=13388) at increased risk for breast cancer because they 1) were 60 years of age or older, 2) were 35-59 years of age with a 5-year predicted risk for breast cancer of at least 1.66%, or 3) had a history of lobular carcinoma in situ were randomly assigned to receive placebo (n=6707) or 20 mg/day tamoxifen (n=6681) for 5 years. Gail's algorithm, based on a multivariate logistic regression model using combinations of risk factors, was used to estimate the probability (risk) of occurrence of breast cancer over time.

RESULTS

Tamoxifen reduced the risk of invasive breast cancer by 49% (two-sided P<.00001), with cumulative incidence through 69 months of follow-up of 43.4 versus 22.0 per 1000 women in the placebo and tamoxifen groups, respectively. The decreased risk occurred in women aged 49 years or younger (44%), 50-59 years (51%), and 60 years or older (55%); risk was also reduced in women with a history of lobular carcinoma in situ (56%) or atypical hyperplasia (86%) and in those with any category of predicted 5-year risk. Tamoxifen reduced the risk of noninvasive breast cancer by 50% (two-sided P<.002). Tamoxifen reduced the occurrence of estrogen receptor-positive tumors by 69%, but no difference in the occurrence of estrogen receptor-negative tumors was seen. Tamoxifen administration did not alter the average annual rate of ischemic heart disease; however, a reduction in hip, radius (Colles'), and spine fractures was observed. The rate of endometrial cancer was increased in the tamoxifen group (risk ratio = 2.53; 95% confidence interval = 1.35-4.97); this increased risk occurred predominantly in women aged 50 years or older. All endometrial cancers in the tamoxifen group were stage I (localized disease); no endometrial cancer deaths have occurred in this group. No liver cancers or increase in colon, rectal, ovarian, or other tumors was observed in the tamoxifen group. The rates of stroke, pulmonary embolism, and deep-vein thrombosis were elevated in the tamoxifen group; these events occurred more frequently in women aged 50 years or older.

CONCLUSIONS

Tamoxifen decreases the incidence of invasive and noninvasive breast cancer. Despite side effects resulting from administration of tamoxifen, its use as a breast cancer preventive agent is appropriate in many women at increased risk for the disease.

Dietary fat consumption and health

Dietary Guidelines have emerged over the past 30 years recommending that Americans limit their consumption of total fat and saturated fat as one way to reduce the risk of a range of chronic diseases. However, a low-fat diet is not a no-fat diet. Dietary fat clearly serves a number of essential functions. For example, maternal energy deficiency, possible exacerbated by very low-fat intakes (< 15% of energy), is one key determinant in the etiology of low birth weight. The debate continues over recommendations for limiting total fat and saturated fatty acid intake in children. Recent evidence indicates that diets with adequate energy providing less than 30% of energy from fat are sufficient to promote normal growth and normal sexual maturation. More attention needs to be devoted to the effect of dietary fat reduction on the nutrient density of children's diets. The association between dietary fat and CHD has been extensively studied. Diets high in saturated fatty acids and trans fatty acids increase LDL cholesterol levels, and in turn, the risk of heart disease. The relationship between high-carbohydrate/low-fat diets and CHD is more ambiguous because high-carbohydrate diets induce dyslipidemia in certain individuals. Obesity among adults and children is now of epidemic proportions in the United States. High-fat diets leading to excessive energy intakes are strongly linked to the increasing obesity in the United States. However, the prevalence of obesity has increased during the same time period that dietary fat intake (both in absolute terms and as a percentage of total dietary energy) has decreased. These trends suggest that a concomitant decrease in total dietary energy and modifications of other lifestyle factors, such as physical activity, also need to be emphasized. Obesity is also an independent risk factor for the development of diabetes. The current availability of fat-modified foods offers the potential for dietary fat reduction and treatment of the comorbidities associated with diabetes. However, to date, few studies have documented the effectiveness of fat-modified foods as part of a weight loss regimen or in reduction in CHD risks among individuals with diabetes mellitus. The association between total dietary fat and cancer is still under debate. While there is some evidence demonstrating associations between dietary fat intake and cancers of the breast, prostate, and colon, there are serious methodologic issues, including the difficulty in differentiating the effects of dietary fat independent of total energy intake. Reported total fat and saturated fatty acid intakes as a percentage of total energy have been declining over the past 30 years in the United States. Despite this encouraging trend, the majority of individuals--regardless of age--do not report consuming a diet that meets the levels of fat and saturated fatty acids recommended by the Dietary Guidelines for Americans. On a relative basis, saturated fat intake has gone down less than has total fat intake. Individuals of all ages who report consuming a diet with < or = 30% of energy from fat consistently have lower energy intakes. Given the increasing rates of obesity in the United States at an earlier and earlier age, dietary fat reduction may be an effective part of an overall strategy to balance energy consumption with energy needs. In each of the age/gender groups reporting consumption of < or = 30% of energy from fat and less than 10% of energy from saturated fatty acids, fat-modified foods play a more important role in their diets than for people who are consuming higher levels of fat and saturated fat. The data are clear than fat-modified foods make a more significant contribution to diets of consumers with low-fat intakes. While one cannot argue cause and effect from the results presented, the patterns of fat-modified foods/low-fat intakes are consistent. The focus on overall diet quality is often lost in the national obsession with lowering fat inta

Breast cancer risk, meat consumption and N-acetyltransferase (NAT2) genetic polymorphisms

Although inconsistencies exist, some studies have shown that meat consumption is associated with breast cancer risk. Several heterocyclic amines (HAs), formed in the cooking of meats, are mammary carcinogens in laboratory models. HAs are activated by polymorphic N-acetyltransferase (NAT2) and rapid NAT2 activity may increase risk associated with HAs. We investigated whether ingestion of meat, chicken and fish, as well as particular concentrated sources of HAs, was associated with breast cancer risk, and if NAT2 genotype modified risk. Caucasian women with incident breast cancer (n = 740) and community controls (n = 810) were interviewed and administered a food frequency questionnaire. A subset of these women (n = 793) provided a blood sample. Polymerase chain reaction and restriction fragment length polymorphism analyses were used to determine NAT2 genotype. Consumption of red meats, as well as an index of concentrated sources of HAs, was not associated with increased breast cancer risk, nor did risk vary by NAT2 genotype. In post-menopausal women, higher fish consumption was inversely associated with risk (odds ratio = 0.7; 95% confidence interval, 0.4-1.0); among pre-menopausal women, there was the suggestion of inverse associations between risk and pork and chicken intake. Our results suggest that consumption of meats and other concentrated sources of HAs is not associated with increased breast cancer risk. However, due to the strong biologic plausibility for a role of some HAs in mammary carcinogenesis, and the likely measurement error in evaluation of sources of HAs in this study, further studies of these possible relationships are warranted.

Design of the Women's Health Initiative clinical trial and observational study. The Women's Health Initiative Study Group

The Women's Health Initiative (WHI) is a large and complex clinical investigation of strategies for the prevention and control of some of the most common causes of morbidity and mortality among postmenopausal women, including cancer, cardiovascular disease, and osteoporotic fractures. The WHI was initiated in 1992, with a planned completion date of 2007. Postmenopausal women ranging in age from 50 to 79 are enrolled at one of 40 WHI clinical centers nationwide into either a clinical trial (CT) that will include about 64,500 women or an observational study (OS) that will include about 100,000 women. The CT is designed to allow randomized controlled evaluation of three distinct interventions: a low-fat eating pattern, hypothesized to prevent breast cancer and colorectal cancer and, secondarily, coronary heart disease; hormone replacement therapy, hypothesized to reduce the risk of coronary heart disease and other cardiovascular diseases and, secondarily, to reduce the risk of hip and other fractures, with increased breast cancer risk as a possible adverse outcome; and calcium and vitamin D supplementation, hypothesized to prevent hip fractures and, secondarily, other fractures and colorectal cancer. Overall benefit-versus-risk assessment is a central focus in each of the three CT components. Women are screened for participation in one or both of the components--dietary modification (DM) or hormone replacement therapy (HRT)--of the CT, which will randomize 48,000 and 27,500 women, respectively. Women who prove to be ineligible for, or who are unwilling to enroll in, these CT components are invited to enroll in the OS. At their 1-year anniversary of randomization, CT women are invited to be further randomized into the calcium and vitamin D (CaD) trial component, which is projected to include 45,000 women. The average follow-up for women in either CT or OS is approximately 9 years. Concerted efforts are made to enroll women of racial and ethnic minority groups, with a target of 20% of overall enrollment in both the CT and OS. This article gives a brief description of the rationale for the interventions being studied in each of the CT components and for the inclusion of the OS component. Some detail is provided on specific study design choices, including eligibility criteria, recruitment strategy, and sample size, with attention to the partial factorial design of the CT. Some aspects of the CT monitoring approach are also outlined. The scientific and logistic complexity of the WHI implies particular leadership and management challenges. The WHI organization and committee structure employed to respond to these challenges is also briefly described.

Meta-analyses of dietary fats and mammary neoplasms in rodent experiments

We review two meta-analyses of experiments on dietary fat and mammary tumor incidence in rodents, emphasizing a recent meta-analysis on the effects of different types of dietary fatty acids. This analysis shows that n-6 polyunsaturated fatty acids most strongly enhance mammary tumors in rodents, and saturated fats also enhance these tumors but less strongly. Further, the analysis shows that energy restriction protects against mammary tumors. We show that these results agree qualitatively with estimates of effects on human breast cancer derived from international correlations.