Dietary fatty acids and insulin secretion: a population-based study

Association between total fat and fatty acid intake and the risk of type 2 diabetes mellitus among Japanese adults: Analysis based on the JACC study

BACKGROUND

We prospectively examined the association between total fat and fatty acid intake and type 2 diabetes (T2D) among Japanese adults.

METHODS

This study was conducted using data from the Japan Collaborative Cohort Study for Evaluation of Cancer Risk (JACC). A validated food frequency questionnaire evaluated the intake of total fat and fatty acids. Diabetes was assessed using self-reported data. Multivariable logistic regression analysis was performed to calculate the odds ratios (ORs) and 95% confidence intervals (CIs) of incident T2D across quintiles of total fat and fatty acid intake after adjusting for potential confounders.

RESULTS

A total of 19,088 non-diabetic participants (age range, 40-79 years) enrolled in the JACC between 1988 and 1990 were included in this study. During the five-year study period, 494 the participants developed T2D. The OR of T2D for the highest versus lowest quintiles was 0.58 (95% CI, 0.37-0.90) for total fat, 0.78 (95% CI, 0.51-1.20) for saturated fatty acid (SFA), 0.55 (95% CI, 0.35-0.86) for monounsaturated fatty acids (MUFA), 0.61 (95% CI, 0.39-0.96) for polyunsaturated fatty acids (PUFA), 0.64 (95% CI, 0.42-0.99) for n-3 PUFA, and 0.70 (95% CI, 0.45-1.09) for n-6 PUFA. Total fat and fatty acid (except SFA and n-6 PUFA) intake were inversely associated with T2D in men. Total fat and fatty acid intake were not associated with T2D in women.

CONCLUSION

Higher intakes of total fats, MUFA, PUFA, and n-3 PUFA were inversely associated with T2D among Japanese men.

Fat Intake and High Triglyceride-Glucose Index in Individuals at Cardiometabolic Risk: An Isocaloric Substitution Analyses

Insulin resistance (IR) is an important risk factor for cardiovascular diseases, and the triglyceride-glucose index (TyG index) is a potential IR biomarker. Evidence also suggests that fat intake may modulate IR status, but this relationship remains unclear. Thus, the present study aimed to analyze the relationship between the TyG index and isocaloric replacement of macronutrients, including the profile of dietary fatty acids in individuals at cardiometabolic risk.

This cross-sectional study enrolled 264 individuals at cardiometabolic risk (age 43.1 ± 16.3 years) who participated in a nutritional intervention study (ReBEC, id: RBR-5n4y2g). The baseline demographic, anthropometric, clinical, dietary, and lifestyle data were used. The TyG index was calculated using the formula ln [fasting triglycerides (mg/dL) × fasting plasma glucose (mg/dL)/2]. Multivariate nutrient density models were used to analyze isocaloric replacement of fatty acids (as 5% of energy). The chance of having a high TyG index (TyG index >8.83, median value) was decreased by 60% after replacing 5% of the energy intake of polyunsaturated fatty acid (PUFA), saturated fatty acid (SFA), and trans fatty acid (TFA) with monounsaturated fatty acid (MUFA) or PUFA and SFA with protein.

Isocaloric replacement of PUFA, SFA, and TFA with MUFA and protein was associated with lower chances of having a high TyG index. These results indicate the importance of macronutrient and dietary fat profiles in the dietary planning of individuals at cardiometabolic risk.

Effect of dietary fat intake and genetic risk on glucose and insulin-related traits in Brazilian young adults

PURPOSE

The development of metabolic diseases such as type 2 diabetes (T2D) is closely linked to a complex interplay between genetic and dietary factors. The prevalence of abdominal obesity, hyperinsulinemia, dyslipidaemia, and high blood pressure among Brazilian adolescents is increasing and hence, early lifestyle interventions targeting these factors might be an effective strategy to prevent or slow the progression of T2D.

METHODS

We aimed to assess the interaction between dietary and genetic factors on metabolic disease-related traits in 200 healthy Brazilian young adults. Dietary intake was assessed using 3-day food records. Ten metabolic disease-related single nucleotide polymorphisms (SNPs) were used to construct a metabolic-genetic risk score (metabolic-GRS).

RESULTS

We found significant interactions between the metabolic-GRS and total fat intake on fasting insulin level (Pinteraction = 0.017), insulin-glucose ratio (Pinteraction = 0.010) and HOMA-B (Pinteraction = 0.002), respectively, in addition to a borderline GRS-fat intake interaction on HOMA-IR (Pinteraction = 0.051). Within the high-fat intake category [37.98 ± 3.39% of total energy intake (TEI)], individuals with ≥ 5 risk alleles had increased fasting insulin level (P = 0.021), insulin-glucose ratio (P = 0.010), HOMA-B (P = 0.001) and HOMA-IR (P = 0.053) than those with < 5 risk alleles.

CONCLUSION

Our study has demonstrated a novel GRS-fat intake interaction in young Brazilian adults, where individuals with higher genetic risk and fat intake had increased glucose and insulin-related traits than those with lower genetic risk. Large intervention and follow-up studies with an objective assessment of dietary factors are needed to confirm our findings.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s40200-021-00863-7.

Mediterranean Diet Effects on Type 2 Diabetes Prevention, Disease Progression, and Related Mechanisms. A Review

The search for a quality diet has grown over the past decade. Diet is considered one of the pillars for the prevention and progression of several diseases, among them: diabetes. Type 2 diabetes (T2D) is an epidemic of western countries that increases the vulnerability of other diseases, such as cardiovascular and cancer. T2D is associated with lifestyle and diet. The traditional Mediterranean diet has proven its benefits over several cardiovascular risk factors, and specifically on diabetes. This review compiles recent published evidence on the effects of the Mediterranean diet on the incidence and progression of type 2 diabetes (T2D) and its relation with several other cardiovascular healthy diets. We will also focus on how the Mediterranean diet could play a role in T2D-related mechanisms, such as anti-inflammatory or antioxidant compounds, glucagon-like peptide agonist compounds, and changes in gut microbiota. Each component of the Mediterranean diet could be involved in processes related to diabetes homeostasis, many of them sharing common physio-pathological pathways. The importance of this diet within the set of habits of a healthy lifestyle must be emphasized.

Computational Analysis of Insulin-Glucagon Signalling Network: Implications of Bistability to Metabolic Homeostasis and Disease states

Insulin and glucagon control plasma macronutrient homeostasis through their signalling network composed of multiple feedback and crosstalk interactions. To understand how these interactions contribute to metabolic homeostasis and disease states, we analysed the steady state response of metabolic regulation (catabolic or anabolic) with respect to structural and input perturbations in the integrated signalling network, for varying levels of plasma glucose. Structural perturbations revealed: the positive feedback of AKT on IRS is responsible for the bistability in anabolic zone (glucose >5.5 mmol); the positive feedback of calcium on cAMP is responsible for ensuring ultrasensitive response in catabolic zone (glucose <4.5 mmol); the crosstalk between AKT and PDE3 is responsible for efficient catabolic response under low glucose condition; the crosstalk between DAG and PKC regulates the span of anabolic bistable region with respect to plasma glucose levels. The macronutrient perturbations revealed: varying plasma amino acids and fatty acids from normal to high levels gradually shifted the bistable response towards higher glucose range, eventually making the response catabolic or unresponsive to increasing glucose levels. The analysis reveals that certain macronutrient composition may be more conducive to homeostasis than others. The network perturbations that may contribute to disease states such as diabetes, obesity and cancer are discussed.

Extra virgin olive oil diet intervention improves insulin resistance and islet performance in diet-induced diabetes in mice

Dietary composition plays an important role in the pathophysiology of type 2 diabetes. Monounsaturated fatty acid consumption has been positively associated with improved insulin sensitivity and β-cell function. We examined whether an extra virgin olive oil (EVOO) high fat diet (HFD) can improve glucose homeostasis. C57BL/6J mice were fed a standard diet or a lard-based HFD to induce type 2 diabetes. Then, HFD mice were fed with three different based HFD (lard, EVOO and EVOO rich in phenolic compounds) for 24 weeks. HFD-EVOO diets significantly improved glycemia, insulinemia, glucose tolerance, insulin sensitivity and insulin degradation. Moreover, EVOO diets reduced β-cell apoptosis, increased β-cell number and normalized islet glucose metabolism and glucose induced insulin secretion. No additional effects were observed by higher levels of phenolic compounds. Thus, EVOO intake regulated glucose homeostasis by improving insulin sensitivity and pancreatic β-cell function, in a type 2 diabetes HFD animal model.

Effects of dietary fat on insulin secretion in subjects with the metabolic syndrome

Objective Impaired insulin secretion and action contribute to the development of type 2 diabetes. Dietary fat modification may improve insulin sensitivity, whereas the effect on insulin secretion is unclear. We investigated the effect of dietary fat modification on insulin secretion in subjects with the metabolic syndrome. Design In a 12-week pan-European parallel, randomized controlled dietary intervention trial (LIPGENE), 486 subjects were assigned to four isoenergetic diets: high-fat diets rich in saturated fat (HSFA) or monounsaturated fat (HMUFA) or low-fat, high-complex carbohydrate diets with (LFHCC n-3) or without (LFHCC control) 1.2 g/day of n-3 PUFA supplementation. Insulin secretion was estimated as acute insulin response to glucose (AIRg) and disposition index (DI), modeled from an intravenous glucose tolerance test. Results There were no overall effect of the dietary intervention on AIRg and DI in the total cohort, in neither the high-fat nor LFHCC groups. We observed significant diet*fasting glucose category interactions for AIRg (P = 0.021) and DI (P = 0.001) in the high-fat groups. In subjects with normal fasting glucose and preserved first phase insulin secretion, the HMUFA diet increased, whereas the HSFA diet reduced AIRg (P = 0.015) and DI (P = 0.010). Conclusions The effects of dietary fat modification on insulin secretion were minor, and only evident in normoglycemic subjects. In this case, the HMUFA diet improved AIRg and DI, as compared to the HSFA diet.

Long-term consumption of a Mediterranean diet improves postprandial lipemia in patients with type 2 diabetes: the Cordioprev randomized trial

Background

Patients with type 2 diabetes (T2D) have an elevated postprandial lipemia (PPL) that has been associated with increased cardiovascular risk.

Objective

We aimed to analyze whether the long-term consumption of 2 healthy dietary patterns is associated with an improvement in PPL and remnant cholesterol (RC) concentrations in patients with T2D.

Design

We selected patients from the Cordioprev study who underwent oral fat load tests (FLTs) at baseline and the 3-y follow-up (241 patients with and 316 patients without T2D). Subjects were randomly assigned to receive either a Mediterranean diet rich in olive oil (MedDiet; 35% of calories from fat [22% monounsaturated fatty acids (MUFAs)] and 50% from carbohydrates) or a low-fat (LF) diet [<30% fat (12-14% MUFAs) and 55% of calories from carbohydrates]. Lipids were measured in serial bloods drawn at 0, 1, 2, 3, and 4 h after the FLT.

Results

After 3 y of dietary intervention, patients with T2D showed an improvement in their PPL measured as postprandial triglycerides (TGs) (P < 0.0001), TG area under the curve (AUC) (P = 0.001), and TG-rich lipoproteins (TRLs-TG; P = 0.001) compared with baseline. Subgroup analysis, based on the type of dietary intervention, showed that those T2D patients randomly assigned to the MedDiet presented a reduction in the TG AUC of 17.3% compared with baseline (P = 0.003). However, there were no differences for T2D patients randomly assigned to the LF diet (P > 0.05) or in patients without T2D (P > 0.05) regardless of the dietary intervention. In addition, the MedDiet induced a significant improvement in the RC AUC in patients with T2D (P = 0.04). However, there was no significant improvement in those following the LF diet.

Conclusions

Our findings show that the long-term consumption of a MedDiet rich in olive oil improves PPL and RC concentrations mainly in patients with T2D. This trial was registered at clinicaltrials.gov as NCT00924937.

Prospective associations of dietary carbohydrate, fat, and protein intake with β-cell function in the CODAM study

PURPOSE

Type 2 diabetes mellitus (T2DM) is characterized by both impaired pancreatic β-cell function (BCF) and insulin resistance. In the etiology of T2DM, BCF basically determines whether a person with a certain degree of insulin resistance develops T2DM, as β-cells are able to compensatorily increase insulin secretion. The effects of dietary intake on BCF are largely unknown. Our study aim was to investigate whether dietary macronutrient intake predicts BCF.

METHODS

Prospective data (median follow-up 7 years) of 303 individuals recruited from the CODAM study population (aged 40-70 years, 39% women) were analyzed. BCF was measured by C-peptide deconvolution and physiological modeling of data from a 5-point, 75-g, 2-h oral glucose tolerance test. Macronutrient intake was estimated by a 178-item Food Frequency Questionnaire.

RESULTS

Associations adjusted for relevant covariates of baseline macronutrient intake with model-derived parameters describing BCF (glucose sensitivity, rate sensitivity or potentiation) or C-peptidogenic index were detected for trans fat [standardized regression coefficient (95%-CI) glucose sensitivity - 0.14 (- 0.26, - 0.01)] per g, cholesterol [potentiation 0.20 (0.02, 0.37)] per 100 mg, dietary fiber [glucose sensitivity 0.21 (0.08, 0.33)] per 10 g, MUFA glucose sensitivity 0.16 (0.02, 0.31) per 10 g, and polysaccharide [potentiation - 0.24 (- 0.43, - 0.05), C-peptidogenic index - 0.16 (- 0.29 - 0.03); odds ratio lowest versus highest tertile (95%-CI) rate sensitivity 1.51 (1.06, 2.15)) per 50 g.

CONCLUSIONS

In this population at high risk for developing T2DM, polysaccharide and trans fat intake were associated with worse BCF, whereas increased intake of MUFA, dietary cholesterol, and fiber were associated with better BCF.

Sunflower Oil but Not Fish Oil Resembles Positive Effects of Virgin Olive Oil on Aged Pancreas after Life-Long Coenzyme Q Addition

An adequate pancreatic structure is necessary for optimal organ function. Structural changes are critical in the development of age-related pancreatic disorders. In this context, it has been reported that different pancreatic compartments from rats were affected according to the fat composition consumed. Since there is a close relationship between mitochondria, oxidative stress and aging, an experimental approach has been developed to gain more insight into this process in the pancreas. A low dosage of coenzyme Q was administered life-long in rats in order to try to prevent pancreatic aging-related alterations associated to some dietary fat sources. According to that, three groups of rats were fed normocaloric diets containing Coenzyme Q (CoQ) for two years, where virgin olive, sunflower, or fish oil was included as unique fat source. Pancreatic samples for microscopy and blood samples were collected at the moment of euthanasia. The main finding is that CoQ supplementation gives different results according to fat used in diet. When sunflower oil was the main fat in the diet, CoQ supplementation seems to improve endocrine pancreas structure and in particular β-cell mass resembling positive effects of virgin olive oil. Conversely, CoQ intake does not seem to improve the structural alterations of exocrine compartment previously observed in fish oil fed rats. Therefore CoQ may improve pancreatic alterations associated to the chronic intake of some dietary fat sources.

Effect of nutritional counseling and long term isomaltulose based liquid formula (MHN-01) intake on metabolic syndrome

The isomaltulose based liquid formula (MHN-01), suppresses postprandial plasma glucose and insulin levels in healthy persons and patients with impaired glucose tolerance (IGT) or type 2 diabetes. MHN-01 intake as a part of breakfast also suppresses glucose and insulin levels after lunch, suggesting second meal effect. The objective of this study was to investigate the effects of nutritional counseling and long-term (24 weeks) MHN-01 ingestion on biomarkers of metabolic syndrome. Forty-one subjects with criteria of metabolic syndrome participated in this study composed with the control period (0–12 week) followed by nutritional counseling and the experimental period (12–36 week) followed by 200 kcal (837 kJ) of MHN-01 or dextrin-based standard balanced liquid formula (SBF) loading as a part of breakfast. In 16 of 41 subjects became to out of criteria for liquid formula loading study during control period (unqualified group). In the unqualified group, several biomarkers were improved. In experimental period, serum HbA_1c levels significantly increased in SBF group (n = 12) but did not change in MHN-01 group (n = 10). Thus, intake of 837 kJ MHN-01 as a part of breakfast may be effective for suppression of deteriorating glucose metabolism in metabolic syndrome.

Changes in thyroid function with age: results from the Pizarra population-based longitudinal study

BACKGROUND

Results of studies examining the influence of age on thyroid function and TSH levels, in the absence of thyroid disease, remain controversial. The aim of this study was to determine the course of thyroid function over 11 years in a population with normal thyroid function.

METHODS

This is a population-based prospective study started in 1995-1997 (first phase), and reassessed 6 (second phase) and 11 years later (third phase).

RESULTS

The TSH and FT4 in the third phase were significantly increased (p=0.001 and p=0.001, respectively), with the values being higher particularly from the age of 50 years. In those persons with a baseline TSH≥1.2 and <3 μIU/mL, the OR of having a TSH of 3-5 μIU/mL in the third phase was 6.10 (p=0.004). In those with a baseline TSH≥3 and ≤5 μIU/mL, the OR of having a TSH of 3-5 μIU/mL in the third phase was 20.8 (p<0.0001). Similar results were found for FT4.

CONCLUSION

In a population free of clinical thyroid disease, TSH and FT4 values rise over the years. This increase occurs in all age groups, but depends mainly on the basal concentrations of TSH and FT4.

Linoleic and alpha linolenic acids ameliorate streptozotocin-induced diabetes in mice

Streptozotocin (STZ)-induced diabetes in mice progresses with decreased desaturase activities and alterations in the metabolism of essential fatty acids (EFA).

OBJECTIVES

Based on our previous studies with soybean oil that ameliorated the STZ damage in mice, we tested here the accountability of its main EFA components, i.e. linoleic acid (LA) and alpha linolenic acid (ALA), in the prevention of pancreas damage and Δ6 desaturase decrease.

MATERIALS AND METHODS

Seven days after injection with STZ and EFA gavage, ICR mice were sacrificed. Plasma glucose and insulin levels, pancreas histology and liver fatty acid desaturases were analysed.

RESULTS

EFA reduced pancreas damage, insulin and glucose plasma levels and restored Δ6 desaturase activity and mRNA expression levels.

DISCUSSION

By reducing pancreas damage, EFA ameliorated insulin levels, Δ6 desaturase and fatty acid metabolism. LA further enhanced Fads2 promoter activity.

CONCLUSION

EFA ameliorate STZ induced diabetes in mice.

Comparative analysis of pancreatic changes in aged rats fed life long with sunflower, fish, or olive oils

An adequate pancreatic structure is necessary for optimal organ function. Structural changes are critical in the development of age-related pancreatic disorders. We aimed to study the effect of oil consumption on pancreas histology in order to find aging-related signs. To this end, three groups of rats were fed an isocaloric diet for 2 years, where virgin olive, sunflower, or fish oil was included. Pancreatic samples for microscopy and blood samples were collected at the moment of sacrifice. As a result, the sunflower oil-fed rats presented higher β-cell numbers and twice the insulin content than virgin olive oil-fed animals. In addition, rats fed with fish oil developed acinar fibrosis and macrophage infiltrates in peri-insular regions, compared with counterparts fed with virgin olive oil. Inflammation signs were less prominent in the sunflower group. The obtained data emphasize the importance of dietary fatty acids in determining pancreatic structure.

Polymorphisms in the SCD1 gene are associated with indices of stearoyl CoA desaturase activity and obesity: a prospective study

SCOPE

The serum fatty acid (FA) composition is influenced by dietary fat and the endogenous production of FAs. Stearoyl CoA desaturase 1 (SCD1) is the rate-limiting enzyme catalyzing the synthesis of MUFAs from saturated FAs. Variations in SCD1 activity have been associated with obesity, diabetes, or inflammation. We evaluated the associations between genetic variation of the SCD1 gene, SCD1 activity, intake of oil, and obesity in a population-based prospective study in southern Spain.

METHODS AND RESULTS

We collected phenotypic, metabolic, nutritional, and genetic information. The type of dietary fat was assessed from samples of cooking oil taken from the participants' kitchens and analyzed by GC. A total of nine single nucleotide polymorphisms (SNPs) of the SCD1 gene were analyzed by SNPlex technology. We found a significant association between SCD1 genetic variation and enzyme activity in four of nine polymorphisms studied. An interaction between rs10883463 and olive oil intake on the [18:1/18:0] desaturase index was found (p = 0.009). We also showed that genetic variations in the SCD1 gene were associated with obesity.

CONCLUSION

Our results show a relationship between genetic variation of the SCD1 gene, enzyme activity, and the risk of obesity, an association that is not independent of the type of oil consumed.

Factors determining weight gain in adults and relation with glucose tolerance

OBJECTIVE

Modifications in lifestyle, diet and certain clinical events are major contributors for the high prevalence of obesity. The aim of this study was to assess factors associated with weight gain in a population of Spanish adults.

DESIGN

The study was undertaken in two population-based cohorts from the north and the south of Spain (baseline and after 6 years). The Asturias Study, in the north, included 1034 persons aged 30-75 years, of whom 701 were reassessed. The Pizarra Study, in the south, included 1226 persons aged 18-65 years, of whom 783 were re-evaluated. Both studies involved a nutritional questionnaire, a physical examination and an oral glucose tolerance test (OGTT).

RESULTS

During the follow-up, 32.3% of the participants lost weight, 34.5% gained fewer than 4 kg and 33.2% gained more than 4 kg. Weight gain was greater in persons younger than 50 years and in those with an initial body mass index below 30. Weight gain was associated with a greater incidence of type 2 diabetes mellitus (T2DM) and abnormal glucose tolerance, whereas weight loss in persons with these disorders was associated with a normal OGTT 6 years later. Persons who took less exercise and those who reported a higher daily calorie intake experienced greater weight gain.

CONCLUSION

The longitudinal changes in weight affect the development of T2DM and abnormal glucose tolerance. The weight is a dynamic phenomenon affected by several social customs.

Diet quality is prospectively associated with incident impaired fasting glucose in older adults

AIMS

Dietary modifications may play an important role in the prevention of diabetes. We aimed to assess the temporal association between diet quality and both impaired fasting glucose and Type 2 diabetes among older adults.

METHODS

A total of 2564 participants aged 49+ years at baseline were examined between 1992 and 1994 and 2002-2004 and had their fasting blood glucose measured. Dietary data were collected using a semi-quantitative food frequency questionnaire. A modified version of the Healthy Eating Index for Australians was developed to determine Total Diet Score. Incident diabetes (or impaired fasting glucose) was defined in participants at risk who were newly diagnosed by a physician during the follow-up or found to have a fasting blood glucose level ≥ 7.0 mmol/l (or 6.1-6.9 mmol/l).

RESULTS

After adjusting for age, sex, current smoking, body mass index, hypertension and serum triglycerides, comparing highest with lowest tertile of total diet score, a significant 75% decrease in risk of incident impaired fasting glucose was observed in men (P(trend) = 0.02). Also, in men, each two-point increase in Total Diet Score was associated with a 52% reduction in the 10-year incidence of impaired fasting glucose, (OR 0.48, 95% CI 0.33-0.69). No significant associations were observed among women or with the 10-year incidence of diabetes.

CONCLUSIONS

Greater compliance with published dietary guidelines (better diet quality) was associated with a reduced risk of pre-diabetes in men, but not women.

Fatty acids as biocompounds: their role in human metabolism, health and disease: a review. part 2: fatty acid physiological roles and applications in human health and disease

BACKGROUND

This is the second of two review parts aiming at describing the major physiological roles of fatty acids, as well as their applications in specific conditions related to human health.

RESULTS

The review included the current literature published in Pubmed up to March 2011. In humans, fatty acids are a principle energy substrate and structural components of cell membranes (phospholipids) and second messengers. Fatty acids are also ligands of nuclear receptors affecting gene expression. Longer-chain (LC) polyunsaturated fatty acids (PUFA), including eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and arachidonic acid are precursors of lipid mediators such as eicosanoids (prostaglandins, leukotrienes, thromboxanes), resolvins and neuroprotectins. Lipid mediators produced by EPA and DHA (LC n-3 PUFA; mainly found in oily fish) are considered as inflammation-resolving, and thus, fish oil has been characterised as antiinflammatory. Recommendations for EPA plus DHA intake from oily fish vary between 250-450 mg/day. Dietary reference values for fat vary between nutrition bodies, but mainly agree on a low total and saturated fat intake. The existing literature supports the protective effects of LC n-3 PUFA (as opposed to n-6 PUFA and saturated fat) in maternal and offspring health, cardiovascular health, insulin sensitivity, the metabolic syndrome, cancer, critically ill patients, and immune system disorders.

CONCLUSION

Fatty acids are involved in multiple pathways and play a major role in health. Further investigation and a nutrigenomics approach to the effects of these biocompounds on health and disease development are imperative and highlight the importance of environmental modifications on disease outcome.

Dietary associations with prediabetic states--the DR's EXTRA Study (ISRCTN45977199)

BACKGROUND/OBJECTIVES

Impaired fasting plasma glucose (IFG) and impaired glucose tolerance (IGT) predict development of type 2 diabetes (T2D), but display different pathophysiology for T2D. We studied the association of selected food items and nutrients with IFG, IGT and combined IFG and IGT (IFG+IGT), independent of cardiorespiratory fitness (VO(2max)).

SUBJECTS/METHODS

In a population-based sample of 1261 individuals, aged 58-78 years, we identified 126 subjects with IFG, 97 with IGT and 49 with simultaneous IFG and IGT by an oral glucose tolerance test. Dietary intake was assessed by 4-day food records. Cardiorespiratory fitness was assessed by defining maximal oxygen uptake (VO(2max)) from respiratory gas analysis during a maximal symptom-limited exercise stress test on a bicycle ergometer.

RESULTS

Increased intake of saturated fat was associated with higher odds for IFG (OR 1.07; 1.01-1.14) after adjustment for age, gender, VO(2max) and energy misreporting variable. Consumption of additional whole-grain bread (50 g/1000 kcal) and intake of dietary fiber (g/1000 kcal) were inversely associated with IGT (OR 0.61; 0.41-0.92, OR 0.91; CI 0.85-0.97, respectively).

CONCLUSION

Dietary fiber and sources of cereal fiber are negatively associated with IGT, and saturated fat intake is positively associated with IFG, but not with IGT. The present data give practical dietary means at the population level for the elimination of prediabetic conditions.

Nonpharmacological interventions for the prevention of type 2 diabetes mellitus

During the past decade, improved understanding of the pathophysiological mechanisms of diabetes development has resulted in advances in therapeutic concepts, but has also supported the potential for diabetes prevention through nonpharmacological means. At the beginning of the century, we experienced a shift in paradigm, as landmark studies have shown that diabetes mellitus is preventable with lifestyle intervention; moderate changes in diet and physical activity produce a substantial and sustained reduction in the incidence of type 2 diabetes mellitus (T2DM) for individuals with impaired glucose tolerance. This evidence must now be translated into clinical and public-health practice, but translational studies have varied in their ability to replicate the results of clinical trials. This variation reflects a number of challenging barriers for diabetes prevention in real-world clinical practice, which makes it necessary to focus on identifying efficient intervention methods and delivery mechanisms. Research is now focusing on these mechanisms, as well as on developing efficient screening and risk-identification strategies and realistic scenarios for public-health policy to implement diabetes prevention programs. In this Review, we will discuss these mechanisms and will consider the implications of diabetes prevention for public-health strategy and policy.

Foods for the prevention of diabetes: how do they work?

With the diabetes epidemic reaching menacing proportions worldwide, there is an urgent need for the development of cost-efficient prevention strategies to be effective at the population level. Great potential in this direction lies in properly designed, large-scale dietary interventions. The macronutrient composition and the caloric content of our diet are major determinants of glucose homeostasis and there is a continuously growing list of foods, nutrients or individual compounds that have been associated with an increased or reduced incidence of diabetes mellitus. These include fat, carbohydrates, fibre, alcohol, polyphenols and other micronutrients or individual dietary compounds, which have been shown to either promote or prevent a progression towards a (pre-)diabetic state. This review aims to briefly summarize relevant epidemiological data linking foods to diabetes and to provide insights into the mechanisms through which these effects are mediated. These include improvement of insulin sensitivity or promotion of insulin resistance, regulation of inflammatory pathways, regulation of glucose transport and tissue glucose uptake, aggravation or attenuation of postprandial glycaemia/insulinaemia, interactions with hormonal responses and β-cell-dependent mechanisms.

Nutritional modulation of insulin resistance

Insulin resistance has been proposed as the strongest single predictor for the development of Type 2 Diabetes (T2DM). Chronic oversupply of energy from food, together with inadequate physical activity, have been recognized as the most relevant factors leading to overweight, abdominal adiposity, insulin resistance, and finally T2DM. Conversely, energy reduced diets almost invariably to facilitate weight loss and reduce abdominal fat mass and insulin resistance. However, sustained weight loss is generally difficult to achieve, and distinct metabolic characteristics in patients with T2DM further compromise success. Therefore, investigating the effects of modulating the macronutrient composition of isoenergetic diets is an interesting concept that may lead to additional important insights. Metabolic effects of various different dietary concepts and strategies have been claimed, but results from randomized controlled studies and particularly from longer-term-controlled interventions in humans are often lacking. However, some of these concepts are supported by recent research, at least in animal models and short-term studies in humans. This paper provides an update of the current literature regarding the role of nutrition in the modulation of insulin resistance, which includes the discussion of weight-loss-independent metabolic effects of commonly used dietary concepts.

The role of diet in the prevention of type 2 diabetes

Type 2 diabetes mellitus is an important preventable disease and a growing public health problem. Epidemiologic and interventional studies suggest that weight loss is the main driving force to reduce diabetes risk. Landmark clinical trials of lifestyle changes in subjects with prediabetes have shown that diet and exercise leading to weight loss consistently reduce the incidence of diabetes. However, from these studies it cannot be established whether dietary changes alone play a significant role in preventing diabetes. Here we review epidemiologic and clinical trial evidence relating nutrients, foods and dietary patterns to diabetes risk and the possible mechanisms involved. The differential effects of carbohydrate and fat quantity and quality, and those of specific foods and whole diets are discussed. Importantly, most dietary components influencing diabetes risk have similar effects on biomarkers of cardiovascular risk and inflammation. The conclusion is that there is no universal dietary strategy to prevent diabetes or delay its onset. Together with the maintenance of ideal body weight, the promotion of the so-called prudent diet (characterized by a higher intake of food groups that are generally recommended for health promotion, particularly plant-based foods, and a lower intake of red meat, meat products, sweets, high-fat dairy and refined grains) or a Mediterranean dietary pattern rich in olive oil, fruits and vegetables, including whole grains, pulses and nuts, low-fat dairy, and moderate alcohol consumption (mainly red wine) appears as the best strategy to decrease diabetes risk, especially if dietary recommendations take into account individual preferences, thus enabling long-time adherence.

Olive oil and health: summary of the II international conference on olive oil and health consensus report, Jaén and Córdoba (Spain) 2008

Olive oil (OO) is the most representative food of the traditional Mediterranean Diet (MedDiet). Increasing evidence suggests that monounsaturated fatty acids (MUFA) as a nutrient, OO as a food, and the MedDiet as a food pattern are associated with a decreased risk of cardiovascular disease, obesity, metabolic syndrome, type 2 diabetes and hypertension. A MedDiet rich in OO and OO per se has been shown to improve cardiovascular risk factors, such as lipid profiles, blood pressure, postprandial hyperlipidemia, endothelial dysfunction, oxidative stress, and antithrombotic profiles. Some of these beneficial effects can be attributed to the OO minor components. Therefore, the definition of the MedDiet should include OO. Phenolic compounds in OO have shown antioxidant and anti-inflammatory properties, prevent lipoperoxidation, induce favorable changes of lipid profile, improve endothelial function, and disclose antithrombotic properties. Observational studies from Mediterranean cohorts have suggested that dietary MUFA may be protective against age-related cognitive decline and Alzheimer's disease. Recent studies consistently support the concept that the OO-rich MedDiet is compatible with healthier aging and increased longevity. In countries where the population adheres to the MedDiet, such as Spain, Greece and Italy, and OO is the principal source of fat, rates of cancer incidence are lower than in northern European countries. Experimental and human cellular studies have provided new evidence on the potential protective effect of OO on cancer. Furthermore, results of case-control and cohort studies suggest that MUFA intake including OO is associated with a reduction in cancer risk (mainly breast, colorectal and prostate cancers).

Polyunsaturated fatty acids effect on serum triglycerides concentration in the presence of metabolic syndrome components. The Alaska-Siberia Project

Serum fatty acids (FAs) have wide effects on metabolism: Serum saturated fatty acids (SFAs) increase triglyceride (TG) levels in plasma, whereas polyunsaturated fatty acids (PUFAs) reduce them. Traditionally, Eskimos have a high consumption of omega-3 fatty acids (omega3 FAs); but the Westernization of their food habits has increased their dietary SFAs, partly reflected in their serum concentrations. We studied the joint effect of serum SFAs and PUFAs on circulating levels of TGs in the presence of metabolic syndrome components. We included 212 men and 240 women (age, 47.9 +/- 15.7 years; body mass index [BMI], 26.9 +/- 5.3) from 4 villages located in Alaska for a cross-sectional study. Generalized linear models were used to build surface responses of TG as functions of SFAs and PUFAs measured in blood samples adjusting by sex, BMI, and village. The effects of individual FAs were assessed by multiple linear regression analysis, and partial correlations (r) were calculated. The most important predictors for TG levels were glucose tolerance (r = 0.116, P = .018) and BMI (r = 0.42, P < .001). Triglyceride concentration showed negative associations with 20:3omega6 (r = -0.16, P = .001), 20:4omega6 (r = -0.14, P = .005), 20:5omega3 (r = -0.17, P < .001), and 22:5omega3 (r = -0.26, P < .001), and positive associations with palmitic acid (r = 0.16, P < .001) and 18:3omega3 (r = 0.15, P < .001). The surface response analysis suggested that the effect of palmitic acid on TG is blunted in different degrees according to the PUFA chemical structure. The long-chain omega3, even in the presence of high levels of saturated fat, was associated with lower TG levels. Eicosapentaenoic acid (20:5omega3) had the strongest effect against palmitic acid on TG. The total FA showed moderate association with levels of TG, whereas SFA was positively associated and large-chain PUFA was negatively associated. The Westernized dietary habits among Eskimos are likely to change their metabolic profile and increase comorbidities related to metabolic disease.

Changes in the serum composition of free-fatty acids during an intravenous glucose tolerance test

Recent studies suggest that measuring the free-fatty acids (FFA) during an intravenous glucose tolerance test (IVGTT) may provide information about the metabolic associations between serum FFA and carbohydrate and insulin metabolism. We evaluated the FFA profile during an IVGTT and determined whether this test changes the composition and concentration of FFA. An IVGTT was given to 38 severely obese persons before and 7 months after undergoing bariatric surgery and also to 12 healthy, nonobese persons. The concentration and composition of the FFA were studied at different times during the test. The concentration of FFA fell significantly faster during the IVGTT in the controls and in the severely obese persons with normal-fasting glucose (NFG) than in the severely obese persons with impaired-fasting glucose (IFG) or type 2 diabetes mellitus (T2DM) (P < 0.05). Significant differences were found in the time to minimum serum concentrations of FFA (control = NFG < IFG < T2DM) (P < 0.001). These variables improved after bariatric surgery in the three groups. The percentage of monounsaturated and n-6 polyunsaturated FFA in the control subjects and in the obese persons, both before and after surgery, decreased significantly during the IVGTT. In conclusion, during an IVGTT, severely obese persons with IFG or T2DM experienced a lower fall in the FFA than the severely obese persons with NFG and the controls, becoming normal after bariatric surgery.

The potential role of olive oil-derived MUFA in insulin sensitivity

Dietary fatty acids play an important role in the development of insulin resistance, the prelude to type 2 diabetes mellitus. This review addresses the potential role of olive oil-derived MUFA in insulin sensitivity, particularly how dietary fat interacts with insulin resistance looking at whole body metabolic measures, as well as molecular effects. The review focuses on the role of non-esterified fatty acids, fatty acid composition in vivo and dietary fat modification on insulin resistance in the metabolic syndrome. Particular emphasis is placed on the role of olive oil within the context of dietary modification to improve insulin sensitivity and for the prevention of the metabolic syndrome.

Decreased levels of uric acid after oral glucose challenge is associated with triacylglycerol levels and degree of insulin resistance

Hyperuricaemia is one of the components of metabolic syndrome. Both oxidative stress and hyperinsulinism are important variables in the genesis of this syndrome and have a close association with uric acid (UA). We evaluated the effect of an oral glucose challenge on UA concentrations. The study included 656 persons aged 18 to 65 years. Glycaemia, insulin, UA and plasma proteins were measured at baseline and 120 min after an oral glucose tolerance test (OGTT). The baseline sample also included measurements of total cholesterol, triacylglycerol (TAG) and HDL-cholesterol. Insulin resistance was calculated with the homeostasis model assessment. UA levels were significantly lower after the OGTT (281·93 (sd92·19)v. 267·48 (sd90·40) μmol/l;P < 0·0001). Subjects with a drop in UA concentrations >40·86 μmol/l (>75th percentile) had higher plasma TAG levels (P = 0·0001), baseline insulin (P = 0·02) and greater insulin resistance (P = 0·034). Women with a difference in plasma concentrations of UA above the 75th percentile had higher baseline insulin levels (P = 0·019), concentration of plasma TAG (P = 0·0001) and a greater insulin resistance index (P = 0·029), whereas the only significant difference in men was the level of TAG. Multiple regression analysis showed that the basal TAG levels, insulin at 120 min, glycaemia at 120 min and waist:hip ratio significantly predicted the variance in the UA difference (r20·077). Levels of UA were significantly lower after the OGTT and the individuals with the greatest decrease in UA levels are those who have greater insulin resistance and higher TAG levels.