Macronutrient composition of the diet and prospective weight change in participants of the EPIC-PANACEA study

Low-Carbohydrate Diet Macronutrient Quality and Weight Change

Importance

The associations of low-carbohydrate diets (LCDs) with long-term weight management remains unclear, and the source and quality of macronutrients within LCDs are less explored.

Objectives

To prospectively examine associations between changes in LCD indices and weight change among US adults.

Design, Setting, and Participants

This prospective cohort study included initially healthy participants at baseline from the Nurses' Health Study (NHS; 1986-2010), Nurses' Health Study II (NHSII; 1991-2015), and Health Professionals Follow-up Study (HPFS; 1986-2018). Data analysis was performed between November 2022 and April 2023.

Exposures

Five LCD indices were examined: (1) a total LCD (TLCD) emphasizing overall lower carbohydrate intake; (2) an animal-based LCD (ALCD) that emphasized animal-sourced protein and fat; (3) a vegetable-based LCD (VLCD) that emphasized plant-sourced protein and fat; (4) a healthy LCD (HLCD) emphasizing less refined carbohydrates, more plant protein, and healthy fat; and (5) an unhealthy LCD (ULCD) emphasizing less healthful carbohydrates, more animal protein, and unhealthy fat.

Main Outcomes and Measures

The outcome of interest was 4-year changes in self-reported body weight.

Results

A total of 123 332 participants (mean [SD] age, 45.0 [9.7] years; 103 320 [83.8%] female) were included in this study. The median carbohydrate intake (as a percentage of energy) of the highest quintiles of TLCD score at baseline ranged from 38.3% in HPFS to 40.9% in NHSII. Mean weight gain over 4-year intervals among participants varied from 0.8 kg in the HPFS to 1.8 kg in the NHSII. After adjusting for demographics and baseline and concomitant changes of selected lifestyle factors, each 1-SD increase in TLCD score was associated with 0.06 (95% CI, 0.04-0.08) kg more weight gain over the 4-year periods. Similarly, participants gained 0.13 (95% CI, 0.11 to 0.14) kg per each 1-SD increase in ALCD score and 0.39 (95% CI, 0.37 to 0.40) kg per each 1-SD change in ULCD score. In contrast, each 1-SD increase in VLCD score was associated with 0.03 (95% CI, 0.01 to 0.04) kg less weight gain, and each 1-SD increase in HLCD score was associated with 0.36 (95% CI, 0.35 to 0.38) kg less weight gain. The associations were more pronounced among obese individuals (per 1-SD increase in HLCD score: BMI ≥30, 0.88 [95% CI, 0.80, 0.97] kg less weight gain; BMI <25, 0.23 [95% CI, 0.20, 0.26] kg less weight gain; P for interaction < .001).

Conclusions and Relevance

These findings suggest that the quality of LCDs may play a critical role in modulating long-term weight change. Only LCDs that emphasized high-quality protein, fat, and carbohydrates from whole grains and other plant-based foods were associated with less weight gain.

Dietary restriction of isoleucine increases healthspan and lifespan of genetically heterogeneous mice

Low-protein diets promote health and longevity in diverse species. Restriction of the branched-chain amino acids (BCAAs) leucine, isoleucine, and valine recapitulates many of these benefits in young C57BL/6J mice. Restriction of dietary isoleucine (IleR) is sufficient to promote metabolic health and is required for many benefits of a low-protein diet in C57BL/6J males. Here, we test the hypothesis that IleR will promote healthy aging in genetically heterogeneous adult UM-HET3 mice. We find that IleR improves metabolic health in young and old HET3 mice, promoting leanness and glycemic control in both sexes, and reprograms hepatic metabolism in a sex-specific manner. IleR reduces frailty and extends the lifespan of male and female mice, but to a greater degree in males. Our results demonstrate that IleR increases healthspan and longevity in genetically diverse mice and suggests that IleR, or pharmaceuticals that mimic this effect, may have potential as a geroprotective intervention.

Different carbohydrate exposures and weight gain-results from a pooled analysis of three population-based studies

BACKGROUND

The role of carbohydrate quantity and quality in weight gain remains unsolved, and research on carbohydrate subcategories is scarce. We examined total carbohydrates, dietary fiber, total sugar, and sucrose intake in relation to the risk of weight gain in Finnish adults.

METHODS

Our data comprised 8327 adults aged 25-70 years in three population-based prospective cohorts. Diet was assessed by a validated food frequency questionnaire and nutrient intakes were calculated utilizing the Finnish Food Composition Database. Anthropometric measurements were collected according to standard protocols. Two-staged pooling was applied to derive relative risks across cohorts for weight gain of at least 5% by exposure variable intake quintiles in a 7-year follow-up. Linear trends were examined based on a Wald test.

RESULTS

No association was observed between intakes of total carbohydrate, dietary fiber, total sugar or sucrose and the risk of weight gain of at least 5%. Yet, total sugar intake had a borderline protective association with the risk of weight gain in participants with obesity (RR 0.63; 95% CI 0.40-1.00 for highest vs. lowest quintile) and sucrose intake in participants with ≥10% decrease in carbohydrate intake during the follow-up (RR 0.78; 95% CI 0.61-1.00) after adjustments for sex, age, baseline weight, education, smoking, physical activity, and energy intake. Further adjustment for fruit consumption strengthened the associations.

CONCLUSIONS

Our findings do not support an association between carbohydrate intake and weight gain. However, the results suggested that concurrent changes in carbohydrate intake might be an important determinant of weight change and should be further examined in future studies.

The Role of Dietary Fats in the Development and Treatment of Endometriosis

Endometriosis is an estrogen-dependent disease in women of childbearing age that affects approximately 5–15% of the female population. The etiology of endometriosis is complex, multifaceted, and not fully understood. In endometriosis, which is an estrogen-related chronic inflammatory condition, estrogen plays a major role in endometrial cellular growth. High estrogen levels could be another risk factor for developing endometriosis. The aim of this review is to update knowledge on the impact of dietary fats on the development of endometriosis and chronic inflammation in women with endometriosis and diet therapy. Dietary fat may be linked with the progression and development of endometriosis, but studies have been contradictory due to various issues including sample size, different study designs, and different methodological aspects. Results have shown that the risk of endometriosis may increase with a higher consumption of products rich in saturated fats, especially palmitic acid and trans-unsaturated fatty acids. Monounsaturated fats and omega-3 polyunsaturated fatty acids may likely be connected with a lower risk of developing endometriosis and with reductions in the severity of disease. Monounsaturated fats, omega-3 polyunsaturated fatty acids, and a suitable eicosapentaenoic acid to arachidonic acid ratio can be used in diet therapy to improve quality of life by reducing pain and inflammation. Further research is needed in order to fully understand the influence of dietary fats on the risk of development of this disease.

Dietary Intake of 91 Individual Polyphenols and 5-Year Body Weight Change in the EPIC-PANACEA Cohort

Polyphenols are bioactive compounds from plants with antioxidant properties that may have a protective role against body weight gain, with adipose tissue and systemic oxidative stress as potential targets. We aimed to investigate the dietary intake of individual polyphenols and their association with 5-year body weight change in a sub-cohort of the European Prospective Investigation into Cancer and Nutrition (EPIC). This study included 349,165 adult participants from nine European countries. Polyphenol intake was estimated through country-specific validated dietary questionnaires and the Phenol-Explorer database. Body weight was obtained at recruitment and after a mean follow-up time of 5 years. Associations were estimated using multilevel mixed linear regression models. From 91 polyphenols included, the majority (n = 67) were inversely associated with 5-year body weight change after FDR-correction (q < 0.05). The greatest inverse associations were observed for quercetin 3-O-rhamnoside (change in weight for doubling in intake: −0.071 (95% CI: −0.085; −0.056) kg/5 years). Only 13 polyphenols showed positive associations with body weight gain, mainly from the subclass hydroxycinnamic acids (HCAs) with coffee as the main dietary source, such as 4-caffeoylquinic acid (0.029 (95% CI: 0.021; 0.038) kg/5 years). Individual polyphenols with fruit, tea, cocoa and whole grain cereals as the main dietary sources may contribute to body weight maintenance in adults. Individual HCAs may have different roles in body weight change depending on their dietary source.

Genome-Wide Association Analysis of Over 170,000 Individuals from the UK Biobank Identifies Seven Loci Associated with Dietary Approaches to Stop Hypertension (DASH) Diet

Diet is a modifiable risk factor for common chronic diseases and mental health disorders, and its effects are under partial genetic control. To estimate the impact of diet on individual health, most epidemiological and genetic studies have focused on individual aspects of dietary intake. However, analysing individual food groups in isolation does not capture the complexity of the whole diet pattern. Dietary indices enable a holistic estimation of diet and account for the intercorrelations between food and nutrients. In this study we performed the first ever genome-wide association study (GWA) including 173,701 individuals from the UK Biobank to identify genetic variants associated with the Dietary Approaches to Stop Hypertension (DASH) diet. DASH was calculated using the 24 h-recall questionnaire collected by UK Biobank. The GWA was performed using a linear mixed model implemented in BOLT-LMM. We identified seven independent single-nucleotide polymorphisms (SNPs) associated with DASH. Significant genetic correlations were observed between DASH and several educational traits with a significant enrichment for genes involved in the AMP-dependent protein kinase (AMPK) activation that controls the appetite by regulating the signalling in the hypothalamus. The colocalization analysis implicates genes involved in body mass index (BMI)/obesity and neuroticism (ARPP21, RP11-62H7.2, MFHAS1, RHEBL1). The Mendelian randomisation analysis suggested that increased DASH score, which reflect a healthy diet style, is causal of lower glucose, and insulin levels. These findings further our knowledge of the pathways underlying the relationship between diet and health outcomes. They may have significant implications for global public health and provide future dietary recommendations for the prevention of common chronic diseases.

Sex and genetic background define the metabolic, physiologic, and molecular response to protein restriction

Low-protein diets promote metabolic health in humans and rodents. Despite evidence that sex and genetic background are key factors in the response to diet, most protein intake studies examine only a single strain and sex of mice. Using multiple strains and both sexes of mice, we find that improvements in metabolic health in response to reduced dietary protein strongly depend on sex and strain. While some phenotypes were conserved across strains and sexes, including increased glucose tolerance and energy expenditure, we observed high variability in adiposity, insulin sensitivity, and circulating hormones. Using a multi-omics approach, we identified mega-clusters of differentially expressed hepatic genes, metabolites, and lipids associated with each phenotype, providing molecular insight into the differential response to protein restriction. Our results highlight the importance of sex and genetic background in the response to dietary protein level, and the potential importance of a personalized medicine approach to dietary interventions.

Multi-Trajectories of Macronutrient Intake and Their Associations with Obesity among Chinese Adults from 1991 to 2018: A Prospective Study

Studies on macronutrient intake and obesity have been inconclusive. This study examined the associations between multi-trajectories of macronutrients and the risk of obesity in China. We used data from 7914 adults who participated in the China Health and Nutrition Survey at least three times from 1991 to 2018. We collected detailed dietary data by conducting three 24 h dietary recalls and weighing foods and condiments in household inventories. We identified multi-trajectories using group-based multi-trajectory models and examined their associations with the risk of obesity with multiple Cox regression models. We found four multi-trajectories in rural areas: balanced macronutrient intake (BM), moderate protein, increasing low fat, and decreasing high carbohydrate (MP&ILF&DHC); decreasing moderate protein, decreasing high fat, and increasing moderate carbohydrate (DMP&DHF&IMC); increasing moderate protein, increasing high fat, and decreasing low carbohydrate (IMP&IHF&DLC)-35.1%, 21.3%, 20.1%, and 23.5% of our rural participant population, respectively. Compared with the BM trajectory, the hazard ratios of obesity in the DMP&DHF&IMC and the IMP&IHF&DLC groups were 0.50 (95% confidence interval (CI): 0.27-0.95) and 0.48 (95% CI: 0.28-0.83), respectively, in rural participants. Relatively low carbohydrate and high fat intakes with complementary dynamic trends are associated with a lower risk of obesity in rural Chinese adults.

The Multifaceted Role of Nutrient Sensing and mTORC1 Signaling in Physiology and Aging

The mechanistic Target of Rapamycin (mTOR) is a growth-related kinase that, in the context of the mTOR complex 1 (mTORC1), touches upon most fundamental cellular processes. Consequently, its activity is a critical determinant for cellular and organismal physiology, while its dysregulation is commonly linked to human aging and age-related disease. Presumably the most important stimulus that regulates mTORC1 activity is nutrient sufficiency, whereby amino acids play a predominant role. In fact, mTORC1 functions as a molecular sensor for amino acids, linking the cellular demand to the nutritional supply. Notably, dietary restriction (DR), a nutritional regimen that has been shown to extend lifespan and improve healthspan in a broad spectrum of organisms, works via limiting nutrient uptake and changes in mTORC1 activity. Furthermore, pharmacological inhibition of mTORC1, using rapamycin or its analogs (rapalogs), can mimic the pro-longevity effects of DR. Conversely, nutritional amino acid overload has been tightly linked to aging and diseases, such as cancer, type 2 diabetes and obesity. Similar effects can also be recapitulated by mutations in upstream mTORC1 regulators, thus establishing a tight connection between mTORC1 signaling and aging. Although the role of growth factor signaling upstream of mTORC1 in aging has been investigated extensively, the involvement of signaling components participating in the nutrient sensing branch is less well understood. In this review, we provide a comprehensive overview of the molecular and cellular mechanisms that signal nutrient availability to mTORC1, and summarize the role that nutrients, nutrient sensors, and other components of the nutrient sensing machinery play in cellular and organismal aging.

Double burden of underweight and overweight among Indian adults: spatial patterns and social determinants

OBJECTIVE

The current study explores the spatial patterns of underweight and overweight among adult men and women in districts of India and identifies the micro-geographical locations where the risks of underweight and overweight are simultaneously prevalent, after accounting for demographic and socio-economic factors.

DESIGN

We relied on BMI (weight (kg)/height squared (m2)), a measure of nutritional status among adult individuals, from the 2015-2016 National Family and Health Survey. Underweight was defined as <18·5 kg/m2 and overweight as ≥25·0 kg/m2.

SETTING

We adopted Bayesian structured additive quantile regression to model the underlying spatial structure in underweight and overweight burden.

PARTICIPANTS

Men aged 15-54 years (sample size: 108 092) and women aged 15-49 years (sample size: 642 002).

RESULTS

About 19·7 % of men and 22·9 % of women were underweight, and 19·6 % of men and 20·6 % of women were overweight. Results indicate that malnutrition burden in adults exhibits geographical divides across the country. Districts located in the central, western and eastern regions show higher risks of underweight. There is evidence of substantial spatial clustering of districts with higher risk of overweight in southern and northern India. While finding a little evidence on double burden of malnutrition among population groups, we identified a total of sixty-six double burden districts.

CONCLUSIONS

The current study demonstrates that the geographical burden of overweight in Indian adults is yet to surpass that of underweight, but the coexistence of double burden of underweight and overweight in selected regions presents a new challenge for improving nutritional status and necessitates specialised policy initiatives.

Macronutrient composition of the diet and long-term changes in weight and waist circumference in the EPIC-Italy cohort

BACKGROUND AND AIMS

The overall macronutrient composition of diet, rather than just calorie intake, may influence long-term changes of anthropometry. We investigated relationships between dietary macronutrient composition and long-term changes in weight and waist circumference in participants of the EPIC-Italy - the Italian section of the European Prospective Investigation into Cancer and Nutrition - study.

METHODS AND RESULTS

A total of 32,119 participants provided anthropometric measures at recruitment and 12 years later (mean). Diet at recruitment was assessed using validated semi-quantitative food frequency questionnaires. Weight and waist changes associated with replacing 10% of energy from one macronutrient with 10% of energy from another macronutrient were assessed by multivariable linear regression. Increased energy from total protein at the expense of any other macronutrient was significantly associated with increased weight and waist circumference. Increased starch at the expense of sugar and total protein was associated with significantly decreased weight and waist circumference; when starch replaced total fat, weight significantly decreased. Increased sugar at the expense of starch and total fat was significantly associated with increased weight and waist circumference; but increase at the expense of total protein was significantly associated with decreased weight and waist circumference.

CONCLUSION

Our results suggest that increasing protein at the expense of fat or carbohydrates, and reducing starch by increasing other macronutrients, might be associated with increased weight and waist gain.

Lifelong restriction of dietary branched-chain amino acids has sex-specific benefits for frailty and lifespan in mice

Protein restricted (PR) diets promote health and longevity in many species. While the precise components of a PR diet that mediate the beneficial effects to longevity have not been defined, we recently showed that many metabolic effects of PR can be attributed to reduced dietary levels of the branched-chain amino acids (BCAAs) leucine, isoleucine, and valine. Here, we demonstrate that restricting dietary BCAAs increases the survival of two different progeroid mouse models, delays frailty and promotes the metabolic health of wild-type C57BL/6J mice when started in midlife, and leads to a 30% increase in lifespan and a reduction in frailty in male, but not female, wild-type mice when fed lifelong. Our results demonstrate that restricting dietary BCAAs can increase healthspan and longevity in mice, and suggest that reducing dietary BCAAs may hold potential as a translatable intervention to promote healthy aging.

Genomic analysis of diet composition finds novel loci and associations with health and lifestyle

We conducted genome-wide association studies (GWAS) of relative intake from the macronutrients fat, protein, carbohydrates, and sugar in over 235,000 individuals of European ancestries. We identified 21 unique, approximately independent lead SNPs. Fourteen lead SNPs are uniquely associated with one macronutrient at genome-wide significance (P < 5 × 10^-8), while five of the 21 lead SNPs reach suggestive significance (P < 1 × 10^-5) for at least one other macronutrient. While the phenotypes are genetically correlated, each phenotype carries a partially unique genetic architecture. Relative protein intake exhibits the strongest relationships with poor health, including positive genetic associations with obesity, type 2 diabetes, and heart disease (r_g ≈ 0.15-0.5). In contrast, relative carbohydrate and sugar intake have negative genetic correlations with waist circumference, waist-hip ratio, and neighborhood deprivation (|r_g| ≈ 0.1-0.3) and positive genetic correlations with physical activity (r_g ≈ 0.1 and 0.2). Relative fat intake has no consistent pattern of genetic correlations with poor health but has a negative genetic correlation with educational attainment (r_g ≈-0.1). Although our analyses do not allow us to draw causal conclusions, we find no evidence of negative health consequences associated with relative carbohydrate, sugar, or fat intake. However, our results are consistent with the hypothesis that relative protein intake plays a role in the etiology of metabolic dysfunction.

Risk of metabolic syndrome and metabolic phenotypes in relation to biomarker-calibrated estimates of energy and protein intakes: an investigation from the Women's Health Initiative

BACKGROUND

Metabolic syndrome (MetS) is associated with increased mortality independent of BMI, resulting in discordant metabolic phenotypes, such as metabolically healthy obese and metabolically unhealthy normal-weight individuals. Studies investigating dietary intake in MetS have reported mixed results, due in part to the limitations of self-reported measures.

OBJECTIVES

To investigate the role of biomarker-calibrated estimates of energy and protein in MetS and metabolic phenotypes.

METHODS

Postmenopausal participants from the Women's Health Initiative (WHI) study who were free of MetS at baseline, had available data from FFQs at baseline, and had components of MetS at Year 3 (n = 3963) were included. Dietary energy and protein intakes were estimated using biomarker calibration methods. MetS was defined as 3 or more of the following: elevated serum triglycerides (≥150 mg/dL), low HDL cholesterol (<50 mg/dL), hypertension [systolic blood pressure (BP) ≥130 or diastolic BP ≥85 mmHg], elevated serum glucose (>100 mg/dL), and abdominal adiposity (waist circumference > 89 cm). Models were adjusted for age, WHI study component, race/ethnicity, education, income, smoking, recreational physical activity, disease history, and parity.

RESULTS

For every 10% increment in total calibrated energy intake, women were at a 1.37-fold elevated risk of MetS (95% CI, 1.15-1.63); a 10% increment in calibrated total protein intake was associated with a 1.21-fold elevated risk of MetS (95% CI, 1.00-1.47). Specifically, animal protein intake was associated with MetS (OR, 1.08; 95% CI, 1.02-1.14), whereas vegetable protein intake was not (OR, 0.99; 95% CI, 0.95-1.03). No differences were seen when examining metabolic phenotypes.

CONCLUSIONS

We found that higher calibrated total energy, total protein, and total animal protein intakes were strongly associated with MetS. If replicated in clinical trials, these results will have implications for the promotion of energy and animal protein restrictions for the reduction of MetS risks.

Effects of a Multicomponent Exercise Program, a Detraining Period and Dietary Intake Prediction of Body Composition of Frail and Pre-Frail Older Adults from the EXERNET Elder 3.0 Study

The aging of humans is associated with body composition and function deterioration creating a burden on an individual level, but also on a societal one, resulting in an economic burden that is socially unsustainable. This study aimed to evaluate changes in body composition after a 6-month MCT (multicomponent training) and a 4-month detraining period, and to examine the possible influence of energy and macronutrient intake in these changes in frail and pre-frail older adults. A total of 43 participants from the training group (TRAIN) and 28 controls (CON) completed the study protocol. Body weight, body mass index (BMI), waist and hip circumferences, fat mass, fat free mass and fat mass percentage were recorded, with a bio-electrical impedance analyzer, at baseline, after 6 months and four months after finishing the MCT. A food frequency questionnaire was used to estimate energy intake. Mixed effect models did not show differences between groups. CON showed increases in hip circumference and waist (3.20 ± 1.41 and 3.06 ± 1.66 cm, respectively) during the first 6 months. TRAIN showed decreases in BMI (−0.29 ± 0.14), fat mass (−0.86 ± 0.38 kg), body fat percentage (−0.98 ± 0.36%) and increases in waist circumference (3.20 ± 1.41). After detraining, TRAIN group showed increases in fat mas (1.07 ± 0.30 kg), body fat percentage (1.43 ± 0.31%) and waist (3.92 ± 1.38 cm), and decreases in fat free mass (−0.90 ± 0.30 kg). CON group only showed an increase in body fat (1.32 ± 0.47%). Energy intake was negatively associated with hip circumference in the first six months and fat mass during detraining in CON. Energy intake showed positive associations with fat mass in TRAIN during detraining. Only carbohydrates were negatively related to detraining changes in fat free mass and BMI in CON. In conclusion, the MCT reduces adiposity of frail and pre-frail older people, leading to a maintenance of fat free mass. In addition, these interventions should not be stopped in this population in order to improve health sustainability.

Associations of fat and carbohydrate intake with becoming overweight and obese: an 11-year longitudinal cohort study

The effects of macronutrient intake on obesity are controversial. This research aims to investigate the associations between macronutrient intake and new-onset overweight/obesity. The relationship between the consumption of carbohydrate and total fat and obesity was assessed by the multivariable Cox model in this 11-year cohort, which included 6612 adults (3291 men and 3321 women) who were free of overweight and obesity at baseline. The dietary intake was recorded using a 24-h recall method for three consecutive days. Moreover, substitution models were developed to distinguish the effects of macronutrient composition alteration from energy intake modification. During 7·5 person years (interquartile range 4·3, 10·8) of follow-up, 1807 participants became overweight or obese. After adjusting for risk factors, the hazard ratio (HR) of overweight/obesity in extreme quintiles of fat was 1·48 (quintile 5 v. quintile 1, 95 % CI 1·16, 1·89; Ptrend = 0·02) in women. Additionally, replacing 5 % of energy from carbohydrate with equivalent energy from fat was associated with an estimated 4·3 % (HR 1·043, 95 % CI 1·007, 1·081) increase in overweight/obesity in women. Moreover, dietary carbohydrate was inversely associated with overweight/obesity (quintile 5 v. quintile 1, HR 0·70, 95 % CI 0·55, 0·89; Ptrend = 0·02) in women. Total fat was related to a higher risk of overweight/obesity, whereas high carbohydrate intake was related to a lower risk of overweight/obesity in women, which was not observed in men.

Interaction between the genetic risk score and dietary protein intake on cardiometabolic traits in Southeast Asian

Background

Cardiometabolic diseases are complex traits which are influenced by several single nucleotide polymorphisms (SNPs). Thus, analysing the combined effects of multiple gene variants might provide a better understanding of disease risk than using a single gene variant approach. Furthermore, studies have found that the effect of SNPs on cardiometabolic traits can be influenced by lifestyle factors, highlighting the importance of analysing gene-lifestyle interactions.

Aims

In the present study, we investigated the association of 15 gene variants with cardiometabolic traits and examined whether these associations were modified by lifestyle factors such as dietary intake and physical activity.

Methods

The study included 110 Minangkabau women [aged 25–60 years and body mass index (BMI) 25.13 ± 4.2 kg/m²] from Padang, Indonesia. All participants underwent a physical examination followed by anthropometric, biochemical and dietary assessments and genetic tests. A genetic risk score (GRS) was developed based on 15 cardiometabolic disease-related SNPs. The effect of GRS on cardiometabolic traits was analysed using general linear models. GRS-lifestyle interactions on continuous outcomes were tested by including the interaction term (e.g. lifestyle factor*GRS) in the regression model. Models were adjusted for age, BMI and location (rural or urban), wherever appropriate.

Results

There was a significant association between GRS and BMI, where individuals carrying 6 or more risk alleles had higher BMI compared to those carrying 5 or less risk alleles (P = 0.018). Furthermore, there were significant interactions of GRS with protein intake on waist circumference (WC) and triglyceride concentrations (P_interaction = 0.002 and 0.003, respectively). Among women who had a lower protein intake (13.51 ± 1.18% of the total daily energy intake), carriers of six or more risk alleles had significantly lower WC and triglyceride concentrations compared with carriers of five or less risk alleles (P = 0.0118 and 0.002, respectively).

Conclusions

Our study confirmed the association of GRS with higher BMI and further showed a significant effect of the GRS on WC and triglyceride levels through the influence of a low-protein diet. These findings suggest that following a lower protein diet, particularly in genetically predisposed individuals, might be an effective approach for addressing cardiometabolic diseases among Southeast Asian women.

Next Generation Strategies for Geroprotection via mTORC1 Inhibition

Inhibition of mTORC1 (mechanistic Target Of Rapamycin Complex 1) with the pharmaceutical rapamycin prolongs the lifespan and healthspan of model organisms including rodents, with evidence now emerging that rapamycin and its analogs may also have rejuvenative effects in dogs and humans. However, the side effects associated with long-term rapamycin treatment, many of which are due to inhibition of a second mTOR complex, mTORC2, have seemed to preclude the routine use of rapamycin as a therapy for age-related diseases. Here, we discuss recent findings suggesting that strong, chronic inhibition of both mTOR complexes may not be necessary to realize the geroprotective effects of rapamycin. Instead, modestly but specifically inhibiting mTORC1 via a variety of emerging techniques, including intermittent or transient treatment with rapamycin derivatives, or specific dietary regimens, may be sufficient to promote health and longevity with reduced side effects. We will also discuss prospects for the development of new molecules that, by harnessing the detailed molecular understanding of mTORC1 signaling developed over the last decade, will provide new routes to the selective inhibition of mTORC1. We conclude that therapies based on the selective inhibition of mTORC1 may soon permit the safer treatment of diseases of aging.

A word of caution against excessive protein intake

Dietary protein is crucial for human health because it provides essential amino acids for protein synthesis. In addition, dietary protein is more satiating than carbohydrate and fat. Accordingly, many people consider the protein content when purchasing food and beverages and report 'trying to eat more protein'. The global market for protein ingredients is projected to reach approximately US$90 billion by 2021, largely driven by the growing demand for protein-fortified food products. This Perspective serves as a caution against the trend of protein-enriched diets and provides an evidence-based counterpoint that underscores the potential adverse public health consequences of high protein intake.

The association of dietary macronutrients with anthropometric changes, using iso-energetic substitution models: Tehran lipid and glucose study

Background

The consequences of optimal dietary macronutrient compositions especially quality of proteins on weight gain still remain controversial. The aim of the current study was to evaluate the iso-energetic substitution of dietary macronutrients in relation to anthropometric changes.

Methods

This prospective study was conducted on 2999 men and 4001 women aged 20–70 years who were followed for 3.6 years. A valid and reliable 168-item semi-quantitative food frequency questionnaire was used to assess usual dietary intakes. Weight (kg) and waist circumference (WC) (cm) changes were calculated by subtracting the weight and WC at baseline from their measurements at follow up. Participants were divided into two groups; those with no change or decrease in weight or WC and those with increase in weight or WC. Dietary macronutrients (percentage of energy) divided by 5 to calculate one unit.

Results

A one unit higher proportion of carbohydrates at the expense of all types of fatty acids was associated with weight loss in men (P < 0.05). A one unit higher proportion of plant proteins at the expense of animal protein (β = − 0.84), non-starch carbohydrates (β = − 0.86), saturated fat (β = − 0.76), mono-unsaturated fat (β = − 0.76) and poly-unsaturated fat (β = − 0.86) was associated with weight loss (P < 0.05). A one unit higher proportion of plant proteins at the expense of animal proteins (OR: 0.49), non-starch carbohydrates (OR: 0.49), saturated fat (OR: 0.49), mono-unsaturated fat (OR: 0.49), and poly-unsaturated fat (OR: 0.48) was associated with a lower risk of increase in WC (P < 0.05).

Conclusions

A higher proportion of dietary plant protein in replacement of simple carbohydrates, fats and animal proteins was associated with a lower increase in weight or WC.

Nature's bountiful gift to humankind: Vegetables & fruits & their role in cardiovascular disease & diabetes

Fruits and vegetables (FVs) are recognized as healthy constituents of diet and a sustainable solution to the existing twin burden of micronutrient deficiencies and non-communicable diseases in developing and developed countries. In general, FVs are nutrient dense foods low in energy, containing varying amounts of vitamins and minerals including carotenoids, B vitamins, vitamin C, iron, zinc, potassium, calcium, magnesium and fibre. These are abundantly rich in phytochemicals that function as antioxidants, anti-atherosclerotic and anti-inflammatory agents. This review summarizes some epidemiological, prospective cohort and intervention studies on the health benefits of FVs in relation to cardiovascular disease, obesity and diabetes. The rich varieties of FVs available, their composition, production scenario in India, dietary intake and trends over time, barriers to sufficient intake mainly sociocultural, economic and horticulture environment, policies for promotion and prevention of diseases are considered.

Modest changes to glycemic regulation are sufficient to maintain glucose fluxes in healthy young men following overfeeding with a habitual macronutrient composition

Currently, it is unclear whether short-term overfeeding in healthy people significantly affects postprandial glucose regulation, as most human overfeeding studies have utilized induced experimental conditions such as the euglycemic-hyperinsulinemic clamp technique to assess glucoregulation. The aim of this study was to quantify glucose fluxes [rates of meal glucose appearance (R_a), disposal (R_d), and endogenous glucose production (EGP)] in response to 5 and 28 days of overfeeding (+45% energy) while maintaining habitual macronutrient composition (31.0 ± 1.9% fat, 48.6 ± 2.2% carbohydrate, 16.7 ± 1.4% protein) in healthy, lean young men. Meal tolerance testing was combined with the triple-stable isotope glucose tracer approach. Visceral adipose volume increased by ~15% with 5 days of overfeeding, while there was no further change at 28 days. In contrast, body mass (+1.6 kg) and fat mass (+1.3 kg) were significantly increased only after 28 days of overfeeding. Fasting EGP, R_d, and insulin were increased at 5 but unchanged after 28 days. Postprandial glucose and insulin responses were unaltered by 5 days of overfeeding but were modestly increased after 28 days (P < 0.05). However, meal R_a and glucose R_d were significantly increased after both 5 and 28 days of overfeeding (P < 0.05). Despite this, overfeeding did not lead to alterations to postprandial EGP suppression. Thus, in contrast to findings from euglycemic-hyperinsulinemic clamp studies, chronic overfeeding did not affect the ability to suppress EGP or stimulate R_d under postprandial conditions. Rather, glucose flux was appropriately maintained following 28 days of overfeeding through modest increases in postprandial glycemia and insulinemia.

Diet-Derived Fatty Acids, Brain Inflammation, and Mental Health

Western societies experienced drastic changes in eating habits during the past century. The modern nutritional profile, typically rich in saturated fats and refined sugars, is recognized as a major contributing factor, along with reduced physical activity, to the current epidemics of metabolic disorders, notably obesity and diabetes. Alongside these conditions, recent years have witnessed a gradual and significant increase in prevalence of brain diseases, particularly mood disorders. While substantial clinical/epidemiological evidence supports a correlation between metabolic and neuropsychiatric disorders, the mechanisms of pathogenesis in the latter are often multifactorial and causal links have been hard to establish. Neuroinflammation stands out as a hallmark feature of brain disorders that may be linked to peripheral metabolic dyshomeostasis caused by an unhealthy diet. Dietary fatty acids are of particular interest, as they may play a dual role, both as a component of high-calorie obesogenic diets and as signaling molecules involved in inflammatory responses. Here, we review current literature connecting diet-related nutritional imbalance and neuropsychiatric disorders, focusing on the role of dietary fatty acids as signaling molecules directly relevant to inflammatory processes and to neuronal function.

Early-life obesity and adulthood colorectal cancer risk: a meta-analysis

Objective

This meta-analysis examines the relationship between early-life obesity and risk of colorectal cancer (CRC) in adulthood.

Methods

A systematic search of Google Scholar, PubMed, and reference data was conducted. Fifteen relevant studies were identified and meta-analyzed, for men and women separately. A random-effects model was used to compare the multivariable-adjusted relative risks (RR) of overall and subsite-specific CRC to the highest versus lowest categories of body mass index (BMI) in early life. Meta-regression was performed on factors that may have contributed to between-study heterogeneity.

Results

High early-life BMI was associated with a 39% increased risk of CRC in adult men (RR = 1.39, 95%CI = 1.20 – 1.62, P < 0.0001) and a 19% increased risk of CRC in adult women (RR = 1.19, 95%CI = 1.06 – 1.35, P = 0.004). No statistically significant heterogeneity was identified in meta-regression according to tumor subsite (RR = 1.06, 95%CI = 0.97 – 1.17, RR = 1.08, 95%CI = 0.99 – 1.18 for male and female proximal colon cancer; RR = 1.51, 95%CI = 1.22 – 1.87, RR = 1.08, 95%CI = 0.98 – 1.19 for male and female distal colon cancer; and RR = 1.39, 95%CI = 1.1 – 1.77, RR = 1.51, 95%CI = 0.94 – 2.03 for male and female rectal cancer) or other factors, including age of BMI assessment, self-reported or measured BMI, and adjustment for smoking.

Conclusions

The results suggest that high early-life BMI is associated with increased risk of CRC in adulthood. Further studies should investigate adult CRC risk in early-life obese individuals from non-Western countries and the underlying mechanisms by which early-life adiposity may influence CRC pathogenesis.

Higher vegetable protein consumption, assessed by an isoenergetic macronutrient exchange model, is associated with a lower presence of overweight and obesity in the web-based Food4me European study

The objective was to evaluate differences in macronutrient intake and to investigate the possible association between consumption of vegetable protein and the risk of overweight/obesity, within the Food4Me randomised, online intervention. Differences in macronutrient consumption among the participating countries grouped by EU Regions (Western Europe, British Isles, Eastern Europe and Southern Europe) were assessed. Relation of protein intake, within isoenergetic exchange patterns, from vegetable or animal sources with risk of overweight/obesity was assessed through the multivariate nutrient density model and a multivariate-adjusted logistic regression. A total of 2413 subjects who completed the Food4Me screening were included, with self-reported data on age, weight, height, physical activity and dietary intake. As success rates on reducing overweight/obesity are very low, form a public health perspective, the elaboration of policies for increasing intakes of vegetable protein and reducing animal protein and sugars, may be a method of combating overweight/obesity at a population level.

Dietary Intake of Protein from Different Sources and Weight Regain, Changes in Body Composition and Cardiometabolic Risk Factors after Weight Loss: The DIOGenes Study

An increase in dietary protein intake has been shown to improve weight loss maintenance in the DIOGenes trial. Here, we analysed whether the source of the dietary proteins influenced changes in body weight, body composition, and cardiometabolic risk factors during the weight maintenance period while following an energy-restricted diet. 489 overweight or obese participants of the DIOGenes trial from eight European countries were included. They successfully lost >8% of body weight and subsequently completed a six month weight maintenance period, in which they consumed an ad libitum diet varying in protein content and glycemic index. Dietary intake was estimated from three-day food diaries. A higher plant protein intake with a proportional decrease in animal protein intake did not affect body weight maintenance or cardiometabolic risk factors. A higher plant protein intake from non-cereal products instead of cereal products was associated with benefits for body weight maintenance and blood pressure. Substituting meat protein for protein from other animal sources increased insulin and HOMA-IR (homeostasis model assessment of insulin resistance). This analysis suggests that not only the amount of dietary proteins, but also the source may be important for weight and cardiometabolic risk management. However, randomized trials are needed to test the causality of these associations.

Nutraceutical approaches to metabolic syndrome

Metabolic Syndrome (MetS), affecting at least 30% of adults in the Western World, is characterized by three out of five variables, from high triglycerides, to elevated waist circumference and blood pressure. MetS is not characterized by elevated cholesterolemia, but is rather the consequence of a complex interaction of factors generally leading to increased insulin resistance. Drug treatments are of difficult handling, whereas well-characterized nutraceuticals may offer an effective alternative. Among these, functional foods, e.g. plant proteins, have been shown to improve insulin resistance and reduce triglyceride secretion. Pro- and pre-biotics, that are able to modify intestinal microbiome, reduce absorption of specific nutrients and improve the metabolic handling of energy-rich foods. Finally, specific nutraceuticals have proven to be of benefit, in particular, red-yeast rice, berberine, curcumin as well as vitamin D. All these can improve lipid handling by the liver as well as ameliorate insulin resistance. While lifestyle approaches, such as with the Mediterranean diet, may prove to be too complex for the single patient, better knowledge of selected nutraceuticals and more appropriate formulations leading to improved bioavailability will certainly widen the use of these agents, already in large use for the management of these very frequent patient groups. Key messages Functional foods, e.g. plant proteins, improve insulin resistance. Pro- and pre-biotics improve the metabolic handling of energy-rich foods. Nutraceutical can offer a significant help in handling MetS patients being part of lifestyle recommendations.

The association of substituting carbohydrates with total fat and different types of fatty acids with mortality and weight change among diabetes patients

BACKGROUND

Substitution of carbohydrates with fat in a diet for type 2 diabetes patients is still debated.

OBJECTIVE

This study aimed to investigate the association between dietary carbohydrate intake and isocaloric substitution with (i) total fat, (ii) saturated fatty acids (SFA), (iii) mono-unsaturated fatty acids (MUFA) and (iv) poly-unsaturated fatty acids (PUFA) with all-cause and cardiovascular (CVD) mortality risk and 5-year weight change in patients with type 2 diabetes.

METHODS

The study included 6192 patients with type 2 diabetes from 15 cohorts of the European Prospective Investigation into Cancer and Nutrition (EPIC). Dietary intake was assessed at recruitment with country-specific food-frequency questionnaires. Cox and linear regression were used to estimate the associations with (CVD) mortality and weight change, adjusting for confounders and using different methods to adjust for energy intake.

RESULTS

After a mean follow-up of 9.2 y ± SD 2.3 y, 791 (13%) participants had died, of which 268 (4%) due to CVD. Substituting 10 g or 5 energy% of carbohydrates by total fat was associated with a higher all-cause mortality risk (HR 1.07 [1.02-1.13]), or SFAs (HR 1.25 [1.11-1.40]) and a lower risk when replaced by MUFAs (HR 0.89 [0.77-1.02]). When carbohydrates were substituted with SFAs (HR 1.22 [1.00-1.49]) or PUFAs (HR 1.29 [1.02-1.63]) CVD mortality risk increased. The 5-year weight was lower when carbohydrates were substituted with total fat or MUFAs. These results were consistent over different energy adjustment methods.

CONCLUSIONS

In diabetes patients, substitution of carbohydrates with SFAs was associated with a higher (CVD) mortality risk and substitution by total fat was associated with a higher all-cause mortality risk. Substitution of carbohydrates with MUFAs may be associated with lower mortality risk and weight reduction. Instead of promoting replacement of carbohydrates by total fat, dietary guideline should continue focusing on replacement by fat-subtypes; especially SFAs by MUFAs.

Main nutrient patterns are associated with prospective weight change in adults from 10 European countries

PURPOSE

Various food patterns have been associated with weight change in adults, but it is unknown which combinations of nutrients may account for such observations. We investigated associations between main nutrient patterns and prospective weight change in adults.

METHODS

This study includes 235,880 participants, 25-70 years old, recruited between 1992 and 2000 in 10 European countries. Intakes of 23 nutrients were estimated from country-specific validated dietary questionnaires using the harmonized EPIC Nutrient DataBase. Four nutrient patterns, explaining 67 % of the total variance of nutrient intakes, were previously identified from principal component analysis. Body weight was measured at recruitment and self-reported 5 years later. The relationship between nutrient patterns and annual weight change was examined separately for men and women using linear mixed models with random effect according to center controlling for confounders.

RESULTS

Mean weight gain was 460 g/year (SD 950) and 420 g/year (SD 940) for men and women, respectively. The annual differences in weight gain per one SD increase in the pattern scores were as follows: principal component (PC) 1, characterized by nutrients from plant food sources, was inversely associated with weight gain in men (-22 g/year; 95 % CI -33 to -10) and women (-18 g/year; 95 % CI -26 to -11). In contrast, PC4, characterized by protein, vitamin B2, phosphorus, and calcium, was associated with a weight gain of +41 g/year (95 % CI +2 to +80) and +88 g/year (95 % CI +36 to +140) in men and women, respectively. Associations with PC2, a pattern driven by many micro-nutrients, and with PC3, a pattern driven by vitamin D, were less consistent and/or non-significant.

CONCLUSIONS

We identified two main nutrient patterns that are associated with moderate but significant long-term differences in weight gain in adults.

Influence of body weight on bone mass, architecture and turnover

Weight-dependent loading of the skeleton plays an important role in establishing and maintaining bone mass and strength. This review focuses on mechanical signaling induced by body weight as an essential mechanism for maintaining bone health. In addition, the skeletal effects of deviation from normal weight are discussed. The magnitude of mechanical strain experienced by bone during normal activities is remarkably similar among vertebrates, regardless of size, supporting the existence of a conserved regulatory mechanism, or mechanostat, that senses mechanical strain. The mechanostat functions as an adaptive mechanism to optimize bone mass and architecture based on prevailing mechanical strain. Changes in weight, due to altered mass, weightlessness (spaceflight), and hypergravity (modeled by centrifugation), induce an adaptive skeletal response. However, the precise mechanisms governing the skeletal response are incompletely understood. Furthermore, establishing whether the adaptive response maintains the mechanical competence of the skeleton has proven difficult, necessitating the development of surrogate measures of bone quality. The mechanostat is influenced by regulatory inputs to facilitate non-mechanical functions of the skeleton, such as mineral homeostasis, as well as hormones and energy/nutrient availability that support bone metabolism. Although the skeleton is very capable of adapting to changes in weight, the mechanostat has limits. At the limits, extreme deviations from normal weight and body composition are associated with impaired optimization of bone strength to prevailing body size.

Decreased Consumption of Branched-Chain Amino Acids Improves Metabolic Health

Protein-restricted (PR), high-carbohydrate diets improve metabolic health in rodents, yet the precise dietary components that are responsible for these effects have not been identified. Furthermore, the applicability of these studies to humans is unclear. Here, we demonstrate in a randomized controlled trial that a moderate PR diet also improves markers of metabolic health in humans. Intriguingly, we find that feeding mice a diet specifically reduced in branched-chain amino acids (BCAAs) is sufficient to improve glucose tolerance and body composition equivalently to a PR diet via metabolically distinct pathways. Our results highlight a critical role for dietary quality at the level of amino acids in the maintenance of metabolic health and suggest that diets specifically reduced in BCAAs, or pharmacological interventions in this pathway, may offer a translatable way to achieve many of the metabolic benefits of a PR diet.

Dietary Protein Intake and Risk of Type 2 Diabetes in US Men and Women

Dietary proteins are important modulators of glucose metabolism. However, few longitudinal studies have evaluated the associations between intake of protein and protein type and risk of type 2 diabetes (T2D). We investigated the associations between total, animal, and vegetable protein and incident T2D in 72,992 women from the Nurses' Health Study (1984-2008), 92,088 women from Nurses' Health Study II (1991-2009) and 40,722 men from the Health Professionals Follow-up Study (1986-2008). During 4,146,216 person-years of follow-up, we documented 15,580 cases of T2D. In pooled multivariate models including body mass index, participants in the highest quintiles of percentage of energy derived from total protein and animal protein had 7% (95% confidence interval (CI): 1, 17) and 13% (95% CI: 6, 21) increased risks of T2D compared with those in the lowest quintiles, respectively. Percentage of energy intake from vegetable protein was associated with a moderately decreased risk of T2D (comparing extreme quintiles, hazard ratio =0.91, 95% CI: 0.84, 0.98). Substituting 5% of energy intake from vegetable protein for animal protein was associated with a 23% (95% CI: 16, 30) reduced risk of T2D. In conclusion, higher intake of animal protein was associated with an increased risk of T2D, while higher intake of vegetable protein was associated with a modestly reduced risk.

Association of Dietary Proportions of Macronutrients with Visceral Adiposity Index: Non-Substitution and Iso-Energetic Substitution Models in a Prospective Study

We aimed to investigate associations between dietary macronutrient proportions and prospective visceral adiposity index changes (ΔVAI). The study included 1254 adults (18–74 years), from the Tehran Lipid and Glucose Study (TLGS), who were followed for three years. Dietary intakes were assessed twice using food frequency questionnaires. Associations of dietary macronutrient with ΔVAI and risk of visceral adiposity dysfunction (VAD) after three years were investigated. The percentage of energy intake from protein in the total population, and from fat in women, were associated with higher increases in VAI. A 5% higher energy intake from protein substituted for carbohydrate, monounsaturated fatty acids (MUFAs), and polyunsaturated fatty acids (PUFAs) was associated with higher ΔVAI. Higher energy intake from animal protein substituted for PUFAs was positively associated with ΔVAI. Substituting protein and PUFAs with MUFAs were related to higher ΔVAI. The associations were similar in men and women, but reached significance mostly among women. Risk of VAD was increased when 1% of energy from protein was replaced with MUFAs. Substituting protein for carbohydrate and fat, and fat for carbohydrate, resulted in increased risk of VAD in women. Higher dietary proportions of protein and animal-derived MUFA may be positively associated with ΔVAI and risk of VAD.

Isocaloric substitution of carbohydrates with protein: the association with weight change and mortality among patients with type 2 diabetes

Background

The health impact of dietary replacement of carbohydrates with protein for patients with type 2 diabetes is still debated. This study aimed to investigate the association between dietary substitution of carbohydrates with (animal and plant) protein and 5-year weight change, and all-cause and cardiovascular (CVD) mortality risk in patients with type 2 diabetes.

Methods

The study included 6,107 diabetes patients from 15 European cohorts. Patients with type 1 diabetes were excluded. At recruitment, validated country-specific food-frequency questionnaires were used to estimate dietary intake. Multivariable adjusted linear regression was used to examine the associations between dietary carbohydrate substitution with protein and 5-year weight change, and Cox regression to estimate hazard ratios (HRs) for (CVD) mortality.

Results

Annual weight loss of patients with type 2 diabetes was 0.17 (SD 1.24) kg. After a mean follow-up of 9.2 (SD 2.3)y, 787 (13%) participants had died, of which 266 (4%) deaths were due to CVD. Substitution of 10 gram dietary carbohydrate with total (ß = 187 [75;299]g) and animal (ß = 196 [137;254]g) protein was associated with mean 5-year weight gain. Substitution for plant protein was not significantly associated with weight change (β = 82 [−421;584]g). Substitution with plant protein was associated with lower all-cause mortality risk (HR = 0.79 [0.64;0.97]), whereas substitution with total or animal protein was not associated with (CVD) mortality risk.

Conclusions

In diabetes patients, substitution with plant protein was beneficial with respect to weight change and all-cause mortality as opposed to substitution with animal protein. Therefore, future research is needed whether dietary guidelines should not actively promote substitution of carbohydrates by total protein, but rather focus on substitution of carbohydrates with plant protein.

Ability of self-reported estimates of dietary sodium, potassium and protein to detect an association with general and abdominal obesity: comparison with the estimates derived from 24 h urinary excretion

As under-reporting of dietary intake, particularly by overweight and obese subjects, is common in dietary surveys, biases inherent in the use of self-reported dietary information may distort true diet–obesity relationships or even create spurious ones. However, empirical evidence of this possibility is limited. The present cross-sectional study compared the relationships of 24 h urine-derived and self-reported intakes of Na, K and protein with obesity. A total of 1043 Japanese women aged 18–22 years completed a 24 h urine collection and a self-administered diet history questionnaire. After adjustment for potential confounders, 24 h urine-derived Na intake was associated with a higher risk of general obesity (BMI ≥ 25 kg/m2) and abdominal obesity (waist circumference ≥ 80 cm; both P for trend = 0·04). For 24 h urine-derived protein intake, positive associations with general and abdominal obesity were observed (P for trend = 0·02 and 0·053, respectively). For 24 h urine-derived K intake, there was an inverse association with abdominal obesity (P for trend = 0·01). Conversely, when self-reported dietary information was used, only inverse associations between K intake and general and abdominal obesity were observed (P for trend = 0·04 and 0·02, respectively), with no associations of Na or protein intake. In conclusion, we found positive associations of Na and protein intakes and inverse associations of K intake with obesity when using 24 h urinary excretion for estimating dietary intakes. However, no association was observed based on using self-reported dietary intakes, except for inverse association of K intake, suggesting that the ability of self-reported dietary information using the diet history questionnaire for investigating diet–obesity relationships is limited.

Understanding nutritional epidemiology and its role in policy

Nutritional epidemiology has recently been criticized on several fronts, including the inability to measure diet accurately, and for its reliance on observational studies to address etiologic questions. In addition, several recent meta-analyses with serious methodologic flaws have arrived at erroneous or misleading conclusions, reigniting controversy over formerly settled debates. All of this has raised questions regarding the ability of nutritional epidemiologic studies to inform policy. These criticisms, to a large degree, stem from a misunderstanding of the methodologic issues of the field and the inappropriate use of the drug trial paradigm in nutrition research. The exposure of interest in nutritional epidemiology is human diet, which is a complex system of interacting components that cumulatively affect health. Consequently, nutritional epidemiology constantly faces a unique set of challenges and continually develops specific methodologies to address these. Misunderstanding these issues can lead to the nonconstructive and sometimes naive criticisms we see today. This article aims to clarify common misunderstandings of nutritional epidemiology, address challenges to the field, and discuss the utility of nutritional science in guiding policy by focusing on 5 broad questions commonly asked of the field.

Interaction between genetic predisposition to adiposity and dietary protein in relation to subsequent change in body weight and waist circumference

Background

Genetic predisposition to adiposity may interact with dietary protein in relation to changes of anthropometry.

Objective

To investigate the interaction between genetic predisposition to higher body mass index (BMI), waist circumference (WC) or waist-hip ratio adjusted for BMI (WHR_BMI) and dietary protein in relation to subsequent change in body weight (ΔBW) or change in WC (ΔWC).

Design

Three different Danish cohorts were used. In total 7,054 individuals constituted the study population with information on diet, 50 single-nucleotide polymorphisms (SNPs) associated with BMI, WC or WHR_BMI, as well as potential confounders. Mean follow-up time was ∼5 years. Four genetic predisposition-scores were based on the SNPs; a complete-score including all selected adiposity- associated SNPs, and three scores including BMI, WC or WHR_BMI associated polymorphisms, respectively. The association between protein intake and ΔBW or ΔWC were examined and interactions between SNP-score and protein were investigated. Analyses were based on linear regressions using macronutrient substitution models and meta-analyses.

Results

When protein replaced carbohydrate, meta-analyses showed no associations with ΔBW (41.0 gram/y/5 energy% protein, [95% CI: −32.3; 114.3]) or ΔWC (<−0.1 mm/y/5 energy % protein, [−1.1; 1.1]). Similarly, there were no interactions for any SNP-scores and protein for either ΔBW (complete SNP-score: 1.8 gram/y/5 energy% protein/risk allele, [−7.0; 10.6]) or ΔWC (complete SNP-score: <0.1 mm/y/5 energy% protein/risk allele, [−0.1; 0.1]). Similar results were seen when protein replaced fat.

Conclusion

This study indicates that the genetic predisposition to general and abdominal adiposity, assessed by gene-scores, does not seem to modulate the influence of dietary protein on ΔBW or ΔWC.

Interactions of dietary protein and adiposity measures in relation to subsequent changes in body weight and waist circumference

OBJECTIVE

To investigate if dietary protein and degree of adiposity interacts in relation to change in body weight and waist circumference (WC) in the general population.

METHODS

In total 22,433 middle-aged individuals with dietary assessment at baseline and anthropometry at baseline and at follow-up about 5 years later were analyzed with multiple linear regression and dietary macronutrient substitution models. Interactions between dietary protein and baseline body mass index (BMI) and baseline WC adjusted for BMI (WCBMI ) (divided in tertiles; nine groups total), were analyzed in relation to changes in body weight (BW) and changes WC adjusted for change in BW.

RESULTS

Baseline intake of protein was not significantly associated with changes in weight or waist circumference. Across the nine groups of baseline BMI and WCBMI there were no distinct trends in the associations between dietary protein, whether replacing carbohydrate or fat, and weight change. However, individuals in the highest tertile of baseline BMI (irrespective of baseline WCBMI ) had significantly inverse change in waist circumference when protein replaced carbohydrate, but not when protein replaced fat.

CONCLUSION

Replacing carbohydrate with protein in the diet may prevent a relative increase in WC in individuals with a greater BMI.

High-protein diets and renal health

High-protein diets (i.e., protein content of more than 25% of energy or more than 2 g/kg body weight per day) based on meat and dairy products are repeatedly promoted for weight reduction and better health, but the evidence supporting these notions is quite dubious. As described in the present review, there is a reason to be concerned about adverse effects of such diets, including glomerular hyperfiltration, hypertensive effects of a concomitant increase in dietary sodium, and an increased risk of nephrolithiasis. These diet-induced physiological consequences might lead to an increase in the prevalence of chronic kidney disease in the general population without preexisting kidney disease. Accordingly, we find medical reasons to refrain from promoting high-protein diets, in particular those based on meat and dairy products, until clear-cut evidence for the safety and for the superiority of such diets on human health has been provided.

Body characteristics, [corrected] dietary protein and body weight regulation. Reconciling conflicting results from intervention and observational studies?

Background/Objectives

Physiological evidence indicates that high-protein diets reduce caloric intake and increase thermogenic response, which may prevent weight gain and regain after weight loss. Clinical trials have shown such effects, whereas observational cohort studies suggest an association between greater protein intake and weight gain. In both types of studies the results are based on average weight changes, and show considerable diversity in both directions. This study investigates whether the discrepancy in the evidence could be due to recruitment of overweight and obese individuals into clinical trials.

Subjects/Methods

Data were available from the European Diet, Obesity and Genes (DiOGenes) post-weight-loss weight-maintenance trial and the Danish Diet, Cancer and Health (DCH) cohort. Participants of the DCH cohort were matched with participants from the DiOGenes trial on gender, diet, and body characteristics. Different subsets of the DCH-participants, comparable with the trial participants, were analyzed for weight maintenance according to the randomization status (high or low protein) of the matched trial participants.

Results

Trial participants were generally heavier, had larger waist circumference and larger fat mass than the participants in the entire DCH cohort. A better weight maintenance in the high-protein group compared to the low protein group was observed in the subgroups of the DCH cohort matching body characteristics of the trial participants.

Conclusion

This modified observational study, minimized the differences between the RCT and observational data with regard to dietary intake, participant characteristics and statistical analysis. Compared with low protein diet the high protein diet was associated with better weight maintenance when individuals with greater body mass index and waist circumference were analyzed. Selecting subsets of large-scale observational cohort studies with similar characteristics as participants in clinical trials may reconcile the otherwise conflicting results.

Dietary protein intake and incidence of type 2 diabetes in Europe: the EPIC-InterAct Case-Cohort Study

OBJECTIVE

The long-term association between dietary protein and type 2 diabetes incidence is uncertain. We aimed to investigate the association between total, animal, and plant protein intake and the incidence of type 2 diabetes.

RESEARCH DESIGN AND METHODS

The prospective European Prospective Investigation into Cancer and Nutrition (EPIC)-InterAct case-cohort study consists of 12,403 incident type 2 diabetes cases and a stratified subcohort of 16,154 individuals from eight European countries, with an average follow-up time of 12.0 years. Pooled country-specific hazard ratios (HRs) and 95% CI of prentice-weighted Cox regression analyses were used to estimate type 2 diabetes incidence according to protein intake.

RESULTS

After adjustment for important diabetes risk factors and dietary factors, the incidence of type 2 diabetes was higher in those with high intake of total protein (per 10 g: HR 1.06 [95% CI 1.02-1.09], P(trend) < 0.001) and animal protein (per 10 g: 1.05 [1.02-1.08], P(trend) = 0.001). Effect modification by sex (P < 0.001) and BMI among women (P < 0.001) was observed. Compared with the overall analyses, associations were stronger in women, more specifically obese women with a BMI >30 kg/m(2) (per 10 g animal protein: 1.19 [1.09-1.32]), and nonsignificant in men. Plant protein intake was not associated with type 2 diabetes (per 10 g: 1.04 [0.93-1.16], P(trend) = 0.098).

CONCLUSIONS

High total and animal protein intake was associated with a modest elevated risk of type 2 diabetes in a large cohort of European adults. In view of the rapidly increasing prevalence of type 2 diabetes, limiting iso-energetic diets high in dietary proteins, particularly from animal sources, should be considered.

Dietary protein and urinary nitrogen in relation to 6-year changes in fat mass and fat-free mass

BACKGROUND

In contrast to the physiological expectation, observational studies show that greater protein intake is associated with subsequent body weight (BW) gain. An increase in fat-free mass (FFM) due to the anabolic effects of protein could explain this.

OBJECTIVE

To examine associations between protein intake and subsequent changes in fat mass (FM) and FFM in longitudinal, observational data.

DESIGN

A health examination, including measures of FM and FFM by bioelectrical impedance at baseline and follow-up 6 years later, was conducted. Diet history interviews (DHI) were performed, and 24-h urinary nitrogen collection at baseline was done. In total, 330 participants with DHI, of whom 227 had validated and complete 24-h urine collection data, were analyzed. Macronutrient energy substitution models were used.

RESULTS

Mean estimated protein intake was 14.6 E% from DHI and 11.3 E% from urinary nitrogen. Estimated from DHI, FM increased 46 g per year, with every 1 E% protein substituted for fat (95% confidence interval (CI) = 13, 79; P = 0.006), and FFM increased 15 g per year (1, 30; P = 0.046). Results were similar in other substitution models. Estimated from urinary nitrogen, FM increased 53 g per year, with 1 E% protein substituted for other macronutrients (24, 81; P < 0.0005), and FFM increased 18 g per year (6, 31; P = 0.004).

CONCLUSION

Within a habitual range, a greater protein intake was associated with BW gain, mostly in FM. This is in contrast to the expectations based on physiological and clinical trials, and calls for a better understanding of how habitual dietary protein influences long-term energy balance, versus how greater changes in dietary proteins may influence short-term energy balance.

The Association Between Diet and Obesity in Specific European Cohorts: DiOGenes and EPIC-PANACEA

This review summarizes evidence from two projects embedded within the European Prospective Investigation into Cancer and Nutrition (EPIC) on the association between dietary factors and obesity risk, in particular change in weight and waist circumference. A total of 12 publications from DiOGenes and six from EPIC-PANACEA were reviewed. The results show that dietary fiber, especially cereal fiber, was inversely associated with weight or waist change, as well as fruit/vegetable intake and the Mediterranean dietary pattern. Energy density and meat consumption were positively associated with the anthropometric changes, as was glycemic index with waist change. Clear associations with macronutrient composition were not observed. In additional studies, interactions with genetic polymorphism were investigated and shown to be present for protein intake and GI, although effect estimates were small. These interactions require replication. These results show that in European populations dietary factors are independently associated with weight/waist change. The findings provide further clues for the prevention of obesity.