Cardio-metabolic consequences of dietary carbohydrates: reconciling contradictions using nutritional geometry

Macronutrient interactions and models of obesity: Insights from nutritional geometry

The global obesity epidemic results from a complex interplay of genetic and environmental factors, with diet being a prominent modifiable element driving weight gain and adiposity. Although excess intake of energetic macronutrients is implicated in causing obesity, ongoing debate centers on whether sugar or fat or both are driving the rising obesity rates. This has led to competing models of obesity such as the "Carbohydrate Insulin Model", the "Energy Balance Model", and the "Fructose Survival Hypothesis". Conflicting evidence from studies designed to focus on individual energetic macronutrients or energy rather than macronutrient mixtures underlies this disagreement. Recent research in humans and animals employing the nutritional geometry framework (NGF) emphasizes the importance of considering interactions among dietary components. Protein interacts with carbohydrates, fats, and dietary energy density to influence both calorie intake ("protein leverage") and, directly and indirectly, metabolic physiology and adiposity. Consideration of these interactions can help to reconcile different models of obesity, and potentially cast new light on obesity interventions.

Macronutrient composition of plant-based diets and breast cancer risk: the E3N prospective cohort study

PURPOSE

Recent evidence suggests that plant-based diets may reduce the risk of breast cancer (BC). However, the macronutrient composition of plant-based diets and its potential impact on BC risk has not been well explored. This analysis investigated the association of macronutrient composition with BC risk across a spectrum of plant-based diet indexes using a multidimensional approach.

DESIGN

This study followed 64,655 participants from the Etude Epidémiologique auprès de femmes de la Mutuelle Générale de l'Education Nationale (E3N) cohort from 1993 to 2014. Diets were evaluated using validated 208-item diet history questionnaires at baseline (1993) and follow-up (2005), to calculate adherence to the overall plant-based diet (PDI), healthful plant-based diet (hPDI), and unhealthful plant-based diet (uPDI). The association of macronutrient composition with BC risk was assessed via generalized additive time-dependent Cox models across different levels of these indexes. Response surfaces were generated to visualize compositional associations at the 25th, 50th, and 75th percentile of each index (low, moderate, and high).

RESULTS

A total of 3,932 incident BC cases were identified during the 21-year follow-up. There was a significant association between macronutrient composition and BC risk for hPDI, uPDI, and PDI (all P < 0.001). Akaike information criterion favored the hPDI model for characterizing the association between macronutrients and BC. BC risk was highest for individuals with a lower hPDI score who also consumed a diet containing lower protein (10%), lower carbohydrate (35%), and higher fat (55%). The lowest risk of BC was observed in those with higher hPDI scores with the lowest intake of protein (10%). At higher PDI and uPDI, diets containing higher protein (30%) and fat (45%) had the highest BC risk.

CONCLUSION

These results demonstrate a complex relationship between macronutrient composition, plant-based diet quality, and BC risk. Further research is needed to examine specific foods that may be driving these associations.

REGISTRY

The protocol is registered at clinicaltrials.gov as NCT03285230.

Low-carbohydrate dietary score and the incidence of metabolically unhealthy phenotype based on BMI status: a cohort study

There is scarce research focusing on the relationship between the low-carbohydrate dietary score and the development of a metabolically unhealthy phenotype. Therefore, this cohort study was designed to assess the association between the low-carbohydrate dietary score and the risk of metabolically unhealthy phenotypes (MUP). This study included 1299 adults with healthy metabolic profiles who were followed for 5.9 years. Results indicated an inverse association between the second tertile of the low-carbohydrate dietary score and the risk of developing metabolically unhealthy obesity (MUO) (HR: 0.76, 95% CI: 0.59-0.98). In addition, we found an inverse association between the healthy low-carbohydrate dietary score and the risk of MUO (HR: 0.77, 95% CI: 0.60-0.99). Our results revealed a nonlinear inverse association between the low-carbohydrate dietary score and the risk of MUP only in subjects with overweight or obesity. This relationship was independent of animal protein and fat intake. Also, we found that a lower intake of unhealthy carbohydrates was associated with a lower risk of MUP only in subjects with overweight or obesity.

Metabolic Syndrome According to Dietary and Health-Related Lifestyle in Male Cancer Survivors and Non-Cancer over 40 Years of Age

Researchers often report higher metabolic syndrome (MetS) pr\4;evalence among cancer survivors than among non-cancer individuals. This study aims to explore the impact of cancer presence, activity type, and dietary lifestyle on MetS in males over 40 years of age. Participants (n = 9846; 618 cancer survivors, 9228 non-cancer) were selected by extracting data from a Korean government database spanning the years 2016 to 2021. Physical activity patterns, dietary habits, and MetS factors were measured, and a multiple logistic regression analysis was statistically processed for an odds ratio (OR). MetS was present in 32.8% of cancer survivors and 28.6% of non-cancer individuals. Gastric cancer survivors exhibited a 16% lower OR for MetS versus non-cancer participants. The ORs were higher by 1.60-, 1.45-, and 1.26-fold for colorectal, urinary, and other cancers, respectively. Cancer survivors with high calorie, carbohydrate, and fat intakes exhibited ORs of 2.01 (95% CI 1.28-4.04), 2.33 (95% CI 1.28-4.54), and 1.39 (95% CI 1.05-2.37) compared to the recommended level. The high fiber-intake group reduced the MetS OR by 20%. In conclusion, The MetS prevalence was higher in survivors with colorectal cancer, urinary cancer, and other cancers, while it was lower in patients with gastric cancer. Survivors with low rates of eating three meals a day, high skipping breakfast, increased eating-out rate, and no nutritional learning opportunity displayed higher MetS prevalence. Additionally, cancer survivors who had more strength and leisure activities had a lower OR of MetS.

Determining the metabolic effects of dietary fat, sugars and fat-sugar interaction using nutritional geometry in a dietary challenge study with male mice

The metabolic effects of sugars and fat lie at the heart of the "carbohydrate vs fat" debate on the global obesity epidemic. Here, we use nutritional geometry to systematically investigate the interaction between dietary fat and the major monosaccharides, fructose and glucose, and their impact on body composition and metabolic health. Male mice (n = 245) are maintained on one of 18 isocaloric diets for 18-19 weeks and their metabolic status is assessed through in vivo procedures and by in vitro assays involving harvested tissue samples. We find that in the setting of low and medium dietary fat content, a 50:50 mixture of fructose and glucose (similar to high-fructose corn syrup) is more obesogenic and metabolically adverse than when either monosaccharide is consumed alone. With increasing dietary fat content, the effects of dietary sugar composition on metabolic status become less pronounced. Moreover, higher fat intake is more harmful for glucose tolerance and insulin sensitivity irrespective of the sugar mix consumed. The type of fat consumed (soy oil vs lard) does not modify these outcomes. Our work shows that both dietary fat and sugars can lead to adverse metabolic outcomes, depending on the dietary context. This study shows how the principles of the two seemingly conflicting models of obesity (the "energy balance model" and the "carbohydrate insulin model") can be valid, and it will help in progressing towards a unified model of obesity. The main limitations of this study include the use of male mice of a single strain, and not testing the metabolic effects of fructose intake via sugary drinks, which are strongly linked to human obesity.

Male reproductive traits are differentially affected by dietary macronutrient balance but unrelated to adiposity

Dietary factors influence male reproductive function in both experimental and epidemiological studies. However, there are currently no specific dietary guidelines for male preconception health. Here, we use the Nutritional Geometry framework to examine the effects of dietary macronutrient balance on reproductive traits in C57BL/6 J male mice. Dietary effects are observed in a range of morphological, testicular and spermatozoa traits, although the relative influence of protein, fat, carbohydrate, and their interactions differ depending on the trait being examined. Interestingly, dietary fat has a positive influence on sperm motility and antioxidant capacity, differing to typical high fat diet studies where calorie content is not controlled for. Moreover, body adiposity is not significantly correlated with any of the reproductive traits measured in this study. These results demonstrate the importance of macronutrient balance and calorie intake on reproductive function and support the need to develop specific, targeted, preconception dietary guidelines for males.

Multi-Nutrient Analysis of Dietary Macronutrients with All-Cause, Cardiovascular, and Cancer Mortality: Data from NHANES 1999-2014

Macronutrients are a major component of the human diet. However, few studies have assessed their collective association with mortality. We sought to evaluate the associations of macronutrient intake with all-cause, cardiovascular, and cancer mortality in US adults using a multi-nutrient approach. This prospective cohort analysis used data from the National Health and Nutrition Examination Survey from the years 1999 to 2014. The participants included 33,681 US adults aged 20−85 years (52.5% female). The maximum follow-up time was 16.8 years, with a total of 4398 total deaths, including 772 cardiovascular deaths and 952 cancer deaths. The associations between mortality and dietary macronutrients were explored using three-dimensional generalized additive models, allowing for visual and statistical inference of complex nonlinear associations. Absolute macronutrient intake demonstrated a three-way interactive association with all-cause mortality (p < 0.001), cardiovascular mortality (p = 0.02), and cancer mortality (p = 0.05), adjusted for age, sex, ethnicity, socioeconomic status, dietary quality, and lifestyle. Compositionally, a high caloric diet composed of moderately high protein (20%), moderate fat (30%), and moderate carbohydrate (50%) levels was associated with the highest mortality risk. Across the total energy intake levels, lower mortality risk was observed in two separate regions consisting of higher protein (30%), higher carbohydrate (60%), and lower fat levels (10%) or lower protein (10%), moderate carbohydrate (45%), and higher fat levels (45%). These findings highlight a complex nonlinear and interactive association between macronutrients and all-cause mortality such that several distinct dietary compositions are associated with similarly high or low risk. Future research is needed to explore the drivers of these associations and whether they differ across varying dietary patterns and populations.

Ketogenic Diet Combined with Moderate Aerobic Exercise Training Ameliorates White Adipose Tissue Mass, Serum Biomarkers, and Hepatic Lipid Metabolism in High-Fat Diet-Induced Obese Mice

Obesity is a serious public health issue worldwide. Growing evidence demonstrates the efficacy of the ketogenic diet (KD) for weight loss, but there may be some adverse side effects such as dyslipidemia and hepatic steatosis. Aerobic exercise is a widely recognized approach for improving these metabolic markers. Here we explored the combined impacts of KD and moderate aerobic exercise for an 8-week intervention on body weight and fat loss, serum biomarkers, and hepatic lipid metabolism in a mouse model of high-fat diet-induced obesity. Both KD and KD combined with exercise significantly reduced body weight and fat mass. No significant adverse effects of KD were observed in serum biomarkers or hepatic lipid storage, except for an increase in circulating triglyceride level. However, aerobic exercise lowered serum triglyceride levels, and further ameliorated serum parameters, and hepatic steatosis in KD-fed mice. Moreover, gene and protein expression analysis indicated that KD combined with exercise was associated with increased expression of lipolysis-related genes and protein levels, and reduced expression of lipogenic genes relative to KD without exercise. Overall, our findings for mice indicate that further work on humans might reveal that KD combined with moderate aerobic exercise could be a promising therapeutic strategy for obesity.

Essential Minerals and Metabolic Adaptation of Immune Cells

Modern lifestyles deviated considerably from the ancestral routines towards major shifts in diets and increased sedentarism. The trace elements status of the human body is no longer adequately supported by micronutrient-inferior farmed meats and crop commodities produced by the existing agricultural food systems. This is particular evident in the increased obesogenic adipogenesis and low-grade inflammation that fails to resolve with time. The metabolically restrictive environment of the inflamed tissues drives activation and proliferation of transient and resident populations of immune cells in favor of pro-inflammatory phenotypes, as well as a part of the enhanced autoimmune response. As different stages of the immune activation and resolution depend on the availability of specific minerals to maintain the structural integrity of skin and mucus membranes, activation and migration of immune cells, activation of the complement system, and the release of pro-inflammatory cytokines and chemokines, this review discusses recent advances in our understanding of the contribution of select minerals in optimizing the responses of innate and adaptive immune outcomes. An abbreviated view on the absorption, transport, and delivery of minerals to the body tissues as related to metabolic adaptation is considered.

Macronutrient (im)balance drives energy intake in an obesogenic food environment: An ecological analysis

OBJECTIVE

The protein leverage hypothesis (PLH) postulates that strong regulation of protein intake drives energy overconsumption and obesity when human diets are diluted by fat and carbohydrates. The two predictions of the PLH are that humans (i) regulate intake to maintain protein within a narrow range and that (ii) energy intake is an inverse function of percentage energy from protein because absolute protein intake is maintained within narrow limits.

METHODS

Multidimensional nutritional geometry was used to test the predictions of the PLH using dietary data from the Australian National Nutrition and Physical Activity Survey.

RESULTS

Both predictions of the PLH were confirmed in a population setting: the mean protein intake was 18.4%, and energy intake decreased with increasing energy from protein (L = -0.18, p &lt; 0.0001). It was demonstrated that highly processed discretionary foods are a significant diluent of protein and associated with increased energy but not increased protein intake.

CONCLUSIONS

These results support an integrated ecological and mechanistic explanation for obesity, in which low-protein highly processed foods lead to higher energy intake because of the biological response to macronutrient imbalance driven by a dominant appetite for protein. This study supports a central role for protein in the obesity epidemic, with significant implications for global health.

A Comparison of the Australian Dietary Guidelines to the NOVA Classification System in Classifying Foods to Predict Energy Intakes and Body Mass Index

NOVA classification distinguishes foods by level of processing, with evidence suggesting that a high intake of ultra-processed foods (UPFs, NOVA category 4) leads to obesity. The Australian Dietary Guidelines, in contrast, discourage excess consumption of “discretionary foods” (DFs), defined according to their composition. Here, we (i) compare the classification of Australian foods under the two systems, (ii) evaluate their performance in predicting energy intakes and body mass index (BMI) in free-living Australians, and (iii) relate these outcomes to the protein leverage hypothesis of obesity. Secondary analysis of the Australian National Nutrition and Physical Activity Survey was conducted. Non-protein energy intake increased by 2.1 MJ (p < 0.001) between lowest and highest tertiles of DF intake, which was significantly higher than UPF (0.6 MJ, p < 0.001). This demonstrates that, for Australia, the DF classification better distinguishes foods associated with high energy intakes than does the NOVA system. BMI was positively associated with both DFs (−1. 0, p = 0.0001) and UPFs (−1.1, p = 0.0001) consumption, with no difference in strength of association. For both classifications, macronutrient and energy intakes conformed closely to the predictions of protein leverage. We account for the similarities and differences in performance of the two systems in an analysis of Australian foods.

An integrative approach to dietary balance across the life course

Animals require specific blends of nutrients that vary across the life course and with circumstances, e.g., health and activity levels. Underpinning and complicating these requirements is that individual traits may be optimized on different dietary compositions leading to nutrition-mediated trade-offs among outcomes. Additionally, the food environment may constrain which nutrient mixtures are achievable. Natural selection has equipped animals for solving such multi-dimensional, dynamic challenges of nutrition, but little is understood about the details and their theoretical and practical implications. We present an integrative framework, nutritional geometry, which models complex nutritional interactions in the context of multiple nutrients and across levels of biological organization (e.g., cellular, individual, and population) and levels of analysis (e.g., mechanistic, developmental, ecological, and evolutionary). The framework is generalizable across different situations and taxa. We illustrate this using examples spanning insects to primates and settings (laboratory, and the wild), and demonstrate its relevance for human health.

Evaluating type and amount of dietary protein in relation to metabolic syndrome among Iranian adults: cross-sectional analysis of Fasa Persian cohort study

BACKGROUND AND AIM

Metabolic syndrome is characterized by several conditions including abdominal obesity, dyslipidemia, impaired glucose levels, and hypertension; which all are directly associated with an increased risk of cardiovascular disease and type 2 diabetes mellitus. This study aimed to evaluate the association of the amount and source of dietary protein with the risk of metabolic syndrome and its components in adult men and women.

MATERIAL AND METHOD

This study was performed using Persian cohort data, Fasa branch, which included 3660 men and 5262 women. Individuals were divided into five groups for total dietary proteins, plant proteins, and animal proteins using the quintiles, and the odds of incidence for metabolic syndrome and each component was evaluated.

RESULTS

A higher intake of total protein was associated with lower odds of having metabolic syndrome (OR: 0.24 95% CI 0.18-0.33, P-trend < 0.001 in men, OR: 0.42 95% CI 0.34-0.51, P-trend < 0.001 in women) and all of its components. men (OR: 0.35 95% CI 0.25-0.48, P-trend < 0.001) and women (OR: 0.41 95% CI 0.33-0.52, P-trend < 0.001) in the highest quintile of plant protein intake had a reduced prevalence of metabolic syndrome and its components. An increased animal protein intake was associated with a lower prevalence of metabolic syndrome (P-trend < 0.001), a declined risk of having elevated triglycerides (P-trend = 0.016) in men, and a reduced risk of having abdominal obesity in men (P-trend < 0.001) and women (P-trend < 0.001).

CONCLUSION

A higher consumption of total protein and plant protein was associated with a lower prevalence of metabolic syndrome and its components. Increased consumption of animal protein seemed to be related to a lower prevalence abdominal obesity. Also, only in men, animal protein was associated with decreased risk of having metabolic syndrome.

A randomised clinical trial to investigate the effect of dietary protein sources on periodontal health

AIM

The aim was to assess two macronutrient interventions in a 2x2 factorial dietary design to determine their effects on oral health.

MATERIALS AND METHODS

Participants (65-75 years old) with a BMI between 20-35 kg/m² of a larger RCT who consented to an oral health assessment were recruited. They had ad libitum access to one of four experimental diets (omnivorous higher fat or higher carbohydrate, semi-vegetarian higher fat or higher carbohydrate) for 4 weeks. Periodontal examination included periodontal probing depth (PPD), clinical attachment level (CAL) and bleeding on probing. Oral plaque and gingival crevicular fluid (GCF) were collected before and after the intervention.

RESULTS

Between baseline and follow up the number of sites with a CAL <5 mm (mean difference (MD) -5.11±9.68, P=0.039) increased and the GCF amount (MD -23.42±39.42 Periotron Units (PU), P=0.050) decreased for the semi-vegetarian high fat diet. For the mean proportion of sites with PPD reduction >1 mm and CAL gain >1 mm significant differences were calculated between the diets investigated. The clinical parameters were not associated with changes of the oral microbiota.

CONCLUSION

The results of this study provided evidence that a semi-vegetarian higher fat diet provides benefits to clinical parameters of periodontal health. ACTRN12616001606471. This article is protected by copyright. All rights reserved.

Social inequalities shape diet composition among urban Colombians: The Colombian Nutritional Profiles cross-sectional study

OBJECTIVE

To explore the influence of socioeconomic position on habitual dietary intake in Colombian cities.

DESIGN

We conducted a cross-sectional, population-based study in five Colombian cities. Dietary intake was assessed with a 157-item semi-quantitative food frequency questionnaire previously developed for the Colombian population. Nutrient analysis was performed using national and international food composition tables. Socioeconomic position was assessed with two indicators: a government-defined, asset-based, household-level index called socioeconomic stratum (SES) and, among adults, highest educational level attained.

SETTING

The five main urban centers of Colombia: Bogotá, Medellin, Barranquilla, Cali and Bucaramanga.

PARTICIPANTS

Probabilistic, multistage sample of 1865 participants (n=1491 for analyses on education).

RESULTS

For both sexes, increasing SES was associated with a lower consumption of energy (p-trend <0.001 in both sexes), carbohydrates (p-trend ˂0.001 in both sexes), sodium (p-trend=0.005 in males, <0.001 in females), saturated fatty acids (p-trend <0.001 in both sexes) and among females, cholesterol (p-trend=0.002). More educated men consumed significantly less energy and carbohydrates (p-trend=0.036 and ˂0.001, respectively). Among men, intake of trans fats increased monotonically with educational level, being 21% higher among college graduates relative to those with only elementary education (p-trend=0.023). Among women, higher educational level was associated with higher MUFA intake (p-trend=0.027).

CONCLUSIONS

SES and educational level are strong correlates of the usual diet of urban Colombians. Economically deprived and less educated segments of society display dietary habits that make them vulnerable to chronic diseases and should be the primary target of public health nutrition policies.

Macronutrient-induced modulation of periodontitis in rodents-a systematic review

CONTEXT

Consumption of dietary macronutrients is associated with the progression of a wide range of inflammatory diseases, either by direct modulation of host immune response or via microbiome. This includes periodontitis, a disease affecting tooth-supporting tissues.

OBJECTIVE

The aim of this work was to systematically review studies focusing on the effect of macronutrient (ie, carbohydrate, protein, fat) intake on periodontitis in rodents.

DATA SOURCES

Electronic searches were performed in February 2021 using the PubMed and Web of Science databases. Out of 883 articles reviewed, 23 studies were selected for additional analysis.

DATA EXTRACTION

Investigators extracted relevant data, including author names; the year of publication; article title; macronutrient composition; number and species of animals and their age at the start of the experiment; intervention period; method of periodontitis induction; and primary and secondary periodontitis outcomes. Quality assessment was done using the risk-of-bias tool for animal studies. After completing the data extraction, descriptive statistical information was obtained.

DATA ANALYSIS

High intakes of dietary cholesterol, saturated fatty acids, and processed carbohydrates such as sucrose, and protein-deficient diets were positively associated with periodontitis in rodents. This included greater amounts of alveolar bone loss, more lesions on periodontal tissues, and dental plaque accumulation. In contrast, high doses of milk basic protein in diets and diets with a high ratio of ω-3 to ω-6 fatty acids were negatively associated with periodontitis in rodents.

CONCLUSION

This work highlights the fact that, despite the large body of evidence linking macronutrients with inflammation and ageing, overall there is little information on how dietary nutrients affect periodontitis in animal models. In addition, there is inconsistency in data due to differences in methodology, outcome measurement, and dietary formulation. More studies are needed to examine the effects of different dietary macronutrients on periodontitis and investigate the underlying biological mechanisms.

Toward an Evidence-Based Definition and Classification of Carbohydrate Food Quality: An Expert Panel Report

Carbohydrate-containing crops provide the bulk of dietary energy worldwide. In addition to their various carbohydrate forms (sugars, starches, fibers) and ratios, these foods may also contain varying amounts and combinations of proteins, fats, vitamins, minerals, phytochemicals, prebiotics, and anti-nutritional factors that may impact diet quality and health. Currently, there is no standardized or unified way to assess the quality of carbohydrate foods for the overall purpose of improving diet quality and health outcomes, creating an urgent need for the development of metrics and tools to better define and classify high-quality carbohydrate foods. The present report is based on a series of expert panel meetings and a scoping review of the literature focused on carbohydrate quality indicators and metrics produced over the last 10 years. The report outlines various approaches to assessing food quality, and proposes next steps and principles for developing improved metrics for assessing carbohydrate food quality. The expert panel concluded that a composite metric based on nutrient profiling methods featuring inputs such as carbohydrate–fiber–sugar ratios, micronutrients, and/or food group classification could provide useful and informative measures for guiding researchers, policymakers, industry, and consumers towards a better understanding of carbohydrate food quality and overall healthier diets. The identification of higher quality carbohydrate foods could improve evidence-based public health policies and programming—such as the 2025–2030 Dietary Guidelines for Americans.

Whole-Grain Intake in the Mediterranean Diet and a Low Protein to Carbohydrates Ratio Can Help to Reduce Mortality from Cardiovascular Disease, Slow Down the Progression of Aging, and to Improve Lifespan: A Review

Increase in the aging population is a phenomenon all over the world. Maintaining good functional ability, good mental health, and cognitive function in the absence of severe disease and physical disability define successful aging. A healthy lifestyle in middle age predisposes successful aging. Longevity is the result of a multifactorial phenomenon, which involves feeding. Diets that emphasize fruit and vegetables, whole grains rather than refined grains, low-fat dairy, lean meats, fish, legumes, and nuts are inversely associated with mortality or to a lower risk of becoming frail among elderly subjects. A regular physical activity and a regular intake of whole grain derivatives together with the optimization of the protein/carbohydrate ratio in the diet, where the ratio is significantly less than 1 such as in the Mediterranean diet and the Okinawan diet, reduces the risk of developing aging-related diseases and increases healthy life expectancy. The purpose of our review was to analyze cohort and case-control studies that investigated the effects of cereals in the diet, especially whole grains and derivatives as well as the effects of a diet with a low protein-carbohydrate ratio on the progression of aging, mortality, and lifespan.

Impact of dietary carbohydrate type and protein-carbohydrate interaction on metabolic health

Reduced protein intake, through dilution with carbohydrate, extends lifespan and improves mid-life metabolic health in animal models. However, with transition to industrialised food systems, reduced dietary protein is associated with poor health outcomes in humans. Here we systematically interrogate the impact of carbohydrate quality in diets with varying carbohydrate and protein content. Studying 700 male mice on 33 isocaloric diets, we find that the type of carbohydrate and its digestibility profoundly shape the behavioural and physiological responses to protein dilution, modulate nutrient processing in the liver and alter the gut microbiota. Low (10%)-protein, high (70%)-carbohydrate diets promote the healthiest metabolic outcomes when carbohydrate comprises resistant starch (RS), yet the worst outcomes were with a 50:50 mixture of monosaccharides fructose and glucose. Our findings could explain the disparity between healthy, high-carbohydrate diets and the obesogenic impact of protein dilution by glucose-fructose mixtures associated with highly processed diets.

Macronutrient Determinants of Obesity, Insulin Resistance and Metabolic Health

Obesity caused by the overconsumption of calories has increased to epidemic proportions. Insulin resistance is often associated with an increased adiposity and is a precipitating factor in the development of cardiovascular disease, type 2 diabetes, and altered metabolic health. Of the various factors contributing to metabolic impairments, nutrition is the major modifiable factor that can be targeted to counter the rising prevalence of obesity and metabolic diseases. However, the macronutrient composition of a nutritionally balanced "healthy diet" are unclear, and so far, no tested dietary intervention has been successful in achieving long-term compliance and reductions in body weight and associated beneficial health outcomes. In the current review, we briefly describe the role of the three major macronutrients, carbohydrates, fats, and proteins, and their role in metabolic health, and provide mechanistic insights. We also discuss how an integrated multi-dimensional approach to nutritional science could help in reconciling apparently conflicting findings.

Obesity and Male Reproduction; Placing the Western Diet in Context

There is mounting evidence that obesity has negative repercussions for reproductive physiology in males. Much of this evidence has accumulated from rodent studies employing diets high in fat and sugar ("high fat" or "western" diets). While excessive fats and carbohydrates have long been considered major determinants of diet induced obesity, a growing body of research suggests that the relationships between diet composition and obesity are more complex than originally thought, involving interactions between dietary macronutrients. However, rodent dietary models have yet to evolve to capture this, instead relying heavily on elevated levels of a single macronutrient. While this approach has highlighted important effects of obesity on male reproduction, it does not allow for interpretation of the complex, interacting effects of dietary protein, carbohydrate and fat. Further, the single nutrient approach limits the ability to draw conclusions about which diets best support reproductive function. Nutritional Geometry offers an alternative approach, assessing outcomes of interest over an extended range of dietary macronutrient compositions. This review explores the practical application of Nutritional Geometry to study the effects of dietary macronutrient balance on male reproduction, including experimental considerations specific to studies of diet and reproductive physiology. Finally, this review discusses the promising use of Nutritional Geometry in the development of evidence-based pre-conception nutritional guidance for men.