Plasma Metabolome Analysis Suggests That L-Arginine Supplementation Affects Microbial Activity Resulting in a Decrease in Trimethylamine N-oxide-A Randomized Controlled Trial in Healthy Overweight Adults with Cardiometabolic Risk Factors

Background

The effects of supplementation with L-arginine (L-arg), the precursor of nitric oxide (NO), on vascular and cardiometabolic health have largely been explored. Whether other mechanisms of the action of L-arg exist remains unknown, as arginine metabolism is complicated.

Objective

We aimed to characterize the effect of low dose L-arg supplementation on overall human metabolism both in a fasting state and in response to an allostatic stress.

Methods

In a randomized, double-blind, crossover study, 32 healthy overweight adults (mean age 45 y) with cardiometabolic risk (fasting plasma triglycerides >150 mg/dL; waist circumference >94 cm [male] or >80 cm [female]) were treated with 1.5 g sustained-release L-arg 3 times/d (4.5 g/d) or placebo for 4 wk. On the last day of treatment, volunteers consumed a high-fat meal challenge (900 kcal, 80% as fat, 13% as carbohydrate, and 7% as protein). Plasma was collected at fasting, 2, 4, and 6 h after the challenge, and the metabolome was analyzed by high-resolution liquid chromatography-mass spectrometry. Metabolic profiles were analyzed using linear mixed models-principal component analysis.

Results

The challenge meal explained most of the changes in the metabolome. The overall effect of L-arg supplementation significantly explained 0.5% of the total variance, irrespective of the response to the challenge meal (P < 0.05). Among the metabolites that explain most of the L-arg effect, we found many amino acids, including branched-chain amino acids, that were decreased by L-arg supplementation. L-arg also decreased trimethylamine N-oxide (TMAO). Other changes suggest that L-arg increased methyl demand.

Conclusions

Analysis of the effect of 4 wk of L-arg supplementation on the metabolome reveals important effects on methyl balance and gut microbiota activity, such as a decrease in TMAO. Further studies are needed to investigate those mechanisms and the implications of these changes for long-term health.This trial was registered at clinicaltrials.gov as NCT02354794.

Environmental pressures and pesticide exposure associated with an increase in the share of plant-based foods in the diet

Diets rich in plant-based foods are encouraged for human health and to preserve resources and the environment but the nutritional quality and safety of such diets is debated. This study aimed to model nutritionally adequate diets with increasing plant food content and to characterise the derived diets using a multicriteria approach including, nutrients intake, environmental pressures and exposure to pesticides. Using data of the NutriNet-Santé cohort (N = 29,413), we implemented stepwise optimization models to identified maximum plant-food content under nutritional constraints. Environmental indicators at the production level were derived from the DIALECTE database, and exposure to pesticide residues from plant food consumption was estimated using a contamination database. Plant-based foods contributed to 64.3% (SD = 10.6%) of energy intake in observed diets and may reach up to 95% in modelled diets without jeopardizing nutritional status. Compared to the observed situation, an increase in plant-based foods in the diets led to increases in soy-based products (+ 480%), dried fruits (+ 370%), legumes (+ 317%), whole grains (+ 251%), oils (+ 144%) and vegetables (+ 93%). Animal products decreased progressively until total eviction, except for beef (- 98%). Dietary quality (estimated using the Diet Quality Index Based on the Probability of Adequate Nutrient Intake) was improved (up to 17%) as well as GHGe (up to - 65%), energy demand (up to - 48%), and land occupation (- 56%) for production. Exposures to pesticides from plant-based foods were increased by 100% conventional production and to a much lesser extent by 100% organic production. This study shows that shifting to nutritionally-adequate plant-based diets requires an in-depth rearrangement of food groups' consumption but allows a drastic reduction environmental impact. Increase exposure to pesticide residues and related risks can be mitigated by consuming foods produced with low pesticide input.

Identifying the most Efficient Detailed Trajectories toward Healthy Diets-A Graph-Based Analysis

BACKGROUND

Much effort has been devoted to defining healthy diets, which could lower the burden of disease and provide targets for populations. However, these target diets are far removed from current diets, so at best, the population is expected to move slowly along a trajectory.

OBJECTIVE

Our aim was to characterize the different possible trajectories toward a target diet and identify the most efficient one for health to point out the first dietary changes being the most urgent to implement.

METHODS

Using graph theory, we have developed a new method to represent in a graph all stepwise change trajectories toward a target healthy diet, with trajectories all avoiding risk of nutrient deficiency. Then, we have identified and characterized the trajectory with the highest value for long-term health. Observed male and female average diets are from the French representative survey INCA3, and target diets were set using multicriteria optimization. The best trajectories were found using the Dijkstra algorithm with the Health risk criteria based on epidemiological data.

RESULTS

Within ∼2.6M diets in the graphs, we found optimal trajectories that were rather similar for males and females regarding the most efficient changes in the first phase of the pathways. In particular, we found that a 1-step increase in the consumption of whole/semirefined bread (60 g) was the first step in all healthiest trajectories. In males, the subsequent decrease in red meat was immediately preceded by increases in legumes.

CONCLUSIONS

We show simple practical dietary changes that can be prioritized along an integral pathway that is the most efficient overall for health when transiting toward a distant healthy diet. We put forward a new method to analyze dietary strategy for public health transition and highlight the first critical steps to prioritize.

Plant to animal protein ratio in the diet: nutrient adequacy, long-term health and environmental pressure

Background

Animal and plant protein sources have contrasting relationships with nutrient adequacy and long-term health, and their adequate ratio is highly debated.

Objective

We aimed to explore how the percentage of plant protein in the diet (%PP) relates to nutrient adequacy and long-term health but also to environmental pressures, to determine the adequate and potentially optimal %PP values.

Methods

Observed diets were extracted from the dietary intakes of French adults (INCA3, n = 1,125). Using reference values for nutrients and disease burden risks for foods, we modeled diets with graded %PP values that simultaneously ensure nutrient adequacy, minimize long-term health risks and preserve at best dietary habits. This multi-criteria diet optimization was conducted in a hierarchical manner, giving priority to long-term health over diet proximity, under the constraints of ensuring nutrient adequacy and food cultural acceptability. We explored the tensions between objectives and identified the most critical nutrients and influential constraints by sensitivity analysis. Finally, environmental pressures related to the modeled diets were estimated using the AGRIBALYSE database.

Results

We find that nutrient-adequate diets must fall within the ~15-80% %PP range, a slightly wider range being nevertheless identifiable by waiving the food acceptability constraints. Fully healthy diets, also achieving the minimum-risk exposure levels for both unhealthy and healthy foods, must fall within the 25-70% %PP range. All of these healthy diets were very distant from current typical diet. Those with higher %PP had lower environmental impacts, notably on climate change and land use, while being as far from current diet.

Conclusion

There is no single optimal %PP value when considering only nutrition and health, but high %PP diets are more sustainable. For %PP > 80%, nutrient fortification/supplementation and/or new foods are required.

Compared with Milk Protein, a Wheat and Pea Protein Blend Reduces High-Fat, High-Sucrose Induced Metabolic Dysregulations while Similarly Supporting Tissue Protein Anabolism in Rats

BACKGROUND

Plant proteins (PPs) have been associated with better cardiovascular health than animal proteins (APs) in epidemiological studies. However, the underlying metabolic mechanisms remain mostly unknown.

OBJECTIVES

Using a combination of cutting-edge isotopic methods, we aimed to better characterize the differences in protein and energy metabolisms induced by dietary protein sources (PP compared with AP) in a prudent or western dietary context.

METHODS

Male Wistar rats (n = 44, 8 wk old) were fed for 4.5 mo with isoproteic diets differing in their protein isolate sources, either AP (100% milk) or PP (50%:50% pea: wheat) and being normal (NFS) or high (HFS) in sucrose (6% or 15% kcal) and saturated fat (7% or 20% kcal), respectively. We measured body weight and composition, hepatic enzyme activities and lipid content, and plasma metabolites. In the intestine, liver, adipose tissues, and skeletal muscles, we concomitantly assessed the extent of amino acid (AA) trafficking using a ¹⁵N natural abundance method, the rates of macronutrient routing to dispensable AA using a ¹³C natural abundance method, and the metabolic fluxes of protein synthesis (PS) and de novo lipogenesis using a ²H labeling method. Data were analyzed using ANOVA and Mixed models.

RESULTS

At the whole-body level, PP limited HFS-induced insulin resistance (-27% in HOMA-IR between HFS groups, P < 0.05). In the liver, PP induced lower lipid content (-17%, P < 0.01) and de novo lipogenesis (-24%, P < 0.05). In the different tissues studied, PP induced higher AA transamination accompanied by higher routings of dietary carbohydrates and lipids toward dispensable AA synthesis by glycolysis and β-oxidation, resulting in similar tissue PS and protein mass.

CONCLUSIONS

In growing rats, compared with AP, a balanced blend of PP similarly supports protein anabolism while better limiting whole-body and tissue metabolic dysregulations through mechanisms related to their less optimal AA profile for direct channeling to PS.

Nutritionally adequate and environmentally respectful diets are possible for different diet groups: an optimized study from the NutriNet-Santé cohort

BACKGROUND

Research has shown that vegetarian diets have a low environmental impact, but few studies have examined the environmental impacts and nutritional adequacy of these diets together, even though vegetarian diets can lead to nutritional issues.

OBJECTIVES

Our objective was to optimize and compare 6 types of diets with varying degrees of plant foods (lacto-, ovolacto-, and pescovegetarian diets and diets with low, medium, and high meat content) under nutritional constraints.

METHODS

Consumption data in 30,000 participants were derived from the French NutriNet-Santé cohort using an FFQ. Diets were optimized by a nonlinear algorithm minimizing the diet deviation while meeting multiple constraints at both the individual and population levels: nonincrease of the cost and environmental impacts (as partial ReCiPe accounting for greenhouse gas emissions, cumulative energy demand, and land occupation, distinguishing production methods: organic and conventional), under epidemiologic, nutritional (based on nutrient reference values), and acceptability (according to the diet type) constraints.

RESULTS

Optimized diets were successfully identified for each diet type, except that it was impossible to meet the EPA (20:5n-3) + DHA (22:6n-3) requirements in lacto- and ovolactovegetarians. In all cases, meat consumption was redistributed or reduced and the consumption of legumes (including soy-based products), whole grains, and vegetables were increased, whereas some food groups, such as potatoes, fruit juices, and alcoholic beverages, were entirely removed from the diets. The lower environmental impacts (as well as individual indicators) observed for vegetarians could be attained even when nutritional references were reached except for long-chain n-3 (omega-3) fatty acids.

CONCLUSIONS

A low-meat diet could be considered as a target for the general population in the context of sustainable transitions, although all diets tested can be overall nutritionally adequate (except for n-3 fatty acids) when planned appropriately.This trial was registered at clinicaltrials.gov as NCT03335644.

Nutritional issues and dietary levers during gradual meat reduction - A sequential diet optimization study to achieve progressively healthier diets

BACKGROUND & AIMS

Reducing meat consumption is a current trend and a strong prospect for the future in Western countries, but its dietary modalities and nutrient challenges remain poorly documented. Using diet optimization under a broad set of constraints, we tried to identify a sequential meat reduction transition and analyze its nutrient issues and dietary levers.

METHODS

Based on the consumption of French adults (INCA3, n = 1 125, 18-64 years old), we modeled a transition towards a nutritionally adequate healthy dietary pattern under the constraint of a gradual reduction in meat consumption in successive 10% steps. Using a multi-criteria optimization procedure, the diet modeled at each meat reduction step was to be healthier but close to the previous diet.

RESULTS

The most significant changes occurred early in the modeled transition process, with drastic reductions in processed and red meats in favor of poultry, which rapidly became the predominant meat before gradually decreasing from 50% to 100% meat reduction. At the same time, whole grain products, fruits and vegetables consumption increased rapidly to reach a plateau from 50% meat reduction onwards. Some nutrients were limiting, in particular bioavailable iron and zinc, and vitamin A, but sufficient intakes were achieved by restructuring diets based on food groups other than meat. Other nutrients mainly supplied by meat such as vitamin B6 and B12, protein and indispensable amino acids, were never limiting.

CONCLUSION

Healthy and nutritionally adequate food patterns can be identified throughout a transition to complete meat reduction. After a 50% reduction in meat consumption, poultry is almost the only meat remaining and its further reduction makes the diet only marginally healthier.

Modeled healthy eating patterns are largely constrained by currently estimated requirements for bioavailable iron and zinc-a diet optimization study in French adults

BACKGROUND

Healthier dietary patterns involve more plant-based foods than current Western diets rich in animal products containing high amounts of bioavailable iron and zinc. Little consideration is given to the bioavailability of iron and zinc when studying healthy eating patterns.

OBJECTIVES

Our aim was to determine whether currently estimated requirements for bioavailable iron and zinc limit the identification of healthier dietary patterns.

METHODS

Using dietary data from a representative French survey and multicriteria nonlinear optimization, we identified diets that maximize health criteria based on food-based dietary guidelines and concomitantly depart only minimally from the observed diet while complying with all nutrient reference values either strictly (nonflexible optimization) or by allowing bioavailable iron and zinc below the current reference values, but to a limited extent (flexible optimization). Using a comparative risk assessment model, we estimated the resulting impact on cardiometabolic and colorectal cancer mortality/morbidity and changes to iron-deficiency anemia.

RESULTS

Under nonflexible optimization, reference values for bioavailable iron and zinc were the most binding of the 35 nutrient constraints, and modeled diets displayed considerable redistributions within grains and meat. With flexible optimization, modeled diets were healthier as they contained less red meat and more whole-grain products, but would increase iron-deficiency anemia to 5.0% (95% CI: 3.9%, 6.4%). Globally, in terms of disability adjusted life years (DALYs), as the loss due to anemia would represent <30% of the gain otherwise made on chronic diseases, adding flexibility in the iron and zinc reference values would result in a further 18% decrease in the disease burden from 84,768 [95% uncertainty interval (UI): 81,066, 88,470] to 99,689 (95% UI: 95,787, 103,591) DALYs averted.

CONCLUSIONS

Currently estimated requirements for bioavailable iron and zinc proved to be critical factors when modeling healthy eating patterns. Considering lower reference values enables the identification of diets that are apparently healthier overall.

Investigating the Postprandial Metabolome after Challenge Tests to Assess Metabolic Flexibility and Dysregulations Associated with Cardiometabolic Diseases

This review focuses on the added value provided by a research strategy applying metabolomics analyses to assess phenotypic flexibility in response to different nutritional challenge tests in the framework of metabolic clinical studies. We discuss findings related to the Oral Glucose Tolerance Test (OGTT) and to mixed meals with varying fat contents and food matrix complexities. Overall, the use of challenge tests combined with metabolomics revealed subtle metabolic dysregulations exacerbated during the postprandial period when comparing healthy and at cardiometabolic risk subjects. In healthy subjects, consistent postprandial metabolic shifts driven by insulin action were reported (e.g., a switch from lipid to glucose oxidation for energy fueling) with similarities between OGTT and mixed meals, especially during the first hours following meal ingestion while differences appeared in a wider timeframe. In populations with expected reduced phenotypic flexibility, often associated with increased cardiometabolic risk, a blunted response on most key postprandial pathways was reported. We also discuss the most suitable statistical tools to analyze the dynamic alterations of the postprandial metabolome while accounting for complexity in study designs and data structure. Overall, the in-depth characterization of the postprandial metabolism and associated phenotypic flexibility appears highly promising for a better understanding of the onset of cardiometabolic diseases.

Halving food-related greenhouse gas emissions can be achieved by redistributing meat consumption: Progressive optimization results of the NutriNet-Santé cohort

BACKGROUND

Diet-related greenhouse gas emissions (GHGe) mainly comes from animal-sourced foods. As progressive changes are more acceptable for a sustainable food transition, we aimed to identify nutritionally adequate and culturally acceptable optimized diets ensuring a gradual reduction in GHGe, using observed diet from a large sample of French adults, while considering the mode of food production (organic vs conventional farming) and the co-production link between milk and beef.

MATERIAL AND METHOD

Based on the consumption of 257 organic and conventional foods among 29,413 participants (75% women, age: 53.5 ± 14.0y) of the NutriNet-Santé study, we modelled optimal diets according to GHGe reduction scenarios in 5% steps, from 0 to 50% with nutritional, acceptability, and coproduct constraints, for men, premenopausal and menopausal women separately.

RESULTS

Gradual GHGe decrease under these constraints led to optimal diets with an overall decrease in animal foods, with marked reductions in dairy products (up to -83%), together with a stable but largely redistributed meat consumption in favor of poultry (up to +182%) and pork (up to +46%) and at the expense of ruminant meat (down to -92%). Amounts of legumes increases dramatically (up to +238%). The greater the reduction in diet-related GHGe, the lower the cumulative energy demand (about -25%) and land use (about -43%). The proportion of organic food increased from ~30% in the observed diets to ~70% in the optimized diets.

CONCLUSION

Our results suggest that meeting both nutrient reference value and environmental objectives of up to 50% GHGe reduction requires the reduction of animal foods together with important substitutions between animal food groups, which result in drastic reductions in beef and dairy products. Further research is required to explore alignment with long-term health value and conflict with acceptability, in particular for even greater GHGe reductions.

Substituting Meat or Dairy Products with Plant-Based Substitutes Has Small and Heterogeneous Effects on Diet Quality and Nutrient Security: A Simulation Study in French Adults (INCA3)

BACKGROUND

Plant-based substitutes are designed to have the same use as animal-based foods in the diet and could therefore assist the transition toward more plant-based diets. However, their nutritional impact has not been characterized.

OBJECTIVES

We assessed and compared the effects of plant-based substitutes on the nutritional quality of the diet.

METHODS

We simulated separately the substitution of meat, milk, and dairy desserts with 96 plant-based substitutes in the diets of 2121 adults (18-79 y old) from the cross-sectional French Third Individual and National Study on Food Consumption Survey (INCA3; 2014-2015). The quality of initial individual diets and the 203,616 substituted diets was evaluated using the Probability of Adequate Nutrient Intake (PANDiet) scoring system, which assesses the probability of adequate (sufficient and not excessive) nutrient intake; also, nutrient security was evaluated using the SecDiet scoring system, which assesses the risk of overt deficiency.

RESULTS

Impacts on PANDiet depended on both the food substituted and the types of substitutes. Soy-based substitutes provided a slight improvement in diet quality (0.8% increase of the PANDiet score when substituting meat), whereas cereal-based substitutes resulted in a 1.1% decrease. Globally, substitutions led to better adequacies for fiber, linoleic acid, α-linolenic acid, vitamin E, folate, and SFAs, but lower adequacies regarding vitamin B-12 and riboflavin, as well as bioavailable zinc and iron when substituting meat, and calcium and iodine when substituting milk/dairy desserts. When they substituted dairy products, calcium-fortified substitutes allowed maintenance of calcium adequacy but there was a higher risk of iodine deficiency when substituting dairy, which may warrant iodine fortification. Substitutions modified the energy share of ultra-processed foods from 29% to 27%-40%, depending on the food substituted and the substitute used.

CONCLUSIONS

Plant-based substitutes had a small effect on overall diet quality and heterogeneous impacts on nutrient adequacy and security. Plant-based substitutes that include legumes appear more nutritionally adequate to substitute animal products than do other substitutes.

A Scoping Review: Metabolomics Signatures Associated with Animal and Plant Protein Intake and Their Potential Relation with Cardiometabolic Risk

The dietary shift from animal protein (AP) to plant protein (PP) sources is encouraged for both environmental and health reasons. For instance, PPs are associated with lower cardiovascular and diabetes risks compared with APs, although the underlying mechanisms mostly remain unknown. Metabolomics is a valuable tool for globally and mechanistically characterizing the impact of AP and PP intake, given its unique ability to provide integrated signatures and specific biomarkers of metabolic effects through a comprehensive snapshot of metabolic status. This scoping review is aimed at gathering and analyzing the available metabolomics data associated with PP- and AP-rich diets, and discusses the metabolic effects underlying these metabolomics signatures and their potential implication for cardiometabolic health. We selected 24 human studies comparing the urine, plasma, or serum metabolomes associated with diets with contrasted AP and PP intakes. Among the 439 metabolites reported in those studies as able to discriminate AP- and PP-rich diets, 46 were considered to provide a robust level of evidence, according to a scoring system, especially amino acids (AAs) and AA-related products. Branched-chain amino acids, aromatic amino acids (AAAs), glutamate, short-chain acylcarnitines, and trimethylamine-N-oxide, which are known to be related to an increased cardiometabolic risk, were associated with AP-rich diets, whereas glycine (rather related to a reduced risk) was associated with PP-rich diets. Tricarboxylic acid (TCA) cycle intermediates and products from gut microbiota AAA degradation were also often reported, but the direction of their associations differed across studies. Overall, AP- and PP-rich diets result in different metabolomics signatures, with several metabolites being plausible candidates to explain some of their differential associations with cardiometabolic risk. Additional studies specifically focusing on protein type, with rigorous intake control, are needed to better characterize the associated metabolic phenotypes and understand how they could mediate differential AP and PP effects on cardiometabolic risk.

Study Protocol: A 2-Month Cross-Over Controlled Feeding Trial Investigating the Effect of Animal and Plant Protein Intake on the Metabolome and Cardiometabolic Health

Objectives

A dietary shift in favor of plant protein (PP) sources over animal protein (AP) sources has been advocated for both sustainability and health reasons, this dietary transition being noticeably associated to decreased cardiovascular and diabetes risks. The differences in amino acid composition between PP and AP may have several effects on the metabolic pathways, and in turn health impacts, which are still poorly characterized. This project aims at characterizing, with a combination of “omics” approaches, the metabolic reorientations induced by a dietary shift from AP to PP sources and understanding their health effects in a population at cardiometabolic risk.

Methods

We will conduct a cross-over randomized feeding trial (NCT04236518) in 20 healthy overweight males (BMI 25–35), aged 25–55, with an enlarged waist circumference (&gt; 94cm) and high plasma triglycerides (&gt;1.5g/L). Participants will be assigned for 1 month each to 2 diets containing predominantly either AP (65% AP:35% PP) or PP (35% AP:65% PP) in a randomized order, separated by a 2-week wash-out period. Lunch and diner will be directly provided while dietary guidelines will be given for breakfast and snacks. Blood, urine and stool samples will be collected at the fasted state every 2 weeks. At the end of each dietary intervention, blood and urine will be collected following a high fat meal, which challenges metabolism and vascular homeostasis. Plasma and urine non-targeted metabolomics analyses (LC-MS) will be combined with Peripheral Blood Mononuclear Cell (PBMC) transcriptomics and fluxomics analyses (D2O tracer) to get a comprehensive overview of the metabolic phenotype associated with AP or PP intake. Flow-Mediated Dilatation (FMD) and Flow Laser Doppler (FLD) will be used to measure respectively macrovascular endothelial function and microvascular skin blood flow at the fasted state and after the high-fat meal. We will also measure anthropometric parameters and analyze biochemistry and inflammatory markers.

Results

Not applicable (protocols abstract).

Conclusions

We expect the multi-omics fingerprinting to reveal subtle metabolic differences associated to AP or PP intake, with a positive effect of PP intake. Improved inflammatory status and endothelial function are also expected to be associated to PP intake.

Funding Sources

INRAE and Roquette Frères.

The Health Value of Modelled Healthy Eating Patterns Is Largely Constrained by the Current Reference Values for Bioavailable Iron and Zinc

Objectives

We aimed to study if, and to what extent, the current nutrient reference values for bioavailable iron and zinc limit the identification of healthier dietary patterns.

Methods

Using observed diets from a representative French survey (INCA3) and multi-criteria optimization, we identified diets that comply with all nutrient reference values and maximize a health criteria based on food-based dietary guidelines while minimally departing from the observed diet. Nutrient reference values included absorbed iron and zinc. This non-linear diet optimization problem was solved in men and women with higher (Fe−) and lower (Fe+) iron requirements separately, either strictly (Non Flexible model, NF) or by allowing some tolerance on absorbed iron and zinc using goal programming to minimize their decreases below reference values (Flexible Model, F). Using a comparative risk assessment framework and a probabilistic approach, we estimated changes in risks of cardiovascular diseases, diabetes and colorectal cancer, and changes in estimates of the prevalence of iron-deficiency anemia for the diets optimized using each model.

Results

With the NF model, the reference values for absorbed iron and zinc were the most binding constraints (over 34 constraints). Compared to the observed diets, the NF-optimized diets showed large redistributions within cereals and meats, with total meat consumption remaining similar in men and Fe- women and doubling in Fe + women. In contrast, the F-optimized diets had higher value for the health criteria objective, being systematically lower in meat, especially red meat, and higher in whole grain products. We estimated that the reduction in mortality risk would be 17.7% wih the NF-optimized diets and 21.5% with the F-optimized diets. However, the later diets would increase the prevalence of iron-deficiency anemia from 2.1% currently to 5.6%.

Conclusions

We evidenced that the reference values for iron and zinc with regard to their bioavailability are critical factors when modelling healthy eating patterns. Considering lower references for iron and zinc leads to identify diets with an apparent higher benefit for the population health with regards long-term health.

Funding Sources

None.

A Scoping Review: Metabolomics Signatures Associated With Animal or Plant Protein Intake and Their Potential Relation to Cardiometabolic Risk

Objectives

The dietary shift from animal protein (AP) sources to plant protein (PP) sources is promoted for both environmental and health reasons. Indeed, PP are associated to lower cardiovascular and diabetes risks compared to AP, but the underlying mechanisms remain mostly unknown. Metabolomics, which has a unique ability to provide an integrative snapshot of the metabolic status of an individual, is a valuable tool to investigate the different metabolic pathways activated by AP or PP intake and to provide biomarkers of their metabolic effects. This scoping review aimed at gathering and analyzing the available data on the metabolomics signatures associated to PP or AP intake, for discussing the metabolic effects underlying these signatures and their potential implication for cardiometabolic health.

Methods

We selected a total of 23 human studies comparing the urine, plasma or serum metabolomes associated to diets with contrasted AP and PP intakes, such as vegetarian and omnivore diets, and collected all discriminant metabolites across diets.

Results

Out of the 447 discriminant metabolites, 44 were repeatedly reported across studies, amino acids (AA) and AA-related products accounting for a high proportion. Branch-chained amino acids (BCAA), aromatic amino acids (AAA), glutamate, short-chained acylcarnitines and Trimethylamine-N-Oxide (TMAO) were associated to AP while glycine was associated to PP intake. TCA cycle intermediates and products from AAA gut microbiota degradation were also often reported, but the direction of their associations with AP or PP remained unclear. As regard to their implication for cardiometabolic health, BCAA, AAA, glutamate, short-chained acylcarnitines and TMAO are known to be associated to increased risk while glycine is rather associated with a decreased risk.

Conclusions

AP or PP intakes result in different metabolomics signatures, several metabolites being plausible candidates to at least partially explain their differential associations with cardiometabolic risk. Additional studies with a specific focus on protein type, deep dietary data and tight intake control are needed to better characterize the associated metabolic phenotype and understand how it could mediate AP or PP effects on cardiometabolic risk.

Funding Sources

INRAE

L-Arginine Supplementation Significantly Affects Plasma Metabolome in Healthy Adults with Cardiometabolic Risk Irrespectively of Their Response to a Challenge Meal

Objectives

We aimed to characterize the effects of a low dose of a sustained-release L-arginine (L-ARG) supplementation on plasma metabolome in healthy overweight adults with cardiometabolic risk factors, and study if its effect could improve the capacity to handle a high fat-high sugar meal, that deeply and acutely challenge metabolic capacities.

Methods

In a randomized, double-blind, controlled trial, 33 healthy overweight adults (BMI &gt; 25kg/m²) with cardiometabolic risk (plasma triglycerides &gt; 150 mg/dL; waist circumference &gt; 94 cm (men) or &gt; 80 cm (women)) were treated with 1.5 g L-ARG 3 times/d (4.5 g/d) or placebo for 4 weeks. On the last day of treatment, the volunteers consumed a high fat, high sugar meal challenge (900 kcal). Plasma was collected at fasting and 2, 4 and

6 h after the meal. Metabolites were analyzed by high-resolution mass spectrometry hyphenated to liquid chromatography, using reversed and normal phase columns, and operated in both positive and negative ionization modes. Annotation was performed using an in-house database referencing more than 1300 metabolites. Metabolic profiles were analyzed using Linear Mixed Models-PCA (LiMM-PCA), which enables to analyze repeated multivariate data. LiMM-PCA combines linear mixed models and PCA to assess the effects of both fixed factors (Treatment, Time before and after meal, interaction Treatment x Time, Order of treatment administration and Period of the study) and random factors (Individual).

Results

521 metabolic features were identified in the plasma. Time accounted for most part of the variance in dataset (30.0%, P &lt; 0.001), showing that the challenge meal leaved the largest imprint on the metabolome, with a clear distinction between fasting and fed states. In contrast, interindividual variability explained 10.1% of the total variance. L-ARG treatment significantly affected plasma metabolome (P &lt; 0.001), explaining 0.6% of the variance. This effect did not differ after the challenge meal (time–treatment interaction, P &gt; 0.10). The analysis of the metabolites contributing the most to these effects is under progress.

Conclusions

L-ARG supplementation has a significant effect on the metabolome in a situation where the metabolome is heavily impacted by a large allostatic load, and these two effects are independent of each other.

Funding Sources

Supported by a grant from Pierre Fabre Research Institute.

Optimizing the Nutritional Composition of a Meat Substitute Intended to Replace Meat in Observed Diet Results in Marked Improvement of the Diet Quality of French Adults

Objectives

While consumers’ demand is growing, meat substitutes have much varied composition, raising questions about their nutritional interest. We aimed to identify the composition of a meat substitute that would best improve diet quality, and analyze the impact on nutrient adequacy.

Methods

We aimed at maximizing the overall diet quality of an average individual representing the nutrient intake of the French adult population (INCA3, n = 1125) by modeling the composition of a meat substitute intended to replace meat, using non-linear optimization (using SAS, proc optmodel). The diet quality was assessed using the PANDiet scoring system, which assesses the probability of adequate nutrient intake. Nutritional constraints were applied in order to not increase the risk of overt deficiency for 12 nutrients. A list of 159 ingredients was used to compose the meat replacer and technological constraints were defined so as to take into account the feasibility of the formulation. The impacts on diet quality of the modelled meat substitute were analyzed and compared with those of 43 meat substitutes on the market.

Results

The optimized meat substitute was composed of 13 ingredients (such as coco bean, yellow sweet pepper, rapeseed oil, dried shiitake mushroom, wheat bran and thyme) and this formulation proved to be relatively robust to variations in the model constraints, as shown by a sensitivity analysis. Meat substitution with this optimized meat substitute largely increased the PANDiet, by 5.5 points above its initial value before substitution (73.7/100). In particular, it led to better adequacies for nutrients that are currently insufficiently consumed (e.g., alpha-linolenic acid, fiber, linoleic acid). It also allowed to compensate for loss of some nutrients partly provided by meat (e.g., vitamin B6, potassium and, to a certain extent, bioavailable iron), but was not sufficient to compensate for bioavailable zinc and vitamin B12. The optimized meat substitute proved to be dramatically more nutritionally efficient than the available meat substitutes, whose individual impact on the PANDiet ranged from −3.1 to +1.5 points.

Conclusions

We proved that it is possible to select appropriate ingredients resulting in a meat substitute that could be a fairly good nutritional lever when substituting meat.

Funding Sources

Partly funded by a PhD fellowship from Terres Univia.

Differential changes to splanchnic and peripheral protein metabolism during the diet-induced development of metabolic syndrome in rats

Little is known about the effects of the development of metabolic syndrome (MS) on protein and amino acid (AA) metabolism. During this study, we took advantage of the variability in interindividual susceptibility to high fat diet-induced MS to study the relationships between MS, protein synthesis, and AA catabolism in multiple tissues in rats. After 4 mo of high-fat feeding, an MS score (Z_MS) was calculated as the average of the z-scores for individual MS components [weight, adiposities, homeostasis model for the assessment of insulin resistance (HOMA-IR), and triglycerides]. In the small intestine, liver, plasma, kidneys, heart, and muscles, tissue protein synthesis was measured by ²H₂O labeling, and we evaluated the proportion of tissue AA catabolism (relative to protein synthesis) and nutrient routing to nonindispensable AAs in tissue proteins using natural nitrogen and carbon isotopic distances between tissue proteins and nutrients (Δ¹⁵N and Δ¹³C), respectively. In the liver, protein mass and synthesis increased, whereas the proportion of AA catabolism decreased with Z_MS. By contrast, in muscles, we found no association between Z_MS and protein mass, protein synthesis (except for a weak positive association in the gastrocnemius muscle only), and proportion of AA catabolism. The development of MS was also associated with altered metabolic flexibility and fatty acid oxidation, as shown by less routing of dietary lipids to nonindispensable AA synthesis in liver and muscle. In conclusion, MS development is associated with a greater gain of both fat and protein masses, with higher protein anabolism that mainly occurs in the liver, whereas muscles probably develop anabolic resistance due to insulin resistance.

Plant-Protein Diversity Is Critical to Ensuring the Nutritional Adequacy of Diets When Replacing Animal With Plant Protein: Observed and Modeled Diets of French Adults (INCA3)

BACKGROUND

There is a current trend in Western countries toward increasing the intake of plant protein. A higher plant-protein intake has been associated with nutritional and health benefits, but these may depend on the pattern of plant-protein sources.

OBJECTIVE

We hypothesized that the diversity of plant foods could be important to nutrient adequacy when increasing plant-protein intake in the diet.

METHODS

Using data on 1341 adults (aged 18-64 y) from a representative French national dietary survey conducted in 2014-2015 (the third Individual and National Study on Food Consumption Survey-INCA3), we studied the links between plant-protein intake, dietary diversity (using various dimensions), and nutrient adequacy [assessed using the PANDiet (Probability of Adequate Nutrient Intake) scoring system, comprising adequacy (AS) and moderation (MS) subscores]. We simulated substituting plant-protein foods for animal-protein foods using different models of plant-protein diversity.

RESULTS

We found that overall diet quality was weakly associated with total and protein diversity and more strongly with plant-protein diversity. Plant-protein intake was inversely associated with animal-protein intake, and positively with the PANDiet and MS, but not with the AS. Plant-protein intake displayed little diversity, mostly taking the form of grains (61% of plant-protein intake), and this diversity was even less marked under a higher plant-protein intake. Finally, modeled substitutions showed that reducing animal-protein intake increased the MS (by 32%) in a similar manner whichever plant protein was used for substitution, whereas it decreased the AS (by 20%) unless using a highly diversified plant-protein mix. These simulated improvements in overall adequacy included marked decreases in adequacy regarding certain nutrients that are typically of animal origin.

CONCLUSIONS

We conclude that in French adults the current pattern of plant-protein intake is hindering the nutritional benefits of a transition toward more plant protein, indicating that the consumption of plant-protein-based foods other than refined grains should be encouraged.

The Willingness to Modify Portion Sizes or Eat New Protein Foods Largely Depends on the Dietary Pattern of Protein Intake

Promoting a more balanced animal/plant dietary protein ratio by changing portion sizes or introducing new foods is a promising means to improve diet quality, but little is known about the willingness of individuals to adopt such changes. Our objective was to assess the willingness to adopt dietary changes by these means. In a French cross-sectional study in 2018 (n = 2055), we analyzed the association between the willingness to eat smaller or larger portions or to introduce non-consumed protein foods and the current dietary patterns of individuals and their socio-demographic characteristics. These modifications had previously been identified as improving the nutrient adequacy of diets. Participants were more willing to eat smaller portion sizes than to introduce new foods and to eat larger portion sizes. The willingness for any modification varied depending on the food groups concerned. Participants were also more willing to eat larger portions and less willing to eat smaller portions when they were the most frequent consumers of the foods concerned. Participants were more willing to eat a new food if it was consumed in large quantities by individuals with a similar dietary pattern. This study underlines the importance of accounting for individual food habits when issuing nutritional recommendations.

The Initial Dietary Pattern Should Be Considered when Changing Protein Food Portion Sizes to Increase Nutrient Adequacy in French Adults

BACKGROUND

Patterns of protein food intake are undergoing a transition in Western countries, but little is known about how dietary changes to protein intake affect nutrient adequacy of the diet.

OBJECTIVES

Our objective was to identify simple modifications to protein food intake that can gradually increase overall nutrient adequacy.

METHODS

We identified patterns of dietary protein intake in 1678 adults from a representative French national dietary survey. For each individual, we identified the increase in portion size of 1 protein food paired with a decrease in the portion size of another protein food that would best increase nutrient adequacy (using PANDiet probabilistic scoring). Then, such an optimum simple dual change was iterated 20 times for each individual according to 2 scenarios, either by manipulating the intake of foods already consumed [scenario 1 (S1)] or by enabling the introduction of foods consumed by >10% of individuals with the same protein pattern [scenario 2 (S2)].

RESULTS

The optimum stepwise changes to protein intake primarily consisted of reducing portions of deli meats (both scenarios), sandwiches, and cheese (S2), while increasing portions of fatty fish and lean poultry (both scenarios) and legumes (S2). However, these changes differed depending on the initial dietary protein pattern of the individual. For example, in S2, legume intake increased among "poultry" and "fish" eaters only and low-fat meat among "take-away eaters" and "milk drinkers" only. The improvements in overall nutrient adequacy were similar among the different initial dietary patterns, but this was the result of changes to the adequacy of different specific nutrients.

CONCLUSION

Beyond generic changes to protein intake in the entire French adult population, the initial dietary protein pattern is key to identifying the food groups most likely to improve overall nutrient adequacy and the profile of nutrients whose adequacy can easily be increased.

Metabolomics Reveals that the Type of Protein in a High-Fat Meal Modulates Postprandial Mitochondrial Overload and Incomplete Substrate Oxidation in Healthy Overweight Men

Background

A meal rich in saturated fatty acids induces a postprandial metabolic challenge. The type of dietary protein may modulate postprandial metabolism.

Objective

We studied the effect of dietary protein type on postprandial changes in the metabolome after a high-fat meal.

Methods

In a 3-period, crossover, postprandial study, 10 healthy overweight men with an elevated waist circumference (>94 cm) ingested high-fat meals made up of cream fat (70% of energy), sucrose (15% energy), and protein (15% energy) from either casein (CAS), whey protein (WHE), or α-lactalbumin-enriched whey protein (LAC). Urine collected immediately before and 2, 4, and 6 h after the meal was analyzed for metabolomics, a secondary outcome of the clinical study. We used mixed-effect models, partial least-square regression, and pathway enrichment analysis.

Results

At 4 and 6 h after the meal, the postprandial metabolome was found to be fully discriminated according to protein type. We identified 17 metabolites that significantly explained the effect of protein type on postprandial metabolomic changes (protein-time interaction). Among this signature, acylcarnitines and other acylated metabolites related to fatty acid or amino acid oxidation were the main discriminant features. The difference in metabolic profiles was mainly explained by urinary acylcarnitines and some other acylated products (protein type, Ps < 0.0001), with a dramatically greater increase (100- to 1000-fold) after WHE, and to a lesser extent after LAC, as compared with CAS. Pathway enrichment analysis confirmed that the type of protein had modified fatty acid oxidation (P < 0.05).

Conclusion

Taken together, our results indicate that, in healthy overweight men, the type of protein in a high-fat meal interplays with fatty acid oxidation with a differential accumulation of incomplete oxidation products. A high-fat meal containing WHE, but not CAS, resulted in this outpacing of the tricarboxylic acid cycle. This study was registered at clinicaltrials.gov as NCT00931151.

A clear trade-off exists between the theoretical efficiency and acceptability of dietary changes that improve nutrient adequacy during early pregnancy in French women: Combined data from simulated changes modeling and online assessment survey

Background

During pregnancy, the diet of a mother-to-be should be adapted to meet increases in nutrient requirements. We analyzed the theoretical efficiency and acceptability of different types of tailored dietary changes for pregnant women.

Methods

The nutrient adequacy of the diet was evaluated using the PANDiet score, by comparing the nutrient intakes of 344 non-pregnant premenopausal women (18–44y) with dietary reference intakes for the first trimester of pregnancy. Simulations were performed to evaluate the theoretical efficiency of three types of ten successive tailored dietary changes in improving nutrient adequacy, with graded difficulty in implementation. The acceptability (declared intention to use in the diet) of most efficient dietary changes was evaluated during an online randomized study including 115 French pregnant women (22–41y).

Results

Modifying the amount consumed of foods (type-1) did not modify the food repertoire and resulted in the smallest theoretical efficiency (increase in the PANDiet score of 9.8±0.2 points), but changes were the most acceptable (probability of the intention to use: 0.30–0.78). Conversely, replacing food items by items from the same group or eaten at the same time (type-3) broadened the food repertoire (3.6±1.3 food subgroups added) and resulted in the greatest theoretical efficiency (+23.9±0.3) but changes were the least acceptable (0.07–0.23). Replacing food items within the same subgroup (type-2) slightly broadened the food repertoire (+8.0±1.3 foods) and resulted in moderate theoretical efficiency (+14.8±0.2) and intermediate acceptability (0.11–0.35).

Conclusion

A clear trade-off exists between the theoretical efficiency and acceptability of dietary changes, with a graded broadening of the food repertoire.

A Slow- Compared with a Fast-Release Form of Oral Arginine Increases Its Utilization for Nitric Oxide Synthesis in Overweight Adults with Cardiometabolic Risk Factors in a Randomized Controlled Study

BACKGROUND

Oral l-arginine supplements can have a beneficial effect on nitric oxide (NO)-related functions when subjects have cardiovascular disease risk factors.

OBJECTIVE

The study was designed to determine the utilization for NO synthesis of oral l-arginine as a function of the cardiometabolic risk and the speed of absorption by comparing immediate-release arginine (IR-Arg), as in supplements, and sustained-release arginine (SR-Arg), which mimics the slow release of dietary arginine.

METHODS

In a randomized, single-blind, 2-period crossover, controlled trial (1 wk of treatment, >2 wk of washout), using [(15)N-(15)N-(guanidino)]-arginine for the first morning dose, we compared the bioavailability (secondary outcome) and utilization for NO synthesis (primary outcome) of 1.5 g IR- and SR-Arg 3 times/d in 12 healthy overweight [body mass index (BMI; in kg/m(2)): 25-30] adults with the hypertriglyceridemic waist phenotype [HTW; plasma triglycerides (TGs): >150 mg/dL; waist circumference: >94 cm (men) or >80 cm (women)] and 15 healthy control adults (CON; BMI: 18.5-25; no elevated TGs and waist circumference).

RESULTS

Plasma oral arginine areas under the curve were lower after supplementation with SR-Arg than with IR-Arg (112 ± 52.3 and 142 ± 50.8 μmol ⋅ h/L; P < 0.01). The utilization of oral arginine for NO synthesis was 58% higher in HTW subjects than in CON subjects and higher with SR-Arg than with IR-Arg (P < 0.05 both), particularly in HTW subjects (group-by-treatment interaction, P < 0.05). In HTW subjects administered the SR form, utilization for NO synthesis was 32% higher than with the IR form and 87% higher than in CON subjects who were administered the SR form.

CONCLUSION

In overweight adults with the HTW phenotype, a slow- compared with a fast-release form of oral arginine markedly favors the utilization of arginine for NO synthesis. The utilization of low-dose, slow-release arginine for NO synthesis is higher in overweight adults with the HTW phenotype than in healthy controls, suggesting that the sensitivity of NO synthesis to the dietary arginine supply increases with cardiometabolic risk. The trial was registered at clinicaltrials.gov as NCT02352740.

l-Arginine Supplementation Alleviates Postprandial Endothelial Dysfunction When Baseline Fasting Plasma Arginine Concentration Is Low: A Randomized Controlled Trial in Healthy Overweight Adults with Cardiometabolic Risk Factors

BACKGROUND

Vascular endothelial dysfunction, the hallmark of early atherosclerosis, is induced transiently by a high-fat meal. High doses of free l-arginine supplements reduce fasting endothelial dysfunction.

OBJECTIVE

We sought to determine the effects of a low dose of a sustained-release (SR) l-arginine supplement on postprandial endothelial function in healthy overweight adults with cardiometabolic risk factors and to investigate whether this effect may vary by baseline arginine status.

METHODS

In a randomized, double-blind, 2-period crossover, placebo-controlled trial (4-wk treatment, 4-wk washout), we compared the effects of 1.5 g SR-l-arginine 3 times/d (4.5 g/d) with placebo in 33 healthy overweight adults [body mass index (BMI, in kg/m(2)): 25 to >30] with the hypertriglyceridemic waist (HTW) phenotype [plasma triglycerides > 150 mg/dL; waist circumference > 94 cm (men) or > 80 cm (women)]. The main outcome variable tested was postprandial endothelial function after a high-fat meal (900 kcal), as evaluated by use of flow-mediated dilation (FMD) and Framingham reactive hyperemia index (fRHI), after each treatment. By use of subgroup analysis, we determined whether the effect was related to the baseline plasma arginine concentration.

RESULTS

In the total population, the effects of SR-arginine supplementation on postprandial endothelial function were mixed and largely varied with baseline fasting arginine concentration (P-interaction < 0.05). In the lower half of the population (below the median of 78.2 μmol arginine/L plasma), but not the upper half, SR-arginine supplementation attenuated the postprandial decrease in both FMD (29% decrease with SR-arginine compared with 50% decrease with placebo) and fRHI (5% increase with SR-arginine compared with 49% decrease with placebo), resulting in significantly higher mean ± SEM values with SR-arginine (FMD: 4.0% ± 0.40%; fRHI: 0.41 ± 0.069) than placebo (FMD: 2.9% ± 0.31%; fRHI: 0.21 ± 0.060) at the end of the postprandial period (P < 0.05).

CONCLUSIONS

Supplementation with low-dose SR-arginine alleviates postprandial endothelial dysfunction in healthy HTW adults when the baseline plasma arginine concentration is relatively low. The benefits of arginine supplementation may be linked to a lower ability to mobilize endogenous arginine for nitric oxide synthesis during a postprandial challenge. This trial was registered at clinicaltrials.gov as NCT02354794.

Casein Compared with Whey Proteins Affects the Organization of Dietary Fat during Digestion and Attenuates the Postprandial Triglyceride Response to a Mixed High-Fat Meal in Healthy, Overweight Men

BACKGROUND

Postprandial lipemia is a risk factor for cardiovascular disease. The potential impacts of the type/nature of dietary protein on postprandial lipemia and associated dysregulations have been insufficiently investigated.

OBJECTIVE

We investigated the postprandial effect of including in a high-fat meal some milk protein fractions that markedly differ in their physicochemical properties and composition [either casein (CAS), whey protein (WHE), or α-lactalbumin-enriched whey protein (LAC)].

METHODS

The protein fractions were incorporated as 15% energy in a high-fat meal in a 3-period, crossover postprandial study of 10 healthy overweight men with an elevated waist circumference (>94 cm). We measured postprandial changes in plasma lipids, amino acids, glucose, and oxidative stress markers, vascular function (using pulse contour analysis), and low-grade inflammation (using plasma markers). We also characterized in vitro the meal structures, including the size of the fat globule, and possible changes during digestion.

RESULTS

The type of protein did not affect postprandial plasma glucose, amino acids, insulin, or nonesterified fatty acids, but, compared with WHE and LAC, which did not differ, CAS markedly reduced postprandial triglycerides (TGs), achieving a 22 ± 10% reduction in the 6-h area under the curve (P < 0.05). Similar trends were shown for plasma chylomicrons [apolipoprotein (apo)B-48; P < 0.05]. However, there were no significant differences between the meals regarding postprandial oxidative stress (plasma hydroperoxides and malondialdehyde), endothelial dysfunction (salbutamol-induced changes in pulse contour analysis), or low-grade inflammation. In vitro studies showed that when the pH of the meal decreased to stomach pH values, the reduction in the solubility of casein resulted in a phase separation between fat and protein, whereas the proteins in the other meals remained suspended with fat globules.

CONCLUSION

In healthy overweight men, casein has specific physical interactions with fat that affect postprandial TGs, leading to the formation of fewer chylomicrons or an increase in chylomicron clearance. This trial was registered at clinicaltrials.gov as NCT00931151.

Natural isotopic signatures of variations in body nitrogen fluxes: a compartmental model analysis

Body tissues are generally ¹⁵N-enriched over the diet, with a discrimination factor (Δ¹⁵N) that varies among tissues and individuals as a function of their nutritional and physiopathological condition. However, both ¹⁵N bioaccumulation and intra- and inter-individual Δ¹⁵N variations are still poorly understood, so that theoretical models are required to understand their underlying mechanisms. Using experimental Δ¹⁵N measurements in rats, we developed a multi-compartmental model that provides the first detailed representation of the complex functioning of the body's Δ¹⁵N system, by explicitly linking the sizes and Δ¹⁵N values of 21 nitrogen pools to the rates and isotope effects of 49 nitrogen metabolic fluxes. We have shown that (i) besides urea production, several metabolic pathways (e.g., protein synthesis, amino acid intracellular metabolism, urea recycling and intestinal absorption or secretion) are most probably associated with isotope fractionation and together contribute to ¹⁵N accumulation in tissues, (ii) the Δ¹⁵N of a tissue at steady-state is not affected by variations of its P turnover rate, but can vary according to the relative orientation of tissue free amino acids towards oxidation vs. protein synthesis, (iii) at the whole-body level, Δ¹⁵N variations result from variations in the body partitioning of nitrogen fluxes (e.g., urea production, urea recycling and amino acid exchanges), with or without changes in nitrogen balance, (iv) any deviation from the optimal amino acid intake, in terms of both quality and quantity, causes a global rise in tissue Δ¹⁵N, and (v) Δ¹⁵N variations differ between tissues depending on the metabolic changes involved, which can therefore be identified using simultaneous multi-tissue Δ¹⁵N measurements. This work provides proof of concept that Δ¹⁵N measurements constitute a new promising tool to investigate how metabolic fluxes are nutritionally or physiopathologically reorganized or altered. The existence of such natural and interpretable isotopic biomarkers promises interesting applications in nutrition and health.

Body proteins ensure vital functions, and their constancy is maintained through the tight coordination of many nitrogen metabolic fluxes, but our understanding of how this flux system is regulated, and sometimes dysregulated, remains fragmentary and incomplete. Besides, body tissues are generally naturally enriched in the heavier stable nitrogen isotope (¹⁵N) over the diet: this ¹⁵N bioaccumulation (Δ¹⁵N) varies depending on tissues and metabolic orientations, likely as the result of isotope effects associated to some metabolic pathways. We used a novel approach, combining multi-tissue Δ¹⁵N measurements and their analysis using modeling, to understand how body Δ¹⁵N values relate to nitrogen fluxes. The multi-tissue model we have developed provides a clearer understanding of the metabolic processes that generate isotopic fractionation, and of how tissue Δ¹⁵N values are modulated in response to changes in the body distribution of specific nitrogen fluxes. We show that Δ¹⁵N values tend to rise when the amino acids intake does not optimally fit the metabolic demand, and that Δ¹⁵N values constitute natural and interpretable signatures of nutritionally-induced variations in nitrogen fluxes. This approach constitutes a new promising tool to investigate how nitrogen metabolism is nutritionally or physiopathologically reorganized or altered, and promises interesting applications in many areas (nutrition, pathology, ecology, paleontology, etc).

Kinetics of the utilization of dietary arginine for nitric oxide and urea synthesis: insight into the arginine-nitric oxide metabolic system in humans

BACKGROUND

The systemic availability of oral/dietary arginine and its utilization for nitric oxide (NO) synthesis remains unknown and may be related to a competitive hydrolysis of arginine into urea in the splanchnic area and systemic circulation.

OBJECTIVES

We investigated the kinetics and dose-dependency of dietary arginine utilization for NO compared with urea synthesis and studied the characteristics of the arginine-NO metabolic system in healthy humans.

DESIGN

We traced the metabolic fate and analyzed the utilization dynamics of dietary arginine after its ingestion at 2 nutritional amounts in healthy humans (n = 9) in a crossover design by using [(15)N-(15)N-(guanido)]-arginine, isotope ratio mass spectrometry techniques, and data analysis with a compartmental modeling approach.

RESULTS

Whatever the amount of dietary arginine, 60 ± 3% (±SEM) was converted to urea, with kinetics indicative of a first-pass splanchnic phenomenon. Despite this dramatic extraction, intact dietary arginine made a major contribution to the postprandial increase in plasma arginine. However, the model identified that the plasma compartment was a very minor (~2%) precursor for the conversion of dietary arginine into NO, which, in any case, was small (<0.1% of the dose). The whole-body and plasma kinetics of arginine metabolism were consistent with the suggested competitive metabolism by the arginase and NO synthase pathways.

CONCLUSIONS

The conversion of oral/dietary arginine into NO is not limited by the systemic availability of arginine but by a tight metabolic compartmentation at the systemic level. We propose an organization of the arginine metabolic system that explains the daily maintenance of NO homeostasis in healthy humans.

Isotopic and modeling investigation of long-term protein turnover in rat tissues

Fractional synthesis rates (FSR) of tissue proteins (P) are usually measured using labeled amino acid (AA) tracer methods over short periods of time under acute, particular conditions. By combining the long-term and non-steady-state (15)N labeling of AA and P tissue fractions with compartmental modeling, we have developed a new isotopic approach to investigate the degree of compartmentation of P turnover in tissues and to estimate long-term FSR values under sustained and averaged nutritional and physiological conditions. We measured the rise-to-plateau kinetics of nitrogen isotopic enrichments (δ(15)N) in the AA and P fractions of various tissues in rats for 2 mo following a slight increase in diet δ(15)N. Using these δ(15)N kinetics and a numerical method based on a two-compartment model, we determined reliable FSR estimates for tissues in which P turnover is adequately represented by such a simple precursor-product model. This was the case for kidney, liver, plasma, and muscle, where FSR estimates were 103, 101, 58, and 11%/day, respectively. Conversely, we identified tissues, namely, skin and small intestine, where P turnover proved to be too complex to be represented by a simple two-compartment model, evidencing the higher level of subcompartmentation of the P and/or AA metabolism in these tissues. The present results support the value of this new approach in gaining cognitive and practical insights into tissue P turnover and propose new and integrated FSR values over all individual precursor AA and all diurnal variations in P kinetics.

The nature of the dietary protein impacts the tissue-to-diet 15N discrimination factors in laboratory rats

Due to the existence of isotope effects on some metabolic pathways of amino acid and protein metabolism, animal tissues are ¹⁵N-enriched relative to their dietary nitrogen sources and this ¹⁵N enrichment varies among different tissues and metabolic pools. The magnitude of the tissue-to-diet discrimination (Δ¹⁵N) has also been shown to depend on dietary factors. Since dietary protein sources affect amino acid and protein metabolism, we hypothesized that they would impact this discrimination factor, with selective effects at the tissue level. To test this hypothesis, we investigated in rats the influence of a milk or soy protein-based diet on Δ¹⁵N in various nitrogen fractions (urea, protein and non-protein fractions) of blood and tissues, focusing on visceral tissues. Regardless of the diet, the different protein fractions of blood and tissues were generally ¹⁵N-enriched relative to their non-protein fraction and to the diet (Δ¹⁵N>0), with large variations in the Δ¹⁵N between tissue proteins. Δ¹⁵N values were markedly lower in tissue proteins of rats fed milk proteins compared to those fed soy proteins, in all sampled tissues except in the intestine, and the amplitude of Δ¹⁵N differences between diets differed between tissues. Both between-tissue and between-diet Δ¹⁵N differences are probably related to modulations of the relative orientation of dietary and endogenous amino acids in the different metabolic pathways. More specifically, the smaller Δ¹⁵N values observed in tissue proteins with milk than soy dietary protein may be due to a slightly more direct channeling of dietary amino acids for tissue protein renewal and to a lower recycling of amino acids through fractionating pathways. In conclusion, the present data indicate that natural Δ¹⁵N of tissue are sensitive markers of the specific subtle regional modifications of the protein and amino acid metabolism induced by the protein dietary source.

Rapeseed and milk protein exhibit a similar overall nutritional value but marked difference in postprandial regional nitrogen utilization in rats

BACKGROUND

Rapeseed is an emerging and promising source of dietary protein for human nutrition and health. We previously found that rapeseed protein displayed atypical nutritional properties in humans, characterized by low bioavailability and a high postprandial biological value. The objective of the present study was to investigate the metabolic fate of rapeseed protein isolate (RPI) and its effect on protein fractional synthesis rates (FSR) in various tissues when compared to a milk protein isolate (MPI).

METHODS

Rats (n = 48) were given a RPI or MPI meal, either for the first time or after 2-week adaptation to a MPI or RPI-based diet. They were divided in two groups for measuring the fed-state tissue FSR 2 h after the meal (using a flooding dose of 13C-valine) and the dietary N postprandial distribution at 5 h (using 15N-labeled meals).

RESULTS

RPI and MPI led to similar FSR and dietary nitrogen (N) losses (ileal and deamination losses of 4% and 12% of the meal, respectively). By contrast, the dietary N incorporation was significantly higher in the intestinal mucosa and liver (+36% and +16%, respectively) and lower in skin (-24%) after RPI than MPI.

CONCLUSIONS

Although RPI and MPI led to the same overall level of postprandial dietary N retention in rats (in line with our findings in humans), this global response conceals marked qualitative differences at the tissue level regarding dietary N accretion. The fact that FSR did not however differed between groups suggest a differential modulation of proteolysis after RPI or MPI ingestion, or other mechanisms that warrant further study.

Absorption kinetics are a key factor regulating postprandial protein metabolism in response to qualitative and quantitative variations in protein intake

We have previously demonstrated that increasing the habitual protein intake widened the gap in nutritional quality between proteins through mechanisms that are not yet fully understood. We hypothesized that the differences in gastrointestinal kinetics between dietary proteins were an important factor affecting their differential response to an increased protein intake. To test this hypothesis, we built a 13-compartment model providing integrative insight into the sequential dynamics of meal nitrogen (Nm) absorption, splanchnic uptake, and metabolism, and subsequent peripheral transfer and deposition. The model was developed from data on postprandial Nm kinetics in certain accessible pools, obtained from subjects having ingested a (15)N-labeled milk or soy protein meal, after adaptation to normal (NP) or high (HP) protein diets. The faster absorption of Nm after soy vs. milk caused its earlier and stronger splanchnic delivery, which favored its local catabolic utilization (up to +30%) and limited its peripheral accretion (down to -20%). Nm absorption was also accelerated after HP vs. NP adaptation, and this kinetic effect accounted for most of the HP-induced increase (up to +20%) in splanchnic Nm catabolic use, and the decrease (down to -25%) in peripheral Nm anabolic utilization. The HP-induced acceleration in Nm absorption was more pronounced with soy than with milk, as were the HP effects on Nm regional metabolism. Our integrative approach identified Nm absorption kinetics, which exert a direct and lasting impact on Nm splanchnic catabolic use and peripheral delivery, as being critical in adaptation to both qualitative and quantitative changes in protein intake.

Hydrolyzed dietary casein as compared with the intact protein reduces postprandial peripheral, but not whole-body, uptake of nitrogen in humans

BACKGROUND

Compared with slow proteins, fast proteins are more completely extracted in the splanchnic bed but contribute less to peripheral protein accretion; however, the independent influence of absorption kinetics and the amino acid (AA) pattern of dietary protein on AA anabolism in individual tissues remains unknown.

OBJECTIVE

We aimed to compare the postprandial regional utilization of proteins with similar AA profiles but different absorption kinetics by coupling clinical experiments with compartmental modeling.

DESIGN

Experimental data pertaining to the intestine, blood, and urine for dietary nitrogen kinetics after a 15N-labeled intact (IC) or hydrolyzed (HC) casein meal were obtained in parallel groups of healthy adults (n = 21) and were analyzed by using a 13-compartment model to predict the cascade of dietary nitrogen absorption and regional metabolism.

RESULTS

IC and HC elicited a similar whole-body postprandial retention of dietary nitrogen, but HC was associated with a faster rate of absorption than was IC, resulting in earlier and stronger hyperaminoacidemia and hyperinsulinemia. An enhancement of both catabolic (26%) and anabolic (37%) utilization of dietary nitrogen occurred in the splanchnic bed at the expense of its further peripheral availability, which reached 18% and 11% of ingested nitrogen 8 h after the IC and HC meals, respectively.

CONCLUSIONS

The form of delivery of dietary AAs constituted an independent factor of modulation of their postprandial regional metabolism, with a fast supply favoring the splanchnic dietary nitrogen uptake over its peripheral anabolic use. These results question a possible effect of ingestion of protein hydrolysates on tissue nitrogen metabolism and accretion. This trial was registered at clinicaltrials.gov as NCT00873951.

Parameter estimation for linear compartmental models--a sensitivity analysis approach

Linear compartmental models are useful, explanatory tools, that have been widely used to represent the dynamic behavior of complex biological systems. This paper addresses the problem of the numerical identification of such models, i.e., the estimation of the parameter values that will generate predictions closest to experimental observations. Traditional local optimization techniques find it difficult to arrive at satisfactory solutions to such a parameter estimation problem, especially when the number of parameters is large and/or few data are available from experiments. We present herewith a method based on a prior sensitivity analysis, which enables division of a large optimization problem into several smaller and simpler subproblems, on which only sensitive parameters are estimated, before the whole optimization problem is tackled from starting points that are already close to the optimum values. This method has been applied successfully to a linear 13-compartment, 21-parameter model describing the postprandial metabolism of dietary nitrogen in humans. The effectiveness of the method has been demonstrated using simulated and real data obtained in the intestine, blood and urine of healthy humans after the ingestion of a [(15)N]-labeled protein meal.

Urea-nitrogen production and salvage are modulated by protein intake in fed humans: results of an oral stable-isotope-tracer protocol and compartmental modeling

BACKGROUND

The influence of protein source on postprandial urea kinetics is poorly understood, despite its nutritional significance with respect to nitrogen homeostasis. Furthermore, traditional tracer infusion studies underestimate acute postprandial change in urea kinetics.

OBJECTIVE

We investigated postprandial, non-steady state urea kinetics and their modulation by qualitative and quantitative factors of protein intake by the combined use of robust clinical data on nitrogen postprandial distribution and mathematical modeling.

DESIGN

In healthy subjects standardized to a normal protein intake for 7 d, dietary and total nitrogen kinetics were measured for 8 h in plasma proteins, body, and urinary urea after the ingestion of a (15)N-labeled milk (n = 8), soy (n = 8), or wheat (n = 8) protein meal. In subjects who received the soy protein meal, these postprandial measurements were repeated after a further 7-d adaptation to a high protein intake. A 4-compartment model was developed to calculate from these data the postprandial kinetics of production, urinary excretion, and intestinal hydrolysis of urea nitrogen from both dietary and endogenous sources.

RESULTS

Urinary urea excretion was not influenced by the protein source in the meal but was influenced by the protein level in the diet. By contrast, urea production and hydrolysis were higher when ingesting plant versus animal protein, together with a higher efficiency of urea hydrolysis (50-60% versus 25% of the urea produced being hydrolyzed, respectively).

CONCLUSIONS

We conclude that urea hydrolysis is an acute nitrogen-sparing mechanism that can counterbalance a postprandial higher urea production, and the efficiency of this recycling is higher when the usual protein intake is lower.