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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., (Copyright © The Author(s) 2019.)

Meat consumption in Western countries is declining and, while the proportion of strict vegetarians remains low, intermediate diets such as flexitarianism have been developing in recent years. Our objectives were to identify the different levels of transition towards low-meat diets, characterize how these diets differ in terms of food intake, and identify whether attitudes and beliefs can explain these degrees of transition. In a representative survey of the French adult population conducted in 2018 (n = 2055), participants declared whether they followed a particular diet and completed a food frequency questionnaire on 29 food sources of protein and a questionnaire on their attitudes and beliefs regarding protein sources. We identified four dietary types based on these declarative data: vegetarians, flexitarians, pro-flexitarians and omnivores. The theory of planned behavior was used to predict meat intake and intentions to reduce meat intake. The sample contained 2.5% vegetarians, 6.3% flexitarians, 18.2% pro-flexitarians and 72.9% omnivores. The diet groups displayed specific dietary profiles and attitudinal scores. Compared with omnivores, pro-flexitarians consumed less red meat, more vegetables and legumes and were much more in agreement about the environmental impacts of meat. Compared with pro-flexitarians, flexitarians consumed less red meat and processed meat, and agreed much more about the health impacts of meat. Finally, versus flexitarians, vegetarians consumed almost no meat but far more legumes, nuts and seeds, and were much more sensitive to animal welfare issues. Attitudes, social norms and perceived behavioral control (PBC) predicted intentions to reduce meat consumption but attitude was the most important predictor. Intentions and PBC were both predictive of meat consumption. The dietary type related to the level of meat intake could be predicted by self-declared attitudes and beliefs regarding protein sources., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

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.

A growing body of evidence supports a role for tissue-to-diet 15 N and 13 C discrimination factors (Δ 15 N and Δ 13 C), as biomarkers of metabolic adaptations to nutritional stress, but the underlying mechanisms remain poorly understood. In obese rats fed ad libitum or subjected to gradual caloric restriction (CR), under a maintained protein intake, we measured Δ 15 N and Δ 13 C levels in tissue proteins and their constitutive amino acids (AA) and the expression of enzymes involved in the AA metabolism. CR was found to lower protein mass in the intestine, liver, heart and, to a lesser extent, some skeletal muscles. This was accompanied by Δ 15 N increases in urine and the protein of the liver and plasma, but Δ 15 N decreases in the proteins of the heart and the skeletal muscles, alongside Δ 13 C decreases in all tissue proteins. In Lys, Δ 15 N levels rose in the plasma, intestine, and some muscles, but fell in the heart, while in Ala, and to a lesser extent Glx and Asx, Δ 13 C levels fell in all these tissues. In the liver, CR was associated with an increase in the expression of genes involved in AA oxidation. During CR, the parallel rises of Δ 15 N in urine, liver, and plasma proteins reflected an increased AA catabolism occurring at the level of the liver metabolic branch point, while Δ 15 N decreases in cardiac and skeletal muscle proteins indicated increased protein and AA catabolism in these tissues. Thus, an increased protein and AA catabolism results in opposite Δ 15 N effects in splanchnic and muscular tissues. In addition, the Δ 13 C decrease in all tissue proteins, reflects a reduction in carbohydrate (CHO) oxidation and routing towards non-indispensable AA, to achieve fuel economy.

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., (© 2019 American Society for Nutrition.)

Due to the existence of isotope effects on some metabolic pathways of amino acid and protein metabolism, animal tissues are (15)N-enriched relative to their dietary nitrogen sources and this (15)N enrichment varies among different tissues and metabolic pools. The magnitude of the tissue-to-diet discrimination (Δ(15)N) 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 Δ(15)N 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 (15)N-enriched relative to their non-protein fraction and to the diet (Δ(15)N>0), with large variations in the Δ(15)N between tissue proteins. Δ(15)N 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 Δ(15)N differences between diets differed between tissues. Both between-tissue and between-diet Δ(15)N 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 Δ(15)N 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 Δ(15)N of tissue are sensitive markers of the specific subtle regional modifications of the protein and amino acid metabolism induced by the protein dietary source.

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.

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.

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.

Background: The postprandial retention of dietary protein decreases when the prevailing protein intake increases., Objective: We investigated the influence of the prevailing protein intake on the regional utilization and anabolic use of wheat protein during the postprandial non-steady state in humans., Design: Healthy adults (n = 8) were adapted for 7 d, first to a normal-protein diet (NP: 1 g x kg(-1) x d(-1)) and then to a high-protein diet (HP: 2 g x kg(-1) x d(-1)). After each adaptation period, the subjects received the same single, solid mixed meal containing [15N]-labeled wheat protein. The postprandial kinetics of dietary nitrogen were then measured for 8 h in blood and urine. These data were further analyzed by using a multicompartmental model to predict the postprandial kinetics of dietary nitrogen in unsampled pools., Results: The postprandial whole-body retention of wheat protein nitrogen, measured 8 h after meal ingestion, decreased by 10% when the subjects switched from the NP diet to the HP diet. According to modeling results, this resulted from an increased splanchnic utilization of dietary nitrogen for urea production, whereas its incorporation into splanchnic proteins was unchanged, leading to a 20-30% decrease in peripheral availability and anabolic use in HP-adapted compared with NP-adapted subjects having ingested the same protein load., Conclusions: By combining clinical experimentation with compartmental modeling, we provide a global overview of postprandial dietary protein metabolism. Increasing prior protein intake was shown to reduce the postprandial retention of wheat protein nitrogen, mainly by diminishing the efficiency of its peripheral availability and anabolic use.

A multi-compartmental model has been developed to describe dietary nitrogen (N) postprandial distribution and metabolism in humans. This paper details the entire process of model development, including the successive steps of its construction, parameter estimation and validation. The model was built using experimental data on dietary N kinetics in certain accessible pools of the intestine, blood and urine in healthy adults fed a [15N]-labeled protein meal. A 13-compartment, 21-parameter model was selected from candidate models of increasing order as being the minimum structure able to properly fit experimental data for all sampled compartments. Problems of theoretical identifiability and numerical identification of the model both constituted mathematical challenges that were difficult to solve because of the large number of unknown parameters and the few experimental data available. For this reason, new robust and reliable methods were applied, which enabled (i) a check that all model parameters could theoretically uniquely be determined and (ii) an estimation of their numerical values with satisfactory precision from the experimental data. Finally, model validation was completed by first verifying its a posteriori identifiability and then carrying out external validation.

Background: The quality of cereal protein has been little studied in humans despite its quantitative importance in the diet, particularly in developing countries., Objective: The objective of this study was to determine the nutritional value of wheat protein in humans as assessed by the measurement of their real ileal digestibility and postprandial retention., Design: Healthy young adults (n = 14) were fitted with an intestinal tube to allow the collection of intestinal fluid in the duodenum or terminal ileum. Subjects received a mixed meal of 136 g wheat toast that contained 24.6 g uniformly and intrinsically [(15)N]-labeled wheat protein. Intestinal fluid, blood, and urine were collected for 8 h postprandially., Results: The real ileal digestibility of dietary wheat nitrogen amounted to 90.3 +/- 4.3%. The cumulative amount of dietary nitrogen transferred to the deamination pools reached a plateau at 8 h of 24.7 +/- 6.8% of the amount ingested. The urinary excretion of dietary nitrogen in ammonia was high (0.8 +/- 0.3% of ingested dose). The incorporation of dietary nitrogen into serum protein reached 7.0 +/- 1.9% of the meal. Postprandial wheat protein retention was 66.1 +/- 5.8%., Conclusions: Our results show that wheat proteins had the same true ileal digestibility as did most of the plant proteins already studied in humans, but also that they had a lower postprandial nitrogen retention value. However, this low value was higher than that predicted from the calculation of indispensable amino acid scores, ie, 89% rather than 30-40% of the nutritional value of milk proteins.

The investigation of protein metabolism under various nutritional and physiological conditions has been made possible by the use of indirect, principally tracer-based methods. Most studies were conducted at the whole-body level, mainly using steady-state isotopic techniques and equations based on simple two-pool models, in which amino acids are either free or protein bound. Because whole-body methods disregard regional contributions to protein metabolism, some regional approaches have tried to distinguish the distribution of protein kinetics in the different tissues. The organ-balance tracer technique, involving the arteriovenous catheterization of regions or organs with concomitant isotopic tracer infusion, distinguishes between amino acid uptake and release in the net amino acid balance and measures protein synthesis and degradation under steady-state conditions. Last, the importance has become clear of the difference in dietary and endogenous amino acids recycled from proteolysis for anabolic and catabolic pathways. In humans, the dual tracer technique, which consists of the simultaneous oral/enteral administration and intravenous infusion of different tracers of the same amino acid, allows an estimate of the splanchnic uptake of amino acids administered. Furthermore, the whole-body retention of labeled dietary nitrogen after the ingestion of a single protein meal has enabled a clearer understanding of the metabolic fate of dietary amino acids. Based on such data, a newly developed compartmental model provides a simulation of the regional distribution and metabolism of ingested nitrogen in the fed state by determining its dynamic fate through free and protein-bound amino acids in both the splanchnic and peripheral areas in humans.