Protéines

La question des protéines est généralement évacuée très vite par les végétariens ou végétaliens : il est généralement affirmé qu’il est possible de trouver sans difficultés dans une alimentation végétale équilibrée l’ensemble des protéines nécessaires. Il semble cependant que cette affirmation puisse être mise en doute pour au moins 3 raisons.

La première raison est que la densité en protéines d’une alimentation végétale est généralement plus faible que celle d’une alimentation omnivore. Or, si les besoins en protéines étaient jusqu’à récemment considérés comme assez faibles (le chiffre généralement donné étant de 0,80 ou 0,83g/j/kg, soit chez un adulte de poids normal, entre 40 et 70g par jour, quelque chose de facilement accessible par une alimentation végétale comprenant des légumineuses, notamment, une méthode de mesure plus récente (l’IAAO) et plus précise suggère que cette valeur est nettement sous-évaluée.

La seconde raison est liée à la valeur des acides aminés contenus dans les différents aliments. Là encore, une nouvelle méthode de mesure plus précise (DIAAS) semble donner une moindre valeur aux acides aminés des végétaux. Ainsi, des sources végétales qui étaient jusque-là considérées comme bonnes ne le sont plus. Frédéric Leroy explique cette question ici.

La troisième raison est liée au fait que certains acides aminés considérés comme non essentiels, et dont, par conséquent, on ne se soucie pas quand on devient végéta*ien, pourraient en fait nécessiter des besoins significatifs en apports alimentaires. Si ces acides aminés sont peu présents dans les végétaux, il y a risque. Voir étude sur la glycine ci-dessous.


Besoin global en protéines

Estimation of interindividual variability of protein requirement by indicator amino acid oxidation method
Hayamizu et al.
Journal of clinical biochemistry and nutrition, 2020
https://www.jstage.jst.go.jp/article/jcbn/advpub/0/advpub_20-79/_pdf

From seven IAAO studies, the interindividual variability was estimated as a coefficient of variation of about 20%. The coefficient of variation of the protein requirement determined by IAAO study was wider than the ordinary coefficient of variation obtained from the nitrogen balance test.

Variable Intensity Exercise Increases Protein Requirements in Active Male and Female Adolescents as Determined by the Indicator Amino Acid Oxidation (IAAO) Technique
Jahmal C Brooks et al., 2017
https://www.fasebj.org/doi/abs/10.1096/fasebj.31.1_supplement.652.11

The breakpoints derived herein exceed current estimated breakpoint values using the IAAO method for sedentary adults and children (0.93 g·kg−1·d−1, and 1.3 g·kg−1·d−1 respectively). Adjusting for the upper 95% CI, a recommended dietary allowance (RDA) was determined to be 1.83 g·kg−1·d−1 and 1.54 g·kg−1·d−1 for males and females respectively. Our estimate of the RDA in active adolescents exceeds the current protein RDA based on the factorial estimate of nitrogen balance for adolescents (0.9 g·kg−1·d−1)

Increased Protein Requirements in Female Athletes after Variable-Intensity Exercise
Wooding et al.
Medicine and science in sport and exercise, 2017
https://europepmc.org/article/med/28692631

an estimated average requirement of 1.41 g·kg·d and recommended dietary allowance of 1.71 g·kg·d

Indicator Amino Acid–Derived Estimate of Dietary Protein Requirement for Male Bodybuilders on a Nontraining Day Is Several-Fold Greater than the Current Recommended Dietary Allowance
Bandegan et al.
The journal of nutrition, 2017
https://academic.oup.com/jn/article/147/5/850/4584703

The Estimated Average Requirement (EAR) of protein and the upper 95% CI RDA for these young male bodybuilders were 1.7 and 2.2 g · kg−1 · d−1, respectively.

Recent developments in understanding protein needs – How much and what kind should we eat?
Pencharz, Paul B. et al., 2016

Using IAAO we have shown that minimum protein requirements have been under estimated by 30-50%. The National Academy of Sciences have for macro-nutrients proposed “Acceptable Macronutrient Distribution Ranges”, which for protein is 10 to 35% of total energy. In practice, we suggest 1.5-2.2 g/kg/d of a variety of high-quality proteins.

Protein: A nutrient in focus
Arentson-Lantz et al.
NRC research press, 2015
https://www.nrcresearchpress.com/doi/full/10.1139/apnm-2014-0530#.XmPb_krjJEYIAAO Arentson-Lantz 2015 récapitulatif

Amino Acid Metabolism and Protein Requirements in Active, Trained Adult Males Using the Indicator Amino Acid Oxidation (IAAO) Technique
Packer, Jeffrey Ethan, 2015

Accounting for a safe intake encompassing the upper 95%CI, the protein requirement of 1.64 g/kg/d determined herein exceeds the current dietary reference intake for non-active individuals as determined by NBAL (EAR = 0.66 g/kg/d; RDA = 0.80 g/kg/d) (FAO, WHO 2007) and the minimally invasive IAAO technique (EAR = 0.93 g/kg/d; RDA = 1.2 g/kg/d) (Humayun et al., 2007). In addition the minimum intake determined herein is at the upper range of general recommendations for athletes (i.e. 1.2-1.7g/kg/d) (American Dietetic Association et al., 2009).

Assessment of protein requirement in octogenarian women with use of the indicator amino acid oxidation technique
Tang et al.
The american journal of clinical nutrition, 2014
https://academic.oup.com/ajcn/article/99/4/891/4637869

The mean protein requirement (95% CI) was 0.85 (0.60, 1.09) g · kg−1 · d−1. This requirement is 29% higher than the current Estimated Average Requirement (EAR) for adults of 0.66 g · kg−1 · d−1 based on the nitrogen balance technique, although the 95% CI includes the current EAR. The corresponding adequate protein allowance of 1.15 (0.77, 1.54) g · kg−1 · d−1 is 44% higher, although the 95% CI includes the Recommended Dietary Allowance (RDA) of 0.80 g · kg−1 · d−1.

Remarque : cette publication se base sur les recommandations classiques. Si les recommandations basées sur l’IAAO sont exactes, il conviendrait de porter la recommandation 40 à 50% plus haut que ce qui est indiqué ici.

Protein dietary reference intakes may be inadequate for vegetarians if low amounts of animal protein are consumed
Kniskern & Johnston
Nutrition, 2011
https://www.sciencedirect.com/science/article/abs/pii/S0899900710003059?via%3Dihub

This research suggests that the protein DRI for vegetarians consuming less than the expected amounts of animal protein (45% to 50% of total protein) may need to be adjusted from 0.8 to about 1.0 g/kg to account for decreased protein bioavailability.


Valeur des diverses protéines en fonction de leur proportion en acides aminés

Can the digestible indispensable amino acid score methodology decrease protein malnutrition
Hannah H. Baylay & Hans H. Stein
Animal Frontiers, 2019
https://academic.oup.com/af/article/9/4/18/5575466/?fbclid=IwAR3uZMJFWnkErlQLn_Cdhv6SgdIyb7iwB2HUZ3Os1HPXkLh7OJLTtcVfGB0

Wheat has a DIAAS value of 45 (Mathai et al., 2017); however, when wheat is processed in the form of a breakfast cereal, it may only have a DIAAS value of 1 (Rutherfurd et al., 2015). In contrast, milk has a DIAAS value of 118 (Rutherfurd et al., 2015). The calculated DIAAS value of a mixed meal of 60% milk and 40% breakfast cereal is 107 (Rutherfurd et al., 2015), demonstrating the ability of milk to complement wheat resulting in a balanced meal that meet the requirement for all indispensable AA. Likewise, it was recently demonstrated that milk and eggs are efficient in complementing low-quality plant proteins to improve the DIAAS value (Shivakumar et al., 2019). Although legumes generally have a greater DIAAS value than cereal grains, they are limiting in methionine and may contain antinutritional factors that often reduce the absorption of amino acids or micronutrients (Rutherfurd et al., 2015, Shivakumar et al., 2019). Consequently, animal proteins are more effective in increasing the protein quality of mixed meals and meeting human amino acid requirements than proteins from legumes.

Potential impact of the digestible indispensable amino acid score as a measure of protein quality on dietary regulations and health
Christopher P.F. Marinangeli and James D. House
Nutrition reviews, 2017

DIAAS vs PDCAAS

Acides aminés non essentiels et semi-essentiels

Un exemple d’acide aminé considéré comme non essentiel, car partiellement synthétisable, mais dont l’apport par la nutrition est nécessaire :

A weak link in metabolism: the metabolic capacity for glycine biosynthesis does not satisfy the need for collagen synthesis.
Melendez-Hevia et al. Journal of biosciences, 2009
https://www.researchgate.net/publication/41111844_A_weak_link_in_metabolism_the_metabolic_capacity_for_glycine_biosynthesis_does_not_satisfy_the_need_for_collagen_synthesis

Pour la carnosine, un peptide considéré lui aussi comme non essentiel, il semble que les capacités de synthèse soient réduites. On en retrouve moins chez les végétariens que dans la population générale.

Vegetarianism, female gender and increasing age, but not CNDP1 genotype, are associated with reduced muscle carnosine levels in humans
Evereaert et al.
Amino acids, 2011
https://link.springer.com/article/10.1007/s00726-010-0749-2?fbclid=IwAR2ri_UTx7kD_RgTOqU6FzhM-GMgf0Egemo0C0NUpX8iIoGcuulkA1gmxa0

Vegetarians have a lower carnosine content of 26% in gastrocnemius compared to omnivores.

Il serait donc judicieux de se demander si les autres acides aminés et peptides non essentiels manquant dans une alimentation végétale sont correctement synthétisés.

Composition of polyamines and amino acids in plant-source foods for human consumption
Hou et al.
Amino acids, 2019
https://link.springer.com/article/10.1007/s00726-019-02751-0?fbclid=IwAR2J9ebl1cQZbAw4wT5A-RL9qlr2upcuZu19z1ugpizO_KXK_oMC8uA8X_k

All of the analyzed plant-source foods lacked taurine, creatine, carnosine and anserine (antioxidants that are abundant in meats and also present in milk), and contained little 4-hydroxyproline. Proper proportions of plant- and animal-source products are likely most desirable for optimizing human nutrition and health.