False equivalence or fake news: is a peanut really an egg?

Martin C G ,08 April 2021 ,False equivalence or fake news: is a peanut really an egg? ,The Journal of Nutrition ,doi: https://doi.org/10.1093/jn/nxab051

Abstract: 

Proteins are essential in the human diet because they provide

the basis for all structural and functional components of living

cells.All proteins are made up of 20 amino acid building blocks.

Of the 20 amino acids in body proteins, 9 are indispensable

or essential (1). Essential amino acids are those which cannot

be synthesized and must be provided from the diet. Therefore,

promoting and achieving adequate protein nutrition within

a population requires knowledge of protein and amino acid

requirements. However, although necessary, this knowledge

alone is not sufficient. What must also be known is the capacity

of food proteins to meet the metabolic demand of the body for

the essential amino acids (the protein quality).

The essential amino acid composition is the most important

predictor of the quality of a dietary protein, while the

digestibility and bioavailability (metabolic availability) are the

next most important factors. Differences in protein digestibility

among foods are related to the nature of the food proteins,

the presence of antinutritional factors (e.g., fiber, tannins, and

phytates), and the presence of antiphysiological factors (e.g.,

trypsin inhibitors) and processing conditions which reduce the

nutritional value of proteins by altering their chemical structure.

Animal proteins contain an essential amino acid profile that is

superior to that of plant proteins (2), and the animal protein

amino acids are highly bioavailable (3). Relative to animal

proteins, plant proteins have lower anabolic potential (2, 4),

largely due to their lower essential amino acid content and

bioavailability.

In setting the cup and ounce equivalents within each food

group, the authors of the Dietary Guidelines for Americans

stated that “cup-and ounce-equivalents identify the amount of

foods from each food group with similar nutritional content”

(5). Because the nutritional relevance of a dietary protein is

predicated primarily on its essential amino acid composition

within the protein food group, the amounts of food identified

as an ounce-equivalent represent a “false equivalence.” For

each plant-based protein source, the total grams of protein per

“ounce equivalent” is no more than half that of the animal

proteins, and except for tofu, the relative content of each

essential amino acid in the plant-based proteins (peanut butter,

kidney beans, mixed nuts) is several-fold lower than the animal

GC-M has received funding from the Canadian Institute of Health Research and

Seeding Food Innovation Grant, George Weston Ltd.

The author reported no funding received for this study.

Author disclosures: The author reports no conflicts of interest.

Address correspondence to GC-M (e-mail: [email protected]).

proteins (beef sirloin, pork loin, egg). However, assessment of

dietary protein quality is required to objectively establish the

ability of the protein intake to support not just the maintenance

but also the synthesis and growth of the total protein in the

whole body.

In this regard, the study by Park et al. (6), published in

this issue of the Journal of Nutrition, makes an important and

timely contribution which could inform expert decisions in

the setting of future Dietary Guidelines for Americans. Using

stable isotope tracer methodology, the authors investigated

the anabolic response in 56 young healthy adult men who

each consumed 1 of 7-oz equivalent protein food sources

(beef sirloin, pork loin, egg, tofu, peanut butter, kidney beans,

mixed nuts). Subjects consumed a weight maintenance diet

which provided 1.2 g.kg−1 protein per day for 3 d before the

study day. On the study day, protein kinetics were studied in

subjects in the fasted state and after consumption of the protein

meal. Subjects were randomly assigned to receive either beef

sirloin, pork loin, egg, tofu, peanut butter, kidney beans, or

mixed nuts (8 subjects per group). Each food was provided

as 2 “ounce equivalents” which equaled 56 g of cooked beef

sirloin and cooked pork loin, 2 cooked eggs, 12

cup (140 g)

red kidney beans, 2 tablespoons (30 g) peanut butter, 4 oz

(112 g) tofu, or 1 oz (28 g) mixed nuts. Protein kinetics

were normalized by calorie and essential amino acid intake.

The primary outcome was the change in net protein balance

(PB) relative to baseline. Secondary outcomes included protein

synthesis (PS), protein breakdown, and the relation between the

essential amino acid content of the food proteins and the protein

kinetics.While the foods were consumed orally, the tracers were

intravenously infused. Therefore, the phenylalanine kinetics and

balance estimates which are used as a surrogate for whole-body

protein balance may not necessarily reflect the effect of splenic

metabolism and could be confounded by correcting for ileal

digestibility of the test proteins. Nonetheless, whole-body PB is

a useful way to assess the metabolic utilization of these proteins.

The main findings of Park et al. (6) were that the wholebody

anabolic response or net PB was greater in the groups that

consumed the animal-based rather than the plant-based proteins

and that changes in the net PB were directly related to the

essential amino acid content of the “ounce equivalent” protein

source. Interestingly, consumption of tofu, which is considered

a complete plant protein and has an essential amino acid profile

similar to that of animal protein, resulted in a net PB lower

than the animal protein and more like kidney beans and peanut

butter.