High-quality protein can prevent overeating and weight gain

Tony Clark, CSO (Author) and Steve Fratini, PhD (Editor), August 28, 2023

When it comes to protein, quantity is not enough; protein quality must also be considered.  We propose a model for determining the protein quality of foods.  We define a food’s protein quality as a function of the indispensable amino acids (IAAs) composition of the protein content in the food.  Example foods are analyzed for their protein quality relative to our selected gold-standard food, which governs a food’s IAA Quality Scores.  We explain why eating higher protein quality foods can be protective against overeating and can help to prevent unwanted weight gain.

In a companion article, we present a charm bracelet analogy for protein, where protein is compared to a charm bracelet and the amino acids, from which protein is made, are compared to the charms of the bracelet.  Recall that certain amino acids (i.e., charms), called indispensable or essential amino acids, can only be obtained through eating food or taking supplements.   We note that there are two important characteristics of protein that should be considered when constructing one’s diet: protein quantity and protein quality.  This article is about protein quality.

Referring again to our charm bracelet analogy, each of the nine IAAs—histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine—are the must-have charms of a protein charm bracelet.  Foods having the highest protein quality contain each of the IAAs (charms) in an ideal proportion needed for the optimal creation, growth, and maintenance of every cell and tissue in our bodies.  In contrast, lower protein quality foods may completely lack, or contain extremely low amounts of certain IAAs (charms).   Therefore, it is insufficient to state that a particular food contains a complete set of IAAs, without also stating the relative quantities of the IAA within the food relative to a gold-standard. 

Modern humans [3] are estimated to have been around for at least the past 200,000 years.  The one food that has been critical to and has sustained modern humans during infancy for all that time is human milk (i.e., breast milk) [1].  Human milk is the one food that has been naturally engineered and optimized for human consumption for more than 8,000 generations.  No other food in modern human history comes close to that track record and, because of this, human milk is the ideal “gold-standard” for IAA composition.    Accordingly, our protein quality model assumes the IAA composition of human milk as its gold-standard composition—see Table 4 image per the World Health Organization (WHO) [2]. 

Setting a gold-standard food for protein content amplifies the importance of protein quality and helps to highlight that the amount of protein one needs to consume via food is both a function of the quantity of the protein in the food and the quality of the protein in the food.  In other words, the higher the quality of the protein in a food, the lower the amount of food that needs to be eaten to obtain the daily minimum required amount of protein.   The lower the quality of the protein, the higher the amount of food that needs to be eaten to obtain the minimum daily amount of protein via the food.  As will be explained by means of an example below, the overconsumption of lower protein quality foods can lead to excessive food cravings and unwanted weight gain.

Formally, the IAA Quality Scores (i.e., protein quality) for a food are determined by comparing the food’s relative indispensable amino acids (IAAs) amounts to the human milk gold-standard reference.  To compute the IAA Quality Scores for a given food item, we compare (as a percentage) the amount of each IAA in the given food (Food:IAA) to the associated amount of that IAA in our gold standard (GS:IAA).  Thus a food’s IAA Quality Scores are computed as follows:

• IAA Quality Scores(i) = [ Food:IAA(i) ÷ GS:IAA(i) ] * 100, for each Food:IAA(i) < GS:IAA(i)

• IAA Quality Scores(i) = 100, for all Food:IAA(i) >= GS:IAA(i)

The IAA Quality Scores for several foods (basically a profile of scores - one per IAA) is shown in the following table. 

The implications of protein quality on diet can be better explained via an example*.    We assume the following:

• Our subject is a 45-year old woman weighing 170 pounds (77.11 kilograms).

• Determined by her body weight, the minimum required amount of protein, expressed as the number of grams of protein that our subject should consume in this example is 54 grams of protein per day. 

• The gold-standard IAA composition per this article (WHO Table 4) is presumed and yields the following daily minimum IAA consumption targets for our female subject—His (1,134 mg), Ile (2,970 mg), Leu (5,184 mg), Lys (3,726 mg), Met (1,782 mg), Phe (5,076 mg), Thr (2.376 mg), Trp (918 mg) and Val (2,970 mg).

• Our female subject is presumed to only choose one of chicken, green peas, or eggs to obtain her daily minimum IAA requirements for the purposes of this example. 

• And, the respective USDA IAA estimates per serving for cooked chicken (3.5 ounces), green peas (3.5 ounces) and eggs (2 boiled) are used.
  
  

The daily amount of food that must be consumed by our example* subject, to obtain her daily minimum IAA requirements, is constrained by the lowest quality IAA component of each food in the example.  Note that the body continues to signal the brain to consume more food until they obtain the minimum amount of each IAA needed for protein synthesis (i.e., protein production).    

To determine the number of servings of each food that our female subject needs to solely eat to obtain her daily minimum amount of each IAA, we do the following:

1. Identify the essential amino acid of each assumed food, which has the lowest IAA Quality Score.  In the case of chicken, the constraining IAA is tryptophan (Trp); for green peas, the constraining IAA is phenylalanine (Phe); and for eggs, the constraining IAA is tryptophan (Trp).    

2. Determine the amount supplied per serving of each of the constraining IAA, identified in the previous step.  From the USDA’s FoodData Central website, for our example, each serving of chicken delivers 292 mg of Trp; each serving of green peas delivers 198 mg of Phe; and each serving of eggs delivers 166 mg of Trp.

3. Determine the daily minimum required amount of each constraining IAA identified in the previous step (specifically) for our female subject:  Phe (5,076 mg) and Trp (918 mg).

4. For each food in our example, divide the daily required amount of the food’s constraining IAA by the amount of the IAA that is delivered per serving of the food.  In the case of chicken, our female subject would need to eat at least 3 servings (our subject’s daily minimum requirement of 918 mg of Trp divided by the 292 mg of Trp in each serving of chicken); for peas she would have to eat 26 servings (our subject’s daily minimum requirement of 5,076 mg of Phe divided by the 198 mg of Phe in each serving of peas); and for eggs she would need to consume 11 eggs (5.5 servings).

Clearly the servings of green peas in our example sticks out and confirms that one needs to eat a lot more lower quality protein food than is suggested by just considering the quantity of the protein in the food.  This affirms that protein quality really does matter.  Again, both protein quality and protein quantity are relevant considerations.  The chicken versus eggs comparison reveals the importance of protein quantity.  Note that even though chicken contains a lower IAA Quality Score for Trp than eggs, chicken’s much higher quantity of Trp per serving of chicken relative to eggs means that one can eat fewer servings of chicken than eggs to obtain their daily minimum requirements for IAAs.

In summary, there are two important factors to consider when evaluating the protein content in a food: protein quantity and protein quality.  Protein quality is especially important for weight management purposes.  Eating higher protein quality foods is protective against overeating and helps to prevent unwanted weight gain.  The closer a given food is to mirroring human milk’s IAA composition, the higher the protein quality is for that food.  Foods that are both protein dense (i.e., contain high amounts of protein) and that have high IAA Quality Scores should be considered by those looking maximize protein consumption while minimizing calorie consumption.

* Example is hypothetical and is not intended to be a recommendation for any diet.  The example assumes that the subject only eats one food during a day to obtain their daily minimum requirements of protein/IAA.  Generally, a mix of foods would be eaten in a balanced diet to meet one’s daily nutritional requirements.   Please consult your doctor or nutritionist to discuss your specific situation.

References

[1]  Dror, D.K. and Allen, L.H., Overview of Nutrients in Human Milk, Advances in Nutrition, Volume 9, Supplement 1, May 2018, https://www.sciencedirect.com/science/article/pii/S2161831322012753.

[2]  Report of an FAO Expert Consultation, Dietary protein quality evaluation in human nutrition, Food and Agriculture Organization of the United Nations, Rome, 2013, ISBN 978-92-5-107417-6.

[3]  Early modern human, Wikipedia, https://en.wikipedia.org/wiki/Early_modern_human, accessed on 4 September 2023.