Protein Myths

PROTEIN MYTHS

By Nethra Vijayakumar

Protein is an essential macronutrient, found throughout the body—in muscle, bone, skin, hair, and virtually every other body part or tissue. It makes up the enzymes that power many chemical reactions and the hemoglobin that carries oxygen in your blood. Protein is made from twenty-plus basic building blocks called amino acids. 

Myth: Animal protein is complete protein.

Fact: Amino acids are the building blocks for protein synthesis. The body needs 20 different amino acids to function. Each amino acid is important, however, 9 of these 20 are considered essential, meaning the human body cannot create them in sufficient amounts on its own. Therefore, we need to consume them in our diet. As for the other 11 amino acids, the body can create on its own (through a process called ‘transamination’).

When it comes to animal versus plant proteins, one of the biggest differences is the proportions of essential and nonessential amino acids. Animal proteins contain all 9 essential amino acids. Because animal proteins contain all essential amino acids, they are classified as complete or “high-quality proteins”.

Some plant-based proteins are lower in one (or two) amino acids and therefore have been classified as incomplete. 

Yes, some plant proteins contain a lower amount of a particular amino acid (i.e. lysine is low in grains, making lysine the limiting amino acid). But plant proteins are not incomplete. In fact, the only incomplete protein is gelatin, which is missing the amino acid tryptophan. 

Since plant proteins (with the exception of soy, which contains all 9 essential amino acids) has a limiting amino acid, they were deemed incomplete proteins. In fact, plant proteins contain all essential amino acids. 

The original study deeming plant proteins incomplete and therefore insufficient for growth dates back to a 1912 study done on rats. The researchers found rats did not grow sufficiently on plants. (2) 

But we aren’t rats. In fact, milk from rats has 10 more protein than human breast milk and rats grow 10 times faster than humans. (3) For the sake of disease prevention, we do not want to grow as quickly as rats (or cows)!

From this rat study, came the myth of complementary proteins: in order to achieve adequate growth and meet our essential amino acid needs, “two or more plant proteins must be combined to compensate for deficiencies in essential amino acid content in each protein”. (1) Again, this has been proved to be inaccurate. 

Myth: Animal protein is more easily absorbed than plant protein.

Fact: The biological value of a protein generally is determined by its amino acid composition (essential vs nonessential, complete vs incomplete) and digestibility. Whether the protein is plant- or animal-based is less of a consideration, although that may play a role in how efficiently our bodies can extract the amino acids from the food’s overall “matrix.”(3,4)

The protein digestibility-corrected amino acid score (PDCAAS) is commonly used in the United States to assess protein quality, while the digestible indispensable amino acid score is supported by the Food and Agriculture Organization of the United Nations.(4)

In the PDCAAS, foods with lower levels of indispensable, or essential, amino acids—the amino acids you must get from food because your body can’t make them—are characterized as “lower-quality” protein.(4) However, the PDCAAS and other measures of biological value don’t account for whether the food is raw or cooked and how it interacts with other protein-containing foods.(3) As a result, many plant foods may have a lower value because they’re too low in an essential amino acid, something that may matter little in the context of a varied diet. Also worthy of consideration is that plant-based protein has benefits for the environment, plus it comes “packaged” with fiber, healthful polyunsaturated and monounsaturated fats, and phytochemicals.

Research does suggest that plant proteins from whole plant foods are slightly less digestible (maybe 10% to 20%) than animal proteins due to the high fiber content interfering with absorption. Another potential concern is how much leucine—one of the branched-chain amino acids—is in a food. Leucine is critical for triggering new muscle protephytochemical (5.6) and animal proteins such as dairy, eggs, meat, and fish contain more leucine than plant-based proteins. What does this mean? It means we need to eat more plant-based protein to get adequate leucine.(3,7) Of the plant-based proteins, soyfoods contain the most leucine.(8)

Myth: Vegetarians and vegans don’t get enough protein.

Fact: In developed countries, at least, vegetarians and vegans get enough protein—and enough leucine.(3,9). This myth likely stems in part from the bioavailability myth but also from the common worry that plant proteins, unlike animal proteins, aren’t complete.

It’s true that most plant foods don’t contain high levels of all nine of the essential amino acids—soy, quinoa, and buckwheat do, but most plant foods are lacking in either lysine or methionine. However, we now know that we don’t need to get all nine essential amino acids from the same food, and we don’t need to combine different plant foods, such as grains and beans, to form a “complete protein” in the same meal. Eating a variety of protein-rich plant foods in the course of your day provides enough protein and easily fills in any amino acid gaps.(10)

“Plant-based folks can easily meet their protein needs through soyfoods, beans and lentils, and nuts and seeds. Whole grains and veggies also contain protein,” says Seattle-based Ginger Hultin, MS, RDN, CSO, a spokesperson for the Academy of Nutrition and Dietetics.

Myth: You can’t be vegan and lose weight because beans are too high in carbs.

Fact: While it’s true that beans and lentils are higher in carbohydrates than animal-based protein foods, observational studies—which can’t establish cause and effect—show that vegetarians and vegans tend to have a lower BMI than nonvegetarians and nonvegans.(11)

In addition, recent clinical research shows that, overall, no one macronutrient ratio is superior for weight loss or for health.(13) Resultsfrom the DIETFITS study, which randomized 609 adults to a low-fat (average 29% fat) or low-carb (average 30% carb) diet, found no average difference in weight change between the groups, although there were dramatic interindividual differences in each group.(12)

References

1. Ardlaw, G. M., & Hampl, J. S. (2009). Perspectives in Nutrition. Boston: McGraw-Hill Higher Education.

2. T B Osborne, L B Mendel. Amino-acids in nutrition and growth. Abtlerhdden: Zeitschr. f. phvsiol. Chem., Ixxvii, p. 27, 1912. 

3. Paddon-Jones D, Coss-Bu JA, Morris CR, Phillips SM, Wernerman J. Variation in protein origin and utilization: research and clinical application. Nutr Clin Pract. 2017;32(1_suppl):48S-57S.

4. Marinangeli CPF, House JD. Potential impact of the digestible indispensable amino acid score as a measure of protein quality on dietary regulations and health. Nutr Rev. 2017;75(8):658-667.

5. Bauer J, Biolo G, Cederholm T, et al. Evidence-based recommendations for optimal dietary protein intake in older people: a position paper from the PROT-AGE Study Group. J Am Med Dir Assoc. 2013;14(8):542-559.

6. Devries MC, McGlory C, Bolster DR, et al. Leucine, not total protein, content of a supplement is the primary determinant of muscle protein anabolic responses in healthy older women. J Nutr. 2018;148(7):1088-1095.

7. Arentson-Lantz E, Clairmont S, Paddon-Jones D, Tremblay A, Elango R. Protein: a nutrient in focus. Appl Physiol Nutr Metab. 2015;40(8):755-761.

8. van Vliet S, Burd NA, van Loon LJ. The skeletal muscle anabolic response to plant- versus animal-based protein consumption. J Nutr. 2015;145(9):1981-1991.

9. Sanders TA. The nutritional adequacy of plant-based diets. Proc Nutr Soc. 1999;58(2):265-269.

10. Marsh KA, Munn EA, Baines SK. Protein and vegetarian diets. Med J Aust. 2013;199(4 Suppl):S7-S10.

11. Farmer B. Nutritional adequacy of plant-based diets for weight management: observations from the NHANES. Am J Clin Nutr. 2014;100(Suppl 1):365S-368S.

12. Gardner CD, Trepanowski JF, Del Gobbo LC, et al. Effect of low-fat vs low-carbohydrate diet on 12-month weight loss in overweight adults and the association with genotype pattern or insulin secretion: the DIETFITS randomized clinical trial. JAMA. 2018;319(7):667-679.

13. Ludwig DS, Willett WC, Volek JS, Neuhouser ML. Dietary fat: from foe to friend? Science. 2018;362(6416):764-770.