Plant Proteins: Fact vs. Fiction

Americans today are obsessed with protein, and many people now favor diets based heavily on animal proteins—meat, poultry, eggs, and dairy. Media headlines proclaim the health benefits of high protein diets, but is all the protein hype justified? We’ve called on Suzanne Dixon, Epidemiologist and Registered Dietitian Nutritionist (RDN), to address three common beliefs about plant proteins. A closer look at the science can help us sort fact from fiction.

3 Common Assumptions about Protein:
1. Plant-based proteins alone can’t provide enough protein to hit your daily target. A vegetarian or vegan likely needs a protein supplement. This is fiction. On average, people around the globe who get all of their protein from plants consume just slightly less protein than meat eaters (1). Even better, plant proteins are as satisfying as animal proteins. In a clinical trial, overweight people who were attempting to lose weight reported equal satisfaction and experienced similar weight loss on a plant-protein diet compared with when they were eating an animal-protein diet (2). If you love a morning or post-workout smoothie or shake, consider adding healthy plant proteins. Whenever possible, opt for whole food protein sources, such as a small chunk of tofu. If you want to try a protein powder, good plant-based options include pea and rice-protein powders, or products made of legumes and grains. Read the fine print to avoid unwanted fillers, colors, preservatives, and added sugars.

2. Because most plant foods do not contain “complete proteins,” they have to be consumed along with other, “complementary” plant foods (i.e. rice with beans). This is fiction. You do not need to “combine” different plant foods at every meal to get all of the essential amino acids. As long as you have a varied diet over the course of the day, or even a few days, your body will do the rest. We can retain essential amino acids from a plant food when we eat it. Then, when you eat the “complementary” plant food with different essential amino acids, your body will draw on the stored amino acids from previously eaten foods, and combine all of the amino acids as needed (3). Consume a variety of plant proteins on average, and let your body work its amino acid-combining magic. Another fiction is that plants never have all of the essential amino acids. Some plants do contain all eight essential amino acids, including soy, hempseed, chia seed, amaranth, buckwheat, and quinoa. The Protein Digestibility Corrected Amino Acid Score (PDCAAS), which is considered the “gold standard” for determining protein quality, runs from 0 to 1.0 (4). Soy protein, with a PDCAAS of 1.0 is a more “complete” protein than beef! The PDCAAS of whole soy beans is 0.91, and for whole beef, it is 0.92 (5-7). Whole foods typically have a slightly lower PDCAAS than pure protein derived from those foods, because the presence other nutrients “dilute” the total protein. However, the bottom line is that whole soy and beef are nearly equivalent in terms of “completeness” and essential amino acids (5).

3. People who rely on plants for most of the protein in their diet tend to have lower risk for disease. This is fact. Consider long-term studies following millions of people for many years. These studies consistently demonstrate that when it comes to animal protein, more is not always better. The healthiest dietary patterns in the world do not contain large amounts (or any) animal protein. They are based predominantly around plants and plant proteins (8-10). Diets differ from one another a bit, but share one key characteristic: heavy reliance on plants for protein, and plants overall (10). The key take-home message is that the exact dietary pattern isn’t critical—but eating more plants and less meat is consistently associated with better health and reduced risk of cardiovascular disease, type 2 diabetes, stroke, hypertension, and some types of cancer.

The bottom line: Replacing a few meat-based meals per week with plant foods is a good first step toward improved health!    

References 1. Foley JA, Ramankutty N, Brauman KA, Cassidy ES, Gerber JS, Johnston M, Mueller ND, et al. Solutions for a cultivated planet. Nature. 2011;478(7369):337-42. 2. Neacsu M, Fyfe C, Horgan G, Johnstone AM. Appetite control and biomarkers of satiety with vegetarian (soy) and meat-based high-protein diets for weight loss in obese men: a randomized crossover trial. Am J Clin Nutr. 2014 ;100(2):548-58. 3. Position of the American Dietetic Association: Vegetarian Diets. J Am Diet Assoc. 2009;109(7):1266-82. 4. Boutrif E. The Food and Agricultural Organization of the World Health Organization. Recent developments in protein quality evaluation. Accessed June 22, 2015: http://www.fao.org/docrep/U5900t/u5900t07.htm. 5. Schaafsma G. The protein digestibility-corrected amino acid score. J Nutr. 2000;130(7):1865S-7S. 6. Hoffman JR, Falvo MJ. Protein – Which is Best? J Sports Sci & Med. 2004;3(3):118-30. Accessed June 20, 2015: http://www.jssm.org/vol3/n3/2/v3n3-2pdf.pdf 7. Schaafsma G. Advantages and limitations of the protein digestibility-corrected amino acid score (PDCAAS) as a method for evaluating protein quality in human diets. Br J Nutr. 2012;108(Suppl 2):S333-36. 8. Liese AD, Krebs-Smith SM, Subar AF, George SM, Harmon BE, Neuhouser ML, Boushey CJ, Schap TE, Reedy J. The Dietary Patterns Methods Project: synthesis of findings across cohorts and relevance to dietary guidance. J Nutr. 2015;145(3):393-402. 9. Harmon BE, Boushey CJ, Shvetsov YB, Ettienne R, Reedy J. Wilkens LR, Le Marchand L, Henderson BE, Kolonel LN. Associations of key diet-quality indexes with mortality in the Multiethnic Cohort: the Dietary Patterns Methods Project. Am J Clin Nutr. 2015;101(3):587-97. 10. Reedy J, Krebs-Smith SM, Miller PE, Liese AD, Kahle LL, Park Y, Subar AF. Higher diet quality is associated with decreased risk of all-cause, cardiovascular disease, and cancer mortality among older adults. J Nutr. 2014;144(6):881-89. 11. Sofi F, Macchi C, Abbate R, Gensini GF, Casini A. Mediterranean diet and health status: an updated meta-analysis and a proposal for a literature-based adherence score. Public Health Nutr. 2014;17(12):2769-82. 12. Willcox DC, Scapagnini G, Willcox BJ. Healthy aging diets other than the Mediterranean: a focus on the Okinawan diet. Mech Ageing Dev. 2014;136-137:148-62. 13. Salehi-Abargouei A, Maghsoudi Z, Shirani F, Azadbakht L. Effects of Dietary Approaches to Stop Hypertension (DASH)-style diet on fatal or nonfatal cardiovascular diseases–incidence: a systematic review and meta-analysis on observational prospective studies. Nutrition. 2013;29(4):611-18. 14. Le LT, Sabaté J. Beyond meatless, the health effects of vegan diets: findings from the Adventist cohorts. Nutrients. 2014;6(6):2131-47.

Suzanne Dixon, MPH, MS, RDN, is a Speciality Dietician with The Heart’s Kitchen. She focuses on chronic disease prevention and nutrition for cancer research while developing and teaching undergraduate and graduate nutrition coursework. www.NoNutritionFear.com

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