Protein in the Vegan Diet
by Reed Mangels, Ph.D., R.D.
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Summary: It is very easy for a vegan diet to meet the recommendations for protein, as long as calorie intake is adequate. Strict protein combining is not necessary; it is more important to eat a varied diet throughout the day.
Some Americans are obsessed with protein. Vegans are bombarded with questions about where they get their protein. Athletes used to eat thick steaks before competition because they thought it would improve their performance. Protein supplements are sold at health food stores. This concern about protein is misplaced. Although protein is certainly an essential nutrient which plays many key roles in the way our bodies function, we do not need huge quantities of it. In reality, we need small amounts of protein. Only one calorie out of every ten we take in needs to come from protein (1). Athletic performance is actually improved by a high carbohydrate diet, not a high protein diet (2). Protein supplements are expensive, unnecessary, and even harmful for some people.
How much protein do we need? The RDA recommends that we take in 8/10ths of a gram of protein for every kilogram which we weigh (or about 0.36 grams of protein per pound that you weigh) (1). This recommendation includes a generous safety factor for most people. When we make a few adjustments to account for some plant proteins being digested somewhat differently from animal proteins and for the amino acid mix in some plant proteins, we arrive at a level of 1 gram of protein per kilogram body weight (0.45 grams of protein per pound that you weigh). Since vegans eat a variety of plant protein sources, somewhere between 0.8 and 1 gram of protein per kilogram would be a protein recommendation for vegans. If we do a few calculations we see that the protein recommendation for vegans amounts to close to 10% of calories coming from protein [For example, a 79 kg vegan male aged 25 to 50 years. His RDA for calories is 2900 calories per day. His protein needs might be as high as 79 kg x 1 gram/kg = 79 grams of protein. 79 grams of protein x 4 calories/gram of protein = 316 calories from protein per day. 316 calories from protein divided by 2900 calories = 10.1% of calories from protein]. If we look at what vegans are eating, we find that between 10-12% of calories come from protein (3). This contrasts with the protein intake of non-vegetarians which is close to 15-17% of calories.
So, in the US it appears that vegan diets are commonly lower in protein than standard American diets. Remember, though, with protein, more (than the RDA) is not necessarily better. There do not appear to be health advantages to consuming a high protein diet. Diets which are high in protein may even increase the risk of osteoporosis (4) and kidney disease (5).
The recommendation for protein for adult male vegans is around 63-79 grams per day; for adult female vegans it is around 50-63 grams per day (see text).
It is very easy for a vegan diet to meet the recommendations for protein. Nearly all vegetables, beans, grains, nuts, and seeds contain some, and often much, protein. Fruits, sugars, fats, and alcohol do not provide much protein, so a diet based only on these foods would have a good chance of being too low in protein. However, not many vegans we know live on only bananas, hard candy, margarine, and beer. Vegans eating varied diets containing vegetables, beans, grains, nuts, and seeds rarely have any difficulty getting enough protein as long as their diet contains enough energy (calories) to maintain weight. [See the sections on Pregnancy, Lactation, and Infants and Children for details about protein needs during these special times.]
The RDA for protein for adult males is 63 grams per day; for adult females it is 50 grams per day. An average of no more than 4.5 grams of protein per 100 calories is recommended (6).
A 3-ounce portion of meat or fish is a small portion, about the size of the palm of an adult woman's hand.
What about combining or complementing protein? Doesn't that make the protein issue much more complex? Let's look at a little background on the myth of complementing proteins. Protein is made up of amino acids, often described as its building blocks. We actually have a biological requirement for amino acids, not for protein. Humans cannot make nine of the twenty common amino acids, so these amino acids are considered to be essential. In other words, we must get these amino acids from our diets. We need all nine of these amino acids for our body to make protein.
Eggs, cow's milk, meat, and fish have been designated as high quality protein (1). This means that they have large amounts of all the essential amino acids. Soybeans, quinoa (a grain), and spinach also are considered high quality protein. Other protein sources of non-animal origin usually have all of the essential amino acids, but the amounts of one or two of these amino acids may be low. For example, grains are lower in lysine (an essential amino acid) and legumes are lower in methionine (another essential amino acid) than those protein sources designated as high quality protein.
Frances Moore Lappe, in her book Diet for a Small Planet (7) advocated the combining of a food low in one amino acid with another food containing large amounts of that amino acid. This got to be a very complicated process, with each meal having specific amounts of certain foods in order to be certain of getting a favorable amino acid mix. Many people got discouraged with the complexity of this approach. Actually, Lappe was being overly conservative to avoid criticism from the "Nutrition Establishment." She has since repudiated strict protein combining, saying "In combating the myth that meat is the only way to get high quality protein, I reinforced another myth. I gave the impression that in order to get enough protein without meat, considerable care was needed in choosing foods. Actually it is much easier than I thought" (8).
We recommend eating a variety of unrefined grains, legumes, seeds, nuts, and vegetables throughout the day, so that if one food is low in a particular essential amino acid, another food will make up this deficit (9,10).
Even if you ate only one food and not the variety of foods typical of a vegan diet, you would probably get enough protein and essential amino acids (11). Remember, almost all protein sources of non-animal origin contain all of the essential amino acids. You would have to eat a lot of the protein source (if there was only one source of protein in your diet) to meet essential amino acid needs. Table 4 (page 147) shows the amounts of various foods an adult male would have to eat if he relied on a single food source for his protein needs. Females would need about 20 percent less of each food due to the lower protein recommendation for women.
References
1. Food and Nutrition Board, National Research Council: Recommended Dietary Allowances, 10th ed. Washington, DC: National Academy Press, 1989.
2. Bergstrom J, Hermansen L, Hultman E, Saltin B. Diet, muscle glycogen and physical performance. Acta Physiol Scan 1967; 71: 140-150.
3. Messina M, Messina V. The Dietitian's Guide to Vegetarian Diets. Gaithersburg, MD: Aspen Publishers, 1996.
4. Kerstetter JE, Allen LH. Dietary protein increases urinary calcium. J Nutr 1990; 120: 134-136.
5. Dwyer JT, Madans JH, Tumbull B, et al. Diet, indicators of kidney disease, and later mortality among older persons in the NHANES I epidemiologic follow-up study. Am J Public Health 1994; 84: 1299-1303.
6. Committee on Diet and Health, Food and Nutrition Board: Diet and Health. Implications for Reducing Chronic Disease. Washington, DC: National Academy Press, 1989.
7. Lappe FM. Diet for a Small Planet. New York: Ballantine Books, 1971.
8. Lappe FM. Diet for a Small Planet, 10th anniversary edition. New York: Ballantine Books, 1982.
9. Young VR, Pellett PL. Plant proteins in relation to human protein and amino acid nutrition. Am J Clin Nutr 1994; 59 (suppl): 1203S-1212S.
10. Position of The American Dietetic Association: Vegetarian diets. J Am Diet Assoc 1997; 97: 1317-1321.
11. Kies C. Bioavailability: A factor in protein quality. J Agric Food Chem 1981; 29: 435-440.