Protein combining (also protein complementing) is the practice of vegetarians, particularly vegans, to eat certain complementary foods like beans and rice together in the same meal, so that plant foods with incomplete essential amino acid content combine to form a complete protein, meeting all amino acid requirements for human growth and maintenance.
Nevin S. Scrimshaw used protein combinations in his battle against kwashiorkor. In Guatemala he used the combination of cottonseed flour with maize, while in India he combined peanut flour with wheat.
The principle of protein combining was explained by J. Rigó:
- The biological value of proteins in general, hence also of grain-proteins, is fundamentally determined by the ratio between the essential amino acids to be found in cereals and the requirement of essential amino acids of the living creature, consuming protein...the most important way of raising the biological value ... [is] given by the technique of complementing.
Many plant proteins are lower in one or more essential amino acids than animal proteins, especially lysine, and to a lesser extent methionine and threonine. Nonetheless, eating a variety of plants can serve as a well-balanced and complete source of amino acids.
As Frances Moore Lappé explained:
- Complementary protein combinations make for delicious recipes – they are combinations that formed the basis of the world’s traditional cuisines. We use them naturally in our cooking without even being aware of it. The three most common complementary protein combinations are:
- Grains (rice, corn, wheat, barley, etc.) + legumes (peas, beans, lentils)
- Grains and milk products
- Seeds (Sesame or sunflower) +legumes
The practice was popularized in F. M. Lappé's 1971 book Diet for a Small Planet, which became a bestseller. The American National Research Council and the American Dietetic Association (ADA) soon picked it up, cautioning vegetarians to be sure to combine their proteins.
Lappé relaxed her position on protein combining in the 1981 edition of Diet for a Small Planet, in which she wrote:
- "In 1971 I stressed protein complementarity because I assumed that the only way to get enough protein ... was to create a protein as usable by the body as animal protein. 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.
- "With three important exceptions, there is little danger of protein deficiency in a plant food diet. The exceptions are diets very heavily dependent on  fruit or on  some tubers, such as sweet potatoes or cassava, or on  junk food (refined flours, sugars, and fat). Fortunately, relatively few people in the world try to survive on diets in which these foods are virtually the sole source of calories. In all other diets, if people are getting enough calories, they are virtually certain of getting enough protein."
Protein combining has drawn criticism as an unnecessary complicating factor in vegetarian nutrition. For instance, Andrew Weil wrote that "you don’t have to worry that you won’t get enough usable protein if you don’t put together some magical combination of foods at each meal."
In Healthy Times Jeff Novick wrote that the necessity of protein combining is a "myth that won’t go away". Necessity of protein combining was not asserted. Rather, the increased biological value of meals where proteins are combined was noted. In a concession, Lappé removed from the second edition "charts that indicate exact proportions of complementary proteins."
The American Dietetic Association reversed itself in its 1988 position paper on vegetarianism. Suzanne Havala, the primary author of the paper, recalls the research process:
- There was no basis for [protein combining] that I could see.... I began calling around and talking to people and asking them what the justification was for saying that you had to complement proteins, and there was none. And what I got instead was some interesting insight from people who were knowledgeable and actually felt that there was probably no need to complement proteins. So we went ahead and made that change in the paper. [Note: The paper was approved by peer review and by a delegation vote before becoming official.] And it was a couple of years after that that Vernon Young and Peter Pellet published their paper that became the definitive contemporary guide to protein metabolism in humans. And it also confirmed that complementing proteins at meals was totally unnecessary.
Some institutions use the Protein Digestibility Corrected Amino Acid Score to assess diets without consideration of protein combining and hence find the use of combinations to be a challenge to their methodology.
- Scrimshaw obituary from Massachusetts Institute of Technology
- J. Rigó (1985) "Nutritional Functions of Cereals", in Amino Acid Composition and Biological Value of Cereal, Radomir Lásztity & Máté Hidvégi editors, International Association for Cereal Chemistry
- Young VR, Pellett PL (1994). "Plant proteins in relation to human protein and amino acid nutrition" (PDF). The American Journal of Clinical Nutrition 59 (5 Suppl): 1203S–1212S. PMID 8172124.
- Lappé 1981 page 238
- Maurer, Donna. 2002. Vegetarianism: Movement or Moment? Philadelphia: Temple University Press. ISBN 1-56639-936-X p.37
- Diet for a Small Planet (ISBN 0-345-32120-0), 1981, p. 162; emphasis in original
- Vegetarians: Pondering Protein?, DrWeil.com, Dec. 11, 2002
- "Complete" Proteins?, Charles R. Attwood, M.D., F.A.A.P., VegSource.com (accessed Sep. 4, 2009)
- Complementary Protein Myth Won't Go Away!, Jeff Novick, M.S., R.D., Healthy Times (May 2003)
- Lappé 1981 p 239
- Maurer, Donna (2002) p.38.
- When Your Friends Ask: "Where Do You Get Your Protein", McDougall Newsletter