1. Health claims: Soy protein and risk of coronary heart disease. Code of Federal Regulations 21CFR101.82 (2001).
2. Feskanich D, Willett WC, Stampfer MJ, Colditz GA. Protein consumption & bone fractures in women. Am J Epidemiol 1996
3. USDA Nutrient Database for Standard Reference, Release 14. US Department of Agriculture. accessed on 18 July 2002.
4. Hu FB, Stampfer MJ, Manson JE, et al. Dietary protein and risk of ischemic heart disease in women. Am J Clin Nutr 1999
5. Wasmuth HE, Kolb H. Cow's milk and immune-mediated diabetes. Proc Nutr Soc 2000
6. Messina M, Gardner C, Barnes S.- …Role of Soy in Preventing and Treating Chronic Disease. J Nutr 2002
7. Anderson JW, Johnstone BM, Cook-Newell ME. Meta-analysis of the effects of soy protein intake on serum lipids. N Engl J Med 1995
8. Erdman JW, Jr. AHA Science Advisory: Soy protein and cardiovascular disease: Nutrition Committee of the AHA. Circulation 2000
9. Vincent A, Fitzpatrick LA. Soy isoflavones: are they useful in menopause? Mayo Clin Proc 2000
10. de Lemos ML. Effects of soy phytoestrogens genistein and daidzein on breast cancer growth. Ann Pharmacother 2001
11. McMichael-Phillips DF, Harding C, Morton M, Am J Clin Nutr1998
12. White LR, Petrovitch H, Ross GW, et al. Brain aging and midlife tofu consumption. J Am Coll Nutr 2000
13. Shipman JT. An Introduction to Physical Science. Boston , MA: Houghton Mifflin Co., 2002.
The aim of the Harvard School of Public Health Nutrition Source is to provide timely information on diet and nutrition for clinicians, allied health professionals, and the public. The contents of this Web site are not intended to offer personal medical advice, which should be obtained from a health-care provider. The information does not mention brand names, nor does it endorse any particular products.
Take away the water, and about 75 percent of your weight is protein. This chemical family is found throughout the body. It's 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. At least 10,000 different proteins make you what you are and keep you that way.
Surprisingly little is known about protein and health. We know that adults need a minimum of 1 gram of protein for every kilogram of body weight per day to keep from slowly breaking down their own tissues. That's about 9 grams of protein for every 20 pounds. Beyond that, there's relatively little solid information on the ideal amount of protein in the diet, a healthy target for calories contributed by protein, or the best kinds of protein.
Around the world, millions of people don't get enough protein. This protein malnutrition leads to the condition known as kwashiorkor. Lack of protein can cause growth failure, loss of muscle mass, decreased immunity, weakening of the heart and respiratory system, and death.
In the United States and other developed countries, it's easy to get the minimum daily requirement of protein. Cereal with milk for breakfast, a peanut butter and jelly sandwich for lunch, and a piece of fish with a side of beans for dinner adds up to about 70 grams of protein, plenty for the average adult.
Too little protein is clearly a problem. What about too much? The digestion of protein releases acids that the body usually neutralizes with calcium and other buffering agents in the blood. Eating lots of protein, such as the amounts recommended in the so-called no-carb diets, requires lots of calcium. Some of this may be pulled from bone. Following a high-protein diet for a few weeks probably won't have much effect on bone strength. Doing it for a long time, though, could weaken bone.
All protein isn't alike
Some of the protein you eat contains all the amino acids needed to construct new proteins. This kind is called complete protein. Animal sources of protein tend to be complete. Other protein lacks one or more amino acids that the body can't make from scratch or create by modifying another amino acid. Called incomplete proteins, these usually come from fruits, vegetables, grains, and nuts.
Vegetarians need to be aware of this difference. To get all the amino acids needed to make new protein--and thus to keep the body's systems in good shape--people who don't eat meat, fish, poultry, eggs, or dairy products should eat a variety of protein-containing foods each day.
The Bottom Line-Recommendations for Protein Intake:
•Get a good mix of proteins. Almost any reasonable diet will give you enough protein each day. Eating a variety of foods will ensure that you get all of the amino acids you need.
•Pay attention to the protein package. You rarely eat straight protein. Some comes packaged with lots of unhealthy fat, like when you eat marbled beef or drink whole milk. If you eat meat, steer yourself toward the leanest cuts. If you like dairy products, skim or low-fat versions are healthier choices. Beans, soy, nuts, and whole grains offer protein without much saturated fat and with plenty of healthful fiber and micronutrients.
•Balance carbohydrates and protein. Cutting back on highly processed carbohydrates and increasing protein improves levels of blood triglycerides and HDL, and so may reduce your chances of having a heart attack, stroke, or other form of cardiovascular disease. It may also make you feel full longer, and stave off hunger pangs. Too much protein, though, could weaken bones.
•Eat soy in moderation. Soybeans, tofu, and other soy-based foods are an excellent alternative to red meat. But don't go overboard. Two to four servings a week is a good target. And stay away from supplements that contain concentrated soy protein or soy extracts, such as isoflavones. Larger amounts of soy may soothe hot flashes and other menopause-associated problems, but the evidence for this is weak.