Protein Introduction Until recently, protein got little attention. Like a quiet child in a classroom of rowdies, it was often overshadowed by fat, carbohydrates, and vitamins. That's changing. Lately there's been an explosion of interest in protein, largely triggered by high-protein diets for weight loss. Surprisingly little is known about protein and health. The Institute of Medicine recommends that adults get a minimum of 0.8 grams of protein for every kilogram of body weight per day to keep from slowly breaking down their own tissues (1). That's just about 8 grams of protein for every 20 pounds of body weight. 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. Q. How much protein do I need each day? A. There is no one-size-fits-all answer to that question, and research on the topic is still emerging. Around the world, millions of people don't get enough protein. 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, getting the minimum daily requirement of protein is easy. 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. All Protein Isn't Alike Some of the protein you eat contains all the amino acids needed to build new proteins. This kind is called complete protein. Animal sources of protein tend to be complete. Other protein sources lack one or more "essential" amino acids—that is, 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. 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 Protein Package What Is Protein? Protein is 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. At least 10,000 different proteins make you what you are and keep you that way. Twenty or so basic building blocks, called amino acids, provide the raw material for all proteins. Following genetic instructions, the body strings together amino acids. Some genes call for short chains of amino acids; others are blueprints for long chains that fold, origami-like, into intricate, three-dimensional structures. Because the body doesn't store amino acids, as it does fats or carbohydrates, it needs a daily supply of amino acids to make new protein. Animal protein and vegetable protein probably have the same effects on health. It's the protein package that's likely to make a difference. A 6-ounce broiled porterhouse steak is a great source of complete protein—38 grams worth. But it also delivers 44 grams of fat, 16 of them saturated. (2) That's almost three-fourths of the recommended daily intake for saturated fat. The same amount of salmon gives you 34 grams of protein and 18 grams of fat, 4 of them saturated. (2) A cup of cooked lentils has 18 grams of protein, but less than 1 gram of fat. (2) The bottom line is that it's important to pay attention to what comes along with the protein in your food choices. Vegetable sources of protein, such as beans, nuts, and whole grains, are excellent choices, and they offer healthy fiber, vitamins, and minerals. Nuts are also a great source of healthy fat. The best animal protein choices are fish and poultry. If you are partial to red meat, such as beef, pork, or lamb, stick with the leanest cuts, choose moderate portion sizes, and make it only an occasional part of your diet, for several reasons: A major report on cancer prevention recommends consuming less than 18 ounces a week of red meat and avoiding processed meats (such as hot dogs, bacon, or ham) to lower the risk of colon cancer. (3) There's also substantial evidence that replacing red meat with fish, poultry, beans, or nuts, could help prevent heart disease, and that lowering red meat can lower the risk of diabetes. (30, 31) Processed meats, especially, have been most strongly linked with cardiovascular disease and diabetes, at least in part due to their high added sodium content. (Learn more about why cutting salt and sodium is good for your health, and learn what you can do to lower your risk of type 2 diabetes.) Protein and Chronic Disease The most solid connection between protein and health has to do with allergies. Proteins in food and the environment are responsible for these overreactions of the immune system. Beyond that, relatively little evidence has been gathered regarding the effect of protein on the development of chronic diseases. Cardiovascular disease: One concern about the high-protein diet craze has been that eating diets high in protein and fat, and low in carbohydrate, would harm the heart. Recent research provides reassurance that eating a lot of protein doesn't harm the heart. Many people think of nuts as just another junk food snack. In reality, nuts are excellent sources of protein and other healthful nutrients. Learn why nuts are healthy for the heart. In fact, it is possible that eating more protein, especially vegetable protein, while cutting back on easily digested carbohydrates may benefit the heart. A 20-year prospective study of 82,802 women found that those who ate low-carbohydrate diets that were high in vegetable sources of fat or protein had a 30 percent lower risk of heart disease, compared to women who ate high-carbohydrate, low-fat diets. (4) But women who ate low-carbohydrate diets that were high in animal fats or proteins did not have a reduced risk of heart disease. Diabetes: Although proteins found in cow's milk have been implicated in the development of type 1 diabetes (formerly called juvenile or insulin-dependent diabetes), ongoing research has yielded inconsistent results. (5) The amount of protein in the diet doesn't seem to adversely affect the development of type 2 diabetes (formerly called adult-onset diabetes), although research in this area is ongoing. A recent 20-year prospective study in women suggests that eating a low-carbohydrate diet that is high in vegetable sources of fat and protein may modestly reduce the risk of type 2 diabetes.(26) Cancer: There's no good evidence that eating a little protein or a lot of it influences cancer risk. Eating a lot of red meat is linked to an increased risk of colon cancer, however, as is eating processed meat. (3) Osteoporosis: Digesting 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 low-carb or no-carb diets, takes 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. In the Nurses' Health Study, for example, women who ate more than 95 grams of protein a day were 20 percent more likely to have broken a wrist over a 12-year period when compared with those who ate an average amount of protein (less than 68 grams a day). (6) But this area of research is still controversial, and findings have not been consistent. Some studies suggest increasing protein increases risk of fractures; others associate high-protein diets with increased bone -mineral density. The evidence is inconclusive, and more research is needed. Protein and Weight Control The notion that you could lose weight by cutting out carbohydrates and eating plenty of protein was once tut-tutted by the medical establishment, partly because such diets were based on little more than interesting ideas and speculation. In the past few years, head-to-head trials that pitted high-protein, low-carbohydrate diets against low-fat, high-carbohydrate diets have provided some evidence that a low-carbohydrate diet may help people lose weight more quickly than a low-fat diet, although so far, that evidence is short term. In two short, head-to-head trials, low-carb approaches worked better than low-fat diets. (7, 8) A more-recent year-long study, published in 2007 in the Journal of the American Medical Association, showed the same thing. (9) In this study, overweight, premenopausal women went on one of four diets: Atkins, Zone, Ornish, or LEARN, a standard low-fat, moderately high-carbohydrate diet. The women in all four groups steadily lost weight for the first six months, with the most rapid weight loss occurring among the Atkins dieters. After that, most of the women started to regain weight. At the end of a year, it looked as though the women in the Atkins group had lost the most weight since the start of the study, about 10 pounds, compared with a loss of almost 6 pounds for the LEARN group, 5 pounds for the Ornish group, and 3½ pounds for the Zone group. Levels of harmful LDL, protective HDL, and other blood lipids were at least as good among women on the Atkins diet as those on the low-fat diet. If you read the fine print of the study, though, it turns out that few of the women actually stuck with their assigned diets. Those on the Atkins diet were supposed to limit their carbohydrate intake to 50 grams a day, but they took in almost triple that amount. The Ornish dieters were supposed to limit their fat intake to under 10 percent of their daily calories, but they got about 30 percent from fat. There were similar deviations for the Zone and LEARN groups. What about longer term studies? POUNDS LOST (Preventing Overweight Using Novel Dietary Strategies), a two-year head-to-head trial comparing different weight loss strategies found that low-carb, low-fat, and Mediterranean-style diets worked equally well in the long run, and that there was no speed advantage for one diet over another. (27) What this and other diet comparisons tell us is that sticking with a diet is more important than the diet itself. (Read more about the POUNDS LOST weight loss trial.) Why, in some studies, do high-protein, low-carb diets seem to work more quickly than low-fat, high-carbohydrate diets, at least in the short run? First, chicken, beef, fish, beans, or other high-protein foods slow the movement of food from the stomach to the intestine. Slower stomach emptying means you feel full for longer and get hungrier later. Second, protein's gentle, steady effect on blood sugar avoids the quick, steep rise in blood sugar and just as quick hunger-bell-ringing fall that occurs after eating a rapidly digested carbohydrate, like white bread or baked potato. Third, the body uses more energy to digest protein than it does to digest fat or carbohydrate. (10) No one knows the long-term effects of eating high-protein diets with little or no carbohydrates. Equally worrisome is the inclusion of unhealthy fats in some of these diets. There's no need to go overboard on protein and eat it to the exclusion of everything else. Avoiding fruits and whole grains means missing out on healthful fiber, vitamins, minerals, and other phytonutrients. It's also important to pay attention to what accompanies protein. Choosing plant-based high-protein foods that are low in saturated fat will help the heart even as it helps the waistline.