High-protein, low-carbohydrate diets are the hottest thing since sliced flank steak, and every food marketer in the known universe appears to want a piece of the protein pie.
Body builders are snatching, grabbing, and gulping down protein shakes. Dieters are gobbling down protein bars (and shunning pasta) in hopes of quick weight loss.
The Power of Protein
It's easy to understand the excitement. Protein is an important component of every cell in the body. Hair and nails are mostly made of protein. Your body uses protein to build and repair tissues. You also use protein to make enzymes, hormones, and other body chemicals. Protein is an important building block of bones, muscles, cartilage, skin, and blood.
Along with fat and carbohydrates, protein is a "macronutrient," meaning that the body needs relatively large amounts of it. Vitamins and minerals, which are needed in only small quantities, are called "micronutrients." But unlike fat and carbohydrates, the body does not store protein, and therefore has no reservoir to draw on when it needs a new supply.
So you may assume the solution is to eat protein all day long. Not so fast, say nutritionists.
The truth is, we need less total protein that you might think. But we could all benefit from getting more protein from better food sources.
How Much Protein Is Enough?
We've all heard the myth that extra protein builds more muscle. In fact, the only way to build muscle is through exercise. Bodies need a modest amount of protein to function well. Extra protein doesn't give you extra strength. According to the U.S. Department of Health and Human Services:
Teenage boys and active men can get all the protein they need from three daily servingsfor a total of seven ounces.
For children age 2 to 6, most women, and some older people, the government recommends two daily servings for a total of five ounces.
For older children, teen girls, active women, and most men, the guidelines give the nod to two daily servings for a total of six ounces.
The Drawbacks of High-Protein Diets
Many people who have jumped on the high-protein/low-carb bandwagon think that they can pack away as much protein as they like. But nutrition experts urge caution. The reasons why have to do with how high-protein/low-carb diets are thought to lead to weight loss. When people eat lots of protein but few carbohydrates, their metabolisms change into a state called ketosis. Ketosis means the body converts from burning carbs for fuel to burning its own fat. When fat is broken down, small bits of carbon called ketones are released into the bloodstream as energy sources. Ketosis, which also occurs in diabetes, tends to suppress appetite, causing people to eat less, and it also increases the body's elimination of fluids through urine, resulting in a loss of water weight.
Christopher D. Gardner, PhD, assistant professor of medicine at Stanford University in Palo Alto, Calif., tells WebMD that high-protein diets like the Atkins regimen may trade short-term benefits for long-term health consequences. Among the risks: The body produces ammonia when it breaks down protein. No one knows the long-term risks of higher levels of ammonia in the body.
Also, there is evidence to suggest that people who eat high-protein diets typically excrete excess calcium in their urine, says Deborah Sellmeyer, MD, assistant professor of medicine and director of the Center for Osteoporosis at the University of California at San Francisco. This suggests that the body is releasing stores of calcium into the bloodstream to counteract an increase in acids caused by protein consumption (calcium buffers, or neutralizes, acids). Too much calcium loss could lead to osteoporosis down the road, Sellmeyer says.
Lastly, there are the obvious concerns. Carbohydrate foods shunned by some people on low-carb diets include fruits and vegetables, which are the best sources for vitamins, fiber, and antioxidants -- nutrients that help prevent disease. By contrast, animal foods that are high in protein are usually also high in saturated fats, which increase the risk for heart disease, stroke, diabetes, and several types of cancer.
The American Heart Association warns: "Reducing consumption of [carbs] usually means other, higher-fat foods are eaten instead. This raises cholesterol levels even more and increases cardiovascular risk." The AHA also notes that by concentrating on protein sources and skipping carbs, dieters may be getting too much salt, and not enough calcium, potassium, or magnesium, which are typically found in fruits, vegetables, and whole grains.
The (Short-Term) Case for High Protein Diets
While no one knows the effect of eating a high-protein diet over the long term, the diet appears to be safe and effective for up to six months.
Frank Hu, MD, PhD, assistant professor in the Department of Nutrition at Harvard University School of Public Health in Boston, asked a student to review published studies on high-protein diets and try to answer these four important questions:
Do high protein diets increase fat burning in the body?
Do they increase satiety (the sense of being "full" or "satisfied" after a meal)?
Do they decrease subsequent energy (calorie) intake by the body?
Do they lead to weight loss?
For the most part, says Hu, the answers are "yes." Protein can be converted by the body into glucose for energy, but it takes twice as much effort as converting carbohydrates or fats into glucose. The extra effort translates into fewer calories available, Hu said at a recent symposium on the science of obesityobesity.
When it comes to feeling full, the clinical studies consistently showed that high-protein diets increase satiety and decrease hunger compared with high-fat or high-carbohydrate diets. In addition, most, but not all of the studies reviewed showed that most people on high-protein diets took in about 10% less energy (roughly 200 calories) per day, which could account for at least some of the weight loss seen with this type of diet.
"There is some evidence that high-protein diets induce great fat loss," Hu told the symposium audience. On average, high-protein diets produced an average weight loss that was about 4.5 lbs greater than that achieved on other diets after six months.
"Most of the studies show results for up to six months, but after six months they begin to lose effectiveness, either because people do not adhere to this diet very well in the long term, or because they get used to this diet biologically," Hu tells WebMD. "So in the long term the high-protein diets tend to lose their ability to maintain the weight."
Choose Your Proteins Wisely
The type of protein you eat may play a role in successful weight loss and in your overall health.
Consumption of large quantities of processed meats such as hot dogs, sausages, and deli meats, have been linked to increased risk of type 2 diabetes, cardiovascular disease, and colorectal cancer, Hu says. You'll have a harder time maintaining weight loss if you eat these proteins often, and you may be damaging your body.
Hu and other nutrition experts recommend getting dietary proteins from the following sources:
Fish: Fish offers heart-healthy omega-3 fatty acids and, in general, less fat than meat.
Poultry: You can eliminate most of the saturated fat by removing the skin.
Beans: Beans contain more protein than any other vegetable protein. Plus, they're loaded with fiber that helps you feel full for hours.
Nuts: One ounce of almonds gives you 6 grams of protein, nearly as much protein as one ounce of broiled ribeye steak.
Whole grains: A slice of whole wheat bread gives you 3 grams of protein, plus valuable fiber.
"A lot of plant-based foods like soy and legumes can give you the same amount of protein as meats. I have nuts for breakfast every day, because they not only give you a lot of protein, but they're healthy sources of fat," Hu says.
So when you decide to cut carbs and boost protein, take Hu's advice: Don't lose sight of the big picture.