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By Elisa Zied, R.D.
msnbc.com contributor
updated 3/12/2010 8:20:43 AM ET 2010-03-12T13:20:43

Who wouldn’t want to lose up to 15 pounds in two weeks?

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The new Atkins diet book, an updated version of the popular high-fat eating plan, promises that kind of quick result. “The New Atkins for a New You: The Ultimate Diet for Shedding Weight and Feeling Great” promotes a program called the “optimal protein diet” that certainly appeals to our cheeseburger cravings (minus the bun, of course). The revised diet book is already a best-seller, but is pumping up protein and cutting carbs really the best way to slim down safely and stay that way? Losing weight that fast could be harmful .

While this latest Atkins incarnation includes far more vegetables, it still shuns, especially in the beginning, healthful whole grains, fruits and legumes. Even when it does allow for some of the vilified carbohydrate-rich foods in later phases, the amount of total carbs suggested continues to fall very short of Dietary Reference Intake (DRI) recommendations, as well as the government's current Dietary Guidelines for Americans

In fact, a recent two-year study in the New England Journal of Medicine found that reduced-calorie diets led to weight loss in overweight adults regardless of which macronutrients — protein, fat, or carbohydrate — were emphasized.

And a just published follow-up study in the Annals of Internal Medicine noted that obese people who followed either a low-carbohydrate or a low-fat diet for one year maintained a modest weight loss — 5 pounds and 9.5 pounds, respectively — at three years. While those who followed a low-carb diet lost more weight initially, they tended to regain more weight by the end of three years.

“These results highlight the difficulty in sticking to a low-carbohydrate diet, as carbohydrate intake did not differ between the low-carbohydrate or low-fat dieters by three years,” according to Dr. Marion Vetter, R.D., one of the study authors. “For some people, low-fat diets may be easier to sustain over time."

Despite efforts to blame carbs for our stubborn pudge, a study published in the November 2009 American Journal of Clinical Nutrition detected no differences in weight-loss maintenance after one year between those who followed a high-protein diet and those who followed a high-carb diet after three months of weight loss.

Before you order that steak
That said, protein does appear to satiate more than carbs or other fats, triggering hormones and other chemicals to send “feel full” messages to the brain. Some research has shown that boosting protein in your diet increases fullness and reduces how many calories you consume.  Consuming dietary protein also increases thermogenesis, meaning more calories are used to digest, absorb, and metabolize protein than for either carbohydrate or fat. It also helps you hold on to lean muscle mass that often shrinks while dieting.

Best (and worst) foods for immunityConsuming more protein (while reducing carbohydrate and/or fat intake) has also been shown in studies to improve insulin sensitivity, glucose tolerance, blood lipids (including cholesterol), and other cardiovascular risk factors. A high-protein diet has also been shown to control blood pressure, especially when the protein comes from plant sources. In older people, adequate protein intake also protects against age-related loss of skeletal muscle mass.

But before you order your next big steak or turkey club sandwich, be mindful that not all proteins are created equal.

Animal sources such as meat, poultry, fish, eggs, milk, cheese and yogurt are considered sources of complete proteins since the proteins they contain are made of all the essential amino acids. These foods also boast vitamin B12, folate, biotin, and iron.

The downside is fatty meats (especially processed ones like hot dogs, salami and bacon), poultry (like fried and/or skinned varieties), and full-fat (and even reduced-fat) versions of dairy products deliver lots of total fat, saturated fat and cholesterol. Too many of these foods (especially in large portions) can mean too many calories — and elevated blood cholesterol levels and heart disease risk.

Choose animal-derived proteins in their lowest fat form, such as sirloin, flank steak or round cuts; fish; and low-fat or nonfat dairy foods. Keep portions small to maximize nutritional benefits while minimizing health risks.

Of the plant proteins such as nuts and seeds, grains, legumes — dried beans, peas, lentils and soybeans — vegetables, and to a lesser extent fruits, only soy is considered a complete protein. All others are incomplete proteins, which means they lack one or more essential amino acids. Plant proteins pack in fiber, folate, potassium, calcium and magnesium, but have little, if any, saturated fat and no cholesterol. Choose some of these foods each day to get enough essential amino acids, especially if you follow a vegetarian or vegan diet. Watch portions since legumes, nuts, and seeds pack in lots of calories in relatively small amounts.

If you have kidney problems or any other disease or condition that warrants a lower protein diet, be sure to consult with a doctor and registered dietitian.

Although the protein and weight-loss connection appears promising, it's not a secret weapon for getting skinny. No matter which diet claims to help you shed pounds quickly, it’s not advisable to lose more than one to two each week. Anything more than that and your metabolism may slow down and actually make your body a less efficient fat-burner. Shedding pounds too fast increases your risk of gallstones, nutritional deficiencies and other serious health problems.

Elisa Zied, R.D., is a spokesperson for the American Dietetic Association. She is author of “Nutrition at your Fingertips” and co-author of “Feed Your Family Right!”

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