Widespread popularity of high-protein diets has drawn controversy as well as scientific interest. By reducing intake of carbohydrates and increasing consumption of fats and proteins, such diets are thought to increase satiety, facilitate weight loss, and improve cardiovascular risk factors. In recent years, many randomized controlled studies have compared the effects of higher-protein diets on weight loss and cardiovascular risk factors with those of lower-protein diets. The aim of this review was to provide an overview of experimental and epidemiologic evidence regarding the role of protein in weight loss and cardiovascular risk.

Emerging evidence from clinical trials indicates that higher-protein diets increase short-term weight loss and improve blood lipids, but long-term data are lacking. Findings from epidemiologic studies show a significant relationship between increased protein intake and lower risk of hypertension and coronary heart disease. However, different sources of protein appear to have different effects on cardiovascular disease. Although optimal amounts and sources of protein cannot be determined at this time, evidence suggests a potential benefit of partially replace refined carbohydrates with protein sources low in saturated fats.

High-protein animal products (eg, meat, high-fat dairy, and eggs) are also primary sources of saturated fat and cholesterol. Positive relationships between saturated fat, cholesterol, and CHD suggest that regular intake of foods high in saturated fat and cholesterol (eg, red meat and eggs) may increase risk of CHD. However, epidemiologic studies suggest that the effects of protein-rich foods on cardiovascular risk are not entirely driven by saturated fat and cholesterol. [Protein, body weight, and cardiovascular health, Harvard School of Public Health, Boston, MA, American Journal of Clinical Nutrition, Vol. 82, No. 1, 242S-247S, July 2005.]

So. Atkins may have been on to something. There's plenty of evidence that eating more saturated fat lowers the risk for heart disease. That's what a recent Harvard University study found: People who had the highest saturated fat intake also had the least plaque buildup on their artery walls. The American Journal of Clinical Nutrition described the findings as an "American Paradox."

Researchers at the Stanford University School of Medicine have completed the largest and longest-ever comparison of four popular diets, and the lowest-carbohydrate Atkins diet came out on top. The Atkins diet, popularized by the 2001 republication of Dr. Atkins’ New Diet Revolution, represents the lowest carbohydrate diet. The Zone diet, also low-carbohydrate, focuses on a 40:30:30 ratio of carbohydrates to protein to fat, a balance said to minimize fat storage and hunger. The LEARN (Lifestyle, Exercise, Attitudes, Relationships and Nutrition) diet follows national guidelines reflected in the U.S. Department of Agriculture’s food pyramid—low in fat and high in carbohydrates. The Ornish diet, based on bestseller Eat More, Weigh Less by Dean Ornish, is very high in carbohydrates and extremely low in fat.

In this study, premenopausal overweight and obese women assigned to follow the Atkins diet, which had the lowest carbohydrate intake, lost more weight and experienced more favorable overall metabolic effects at 12 months.

Researchers have several ideas for why the Atkins diet had the overall best results. The first is the simplicity of the diet. “It’s a very simple message,” he said. “Get rid of all refined carbohydrates to lose weight.” This message directly targets a major concern with the American diet right now—the increasing consumption of refined sugars in many forms, such as high-fructose corn syrup. Beyond pinpointing this high sugar intake, the Atkins diet does the best at encouraging people to drink more water, said Gardner. And when people replace sweetened beverages with water, they don’t generally eat more food; they simply consume fewer calories over the course of the day.

The third theory Gardner offered as to why the Atkins diet was more successful is that it is not just a low-carbohydrate diet, but also a higher protein diet. “Protein is more satiating than carbohydrates or fats, which may have helped those in the Atkins group to eat less without feeling hungry,” C. Gardner said.

Although the Atkins group led in terms of the average number of pounds lost, this group also gained back more weight in the second half of the study than those in the three other groups. Gardner also noted that the women in the Atkins group had lost an average of almost 13 pounds after six months, but ended the one-year period with a final overall average loss of 10 pounds. [Christopher D. Gardner, PhD, Stanfod University Medical Center, JAMA. 0MAR07; 297:969-977.]

Are your meals unsatisfying? The reason may be because they're lacking in protein, a nutrient that is both filling and calorie burning. Foods high in protein can help slow the digestion process, leaving you feeling full longer. Plus, your body uses more energy when digesting protein than digesting a fat or carbohydrate, according to the Harvard School of Public Health. These factors help explain why studies have shown than people are more likely to decrease their caloric intake after eating protein.

Protein may also boost the hunger-fighting properties of the hormone peptide YY (PYY). A study conducted in 2006 by Rachel Batterham of University College London found that enhanced-protein meals stimulated a greater release of PYY than either high-fat or high-carbohydrate meals, resulting in greater satiety. PYY deficiency may be a factor in obesity. One potential weight loss strategy is therefore to add dietary protein.

In order to maintain healthy body functioning like muscle growth and development during childhood, adolescence and pregnancy, it is recommended to consume seven grams of protein for every 20 pounds of body weight -- or about 50 to 65 grams of protein each day for the average person, but more may be better for your waistline.

Try lean chicken, turkey, beef, or pork. Fatty fish is another option that provides both unsaturated fats and is a good source of omega 3s. Proteins from meat, other animal products and soybean products are complete proteins, meaning they provide the nine essential amino acids we can't produce on our own. Plant proteins are incomplete and must be combined to ensure you get the daily amino acids needed for functioning. Beans are one of the best sources of protein because they provide fiber along with the protein, and are therefore very filling.

The major public health concern that motivates research of how protein and calcium interact is the growing prevalence of osteoporosis, which is estimated to afflict 200 million people worldwide. The current advice to the public for prevention of osteoporosis is to consume more calcium but to limit their intake of protein, the other major constituent of bone matrix (NIH Consensus Development Conference Statement, 1994). Recent findings challenge this view and indicate that dietary protein may have a constructive role in bone metabolism.

One might have thought that nutritional science would have figured out long ago of what is needed to know about protein to ensure optimal health. Instead, we see the Food and Nutrition Board currently deliberating whether the recommended dietary allowance for protein for adults should be raised, especially for the elderly. Of special consideration is the conflicting data on the effects of protein with calcium absorption, loss or gain.

Considered in isolation, a positive effect of protein on bone is not surprising, inasmuch as bone tissue is nearly 50% protein by volume. A substantial fraction of the amino acids in bone collagen cannot be reutilized in new protein synthesis. In the face of inadequate intake, bone rebuilding is low on the body's priority list. Hence, bone turnover requires continuous ingestion of new protein. The other 50% of bone is mineral, and here calcium is integral.

One study found that protein intake in the calcium-supplemented group was positively associated with bone gain, whereas there was a nonsignificant trend in the opposite direction in the placebo group. The calcium-supplemented subjects as a group gained bone mass over the 3-y course of the trial, whereas the unsupplemented group lost bone. Those with the highest protein intakes gained bone, whereas those with the lowest intakes actually lost bone. Clearly, calcium was not enough to protect the skeleton when protein intakes were low. [Dawson-Hughes B, Harris SS. "Calcium intake influences the association of protein intake with rates of bone loss in elderly men and women." Am J Clin Nutr 2002;75:773–9.]

Other studies, in brief, establish that protein and calcium act synergistically on bone if both are present in adequate quantities in the diet, but that protein may seem effectively antagonistic toward bone (because of its calciuric effect) when calcium intake is low. [Robert P. Heaney, "Protein and calcium: antagonists or synergists?"The Am J Clin Nutr.]