High-protein diets may also limit weight regain following weight loss. Researchers from Maastricht University, the Netherlands, found that overweight and moderately obese men and women who had recently come off a weight-loss program regained less weight after three months when consuming an 18% protein diet vs. a 15% protein diet. Similar effects occurred at six months and after a year. “In addition,” Pikosky says, “when the composition of the weight regained was assessed, the 18% protein group gained predominantly fat-free mass, while the 15% protein group gained both fat-free mass and body fat.”
A study published in the Jan. 2008 American Journal of Clinical Nutrition (87(1):150-155) came to similar lean-sparing conclusions. “Houston et al found that dietary protein intake was associated with changes in lean mass over three years in older adults in the Health ABC Study cohort,” says Marcia Greenblum, M.S., R.D., director, nutrition and food safety education, Egg Nutrition Center, Washington, D.C. “Participants in the highest quintile of energy-adjusted protein intake lost around 40% less lean mass and appendicular lean mass than those in the lower protein intake quintile. Amongst those who lost weight over the three-year period, lower protein intake was associated with the greater loss of lean mass.”
This lean-to-fatty ratio is important because muscle is more metabolically active than fat, burning more calories when active and at rest. “In practical terms,” Pikosky says, “muscle can be considered the furnace in which calories are burned. The larger your furnace, the greater your capacity will be to burn calories.”
Allison co-conducted an “extensive review,” published in the May 2008 issue of Obesity Reviews (9(3):219-235), of previous studies on the effects of soy and obesity. He says some studies in mice “show that even if you feed mice the same amount of calories and protein, but one protein source is casein from milk vs. soy protein, they lose more fat with the soy protein.” While noting that none of these studies “unequivocally confirms” the effect, he does say “there are any number of mechanisms that could be driving it,” and soy phytoestrogens might be involved. The loss of estrogen following menopause often equates with a less-healthy distribution of body fat in women, he explains. “We also know that, if you take a mouse and manipulate it such that it doesn’t have as effective estrogen signaling, you get a mouse that has more visceral adipose tissue—the unhealthy kind.”
On the branched-chain gang
The branched-chain amino acids (BCAAs) leucine, isoleucine and valine also show potential to improve body composition. “Milk products such as whey proteins are particularly helpful to athletes because they are high in branched-chain amino acids, which protect muscle tissue against catabolism—muscle breakdown during heavy exercise,” says Gwen Bargetzi, director of marketing, Hilmar Ingredients, Hilmar, CA. “Research reveals that consuming as little as 10 grams of whey protein with carbohydrate following resistance exercise stimulates muscle protein synthesis.”