While the diets all caused initial weight loss, the Atkins and Stillman diets mostly caused water weight loss, the study says. The Zone, Protein Power, and Sugar Busters diets caused weight loss via calorie restriction, but rigidity of the diet and limited food choices made them impractical for the long term.
A popular premise of high-protein diets is that excess carbohydrates cause elevated insulin levels, which in turn, promotes storage of body fat, according to the study. Supporters of high protein diets say that the high amount of protein and fat relative to carbohydrates helps reduce insulin levels. The researchers counter, however, that protein stimulates insulin secretion, and changes in calorie intake do not influence insulin action.
Bottom line: high-protein diets aren't a good way to lose weight, says Chris Rosenbloom, PhD, chairwoman of nutrition at Georgia State University in Atlanta and spokeswoman for the American Dietetic Association.
"Almost everyone I've seen who has been on this diet can't keep the weight off," Rosenbloom tells WebMD. "Initially, they'll lose maybe 25 pounds. But then it comes back."
The initial water weight loss is "the diuretic effect, which happens when you restrict carbohydrates," she says. "On the bathroom scales, it looks like you've dropped weight, but it's not fat weight."
Without carbohydrates, the diets often create a condition called ketosis, which serves to curb appetite. "It's the body's natural response to starvation," she tells WebMD. "It keeps you from feeling hungry. It makes sense that the body would give us a mechanism to protect us during true starvation."
However, that effect doesn't last forever, she says.
"People begin feeling fatigued. They run out of energy, complain of headaches; they can't exercise as much," says Rosenbloom. "The initial euphoria, the positive energy, fades."
The average person requires 102 grams of protein a day, and that should come from lean animal and vegetable proteins. In fact, eating too much protein -- in excess of your caloric needs -- will cause weight gain, says Lichtenstein.
To truly lose weight, the rule of thumb is to eat a nutritionally adequate diet, with a daily minimum of 1,200 calories for women and 1,500 calories for men, unless instructed by your doctor to limit your calories even further.