Cutting Carbs May Be the Key, Not Raising Protein, Researchers Say
April 15, 2005 -- Diets that lower carbohydrates may not get any extra advantage from boosting protein.
When diets substitute proteins for carbohydrates, studies show greater fat loss in women. But it's not known whether the effect is due to the increased protein content of the diets or the reduction in carbohydrates, write the researchers.
The study appears in the April 1 edition of The American Journal of Clinical Nutrition.
"In previous studies, we have shown differences between high-protein diets and lower-protein diets when we substituted protein for carbohydrate and kept fat constant," says Peter M. Clifton, FRACP, PhD, of the University of Adelaide's medicine department.
"The question: Was it protein or the carbohydrates? This study suggested that perhaps it was the decrease in carbohydrates, rather than the increase in protein that made the difference we saw previously," Clifton tells WebMD in an email.
Do Carbs Count More Than Protein?
Participants were 73 obese men and women; none had type 2 diabetes. They were divided into two groups for a 12-week diet.
Both diets cut carbs to the same level: no more than 30% of total daily calories. One diet featured low-fat (29% total calories), high-protein (24% total calories) items. It was based on lean meat, poultry, and low-fat dairy foods, says Clifton's study.
The other low-carb diet had a standard amount of protein (8% total calories) and a higher amount of monounsaturated fat (45% total calories). Those menus included lean meat, poultry, higher-fat milk, and oil and nuts high in monounsaturated fat.
After 12 weeks of the calorie-restricted diet -- followed by four weeks of a maintenance diet -- the two groups had no differences in weight loss, fat or lean-mass loss, insulin resistance (a risk factor signaling heart disease and type 2 diabetes), or fasting cholesterol and triglyceride levels.
On average, the low-fat, high-protein group lost about 21 pounds. The average weight lost by the high-fat, standard-protein group was 22.5 pounds.