A study published in the Journal of the American Medical Association suggests that people who consume excess calories on low-protein diets gain less weight compared to those on high-protein diets, but lose lean body mass. So what’s better? To gain more weight along with lean muscle, or gain less weight but also lose lean muscle?
The study included 25 people who lived in a controlled research facility for up to three months, barely exercising and eating about 1,000 more calories per day than they needed to maintain their weight. They consumed different amounts of protein, eating either a low-protein or high-protein diet.
The low-protein group gained roughly half as much weight as those assigned to a standard or high protein diet, but their weight gain was mostly fat, and not lean muscle. In fact, they lost lean muscle, and approximately 90% of the extra calories were stored as body fat! In the other groups, just 50% of the added calories were stored as fat and most of the remainder was burned off. The low-protein group lost an average of 1.5 pounds of lean body mass, while the normal and high-protein dieters gained about 6-7 pounds of lean mass.
But along with the lean mass came some fat gains, too. People in the low-protein group gained about 7 pounds, on average, compared to 13 pounds for the normal-protein group and 14 pounds for the high-protein group. All three groups gained roughly the same amount of body fat, but only the low-protein group actually lost muscle mass, increasing their percentage of body fat.
So both too little and too much protein in the diet can cause weight gain if you’re consuming more than you burn. But if you don’t eat enough protein you risk losing muscle mass, which increases body fat percentage and decreases resting calorie expenditure. If you’re trying to lose weight you do NOT want to lose lean mass.
“The key finding of this study is that calories are more important than protein while consuming excess amounts of energy with respect to increases in body fat,” say the study authors.
So keep it simple: Eat less than you burn, exercise, and aim for about 20% of calories from protein in your diet.
