It’s the calories, stupid? Well, kind of. Time’s Healthland blog is heralding a ‘clever new study’ from Pennington Biomedical Research Center as evidence that popular diets centered on decreasing carbs or increasing protein are bunk—it’s really just calorie counts that matter. But a little examination shows that’s not quite what researchers found. While overeating will lead to weight gain regardless of where the calories come from, a diet high in protein seems better for warding off body fat. The composition of your diet does make a difference.
Researchers put a group of 25 healthy, normal-weight people on a high-calorie diet—about 40% more calories than they needed, or 954 extra calories per day. Some participants were given extra calories from protein, while some were given extra calories from fat. In the end, all of them gained weight.
Time’s Sora Song concluded: “It’s not what you eat but how much that matters when it comes to body weight.” CBS News says “changing the amount of protein in your diet probably won’t help you lose weight.” The Daily Mail says, “Forget low-carb diets—it’s simple calorie-counting that works best.”
But that’s not really what the research shows. Participants who ate lower-protein (and, thus, higher-fat) diets actually gained only half as much weight as those who ate high- or normal-protein diets—though they did gain just as much body fat. In fact, the weight put on by the low-protein group was almost entirely fat. And while the other two groups gained both fat and lean body mass (like muscle), the low-protein group lost about 1.5 pounds of lean mass.
Sounds like what you eat does make a difference, then—even if it’s only the difference between gaining more weight and less fat, or more fat and less weight. But let’s remember that this was a study of overeating; participants were deliberately given about 950 extra calories per day. That’s the opposite of what dieters are supposed to do—and, thus, this study says nothing about the effectiveness of low-carb or high-protein diets. If anything, we learn that calories from protein are less likely to be converted into fat, which seems to imply that a diet focused on taking in more protein but less calories could be beneficial for weight loss, or at least changing body composition.
The bottom line from this research isn’t that only calories matter, or that protein composition is useless. It’s simply, as lead researcher George Bray put it, that protein “does some very different things than what the total calories do.”