Protein and Weight Gain

A new study in JAMA adds to the growing body of literature showing that protein is critical for managing weight.  In this study, the researchers wanted to see what effect (if any) different amounts of protein in the diet would have on weight gain.

They started with the basic premise that anyone who overeats—however “overeating” may be defined for each person— is going to gain weight. OK, so far, so good. If the researchers were to overfeed a bunch of subjects by, say, 1000 calories a day for a couple of weeks, they could reasonably expect all of them to gain some weight.

The question for the researchers, however, was this: does it matter what we feed them? Specifically, would the amount of protein in the “over-eating” diet make any difference when it comes to weigh-in time?

So they took 25 healthy men and women and put them on a “weight-stabilizing” diet for 13-25 days. After that, the folks were divided into three groups. For the next eight weeks, each person ate a daily diet containing 1000 more calories than that individual needed to maintain his or her weight, regardless of which group they were in.

  • Group One ate a diet consisting of 5% protein (low protein diet)
  • Group Two’s diet contained 15% protein (average protein diet)
  • Group Three’s diet was 25% protein (high-protein diet)

The researchers weren’t just interested in whether protein in the diet affected weight gain. They were also interested in whether or not it affected body composition  researchers were also interested in body composition. They wanted to know how much of the expected weight gain was fat and how much was muscle, and whether those results were impacted by the amount of protein eaten.


  • The low-protein group gained the least amount of weight (approximately 7 pounds)
  • The “normal” protein group gained 13.3 pounds
  • The “high-protein” group gained more than twice as much as the low-protein group, weighing in at an average of 14.4 pounds heavier than when they started


When the researchers looked at body composition, it was a whole different story:

  • The low-protein group lost about 1.5 pounds of muscle (or lean body mass)
  • The medium (“normal”) protein group gained 6.3 pounds of lean body mass.
  • The high-protein group gained about 7 pounds of muscle!

“The low-protein group stored a higher percentage of calories as fat than the other groups”, lead researcher George Bray told WebMD.  “The low-protein diet was clearly not good in terms of preserving lean body mass”.

Another great “side-effect” of the higher protein intakes: a boost in metabolism. The researchers found that resting energy expenditure (the amount of calories you burn when laying around on the couch) actually went up for the people in both the “normal” (15%) and “high” (25%) protein groups. For the low-protein group? Not so much. (Not at all, actually.) This is hardly surprising, since the more muscle you have the more calories you burn– one of the many reasons to use weight training for fat loss.

Years ago, the distinguished past-president of the American Society of Bariatric Physicians Mary Vernon, MD, told me that in her own clinical practice she saw case after case of overweight people putting on muscle even without exercising, just by eating more protein. Obviously, that was an anecdotal story albeit from a very reliable source, but this study seems to confirm the likelihood of that happening.

This study demonstrates the importance of protein in putting on muscle (and, of course, in preserving lean body mass when losing weight). Remember, most people in America are on the low-end of protein consumption, not the high end!

People who eat according to my Unleash Your Thin weight loss meal plans usually lose weight while preserving lean body mass because they are eating a large portion of protein at every meal.