Is your diet endangering your muscles?

Bad news for overeaters who prefer their treats in the form of carbs and fat (cake, French fries, and chips come to mind). And good news for those who’d rather indulge with a nice steak.

Last week a fascinating study, published in the Journal of the American Medical Association, reported what had happened to the bodies of healthy adults who were overfed to the tune of 1,000 extra calories a day for 10 to 12 weeks. Oh—and they performed no exercise during this time.

Well, obviously they gained weight. But what they gained—how much muscle and how much fat—had everything to do with how much protein they consumed.

Let me give you the high points. People were divided into a low-protein group (6 percent of daily calories from protein), a normal-protein group (15 percent), and a high-protein group (26 percent). Carbohydrates were held more or less steady among the three groups, at 41 to 42 percent. The low-protein people ate quite a lot of fat—52 percent of daily calories; the others ate 44 and 33 percent fat, respectively.

Just FYI, the high-protein guys and gals were on something pretty close to the nutrient ratios favored by lots of bodybuilders and strength athletes.

So here’s the really interesting bit. The low-protein group gained much less weight. This gives me a chance to drive home the point I’m always making about why we should care about body fat, not weight.

Yup, they gained less “weight.” And what they gained was all fat.

In the meantime, they actually lost lean body mass—about .7 kilograms (1.5 pounds) on average. Why do we care about that? Because every ounce of lean mass (muscle) lost means a slower metabolism.

Let me give you a point-by-point summary of the results for all three groups:

Low-protein diet

• average weight gain of 3.16 kg
• average loss of .7 kg lean mass
• no increase of resting energy expenditure (amount of calories burned on a daily basis)

Summary: They gained fat and lost muscle. As the study authors put it, “the failure to increase lean body mass in the low-protein group accounted for their smaller weight gain.” Note that since they gained 3.16 kg of “weight” yet lost .7 kg of muscle, their total fat gain was an average of 3.86 kg. That’s a greater fat gain than the other two groups.

Moderate-protein diet

• average weight gain of 6.05 kg
• 3.18 kg of the weight gain was fat, 2.87 kg was lean mass
• increase in resting energy expenditure was 160 calories per day

Summary: These subjects gained both fat and muscle—about half and half.

High-protein diet

• average weight gain of 6.51 kg
• 3.33 kg of the gain was fat, 3.18 kg was lean mass
• increase in resting energy expenditure was 227 calories per day

Summary: Like the moderate-protein group, the high-protein group gained about equal amounts of fat and muscle.

Now, if people on a low-protein diet can lose lean mass (a metabolic disaster) even when they’re overeating by a significant amount, how much more likely is it that eating too little protein can cause a loss of lean mass when dieting? How much more likely when we’re over-dieting and slashing calories too dramatically?

It’s something I preach about a lot (you can see a recent sermon here) because women tend to be notorious undereaters of protein and—when dieting—under-consumers of calories.

My challenge to you: Given your daily caloric intake (if you’re not sure what it should be, use this calculator), figure out what 15 percent of calories from protein would be.

Let’s say your total daily energy expenditure is 2,000 calories. Multiply 2,000 x .15, and you get 300 calories.

Protein has four calories per gram. So if I divide 300 by 4, I get 75. That’s how many grams of protein you need per day if you’re shooting for a moderate-protein diet.

If your current intake provides less than 15 percent protein, consider beefing it up (pun intended) to get closer to that percentage.

Those who lift weights regularly and are committed to adding more muscle tissue (atta girl!), might consider 25 percent of daily calories from protein.

Added benefit: whether you’re dieting or maintaining weight, protein keeps you satisfied longer than either carbohydrates or fat. But that’s a post for another day.

Note: You can read the full study report here.

Flickr photo by artfulgourmetnyc

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