by Marion Nestle
Jan 5 2012

The new study of protein and weight gain: calories count!

I was intrigued by the new study from the Pennington Research Center concluding that weight gain depends on calories, not how much protein you eat.

The idea that the protein, fat, or carbohydrate content of your diet matters more to weight than how many calories you eat persists despite much evidence to the contrary.

This study did something impressive.  It measured what people ate, how much they ate, and how much energy they expended under tightly controlled conditions.

This is unusual.  Most studies of weight gain and loss depend on participants’ self reports.

Measuring is much more accurate, as I discuss in my forthcoming book with Malden Nesheim, Why Calories Count: From Science to Politics (out April 1).  If you want calorie balance studies to be accurate, you have to measure and control what goes in and out.  The Pennington is one of the few laboratories in the country that can do this.

Pennington researchers got 25 brave people to agree to be imprisoned in a metabolic ward for the 12 weeks of the study.  The volunteers had to eat nearly 1,000 extra calories a day over and above what they needed to maintain weight.  Their diets contained either 5%, 15%, or 25% of calories from protein.

All of the volunteers gained weight (no surprise), although the low-protein group gained the least.  Most of the weight ended up as body fat.  The medium- and high-protein groups also gained muscle mass.  The low-protein group lost muscle mass.

All of the differences in weight gain among individuals could be accounted for by energy expenditure, either as activity or heat (protein causes higher heat losses).

The Wall Street Journal (January 4) did a terrific summary of the results:

This tells you that low-protein diets cause losses in muscle mass (not a good idea), and that there isn’t much difference between diets containing 15% protein (the usual percentage) and higher levels.

The study also suggests that higher protein diets won’t help you lose weight—unless they also help you cut calories.  That calories matter most in weight gain and loss is consistent with other studies based on measurements, not estimations.

Of course the quality of the diet also matters: it’s easier to cut calories if you are eating plenty of vegetables, fruits, whole grains and a varied diet based largely on relatively unprocessed foods—and it’s harder to gain weight on such diets.

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  • @NutritionMagician It comes from the WSJ article. What it’s referring to is total fat mass vs. body weight or BMI. When it says “Its the Fat That Counts” they mean the fat you gain not fat you eat. The low protein group gained less weight than the normal and high protein groups, so just looking at the scale would suggest that they came out better, but of course they lost muscle so they actually came out worse.

  • Goodmorning, I’m afraid this study doesn’t bring us any news. First conclusion: extra calories without extra excersise leads to weight gain. That’s nothing new. For this conclusion it doesn’t even matter what kind of fuel you use (proteines, carbons or fat). The other conslusion is a half one: A suggestion that higher proteine diets do not help. Although this diagram is not very accurate you can cleary see that the group with the higher proteine diet has a higher lean body mass. I estimate this is at least one percent. this is an big difference in outcome, espacially on the long term. For example: a 80kg male with one percent of extra muscle is 800 grammes. These 800 grammes burn 300% more calories than a male from the lower protein group. Finally weight gain is not a bad thing when the gain of weight consist of muscle. In this article there are no statements about how much of the weight gain is fat and how much is muscle. And that makes all the difference in a unhelathy or a healthy future.
    It would really help if these meassurements were available!?

    Have a nice day, Robert

  • @Margeretrc I totally agree with you on the fat thing (and I’ve read most the same books) so maybe I wasn’t clear. I meant that it’s not ideal to gain a higher % of fat vs muscle. Muscle mass is integral to metabolism & weight maintenance – according to what I read the low protein group gained a higher % of fat mass. Muscle weighs more than fat. THAT is what I meant is not ideal. I eat fat like it’s my job; – avocados, almonds, olive oil & flax are my favorites!

  • I am big fun of protein consumption and and I believe it can benefit people in weight loss. I would be cautious I would wait for more studies that confirm that before accepting it as a fact.

  • Deb

    While this study did a great job of controlling variables and measuring results, it seems to fail in the design: Carbs were held constant, and fat level was adjusted to compensate for the variation in protein level. In the “low protein” group, the fat was over 50% of calories if I understand the WSJ article correctly. The chart could have been labeled “high, medium, and low fat” … and results attributed to fat not protein. Would have been nice to see a factorial experiment where carbs, fat, and protein were evaluated, plus a high and low exercise variable.

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  • Does this study specifically use animal proteins? Or does it use a mix of plant and animal? I’d be interested to see the same study repeated with only plant proteins used.

  • Jon

    In this study, the proportion of carbohydrates in the diet are held almost exactly constant (42% in the low protein group, 41% in the medium and high protein group). Isn’t this study equally consistent with the claim that its carbs that cause fat?

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  • Marion,

    Quoting you: “The study also suggests that higher protein diets won’t help you lose weight—unless they also help you cut calories.”

    Here’s the thing: Many high-protein diets, when followed to the letter, are VERY low in calories and promise to curb hunger and prevent muscle loss (theoretically helping keep metabolism up) with all the protein.

    I’m seeing this post being used to discredit high protein weightloss plans generally when the study doesn’t address the effectiveness of protein in weightloss or preventing muscle loss when restricting calories.

    As a vegetarian who rejects artificial sweeteners and won’t eat huge amounts of fake meats, I’ll never follow South Beach (or any other mainstream protein diet) to the letter, but I did loose bunch of weight on following the basic high-protein/low-calorie principles. I generally notice that if I eat a higher-protein breakfast and mid-morning snack, I’m less hungry in the afternoon and evening than if I ate more calories in the forms of cereals or other carbohydrates in the mornings.