Currently browsing posts about: Protein

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.

Reading the New York Times dining section this morning kicked up my annoyance at use of the term “protein” to refer to meat.  A story about what to do with holiday leftovers says “…repurposing top-quality proteins into dinner is easier than it seems.”

Another on Simon Doonan’s new book, Gay Men Don’t Get Fat, quotes him as pointing out that “straight food…tends to be leaden, full of protein, thick with fat.” Now you know.

But protein is a nutrient.  Foods are sources of nutrients.

Nutritionists like me consider protein a “macronutrient,” meaning that foods contain many grams of protein and also that protein is a source of calories (4 per gram as opposed to 9 for fat and 4 or so for carbohydrate).

Diets contain about 15% of calories from protein on average, an amount much greater than most people need—about twice the minimum required for maintenance and growth.

“Protein” is most definitely not a synonym for meat or even tofu (see table).  I’ve listed the plant sources of protein in Italics.

FOOD SOURCES OF PROTEIN IN U.S. DIETS

Source: J Am Diet Assoc. 2010 February ; 110(2): 291–295.

Grains, vegetables, and fruits are not the biggest sources, but they are important contributors.  Vegans, who consume no animal products at all, do not lack for protein.

And while proteins from meat resemble our own proteins more than do proteins from vegetables, their constituent amino acids are the same in all foods.  Varying food intake and eating enough food takes care of amino acid balance.

Hence, my peevishness at the use of “Protein” as a separate category in USDA’s MyPlate (see previous post).

Grains and dairy, each with its own sector, are important sources of protein in American diets.

Why protein?  USDA used to call the group “meat” even though it contained beans, poultry, and fish.  The meat industry ought to be happy about “protein.”  Meat producers have spent years trying to convince Americans to equate meat with protein.

A plea: let’s keep terms clear and talk about nutrients when we mean nutrients and foods when we mean foods.  Protein is not food.

NOTE: More about protein tomorrow when I discuss the new JAMA study on whether high-protein diets help you lose weight (spoiler alert: they don’t).