Protein Helps Curb Hunger

All things being equal, diets higher in protein are better at holding hunger at bay than meals richer in fat or carbs. That's the finding of a set of prolonged feeding trials run by scientists at Purdue University.

John W. Apolzan and his coworkers advertised for volunteers in the local newspapers and ended up enrolling 12 men between the ages of 21 and 43 and another 10 between the ages of 63 and 79. After calculating how many calories it would take for each man to maintain his current weight, the researchers tailored diets to deliver just that much energy to each man over the course of three 18-day cycles. All foods except for water were supplied the participants, and any uneaten food was returned and weighed.

The recommended intake of protein is 0.8 gram per kilogram of bodyweight—or about 2 ounces for a 155 pound man. In one cycle, each man got slightly more than that: 1 g of protein per kilogram of bodyweight per day. In the other cycles, he got 0.5 or 0.75 g/kg day. The ordering of these 18-day dietary cycles were randomly assigned to each participant. At the end of each cycle, the scientists administered hourly questionaires throughout the waking hours of one day to assess hunger and desire to eat in each of the volunteers.

In the May Journal of Nutrition, Apolzan's group reports that the men reported being 20 percent less hungry after the highest protein diet phase than after either of the others. Similarly, each man's desire to eat was, on average, almost 30 percent greater on the mid-level protein diet and 50 percent greater on the low-protein diet than when the volunteers got the high-protein fare.

It now appears that for those of us wishing to curb the siren call of calories, eating too little protein—as 15 to 40 percent of older Americans do—might foster overeating.