Diets that are too low in protein may add more body fat than lean body mass,… (Carlos Chavez / Los Angeles…)
Eating excess calories will add extra pounds, but eat too little protein and you could be putting more fat on your body, a study suggests.
The study, released Tuesday in the Journal of the American Medical Assn., looked at how three diets with different protein contents influenced weight gain and body composition. Those findings may have larger implications for combating obesity.
Researchers, led by Dr. George Bray of the Pennington Biomedical Research Center in Louisiana, put 25 people age 18 to 35 on a weight maintenance diet for 13 to 25 days. After that they were assigned to one of three diets for eight weeks: one that had 5% of calories from protein (considered low protein), one that had 15% of calories from protein (normal protein), and one that had 25% of calories from protein (high protein).
For those eight weeks the study participants were purposely overfed by about 950 calories a day, or 40% more calories than they were previously eating, so they would gain weight. They stayed in an inpatient facility to ensure meals and calories were very carefully controlled.
The low-protein group gained the least weight: an average of about 7 pounds. The normal-weight protein group gained an average 13 pounds, and the high-protein group gained an average 14 pounds. All groups gained body fat. But in the low protein diet, more than 90% of excess calories were stored in the body as fat, while in the normal and high protein groups about 50% of the extra calories were stored as fat.
In the low protein group lean body mass dropped by an average 1.5 pounds, while in the normal and high protein groups it increased by an average of about 6.3 pounds and 7 pounds, respectively.
The normal and high protein groups also saw a substantial increase in their resting energy expenditure--how many calories the body burns while at rest. The low protein group's resting energy expenditure did not change significantly during the period when calories were increased. Generally, the more fit a person is and the more muscle mass he or she has, the higher the resting energy expenditure.
An accompanying editorial in the journal says the study points out how what we eat may affect our current levels of obesity. "These findings have important ramifications because the Western diet tends to be high in fat and carbohydrates and low in protein," the authors wrote. "The study results also suggest that body weight may underestimate the true hazards of overnutrition."