High-protein, low-carbohydrate diets are safe and effective for severely obese adolescent, according to University of Colorado researchers.
Childhood obesity in the U.S. tripled from the early 1980s to 2000, ending with a 17% obesity rate. Overweight and obesity together describe 32% of U.S. children. Some experts believe this generation of kids will be the first in U.S. history to suffer a decline in life expectancy, related to obesity.
Colorado researchers wondered if a low-carb, high-protein diet is a reasonable treatment option. Why high protein? It’s an effort to preserve lean body mass (e.g., muscle).
They randomized 46 adoloscents (age 12–18) to either a high-protein, low-carb diet (HPLC diet) or a calorie-restricted low-fat diet to be followed for 13 weeks. HPLC dieters could eat unlimited calories as long as they attempted to keep carb consumption to 20 g/day or less. Low-fat dieters were to choose lean protein sources, aiming daily for 2 to 2.5 grams of protein per kilogram of ideal body weight. Study participants underwent blood analysis and body compositon analysis by dual x-ray absorptiometry. These kids weighed an average of 108 kg (238 lb) and average body mass index was 39.
Analysis of food diaries showed the following:
- Average caloric intake was 1300-1450/day, toward the lower end for the HPLC dieters
- Energy composition of the HPLC diet: 32% from protien, 11% from carb, 57% from fat
- Energy compositon of the LF diet: 21% from protein, 51% from carb, 29% from fat
- Average daily carb consumption for the HPLCers ended up closer to 40 g (still very low)
Both groups lost weight, with the HPLC dieters trending to greater weight loss, but not to a statistically significant degree. They did, however, show a greater drop in body mass index Z-score, however. Study authors didn’t bother to explain “body mass index Z-scores,” assuming I would know what that meant. Average weight in the HPLC group dropped 13 kg (29 lb) compared to 7 kg (15 lb) in the low-fat group.
Total and LDL cholesterol fell in both groups, and insulin resistance improved. Neither diet had much effect on HDL cholesterol.
As usual, triglycerides fell dramatically in the HPLC dieters.
Nearly 40% of the kids—about the same number in both groups—dropped out before finishing the 13 weeks.
The HPLC group did not see any particular preservation of lean body mass, and actually seemed to lose a bit more than the low-fat group.
There were no serious adverse effects in either group.
Surprisingly, satiety and hunger scores were the same in both groups. [Low-carb, ketogenic diets have a reputation for satiation and hunger suppression.]
This is a small short-term study with a large drop-out rate; we must consider it a pilot study. That’s why I’m not as enthusiastic about it as the researchers. Nevertheless, it does indeed suggest that high-protein, low-carb diets are indeed safe and effective in obese adolescents. It’s a start.
Steve Parker, M.D.
Reference: Krebs, N., Gao, D., Gralla, J., Collins, J., & Johnson, S. (2010). Efficacy and Safety of a High Protein, Low Carbohydrate Diet for Weight Loss in Severely Obese Adolescents The Journal of Pediatrics, 157 (2), 252-258 DOI: 10.1016/j.jpeds.2010.02.010