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Postprandial Thermogenesis Is Increased 100% on a High-Protein, Low-Fat Diet versus a High-Carbohydrate, Low-Fat Diet in Healthy, Young Women

Department of Nutrition (C.S.J., C.S.D.), Arizona State University East, Mesa, Arizona
Department of Exercise Wellness (P.D.S.), Arizona State University East, Mesa, Arizona

Address reprint requests to: Carol Johnston, PhD, Department of Nutrition, Arizona State University East, 7001 E. Williams Field Rd, Mesa, AZ 85212. E-mail: carol.Johnson{at}asu.edu.

Objective: The recent literature suggests that high-protein, low-fat diets promote a greater degree of weight loss compared to high-carbohydrate, low-fat diets, but the mechanism of this enhanced weight loss is unclear. This study compared the acute, energy-cost of meal-induced thermogenesis on a high-protein, low-fat diet versus a high-carbohydrate, low-fat diet.

Methods: Ten healthy, normal weight, non-smoking female volunteers aged 19-22 years were recruited from a campus population. Using a randomized, cross-over design, subjects consumed the high-protein and the high-carbohydrate diets for one day each, and testing was separated by a 28- or 56-day interval. Control diets were consumed for two days prior to each test day. On test day, the resting energy expenditure, the non-protein respiratory quotient and body temperature were measured following a 10-hour fast and at 2.5-hour post breakfast, lunch and dinner. Fasting blood samples were collected test day and the next morning, and complete 24-hour urine samples were collected the day of testing.

Results: Postprandial thermogenesis at 2.5 hours post-meal averaged about twofold higher on the high protein diet versus the high carbohydrate diet, and differences were significant after the breakfast and the dinner meals (p < 0.05). Body temperature was slightly higher on the high protein diet (p = 0.08 after the dinner meal). Changes in the respiratory quotient post-meals did not differ by diet, and there was no difference in 24-hour glomerular filtration rates by diet. Nitrogen balance was significantly greater on the high-protein diet compared to the high-carbohydrate diet (7.6 ± 0.9 and -0.4 ± 0.5 gN/day, p < 0.05), and at 24-hour post-intervention, fasting plasma urea nitrogen concentrations were raised on the high protein diet versus the high-carbohydrate diet (13.9 ± 0.9 and 11.2 ± 1.0 mg/dL respectively, p < 0.05).

Conclusions: These data indicate an added energy-cost associated with high-protein, low-fat diets and may help explain the efficacy of such diets for weight loss.

Key words: high-protein diets, postprandial thermogenesis