Postprandial thermogenesis is increased 100% on a high-protein, low-fat diet versus a high-carbohydrate, low-fat diet in healthy, young women.
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.
Johnston
Carol S
CS
Departments of Nutrition, Arizona State University East, Mesa 85212, USA. carol.Johnson@asu.edu
Day
Carol S
CS
Swan
Pamela D
PD
D000293:Adolescent; D000328:Adult; D018592:Cross-Over Studies; D004040:Dietary Carbohydrates / Q000008:administration & dosage*; D004041:Dietary Fats / Q000008:administration & dosage*; D004044:Dietary Proteins / Q000008:administration & dosage*; D005260:Female; D005919:Glomerular Filtration Rate / Q000502:physiology; D006801:Humans; D009584:Nitrogen / Q000378:metabolism; D009765:Obesity / Q000178:diet therapy* / Q000378:metabolism; D019518:Postprandial Period / Q000502:physiology*; D022722:Thermogenesis / Q000502:physiology*; D016896:Treatment Outcome
D004040:Dietary Carbohydrates; D004041:Dietary Fats; D004044:Dietary Proteins; D009584:Nitrogen