High-fat/low carbohydrate (HFLC) diets in humans, such as the Atkins diet, are claimed to work in an ad libitum setting. In a previous study, we had demonstrated reduced bodyweight (BW) gain in rats when pair-fed isocaloric amounts of a HFLC compared to normal chow (CH). However, rats on HFLC also showed increased body fat and low serum IGF-I. We now compared BW development, food intake and resting energy expenditure (EE) in an ad libitum setting in male Wistar rats fed a HF-LC or CH matched in protein content (n=8 per group). After 20 days (d) the HFLC group had gained significantly more BW (HF-LC: 41.1±7.1 g versus CH: 27.1±13.8 g; P=0.02). BW-gain in the HFLC group was significantly higher between d10 and d20 than between d1 and d10 (d110: 15.5±6.1 g; d1020: 25.6±6.7 g; P<0.01) despite comparable caloric intake. CH fed controls gained similar weight in both intervals (d110: 12.4±9.1 g; d1020: 14.7±10.4 g; P=0.65). No differences in EE were observed between the groups. EE did not change with duration of the diet, but the respiratory exchange ratio continuously decreased on HFLC group. Daily energy excess was greater in the HFLC group (CH: 18.95±6.97 kcal; HFLC; 39.71±7.6 kcal; P<0.01). HFLC fed rats have severely reduced daily faeces amounts (CH: 9.53±1.5 g versus HFLC: 2.92±0.3 g; P<0.001), remaining energy in the faeces is under investigation. Preliminary results indicate that IGF-I levels are also reduced with ad libitum access to HFLC. In conclusion, the weight loss observed on HFLC diet with pair feeding was not seen in an ad libitum setting, but changes in metabolic parameters and IGF-I seem to be similar. Also in humans reduced palatability and availability of food items on HFLC diets might lead to a reduced caloric intake and thus explain the observed weight loss.
03 - 07 May 2008
European Society of Endocrinology