Endocrine Abstracts

High-fat/low carbohydrate (HF–LC) diets in humans, such as the Atkin’s 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 HF–LC compared to normal chow (CH). However, rats on HF–LC 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 HF–LC 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 HF–LC group was significantly higher between d10 and d20 than between d1 and d10 (d1–10: 15.5±6.1 g; d10–20: 25.6±6.7 g; P<0.01) despite comparable caloric intake. CH fed controls gained similar weight in both intervals (d1–10: 12.4±9.1 g; d10–20: 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 HF–LC group. Daily energy excess was greater in the HF–LC group (CH: 18.95±6.97 kcal; HF–LC; 39.71±7.6 kcal; P<0.01). HF–LC fed rats have severely reduced daily faeces amounts (CH: 9.53±1.5 g versus HF–LC: 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 HF–LC. In conclusion, the weight loss observed on HF–LC 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 HF–LC diets might lead to a reduced caloric intake and thus explain the observed weight loss.