Adult female rats defend "appropriate" energy intake after adaptation to dietary energy.

OBJECTIVE

To determine if adult female rats adapt to lower and higher dietary energy density.

RESEARCH METHODS AND PROCEDURES

Study 1 compared high-fat (56%), high-energy density (HD) (21.6 kJ/g) and high-fat (56%), low-energy density (LD) (16.0 kJ/g) diets before surgery (two groups, 2 weeks, n = 16) and after surgery [ovariectomy (O) Sham (S); 2 x 2 factorial, n = 8; 6 weeks]. The second study (no surgery) compared high-fat (60.0%), high-energy (22.0 kJ/g) and low-fat (10.0%), low-energy (15.1 kJ/g) diets (n = 8).

RESULTS

In study 1, food intake was similar for the first 2 weeks, but rats on the LD diet consumed less energy, gained less weight, and had lower nonfasted serum leptin (all p < 0.0001) than rats on the HD diet. After surgery, rats on the LD and HD diets had similar weight gain, but rats on the LD diet consumed more food (p < 0.0001) and less energy (p < 0.009). O rats consumed more food and gained more weight (p < 0.0001) than S rats. Results from study 2 were similar to those from study 1.

DISCUSSION

The results demonstrated that O and S surgery rats and rats with no surgery adjust their food intake to defend a level of energy intake. This defense only occurred after a 2-week adaptation period. The major differences in final body weights and abdominal fat resulted from the initial 2 weeks before adaptation to energy density. Rats fed higher-energy diets seemed to "settle" at a higher level of adiposity, and rats fed lower-energy diets consumed more food to increase energy consumption.