Diets involving intermittent energy restriction have recently gained popularity. Such diets involve restricting energy intake to ~0-50% of energy requirements for one or more consecutive or non-consecutive days/week, and eating ad libitum at other times. To investigate whether weight loss during intermittent energy restriction is entirely due to reduced energy intake, or whether alterations in weight loss efficiency may also be involved, we conducted a study in mice, where energy intake can be unambiguously defined.

Male C57/Bl6 mice were fed a high fat diet for 22 weeks. They were then fed one of two energy-restricted normal chow diets for 13 weeks. The continuous diet (CD) provided ~80% of the energy intake of age-matched chow-fed controls. The intermittent diet (ID) provided ~80% of energy requirements for 4-5 consecutive days/week, and ad libitum intake for the remaining 2-3 days/week.

Mice on the ID showed compensatory hyperphagia relative to controls during each 2-3 day period of ad libitum feeding. This was not enough to normalise overall energy intake relative to controls, but they did eat significantly more than mice on the CD (91.1±1.0% versus 82.2±0.5% of control intake respectively, n=10, p<0.05). In the first 10 weeks of the weight loss phase, mice on the ID loss less weight than those on the CD, but by the end of the weight loss phase the difference was less apparent, and there was no difference in body weight between ID and CD at the end of a 3-week ad libitum weight regain period. There were no significant differences between ID and CD at the end of the weight loss or weight regain phases with respect to fat mass, as determined by DXA or adipose tissue dissection. Thus, intermittent energy restriction induces greater fat loss per unit energy restriction than continuous energy restriction in mice.