Intermittent energy restriction for weight loss: Spontaneous reduction of energy intake on unrestricted days

There is increasing interest for the use of intermittent energy restriction (IER) in weight management. However, there are concerns that IER could result in 'rebound' overconsumption of energy on unrestricted days. We studied self-reported food records from participants in two trials of IER versus continuous energy restriction (Study 1; 44 women on IER for 6 months and Study 2; 72 women on two types of IER for 4 months). Energy intake was assessed on restricted and unrestricted days immediately before and after restricted days and on other unrestricted days. We assessed consistency of days of the week chosen as restricted days, and whether this was associated with greater weight loss. Reported energy intake was reduced on unrestricted days in Study 1 and 2 and was 19% lower compared with the allocated isoenergetic diet, and respectively 21% and 29% lower than their baseline reported daily intakes. Energy intake appeared to be similarly reduced the day immediately before and after restricted days and on other unrestricted days. Seventy percent of women in Study 1 and 79% in Study 2 undertook consistent days of restriction each week (>50% of restricted days on the same 2 days each week). When studies were combined percentage weight loss at 3 months was -5.8 (-6.7 to -4.7) % in the consistent group and -7.4 (-8.7 to -6.2) % in the non-consistent group (p = .09). Food records from patients undertaking IER suggest a spontaneous reduction in energy intake below their baseline reported intakes and the prescribed isoenergetic diet during all unrestricted days including the days immediately before and after restricted days which contributes to the weight loss success with these diets. Consistency of restricted days was not associated with weight loss success. These findings need to be confirmed in larger groups of patients ideally using objective measures of energy balance.