Background and objective: Intermittent energy restriction (IER) is an alternative to continuous energy restriction (CER) for weight loss. There are few long-term trials comparing efficacy of these methods. The objective was to compare the effects of CER to two forms of IER; a week-on-week-off energy restriction and a 5:2 program, during which participants restricted their energy intake severely for 2 days and ate as usual for 5 days, on weight loss, body composition, blood lipids, and glucose.
Subjects and methods: A one-year randomized parallel trial was conducted at the University of South Australia, Adelaide, Australia. Participants were 332 overweight and obese adults, ages 18-72 years, who were randomized to 1 of 3 groups: CER (4200 kJ/day for women and 5040 kJ/day for men), week-on-week-off energy restriction (alternating between the same energy restriction as the continuous group for one week and one week of habitual diet), or 5:2 (2100 kJ/day on modified fast days each week for women and 2520 kJ/day for men, the 2 days of energy restriction could be consecutive or non-consecutive). Primary outcome was weight loss, and secondary outcomes were changes in body composition, blood lipids, and glucose.
Results: For the 146 individuals who completed the study (124 female, 22 male, mean BMI 33 kg/m2) mean weight loss, and body fat loss at 12 months was similar in the three intervention groups, -6.6 kg for CER, -5.1 kg for the week-on, week-off and -5.0 kg for 5:2 (p = 0.2 time by diet). Discontinuation rates were not different (p = 0.4). HDL-cholesterol rose (7%) and triglycerides decreased (13%) at 12 months with no differences between groups. No changes were seen for fasting glucose or LDL-cholesterol.
Discussion and conclusion: The two forms of IER were not statistically different for weight loss, body composition, and cardiometabolic risk factors compared to CER.