Intermittent fasting and fast-mimicking diets are the latest trend in the diet world. One of the most popular fast-mimicking diet is the 5:2 diet, where calories are severely restricted for 2 days per week. But is this type of diet approach more effective compared to a more moderate daily restriction of calories?
Animal models have suggested that intermittent calorie restriction can have a significant on glucose, insulin, leptin and other metabolic markers that influence body weight. The results are even stronger than those of the standard continuous calorie restriction. There are also promising results from human trials showing reduction in insulin and fat mass.
However, there is a need for more randomised control trials to assess whether intermittent restriction is more effective for weight loss and maintenance compared to continuous restriction.
Researchers designed a randomised control trial to explore whether intermittent calorie restriction in the form of a 5:2 diet has a greater impact on weight loss. Participants were eligible if they had a BMI between 25-40kg/m2 and aged between 35-65 years. Exclusion criteria included smoking.
150 participants were randomised into one of three groups. The intervention group followed a 5:2 protocol, with each week having 5 days with no energy restriction and 2 days of a restriction to 25% of maintenance calories. The second group had a standard energy restriction diet of 20% deficit each day, and the third group was a control group with no energy restriction.
The trial consisted of a 12 week intervention phase followed by 12 weeks of maintenance and a 26 week follow-up phase. Outcomes included expression of adipose tissue genes, body composition and measurements, and metabolic biomarkers.
After the 12 week intervention period, there was a slightly greater weight loss for the intermittent restriction group of 7.1% compared to the continuous restriction group, with 5.2%. Both saw a greater loss compared to the control group’s 3.3% loss. However, there were no significant differences in the expression of 82 genes in the adipose tissue that are linked to obesity.
In the final follow up assessment by week 50, the intermittent restriction group had lost 5.2%, the continuous restriction group lost 4.9%, and the control group just 1.7%. There were no significant differences between the two restriction groups in terms of metabolic biomarkers.
It was also noted that there was a slight trend for regaining weight after initial loss in the intermittent restriction group. Both approaches showed a good level of compliance.
The researchers concluded that intermittent restriction may be equivalent to continuous restriction, in terms of weight loss and prevention of metabolic disease, but that it is not superior.
Limitations that were noted include the sample of generally healthy overweight and obese people of European ancestry and the inability to directly monitor the compliance of participants.
Further studies are required to further explore the effectiveness of intermittent calorie restriction and whether it is a safe and practical alternative to continuous restriction.
Schübel, R., Nattenmüller, J., Sookthai, D., Nonnenmacher, T., Graf, M.E., Riedl, L., Schlett, C.L., von Stackelberg, O., Johnson, T., Nabers, D. and Kirsten, R., 2018. Effects of intermittent and continuous calorie restriction on body weight and metabolism over 50 wk: a randomized controlled trial. The American Journal of Clinical Nutrition, 108(5), pp.933-945.