“Alternate-day fasting is a safe and tolerable approach to weight loss. [It] produced similar changes in weight, body composition, lipids, and Si at eight weeks and did not appear to increase risk for weight regain 24 weeks after completing the intervention,” write the authors.
Current dietary guidelines for treating obesity and overweight suggest cutting energy intake by 20 - 30% accompanied by an active lifestyle. And while this is usually effective, typically resulting in weight loss of around 5 – 10% over a period of six months, the rate of relapse is high.
This, combined with the increasing popularity of fasting for its perceived health benefits and efficacy in losing weight, prompted the researchers based at the University of Colorado, to investigate its safety and effectiveness.
Previous reviews have found that fasting every other day may be beneficial in reducing diabetes, cardiovascular disease and in impacting the hormone that regulates hunger, but none have assessed its effectiveness as a weight loss strategy.
In their study, the researchers found that fasting every other day resulted in consuming 376 fewer calories per day.
Although this energy deficit did not result in any significant changes in weight between the two groups, after 8 months of unsupervised follow-up the percentage change in fat mass and lean mass from the baseline measurements were more favourable for the fasting group.
“Importantly, alternate day fasting was not associated with an increased risk for weight regain after 24 weeks of unsupervised follow-up,” they write.
“Alternate day fasting may represent a reasonable alternative dietary strategy for treatment of obesity (especially for those that find daily calorie restriction difficult) and should be explored in larger efficacy studies with a longer intervention period and more detailed measures of components of energy balance.”
Yet the usefulness in encouraging people to take up alternate day fasting has been questioned by some. Emer Delaney from the British Dietetic Association told Boots WebMD it is not surprising that cutting calorie intake – be it on a daily basis or on alternate days - will reduce in weight loss. But he added: "There has been some debate recently that this 'new' way of eating can offer major health benefits, however there simply isn't the evidence to back this up."
"Whilst it may work for some people, they need to ensure their diet on 'non-fast' days is packed with fruit and vegetables, wholegrains, lean protein rich foods such as chicken, fish, turkey and low fat dairy products."
Study details
Adults aged between 18 to 55 and with a BMI of more than 30 kg/m2 were recruited to take part in the study.
After an eight-week intervention period, during which 14 adults followed a fasting diet and 12 followed a calorie-restricted diet (−400 kcal/day), participants then continued the diet unsupervised for a further 24 weeks.
During the intervention period all food was prepared and provided by the research institute, with the same macronutrient content for both groups (55% carbohydrate, 15% protein, and 30% fat) and any uneaten food was returned to the researchers to be weighed.
At the end of the intervention period, there was no change in absolute weight although total cholesterol, HDL, and LDL decreased significantly in both groups and triglycerides decreased significantly in the fasting group.
The researchers expected to weight loss in the fasting group that was several kilograms greater than the traditional diet group, although this was not the case with weight loss only 1.1 kg greater. They suggest this was because the fasting group did not report food eaten on fast days.
Source: Obesity Journal
First published: 29 August 2016, DOI: 10.1002/oby.21581
“A randomized pilot study comparing zero-calorie alternate-day fasting to daily caloric restriction in adults with obesity”
Authors: Victoria A. Catenacci, Zhaoxing Pan, Danielle Ostendorf et al.