Is Alternate Day Fasting The Best Way To Lose Weight?

The Study

The efficacy and safety of alternate day fasting as a method of weight loss has not been proven despite the popularity of this weight loss strategy. A study recently published in JAMA Internal Medicine attempts to answer this question. In this investigation, 100 subjects were randomly assigned to one of three groups:

Alternate day fasting: these subjects consumed 25% of their energy needs on “fast days” and then 125% of their energy needs on alternate “feast days”.

Calorie restriction: these subjects consumed 75% of their energy needs each day.

Control group: these subjects had no intervention.

The trial consisted of a 6-month weight loss phase and then a 6-month weight maintenance phase. Primary outcome measures were weight loss and risk factors for heart disease. The results were fascinating:

1) Drop out rates were higher in the fasting group when compared to the calorie restriction group (38% vs. 29%).

2) There were no significant differences in weight loss between the two groups by the end of follow-up.

3) Mean LDL cholesterol rose significantly in the alternative day fasting group.

JAMA Internal Medicine 2017; 177:930-38.

Take Home Message

The results of this well-designed trial are not encouraging for proponents of alternative day fasting. Compared to a more conventional approach, fasting did not improve weight loss, was more difficult to follow and even had a negative impact on health, as higher LDL cholesterol translates to an increased risk of cardiovascular disease. 

Other studies I’ve reported on in this blog have shown evidence of glucose dysregulation with fasting (see them here). While we will wait for more research to be conducted in this area, it appears that fasting is not the way to go if weight loss and improved health are your goals.