Fasting. Is Intermittent Fasting an effective treatment of obesity and overweight? In a word: Yes

The Evidence:

Harris, L., Hamilton, S., Azevedo, L. B., Olajide, J., De Brún, C., Waller, G., ... & Ells, L. (2018). Intermittent fasting interventions for treatment of overweight and obesity in adults: A systematic review and meta-analysis. JBI Database of Systematic Reviews and Implementation Reports, 16, 507-547. doi: 10.11124/JBISRIR-2016-003248

What did the meta-analysis look into?

This meta-analysis investigated whether intermittent fasting (IF) programmes, also known as intermittent energy restriction programmes, can effectively treat overweight and obesity. The meta-analysis synthesized evidence from 6 experimental studies, including 400 overweight to obese adults from the USA and the UK. The weight loss of the people who fasted was compared to the weight loss of those who were on ‘usual diets’ (i.e., counting & reducing calories), or to the weight loss of people who were on no diet whatsoever. The IF programmes lasted between 3-12 months and varied in nature (e.g., alternate day fasting, fasting for two days, and up to four days per week). All IF programmes allowed people to consume ≤800 calories on at least one day per week, but on no more than six days per week. The meta-analysis primarily focused on weight loss, and, when enough data were available, provided measures of body fat; waistline circumference; and cardio-metabolic outcomes (cholesterol, triglycerides, glucose, insulin, satiety hormones, and inflammation). People who exercised were not included in the study.

What did the evidence suggest for weight loss and cardio-metabolic outcomes?

IF versus dieting (i.e., counting & reducing calories):

IF and dieting resulted in similar weight loss (minus 1 kilo on average), but IF resulted in greater fat loss (minus 1.38 kilos on average) and greater waistline circumference reduction (minus 2.14 centimeters on average). Fasting improved insulin levels more, but other cardio-metabolic outcomes were similar.

IF versus no diet (i.e., eating freely):

Compared to no diet, IF resulted in more weight loss (minus 4.14 kilos on average) and more fat loss (minus 3.24 kilos on average). Data were not enough to provide information for other outcomes.

The take-home message

Intermittent fasting appears to be as effective as dieting (i.e., calorie restriction) when it comes to achieving weight loss, but more effective when it comes to minimizing fat, waistline circumference, and insulin concentrations in the blood. Also, IF appears to be more effective than ‘eating freely’ when it comes to weight and fat loss. Notably, all types of IF programmes appeared to be equally effective in achieving these outcomes. Broadly speaking, IF seems to be a successful strategy for the treatment of overweight and obesity, but this is based on data from 400 people, only. More studies, confirming these results, are required before the (routine) use of IF can be recommended.