Can intermittent fasting help people who have overweight lose weight? It is likely that intermittent fasting is not superior to other diets for weight loss and may not lead to higher quality of life, according to a Cochrane review now published by Luis Ignacio Garegnani of the University Institute of the Italian Hospital, Buenos Aires, Argentina, and colleagues. Garegnani and his team analyzed 22 randomized controlled trials.

The studies were evaluated according to two questions:

• Is intermittent fasting more effective for adults with overweight and obesity than conventional dietary recommendations?
• How does intermittent fasting affect quality of life, diabetes status, blood lipids, and adverse events?

“Intermittent fasting” groups together different eating approaches that divide time into regular eating and fasting periods, including variants such as alternate-day fasting, early and late time-restricted eating, one-meal-a-day and 5:2 fasting. The fasting and eating periods can vary greatly depending on the method.

The Cochrane Review

“Previous meta-analyses with other or similar inclusion criteria have consistently found no advantage of intermittent fasting compared with comparable dietary interventions of similar calorie reduction. The Cochrane review therefore fits the existing picture,” Stefan Kabisch, study physician in the Clinic for Endocrinology and Metabolic Medicine at the German Center for Diabetes Research (DZD), Campus Benjamin Franklin, Charité — Berlin University Medicine, Berlin, Germany, told the Science Media Center. He said the hype surrounding intermittent fasting has never been supported by convincing human studies but rather was premature and unjustified. Even in Germany, a recommendation was issued prematurely, one that was not based on high-quality study data.

The review provides evidence that intermittent fasting appears to be similarly effective for weight loss in people with overweight and obesity as other dietary approaches. “But to be clear: so far these are indications, not proof,” said Jörg Meerpohl, director of the Institute for Evidence in Medicine at University Medical Center Freiburg, Freiburg, Germany, and director of Cochrane Germany.

Intermittent Fasting

The selected studies are “extremely heterogeneous,” emphasized Annette Schürmann, spokesperson and board member of the DZD and former head of the Department of Experimental Diabetology at the German Institute of Human Nutrition Potsdam-Rehbrücke, Nuthetal, Germany. She said she was a bit disappointed by the review because she had hoped it would provide a clearer summary of the evidence on intermittent fasting. It appears the review authors wanted to promote the idea that intermittent fasting is not a good strategy for weight loss and health.

“Intermittent fasting does lead to a statistically significant weight loss. In the six studies evaluated for claim 2, intermittent fasting resulted in approximately 3.4% greater weight loss than the control group achieved. That is clinically significant — for example, UK NICE guidelines consider 3% meaningful, while US guidelines use 5% as a benchmark,” explained Leonie Heilbronn, head of the Obesity and Metabolism research group at the School of Medicine, College of Health, Adelaide University, Adelaide, Australia.

If the goal is substantial weight loss — for example, 20%-30% — intermittent fasting is not sufficient, Schürmann noted. Intermittent fasting generally achieves only 3%-7% body-weight loss, which can nevertheless be health-relevant. “If a more ambitious goal is sought, medical or surgical therapy is required,” Schürmann emphasized. Still, the statement that “intermittent fasting has no effect on weight loss” cannot simply be made. A 3% loss in body weight is not trivial and can have a very positive effect on blood pressure and glucose metabolism, she said.

Animal studies using obese, diabetes-prone models have shown that an intermittent fasting diet can have a positive effect on the pancreatic islets of Langerhans and thus on blood glucose levels, even if the animals make up for it during the eating window and consume as much as their obese control group, which was not subject to an intermittent fasting diet. “We cannot test that in humans, but it is reasonable to assume the findings are transferable,” Schürmann said. For that reason, an intermittent fasting diet could be particularly interesting for patients with prediabetes.

This story was translated from Medscape’s German edition.