Intermittent fasting won’t fast-track weight loss: study

Intermittent fasting has become a buzzword in nutrition circles, with many people looking to it as a way to lose weight or improve their health.

But new research from the Cochrane Collaboration shows intermittent fasting is no more effective for weight loss than receiving traditional dietary advice or even doing nothing at all.

In this international review, researchers assessed 22 studies involving 1,995 adults who were classified as overweight (with a body mass index of 25-29.9 kg/m²) or obese (with a BMI of 30 kg/m² or above) to assess the effectiveness of intermittent fasting for up to 12 months.

The authors found, when compared to energy restricted dieting, intermittent fasting doesn't seem to work for people who are overweight or obese and are trying to lose weight. However they note intermittent fasting may still be a reasonable option for some people.

Remind me, what's intermittent fasting?

Intermittent fasting is a tool for weight management, which includes three main strategies: alternate day fasting, where every second day is reduced to low or no energy intake periodic fasting or the 5:2 diet, where one or two days of the week are spent with low or no energy intake time-restricted eating or the 16:8 diet, where daily energy intake is reduced to a shorter window, usually between eight and ten waking hours.

What did previous research show?

Previous reviews have found differences between types of intermittent fasting. Alternate day fasting, for example, resulted in more weight loss when compared to time-restricted eating. This is because participants who fasted every second day consumed about 20% less energy than those following time-restricted eating. no better than getting dietary advice

The researchers found intermittent fasting and receiving dietary advice to restrict energy intake led to similar levels of weight loss. This finding was based on 21 studies involving 1,713 people, with the researchers measuring the change from the participants' starting weight.

Dietary advice (from registered dietitians or trained researchers) could include an eating plan focused on fruit, vegetables, whole grains and seafood, restricting calories, or any specific dietary advice for weight loss.

The amount of weight the participants lost ranged from a 10% loss to a 1% gain, with either intermittent fasting or dietary advice. These findings are similar to several recent meta-analyses which found intermittent fasting is no better than dieting.

Previous research has found most of the alternate day fasting and periodic diet studies leads to about 6% to 7% weight loss. This is compared to very low energy "shake" diets (about 10%), GLP-1 medications (15% to 20%) and surgery (above 20%).

Intermittent fasting was no better than doing nothing

The researchers found intermittent fasting and no intervention led to similar levels of weight loss. This finding was based on six studies involving 448 people. In the intermittent fasting studies, participants experienced about 5% weight loss.

The "no intervention" or control group lost about 2% of their original weight. In research, a 3% difference in weight loss is not considered clinically meaningful. That's why the authors of this review concluded intermittent fasting is no more effective for weight loss than doing nothing at all.

However, the result for the "no intervention" condition could be due to the Hawthorne effect: the tendency for people to behave differently because they know they are being watched, such as in a clinical trial.

What about the other health benefits of fasting?

Studies have found intermittent fasting can lower blood pressure, improve fertility, and reduce the incidence of metabolic syndrome which refers to a group of conditions that increase the risk of cardiovascular disease.

In one 2024 study, researchers found intermittent fasting may lead to changes in metabolism and the gut that restrict how cancer develops. Another study from 2025 found intermittent fasting could improve the metabolic health of shift workers.

(The writer is a senior lecturer at the Australian Catholic University, Australia)