A popular diet may be far less effective at helping people lose weight than fanfare suggests.
Endorsed by stars like Jennifer Aniston, Hugh Jackman and Chris Hemsworth, it’s a go-to among many famous faces who are considered fit and healthy — but more and more research is casting doubt on how useful it actually is.
In fact, a new Cochrane review found that it’s unlikely to lead to meaningful weight loss in overweight or obese adults.
Intermittent fasting — which involves restricting when you eat, most commonly consuming food within an eight-hour window and fasting for the other 16 hours — has long been touted as an effective weight loss strategy and a way to boost metabolic function. But is it?
“Intermittent fasting may be a reasonable option for some people, but the current evidence doesn’t justify the enthusiasm we see on social media,” said Luis Garegnani, lead author of the review from the Universidad Hospital Italiano de Buenos Aires Cochrane Associate Centre.
The review incorporated evidence from 22 randomized trials and roughly 2,000 participants worldwide. These trials evaluated myriad forms of fasting, including alternate-day fasting, periodic fasting and time-restricted feeding.
Results showed that restricted eating did not lead to significant weight loss compared to these other modalities.
“Intermittent fasting just doesn’t seem to work for overweight or obese adults trying to lose weight,” said Garegnani.
Despite the growing popularity of restricted eating, he noted, few trials have assessed the long-term effects of intermittent fasting.
“Obesity is a chronic condition. Short-term trials make it difficult to guide long-term decision-making for patients and clinicians.”
Being classified as overweight or obese is based on body mass index, which has been criticized as a poor metric of health but remains a widely used and practical measure.
The US has the highest rates of obesity among high-income countries, with about 42% of men and 46% of women considered obese in 2021.
Recent research suggests that nearly half of American adults will be living with obesity by 2035, though the explosive use of GLP-1 medications may change that projection.
Doctors say treating obesity is of dire importance as the condition increases the risk of Type 2 diabetes, high blood pressure, cardiovascular diseases and several cancers.
The study authors emphasized that their findings can provide valuable insights into the efficacy of fasting, but decisions regarding the management of obesity should remain individualized.
“With the current evidence available, it’s hard to make a general recommendation,” said Eva Madrid, senior author from Cochrane Evidence Synthesis Unit Iberoamerica. “Doctors will need to take a case-by-case approach when advising an overweight adult on losing weight.”
Prior intermittent fasting research has yielded mixed results. Some studies have linked the diet plan to weight loss, a lower risk of Type 2 diabetes and heart disease, reduced inflammation and improved cholesterol levels.
But medical experts have cautioned that intermittent fasting is not for everyone. One major study found that those who limit their eating to less than eight hours a day are more likely to die from cardiovascular disease than people who eat in a 12- to 16-hour window.
Last month, a small German study found that participants who followed restricted eating schedules lost weight but showed no improvement in blood glucose, blood pressure, cholesterol, or other key cardiometabolic markers.
