Meta-analysis finds intermittent fasting provides similar benefits to traditional diets

By Rebecca Jenkins

Intermittent fasting diets result in similar weight loss and cardiometabolic risk factor changes to traditional calorie-restricted diets, a large meta-analysis finds.

Intermittent fasting, which involved periods of restricted energy intake interspersed with periods of unrestricted intake, had become a popular weight loss strategy, an international group of researchers wrote in the BMJ.

Emerging evidence suggested that the strategy might offer improvement in weight and other cardiometabolic risk markers such as glucose control and blood pressure beyond that of typical diets; however, the effect in humans remained unclear.

To fill this evidence gap, researchers undertook a systematic review and network meta-analysis of 99 randomised controlled trials comparing intermittent fasting diets with continuous energy restriction or unrestricted intake diets on body weight and various cardiometabolic outcomes.

Overall, participants had a median age of 45 years, had overweight or obesity (median body mass index of 31.3 kg/m²) and were mostly female (66%).

Almost 90% of participants (5862) had existing health conditions including type 1 or type 2 diabetes, metabolic syndrome or metabolic dysfunction-associated fatty liver disease.

The researchers found that compared with an unrestricted diet, both intermittent fasting strategies and continuous energy restriction diets resulted in body weight reduction.

Of the three intermittent fasting diets studied (alternate day fasting, time restricted eating and whole day fasting), alternate day fasting showed a benefit in body weight reduction compared with continuous energy restriction.

‘Minor differences were noted between some intermittent fasting diets and continuous energy restriction, with some benefit of weight loss with alternate day fasting in shorter duration trials,’ the researchers concluded.

All diet strategies presented similar benefits in cardiometabolic risk over an unrestricted diet, they added.

Commenting on the findings, Professor Luigi Fontana, the Ullmann Chair in Translational Metabolic Health at The University of Sydney, said although animal studies had suggested intermittent fasting could extend lifespan and reduce inflammation, translating those findings into humans was not straightforward.

Professor Fontana, who is also Scientific Director of the Charles Perkins Centre Royal Prince Alfred Clinic, Sydney, and a world-leading expert in nutrition and healthy ageing, said he had conducted a randomised clinical trial where participants had followed an intermittent fasting protocol for six months resulting in about 8% weight loss and a 16% reduction in body fat, but with only small effects on insulin sensitivity and no impact on inflammation.

‘These results underscore the fact that findings in rodents – who have rapid metabolisms – don’t necessarily reflect outcomes in humans, who have more complex dietary and behavioural patterns,’ he said.

Intermittent fasting could also mean that people concentrated on when they were eating, rather than what they were eating, to the detriment of their diet’s quality.

‘Ultimately, promoting health is about much more than calorie counts or meal timing. Sustainable benefits come from consistent, high-quality dietary habits – ideally based on minimally processed, nutrient-dense foods – whether or not fasting is involved,’ Professor Fontana said.

Furthermore, a truly effective strategy for preventing cardiovascular ageing and chronic disease involved a holistic, lifestyle-based approach, he stressed, which included nutrition, together with physical activity, sleep, stress management, emotional health, social connection and environmental awareness.

BMJ 2025; 389: e082007; doi: https://doi.org/10.1136/bmj-2024-082007.