For many seeking to lose weight, the promise of intermittent fasting has become an inescapable message, amplified by social media influencers promoting it as a biological hack that requires no calorie counting. However, a major new scientific review suggests the reality for overweight and obese adults is far less transformative, finding the popular diet is unlikely to lead to greater weight loss than standard dietary advice or even making no change at all.
The analysis, a Cochrane review considered a gold standard in evidence-based medicine, examined 22 randomised clinical trials involving 1,995 adults across four continents. It assessed multiple fasting methods—alternate-day fasting, periodic fasting, and time-restricted feeding, where eating is condensed into an eight-hour window—with most studies following participants for up to 12 months. The conclusion from the international research team was definitive: intermittent fasting does not have a clinically meaningful effect on weight loss in this group.
“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 Dr Luis Garegnani, lead author of the review from the Universidad Hospital Italiano de Buenos Aires Cochrane Associate Centre. “Intermittent fasting just doesn’t seem to work for overweight or obese adults trying to lose weight.” While some individual studies showed a small, statistically significant average weight reduction of 2-5% over 6-12 months compared to no intervention, the overall evidence points to minimal benefit.
The significant challenge of sustaining the fast
Experts point to a critical flaw: long-term sustainability. Studies indicate a substantial percentage of people abandon intermittent fasting within a year due to hunger, social isolation, and the difficulty of adhering to restrictive eating windows. This challenge of adherence is a key reason why the practice often fails to deliver lasting results.
“Where fasting can fall down is adherence because restrictive eating windows or very low-intake days can lead to compensatory overeating, low energy, or simply not being sustainable over the long term,” Rob Hobson, a registered nutritionist, told The Independent. This biological push to overeat following a fast can negate any calorie deficit, a concern echoed in the research briefing which lists potential side effects including headaches, fatigue, irritability, and nausea.
Dr Earim Chaudry, chief medical officer at online pharmacy Voy, added that while fasting can help in the short term, it’s not more effective than holistic changes. “Limiting eating windows does not address the biological drivers of appetite, metabolic adaptation and weight regain, and it is often difficult to sustain,” he said.
A hidden risk and the public health context
A more serious concern highlighted in the research is the potential for intermittent fasting to trigger or exacerbate disordered eating behaviours. Its restrictive nature can foster an unhealthy relationship with food, leading to a hyperfixation on food and body size, and may serve as a “socially acceptable disguise” for restrictive eating, with experts advising particular caution for those with a history or predisposition to eating disorders.
The search for effective weight management strategies is urgent within a stark public health landscape. Obesity is a leading cause of cancer, second only to smoking, and is linked to at least 13 types of the disease. In England, by 2022-2023, an estimated 64.0% of adults were overweight or living with obesity, with 26.2% estimated to be living with obesity. The condition costs the NHS around £6.5 billion annually.
Globally, the scale is vast, with the World Health Organization noting that in 2022, 2.5 billion adults were overweight, of whom 890 million were living with obesity.
Weighing potential benefits against proven alternatives
Proponents of intermittent fasting point to potential physiological benefits beyond simple calorie reduction. The practice can induce “metabolic switching,” a transition from glucose to fat-based energy that begins within 12-16 hours of fasting and may improve insulin sensitivity. Furthermore, some research suggests that time-restricted feeding, particularly with an earlier eating window, can align with the body’s circadian biology, potentially supporting metabolic health.
Nutritionist Kim Pearson, who specialises in weight loss, acknowledged this to The Independent, stating that not eating overnight for 12-14 hours “aligns with our circadian biology and gives the body time to move out of a constant fed state”. However, she stressed there is no need for extreme fasting, a sentiment that underscores the expert consensus: the modest potential metabolic benefits do not consistently outweigh the drawbacks for weight loss.
The collective advice from nutritionists and the research briefing points firmly towards a focus on overall diet quality and sustainable lifestyle changes. “Improving overall diet quality is more likely to help with weight loss,” said Kim Pearson. She and other experts, including Rob Hobson, urge a focus on eating protein, fibre, and healthy fats while reducing ultra-processed foods, sugar, and refined starchy carbohydrates.
“This helps regulate appetite naturally, supports stable blood sugar and allows the body to burn stored body fat more efficiently,” Pearson added. Other evidence-based approaches noted in the research include intermittent energy restriction—alternating periods of lower and normal intake—which may be more sustainable than continuous restriction, and moderating carbohydrate intake.
The definitive finding from the latest high-quality evidence is that intermittent fasting is not a magic solution. For individuals and public health authorities grappling with the obesity crisis, the path forward appears to lie not in restrictive dietary trends amplified online, but in the less sensational, evidence-supported fundamentals of balanced nutrition and sustainable habit change.
