Fasting vs calorie cutting: less magic than you think

Intermittent fasting has become one of the most popular dietary strategies for people trying to lose weight and improve blood sugar control, including those with prediabetes or type 2 diabetes. The key scientific question is not just whether fasting works, but whether it works any better than simply eating fewer calories spread normally through the day. If restricting the eating window offers no advantage over ordinary calorie restriction, that changes how the approach should be framed. This meta-analysis set out to test intermittent fasting against both a control diet and calorie restriction in exactly this population.

The researchers searched PubMed, Web of Science and Scopus from inception to March 2024 for randomised trials with parallel or crossover designs studying the effects of intermittent fasting on body composition and cardiometabolic health in adults with prediabetes or type 2 diabetes. Fourteen studies involving 1,101 adults were included. Comparisons were made against control diets and against calorie restriction, with weighted mean differences calculated using random-effects models across outcomes including body weight, BMI, glycaemic markers, lipids and blood pressure.

Versus control diets, intermittent fasting decreased body weight by 4.56 kg, BMI by 1.99 kg/m2, HbA1c by 0.81%, fasting glucose by 0.36 mmol/L, total cholesterol by 0.31 mmol/L and triglycerides by 0.14 mmol/L. However, it did not significantly reduce fat mass, insulin, LDL, HDL or blood pressure compared with control. Versus calorie restriction, fasting produced a further 1.14 kg of weight loss and a 0.43 kg/m2 reduction in BMI, but had no significant effect on fat mass, lean mass, visceral fat, insulin, HbA1c, lipids or blood pressure.

This pooled analysis confirms that intermittent fasting is effective for weight loss and several cardiometabolic markers in people with prediabetes or type 2 diabetes when compared with doing nothing different. But it complicates the popular idea that fasting delivers unique metabolic benefits: against plain calorie restriction, the glycaemic and lipid outcomes were indistinguishable, leaving only a modest weight edge. Open questions remain about which fasting protocols were pooled, how long benefits persist, and adherence over the long term.

If you are managing blood sugar or working to head off type 2 diabetes, this is a reason to think intermittent fasting is a legitimate, effective structure for eating less — not a metabolic trick that outperforms ordinary calorie control. The choice between fasting and conventional calorie restriction may come down largely to which one you can sustain. Anyone with diabetes considering a change in eating pattern should involve their healthcare team, particularly where medication is concerned.