Fasting beats plain calorie cutting by less than a kilogram of fat

Intermittent fasting has become one of the most popular approaches to weight loss, but much of the supporting evidence comes from short trials. The practical question for anyone choosing a diet is what happens over the longer term, and specifically whether fasting outperforms the standard alternative of simply eating fewer calories every day. This review set out to answer that by restricting itself to randomised trials lasting at least six months in adults with overweight and obesity. It compared fasting both against control diets and against continuous caloric restriction head to head.

The authors searched PubMed, Web of Science and Scopus from inception to March 2024 for randomised trials testing intermittent fasting against either a control diet or continuous caloric restriction. Eligible participants were adults with overweight or obesity, and interventions had to run for six months or longer. Twenty-four studies involving 2032 participants were pooled. Outcomes covered body weight, BMI, fat mass, fat-free mass, waist circumference, visceral fat, blood glucose and insulin measures, blood lipids and blood pressure, with subgroup analyses examining the mode of fasting and intervention duration.

Against control, intermittent fasting reduced body weight by 2.84 kg, BMI by 1.41, fat mass by 3.06 kg, fat-free mass by 0.81 kg, waist circumference by 3.85 cm and visceral fat, while lowering fasting glucose by 0.14 mmol/l, triglycerides by 0.12 mmol/l and diastolic blood pressure by 2.24 mmHg, and raising HDL by 0.04 mmol/l. It had no effect on insulin, haemoglobin A1c, total cholesterol, LDL or systolic blood pressure. Against continuous restriction, fasting produced 0.70 kg more fat loss, 0.59% lower body fat, 0.91 mmHg lower diastolic pressure and slightly higher HDL, with no other significant differences. Mode of fasting and duration moderated the effects.

This extends the fasting literature past the short-term studies that dominate it, and its conclusion is measured: over six months or more, intermittent fasting and continuous calorie restriction are comparably effective for reducing weight and adiposity and improving cardiometabolic markers. The small advantages for fasting on fat mass and a few markers are statistically detectable but modest in size. The loss of some fat-free mass alongside fat is worth noting, as it appears in the control comparison. Which fasting mode works best, and for whom, remains an open question the subgroup findings only begin to answer.

If you have been weighing fasting against ordinary calorie counting, this is a reason to think the decision matters less than sticking with whichever you choose: over the long haul the two approaches produced very similar results. Fasting clearly worked against no intervention, with meaningful reductions in weight, fat and waist size and several improved health markers. Its edge over daily restriction, though, amounted to well under a kilogram of extra fat loss. That makes personal preference and sustainability the sensible tiebreakers, which is information, not a prescription.