Every 30 weekly minutes of cardio trims weight, but 150 is where it starts to count

Exercise guidelines tell people how many minutes of aerobic activity to aim for, but those durations have come mainly from individual trials rather than from analyses that map the full dose-response curve. For adults carrying excess weight, the practical question is how much each additional half hour of cardio actually buys in terms of weight, waist size and body fat, and whether there is a threshold below which the effect is too small to matter. This meta-analysis set out to draw that curve directly from the randomised trial evidence.

The researchers pooled 116 randomised clinical trials involving 6880 adults with overweight or obesity, 61% of them female, with a mean age of 46 years. Eligible trials tested supervised aerobic training lasting at least 8 weeks. Outcomes included body weight, waist circumference, body fat percentage, visceral and subcutaneous fat areas, adverse events, and health-related quality of life, with the certainty of each finding graded. Dose-response models estimated the change linked to every 30 minutes per week of exercise and traced the shape of the association up to 300 minutes per week.

Each 30 minutes per week of aerobic exercise was associated with 0.52 kg less body weight, 0.56 cm less waist circumference and 0.37% less body fat, along with reductions in both visceral and subcutaneous fat areas. Weight, waist and fat measures fell linearly or steadily as weekly duration increased up to 300 minutes per week. Exercise at 150 minutes per week at moderate to vigorous intensity produced reductions in waist circumference and body fat judged clinically important. One small trial of 80 people suggested improved physical and mental quality of life, at low certainty. Mild to moderate adverse events, mostly musculoskeletal, were slightly more common, about 2 extra events per 100 participants.

This analysis fills a gap the authors identify directly: guidance on exercise duration had rested on single trials, not on a pooled dose-response picture. The findings support the familiar 150 minutes per week benchmark, but reframe it as roughly the point where fat and waist reductions become clinically meaningful rather than merely detectable. The certainty was moderate to high for the main body composition outcomes, weaker for quality of life and adverse events. What longer durations beyond 300 minutes deliver, and how unsupervised exercise compares, remain open questions.

The honest reading is that cardio reliably trims weight and waist size, but each half hour buys a modest amount, about half a kilogram over a trial's duration. That makes small amounts of exercise worthwhile without overselling them, and it gives the 150 minutes per week figure a concrete meaning: it is roughly where reductions in body fat and waist size become big enough to matter for health. It is also a reason to expect gradual change rather than dramatic loss from aerobic exercise alone.