Belly fat shrinks with cardio or weights alike, and most when you do both

Subcutaneous abdominal fat is the body's largest fat depot and a major supplier of free fatty acids to the liver, and abdominal fat is indirectly linked, through raised low-grade inflammation, to many of the adverse health effects of obesity. Exercise is one of the most prominent tools in obesity management, yet its specific effect on this fat depot has been surprisingly unclear. Trials have tested aerobic training, resistance training and combinations of the two, with scattered results. This review set out to compare the modes directly and establish which, if any, reliably shrinks the fat under the belly skin.

The authors searched PubMed, SCOPUS and Google Scholar for randomised clinical trials published up to November 2018. Forty-three trials qualified, enrolling 3552 adults, of whom 2684 were women. Each trial tested aerobic training, resistance training or a combined programme against a control group, with subcutaneous abdominal fat measured in square centimetres. Effect sizes were pooled as weighted mean differences, the disagreement between studies was formally examined, and outlying results were removed before the main estimates were combined.

All three approaches beat control. Aerobic training reduced subcutaneous abdominal fat by 13.05 cm2, resistance training by 5.39 cm2, and combined training by 28.82 cm2, the largest reduction of the three. When aerobic training was compared directly against combined training, the combined approach came out significantly ahead. When aerobic and resistance training were compared directly against each other, however, the difference of 0.73 cm2 was not statistically significant. So the honest reading is that both single modes work, neither clearly beats the other head to head, and the combination delivered the biggest measured change.

This pooled analysis firms up a previously murky picture: exercise of any of these three types reduces subcutaneous abdominal fat relative to no exercise. The advantage of combined programmes over aerobic training alone extends the common intuition that more varied training does more, though the review cannot say whether that reflects the mix itself or simply more total exercise. The search closing in November 2018 means more recent trials are absent. How these reductions in the under-skin fat depot relate to the health outcomes tied to abdominal fat also remains an open question.

If a flatter waist measurement is one of your goals, this is evidence that the mode of exercise matters less than doing it: cardio and lifting reduced subcutaneous belly fat by statistically similar amounts when compared directly. The standout result for combined programmes is a reason to think mixing both may do more than either alone, at least as tested in these trials. Worth remembering that this review measured the fat layer under the skin specifically, not the deeper abdominal fat, so it answers one question about body composition rather than all of them.