In overweight and obese adults on an energy-restricted diet, replacing ultra-processed foods with minimally processed foods was not associated with significant changes in waist circumference over six months, despite significant reductions in trunk fat.

When people eat whole foods instead of processed ones, their blood sugar and insulin levels stay lower after meals, which stops fat from being stored in belly fat cells. At the same time, their gut bacteria change to absorb less energy from food and reduce inflammation, so the body burns more fat. Even though fat around the organs drops, the size of the waist doesn't shrink because the fat loss happens deep inside the abdomen where it doesn't push outward on the skin and muscles.