After 30, the same diet can lead to more belly fat due to natural metabolic changes, says Harvard and Stanford-trained gastroenterologist Dr Saurabh Sethi. Muscle mass declines, insulin sensitivity drops and hormonal shifts favour visceral fat storage, especially around the abdomen. Those with fatty liver or diabetes are affected more. Dr Sethi advises protein-rich diets, strength training, daily walking and adequate sleep, stressing sustainable habits over extreme dieting.