AIIMS-trained gut doctor explains why Dr Saurabh Sethi, a gastroenterologist trained at AIIMS, Harvard and Stanford University, explains why some people put on weight despite eating very little, while others seem unaffected, pointing to differences in metabolism, muscle mass, and how the body burns energy. But weight gain isn’t only about how much food goes in. He spoke about why some people gain weight even when they feel they’re barely eating, while others don’t seem affected at all. According to Dr Sethi, some people are born with a naturally faster BMR. This pattern is often seen in people with fatty liver, PCOS, prediabetes, and diabetes, where weight gain can happen even when food intake feels controlled.