Habits of people who don’t gain weight easily — including what the research says, common behaviours you can observe, and how you might incorporate helpful practices (if your goal is weight-maintenance rather than weight-gain).

Why some people resist weight gain

Before diving into habits, it’s helpful to understand why some people appear to eat (or at least live) differently and maintain a stable weight.

Biological and physiological factors
• Some people have a higher rate of resting energy expenditure, meaning their body burns more calories even at rest. For instance, a study by Mayo Clinic found that people who gained the least fat when over-eating also had the greatest increases in non-exercise activity (fidgeting, standing more, moving around) — termed “NEAT” (non-exercise activity thermogenesis). 
• Genetics play a role: some people have genes or gene-variants making them more resistant to fat accumulation, or with a more sensitive appetite regulation system. 
• Gut microbiome differences may influence how many calories are absorbed, how satiety is signalled, or how energy is processed. 

Thus, while habits matter, some underlying physiological differences give some people a natural “advantage” in maintaining weight. But behaviour still counts a lot.