Why do some people gain weight more easily than others?

Some people are more prone to being overweight than others. Two factors are genetics and behaviors. Certainly, one key factor is heredity. Some of us are born thin, and some of us aren't. Our genes determine all kinds of influences on height, weight, and metabolic rate, and these vary incredibly from person to person. Also, some of us are born with an emotional make-up, and acquire emotional predispositions, that make it harder or easier to lose weight. The study of genetic factors affecting weight gain is a burgeoning field, and scientists have discovered some genes and gene products that are tied to weight gain. One of the first hormones tied to fat regulation-leptin-was characterized in the now-famous studies of "fat mice": Mice with genetically-created obesity were given injections of leptin and lost weight. Despite the initial belief that a magical new weight-loss drug had been found, the discovery of leptin proved how complicated the genetics of food metabolism and weight gain are. Subsequent investigation showed that leptin is just one hormone out of many involved in a complicated metabolic pathway. Some people with genetically-caused weight problems have leptin-related disorders, but others don't. Some people clearly have gherlin-related disorders. There are probably going to be other hormones discovered as well. We hope that magic pills will be invented that allow us to combat the effect of each and every one of these potential hormones. However, no one knows what the future holds in this regard. Weight regulation is a complex genetic trait: Many different genes and proteins interact to determine body size. We are still years from understanding the interactions. Fortunately, heredity isn't everything.