Obesity causes serious changes in hormones controlling blood sugar, fat deposition, appetite and metabolic rate. It is not entirely clear whether hormone changes cause obesity or the other way around. Obesity triggers high insulin levels, which promotes fat storage. Coupled with this is insulin resistance, which makes it more difficult to regulate blood sugar and carbohydrate metabolism.

Obesity decreases growth hormone release, which is important for mobilizing and using fat as fuel. Obesity also interferes with ghrelin and leptin metabolism, which control appetite and metabolic rate, and causes abnormal thyroid regulation.