Hormonal imbalances might predispose both dogs and cats to obesity. They alter energy homeostasis and appetite control. Energy homeostasis is the process that balances energy intake with energy expenditure, allowing the body to maintain stable energy reserves and body weight. Leptin normally signals satiety, but in obese dogs and cats, chronic elevation leads to leptin resistance, where the brain fails to respond adequately, leading to overeating and fat storage. Insulin dysregulation impairs glucose uptake and promotes further fat deposition, particularly in visceral areas. Hypothyroidism in dogs, reduces basal metabolic rate and energy expenditure. Neutering exacerbates these risks by removing sex hormones like oestrogen and testosterone, which help regulate metabolism. Research shows that, in dogs, this procedure increases obesity likelihood. Similar effects occur in cats, where ovariohysterectomy leads to hyperinsulinemia and reduced energy needs.