Many people are reluctant to spay or neuter their dogs for fear that they will become overweight or even obese. Indeed, this may occur. Although there is a relationship between sterilization and weight, it is not a direct cause and effect.
Both estrogen and testosterone are powerful anabolic steroids. Both produce metabolic activity and behaviors which demand a high level of caloric consumption. After sterilization the hormone levels decrease over a 6-8 week period and so the body's need for caloric intake also decreases.
We recommend sterilization at or just prior to the onset of puberty, when the rapid growth stage is ended. This is also when you should switch from "puppy" to "adult" formula foods.
Animals become overweight because they eat more than they need. It's simply a question of calories in versus calories used. So to avoid weight problems after sterilization slowly switch to an adult formula, keep your pet active and/or simply feed them less food.