They ensure they leave the system and they also ensure that people get the nutrients they need.
Because there are several factors that determine weight loss or gain and reducing calorific intake is just one of them (for reducing weight loss). Other factors that should be considered is exercise. Doing regular exercise ensures that the metabolic rate of the body is increased so much of the calories are burned even after intake. Having a lower metabolic rate can result to increased weight gain even with low calorie intake.
It is because that's a place where no one lives so they're safe.
