The amount of weight you lose by not eating depends upon your body's energy needs. In addition to your Basal Metabolic Rate, which accounts for the energy needed for fundamental functions like breathing, there is also the energy cost of physical activity.

Features

The body uses the energy contained in the food you eat, which is measured in calories, to fuel its energy requirements.

Cause of Weight Loss

The only way to lose weight is for your energy need to exceed your caloric intake. By not eating, you force your body to meet its energy demands by drawing all of its calories from its reserves of glycogen, body fat, and cannibalized muscle protein. This results in weight loss.

Starvation Weight Loss

Calorie malnourishment pushes the body into starvation mode. Your Basal Metabolic Rate slows down and your body tends to conserve fat and burn muscle to meet its energy needs. The initial loss of four pounds through starvation results in approximately one pound of muscle loss and three pounds of water loss.

Misconceptions

The goal of weight loss is to reduce body fat. The loss of muscle mass is counterproductive.

Warning

It cannot be stressed enough how dangerous it is to starve the body of the nutrients it needs to function. This not only means vitamins and minerals, as calories also qualify as a nutrient. The most serious health complication that can arise from this method of dieting is death.

Tips

A gradual but steady rate of weight loss is healthiest. It's recommended that you reduce your daily calorie intake by only 250 to 500 calories less than your daily calorie requirement.

Source:

UC: Obesity and Weight Management 1

UC: Obesity and Weight Management 2

OSU: Realistic Weight Loss Goals

Resource:

Daily Calorie Need Calculator