To lose weight you must create a negative energy balance: calories taken must be less than calories expended. Result: Fat, glycogen and muscle are used for energy to make up the caloric deficit and ideally weight is lost and fat stores are reduced. However, losing weight and losing fat are two different stories. Weight loss does not necessarily equal fat loss. When someone comes into my weigh loss clinic and tells me they wish to lose weigh what they really mean is they wish to lose body fat.

In order to achieve any long lasting weight loss you need to “fool” the starvation protective mechanism of the body.  These very low calorie diets may works for a certain length of time (2-3 weeks) however two things can happen when an individual follows a low calorie diet for too long. 

The first is you find you are too hungry and following a plan like this becomes near impossible. You may get headaches from lack of food and sustenance or feel lightheaded or even feel faint. You then cease to follow this low calorie diet any longer thus putting on the weight you may have lost because you have hindered your metabolism.

The second outcome from following a low calories diet is your body believes it’s starving/in a famine environment. Your body does not know you are living in an environment surrounded by food all it knows is food is scarce, the reasoning behind the scarcity is not important.  As a result your body goes into what’s known as starvation protective mechanism. Very low calorie diet is described as <1200 calories for women and <1800 for men.

Starvation protective mechanism involves the body making the most of the calories it does get from food and drink. 

Your body responds to very low calorie diets in a very negative way and your metabolism become affected as a result. The initial reaction by the body if too few calories are consumed (crash diets) is to protect its fat stores. As a result it uses lean tissue or muscle to provide the body with calories in order to function and preform biological processes. 

For someone who eats there RDA (recommended daily allowance) of calories then the body will function ideally as it’s getting calories from food and will break down fat if more energy is require. This is how people who eat little and regularly maintain a healthy weight. 

However, when your body feels threatened (crash diet) the body’s leptin levels (a hormone that breaks down stored body fat) decrease and only allows fat cells to release energy in order to sustain your most basic bodily functions. Even though you continue to follow a crash diet/low calorie diet and think you are doing well by losing weigh you are in fact losing muscle and not fat (may lose a small portion). Your body has shut down its fat-burning ability in order to conserve energy.

To make situations worse when you do consume food your body stores the nutrients including fat (calorie reservoir) for use later. Instead of burning the fat straight away for day to day activities, your body has now panicked that calories will be in short supply again so it stores them in the form of fat. As a result fat cells increase and you end up gaining weight. This is how yoyo dieting comes into play as you may damage your metabolic rate from constant dieting.

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