Although losing weight quickly is possible, not only is it bad for your health, it is almost certainly a recipe for becoming even fatter later on.
Kelly D. Brownell, Director of the Rudd Centre for Food Policy and Obesity at Yale University, who coined the term "yo-yo dieting", explained why crash dieters eventually get into a cycle of crash diets and high food intake and gain weight in the long-term.
The vicious circle of crash diets
A weight-loss diet needs to include all the vital nutrients for good health
When the human body consumes less energy than it requires, it uses its stored energy.
Initially, the body starts using up its glycogen stores because they can be easily turned into glucose. In humans, glycogen is stored primarily in the cells of the liver and the muscles.
When the glycogen runs out, the body then starts breaking down amino acids from protein (muscle) to make glucose.
Finally, when glycogen has been used up and non-vital protein is depleted, fat is broken down to release triglyceride for energy.
Glycogen and protein hold water, if you lose the glycogen or protein you lose water. Experts estimate we carry between 60 to 120 grams of glycogen in the liver, which is stored in about 6 pounds of water.
So if you use up the glycogen, you lose that weight in water. Add to that, the water loss when protein is used up to make energy.
Crash dieters at this point are extremely excited. They have lost a great deal of weight. However, most of it is water released when the glycogen and non-essential protein is used up. Not much fat has been lost at this point.
In order to lose 1 pound of fat you need a calorific deficit of 3,500 kilo calories.
The trouble is, by the time the body starts turning to its reserves of fat to make up for the energy deficit caused by the crash diet, its metabolism has slowed right down.
The body's metabolism slows down for several reasons. The hypothalamus, a region in the brain, realizes that fat stores have changed and consequently lowers metabolism to replace the lost fat. During the breaking down of amino acids into glucose, protein is lost, which means loss of lean tissue (muscle). The less muscle you have, the slower your metabolism will be.
Eventually the crash dieters weight loss slows right down and he or she loses motivation. Other psychological factors start to kick in too.
When lower motivation results in the person abandoning their diet, they put on weight rapidly because their metabolism is now much lower, the brain is telling the body to store (in fat) every possible reserves of energy, and the disappointment and sense of failure often encourages further eating.
Researchers at the University of Oviedo in Spain reported in the journal Physiological Health & Medicinethat the short-term effects of crash diets are not maintained in the medium to long term. They added that such diets typically result in a subgroup becoming obese or overweight, due more to psychological consequences than biological mechanisms.
Put simply -Crash diets are more likely to make you fat or fatter over the long term.
It is possible to lose weight comparatively rapidly, and in a healthy way. This involves good nutrition andplenty of good quality sleep, and exercise.
Healthy weight loss is about adopting a lifestyle that you can maintain over the long-term.
The CDC (Centres for Disease Control and Prevention) says that according to available evidence, people who lose about 1 to 2 pounds per week are better at keeping weight off.
If you plan to lose weight faster than 3 pounds per week you should check with your doctor. It is possible, especially if you have the help of a qualified dietitian, an effective exercise program, and sleep at least seven hours each night. It is important to remember that the faster you lose weight, the higher the risk of undesirable consequences, including malnutrition, weaker bones, irritability, depression, insomnia, and eventually putting even more weight back on over the long term.