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A crash diet is a diet which is extreme in its nutritional deprivations, typically severely restricting calorie intake. It is meant to achieve rapid weight loss and may differ from outright starvation only slightly. It is not meant to last for long periods of time, at most a few weeks. Importantly, the term specifically implies a lack of concern for proper nutrition. Crash diets are also known as "fad diets" and are often seen as quick fix solutions. Contrary to the belief of many who start this sort of diet, this form of dieting is neither healthy nor largely successful in achieving long term weight loss as it provokes a slow down of the body's basal metabolic rate - the body seeks to conserve every calorie and so weight loss becomes increasingly difficult. While some initial weight is often lost, the weight is usually regained quickly in the weeks that follow, as the individual reverts to their original pre-crash diet. It often becomes a vicious cycle in which the weight that is regained is often more than the starting weight, causing the dieter to revert to the crash diet, lose weight, regain the weight, and so on.
Obesity and the Diet Industry 
Obesity results from the long-term imbalance of energy intake and energy expenditure, where more calories are consumed than used in the body. The rising rates of obesity in North America is of great concern. In the United States, 1 out of 3 adults are obese, whereas in Canada 1 out of 4 adults are obese. Obesity is associated with many negative health implications such as higher risks of type 2 diabetes, coronary heart disease, hypertension, cancer, and premature death. As obesity has physical and psychological implications, it also affects the economy with the financial burden of this disease. The economic burden of obesity in Canada has been estimated to range from $4.6 billion to $7.1 billion annually, due to direct medical costs such as preventive, diagnostic, and treatment services related to obesity, and indirect costs value of income lost from decreased productivity, restricted activity, absenteeism, and bed days. Many of those who struggle with their weight often look for a quick fix diet solution. With all of the diet pills, books, and programs that exist these days, it's often hard to determine which programs actually work and which ones are detrimental to one's health. In a 2004 survey conducted by the U.S. Federal Trade Commission, it found that 40% of the ads for weight loss products or plans made at least one representation that was almost certainly false, and 55% made at least one representation that was very likely to be false 
Crash Diets and the Vicious Cycle 
When energy intake is not sufficient to meet the body's requirement, its stored energy is utilized. Glycogen stores are the first to be broken down as they can easily yield glucose molecules, which is the body's preferred energy source. Amino acids from body protein can then be broken down to make glucose. Eventually, once glycogen stores have been depleted and the protein available in the body that is not vital for survival has been utilized, fat tissues are then broken down to release triglycerides for energy. The amount of glycogen stored in the liver can range from 60 – 120 grams and the amount stored in muscle mass can range from 200 – 500 g. This can equate to 6 pounds of excess water stored in the body, but varies with individuals. Protein also holds water, about four times its weight. Therefore, once protein sources are utilized for energy, there will be also be corresponding loss of fluid. A loss of glycogen fluid along with protein fluid can result in some dieters losing between ten and thirty pounds in weight fairly quickly.
When individuals go on these crash diets, they are motivated initially due to the rapid weight loss that occurs. Although weight loss does occur, water weight is lost through the reduced glycogen stores and not the fat loss that individuals often strive for. In order to lose 1 pound of fat, a caloric deficit of 3500 kcals has to be made. Eventually the ability to rapidly lose weight diminishes due to numerous factors. A vicious cycle often exist for dieters who go on these crash diets. It is often known as yo-yo dieting, which is the repeated loss and regain of body weight due to dieting. Diets often cause caloric deficits, resulting in weight loss in the initial start of the program due to the use of glycogen, protein, and fat stores. However, eventually metabolism begins to slow down to preserve the energy stores that are left in the body. This is caused by the numerous factors, such as the hypothalamus detecting changes in fat stores and thus lowering metabolism to replenish the fat lost. As lean body mass is also broken down to supply protein, the loss of muscle mass further accelerates the decline in metabolism, as muscles are energy utilizing organs. Eventually the individual reaches a weight loss plateau, loses motivation as rapid weight loss is no longer occurring, and thus returns back to their normal eating habits. As normal dietary habits are resumed, the weight that was lost is often regained quickly, and even more. As the caloric intake increases along with carbohydrate consumption, glycogen stores become replenished and thus the water weight. Since the basal metabolic rate is now lower than the rate at the initial start of the diet in the individual, further weight gain occurs as the body is "less efficient" than it was before in burning calories. Studies have proven that weight is readily regained at a much faster rate than it was lost. With the rapid regain in weight, eventually the dieter may find a new crash diet to try or a new gain in confidence, thus resulting in the vicious cycle seen below. With repeated bouts of starvation, it results in faster and more significant lowering of the basal metabolic rate, and thus weight being regained faster.
Crash diets are low caloric diets that often include some gimmick to attract consumers that desire a "quick fix" solution. Along with the vicious cycle that is seen, crash diets can have negative implications for one's health, especially if carried over the long term due to the avoidance and elimination of food groups. Depending on the diet, negative health effects can include malnutrition, electrolyte imbalances, and increased susceptibility to chronic conditions such as osteoporosis. Side effects include nausea, diarrhea, lethargy, headaches, dehydration, and much more.
Examples of some Crash Diets 
Some of the common diets that have been followed in the past are listed below.
Ending the Cycle 
The American Heart Association emphasizes that long-term weight loss is a product of changing our behavior, good nutrition and physical activity. In its model, it emphasizes the components: Think Smart, Eat Well, and Move More.
Safe weight loss is considered to be no more than 1-2 pounds per week. A single food or meal does not make or break a healthful diet, as all foods can fit into a healthy diet when consumed in moderation and the appropriate portion size. Along with the health benefits of physical activity, such as promoting a feeling of well-being and reducing the risk of chronic diseases, it can help manage weight and helps offset the lowering of the metabolic rate that occurs with reduced caloric intakes. The key to healthy weight loss is healthy eating and physical activity.
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