While one-day fasts pose no serious threat for healthy adults, longer fasts (more than 24 hours) can have grave results.
Whether it's a 'water-only' fast used to detox, skipping meals or surviving on only grapefruit, the body only recognises one thing - starvation.
When you don't consume enough calories to sustain essential functions (such as keeping the heart beating or the lungs breathing), the body reacts by drawing on its own reserves to provide energy.
This puts your body under stress - not rest - and is certainly not the answer to permanent weight loss.
Biggest dangers of starvation diets & fasting...
Fasting results in rapid initial weight loss
Under normal circumstances, the principal fuel for the body is glucose. The brain, in particular, must receive a constant supply of glucose in order to function properly. During a period of calorie restriction, glucose, which is stored in the liver as glycogen, is used first to supply energy.
Glycogen is stored with water, so when it is broken down for energy, water will be released as well. It is this fluid that is responsible for the rapid weight loss that occurs in the first one to two days (anywhere between 3-5lbs pounds per day) of severely calorie-restricted diets.
If it sounds too good to be true, it is: this weight loss won't last.
When normal eating is resumed, glucose and water stores will be replenished and the original body weight will be attained. The rapid loss of fluid can also lead to the loss of electrolytes and dehydration.
The sudden drop in sugar in the blood, as glycogen stores are diminished, will result in tiredness, confusion and mood swings. These are the symptoms that are often mistakenly thought to be the first step in the cleansing process of a detox diet.
Cutting calories slows down weight loss
The liver stores only enough glycogen (energy) to last for one day, so when fasting lasts longer than 24 hours, the body will then turn to muscle to produce glucose for energy.
After following a very low-calorie diet or fast for one week, 30% of the total weight loss is muscle and the rest is fluid.
The amount of muscle in the body sets your metabolic rate (the rate at which you burn calories). So, as muscle is lost, less metabolic work is performed, saving calories and hence energy. In short, your rate of weight loss will slow down.
When you eat a meal, overall metabolism is increased due to the energy required for digestion. Skipping a meal will have the reverse effect, decreasing the metabolism, which lasts until you eat something.
Overall, the body will then save - rather than burn - calories to ensure it has adequate energy during the times of fasting. So, meal skipping to avoid unwanted calories is a counterproductive method for sustained weight loss.
When calorie levels are increased to a normal level, weight gain will be faster and the weight will come back as fat, since your metabolic rate has slowed, and you may even end up heavier than before you began dieting.
The loss of muscle will have an effect on your ability to maintain weight loss in the long term, unless muscle is regained by exercising.
Fasting results in fatigue
Body protein provides most of the energy needed in the first days of a fast, but after that the body will adapt to using fat for energy in an attempt to preserve muscle.
Fat is then metabolised to ketones, which can be used by the brain for energy. However, prolonged inadequate carbohydrate intake results in the build-up of ketones, which become toxic, resulting in a condition called ketosis.
The kidneys and liver become burdened with toxic waste from the breakdown of fat and muscle tissue and the body's normal functions are disrupted.
Ketosis can cause fatigue, constipation, nausea and vomiting. The potential long-term side-effects of ketosis include heart disease, bone loss and kidney damage.
In addition, the lack of calories will deprive your body of essential vitamins and minerals so hair, nails and skin will show signs of deterioration. Ironically, if you're using fasting as a means of detoxifying or cleansing the body, you will actually be achieving the opposite effect.
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