Losing more than a pound or two a week is not healthy. Fast weight loss is bad for two main reasons.
Lose weight fast and you will lose muscle
Firstly, if you lose weight quickly you lose muscle along with fat. This is bad when it comes to weight loss.
Muscle burns more calories than fat. The more muscle you have the more calories you burn and this applies to when you're not doing anything strenuous. Losing muscle is therefore not a good idea.
Lose weight fast and you slow your metabolism
Secondly, if you lose weight too quickly your body will slow down your metabolism.
When we skip meals or crash diet, our body is programmed to think it's starving and slows down our metabolism to conserve energy.
What is conserved is our fat stores; our weight loss comes from water and muscle.
A Graphic example
For example, studies show that when dieting, the weight we lose is approximately 75 percent fat and 25 percent muscle.
In addition, a relatively high percentage of this weight loss is likely to be water.
Keep in mind, water accounts for about 70 percent of the total body weight of an average person, with muscle tissue containing approximately 75 percent water and body fat containing about 50 percent water.
Losing weight quickly is therefore very difficult as we are simply losing water in the sort term.
The dangers of crash dieting
Crash dieting refers is a method in which we lose weight simply by restricting the number of calories consumed.
This method of losing weight fast is considered unhealthy, and it is rare that people who do it keep weight off.
They cannot adjust to these new unhealthy eating habits and then put the weight straight back on.
Your goal should be long term weight loss
Consider this, if you only lost a pound a week that would be 52 pounds a year and that is a lot of weight.
If you lose weight slowly you will remain healthy and also stand a good chance of keeping it off.
The maximum amount of body fat a healthy person can lose is about 1 or 2 pounds per week.
The human body is simply not designed to lose weight quickly and this is a healthy amount of weight loss to aim for.
Reasons why losing weight fast is difficult and unhealthy
Our bodies are programmed to help us survive in times of starvation.
Our basic body reactions have been set since man first walked the earth and in those days food was not just a phone call, or short walk away.
In times gone by, famine was the biggest threat to mans survival and your body is programmed to protect you.
This is why it won't ever lose excessive amounts of fat in a short period of time; your body is programmed to conserve fat.
If you drastically reduce your calorie intake, you slow down your metabolism, in order to conserve calories, as we discussed earlier.
This is one reason why we encounter a weight loss quickly is, so difficult as your body actively fights to conserve weight, it's a survival reflex.
Side Effects of Losing Weight quickly
In addition losing weight quickly has serious side affects that can harm us
Appearance of Loose Skin
If you shed weight too quickly, your skin does not have time to shrink to your new body dimensions.
The only effective treatment for this is to fix the lose skin with surgery.
Gallstones
Studies have shown that people who lose weight quickly, have a greater risk of developing gallstones.
Lack of energy and illness
Depending on the diet there are a host of other complications including lack of energy and nausea for those who cut out carbs and a general feeling of ill health and lack of energy as you deprive your body of food.
Lose weight slowly
Don't be taken in by quick fix weight loss, its not possible aim for longer term weight loss.
You will lose weight, keep it off and feel both healthier and happier.

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