During crash dieting (about <1000-1200 calories for women and <1600-1800 for men depending on body size) scales show that weight is being lost. However, in truth, body fat hasn’t decreased much and instead healthy muscle is lost. Furthermore, since about 1/3 of body weight is water, often much of the weight lost during crash diets is water, this is especially true for low carbohydrate diets. Once the body gets re-hydrated with water, the weight will come right back.
1. CRASH DIETS SLOW METABOLISM
Your metabolic rate slows down, which means that you require less calories/ day. This means that weight loss slows down or stops. For weight loss to continue, you need to create a bigger calorie deficit, which means you’ve got to reduce your calories further, creating a vicious circle. Your body catches on, has started conserving energy and you hit a weight loss plateau.
2. WEIGHT LOSS DOES NOT LAST
95% of conventional dieters and crash dieters are unable to maintain weight loss. Some even experience additional weight gain. Possibly one of the worst effects of metabolic slowdown is that once you stop the diet and start to eat what used to be your normal daily maintenance level of calories, you may gain the weight you lost right back and some people put on even more. Since your metabolism has slowed down you require fewer calories than before you started the diet. This means that when you eat a normally you gain weight.
3. CRASH DIETS CAN INCREASE BODY FAT PERCENTAGE
The weight gained back after crash dieting is fat. However, the weight lost during the crash diet was unlikely to have been 100% fat. This means that even if you have only put back on the same amount of weight you lost, you may still be worse off, because you have a greater amount of fat than what you started off with.
4. CRASH DIETS CAUSE MUSCLE LOSS
Research suggests that the body loses a disproportionately high amount of muscle during very low calorie intake and that this may suppress metabolism by up to 45 percent.