With studies showing that more than half of all adults are overweight and that exercise is at an all-time low, Americans are constantly searching for ways to slim down without drastically changing their lifestyles.

The low-carb diet created by Dr. Robert Atkins more than 20 years ago has become an attractive weight-loss solution for many Americans. But even with its popularity, many health experts insist the diet is unhealthy and the weight loss is temporary. Here are the most common problems doctors bring up:

1. Unbalanced Nutrition
They violate almost every known fact about nutritionally balanced eating. For some dieters, these diets can even be life-threatening.

2. High in Cholesterol & Saturated Fat
Popular high protein diet foods are high in cholesterol and saturated fat, which are now established as major culprits in heart attacks and strokes.

3. Loss of Calcium
They overload you with protein, which results in loss of calcium from your bones, which may lead to osteoporosis. Protein overload also pressurizes your kidneys as they try to eliminate large amounts of urea, a by-product of protein metabolism.

4. Heart Disease
They forbid foods known to lower the risk of heart disease and many cancers.

5. Loss of Energy
They deprive you of carbohydrates, the nutrient group most readily converted to energy. Even moderately active people will notice this lack during exercise.

6. Sluggish Feeling
They deprive your brain of glucose, which it needs for normal functioning. The result is a slowdown in thinking and reaction time.

7. Loss of Fiber
They deprive you of the enormous benefits of fiber, which is a form of carbohydrate (cellulose).

8. Lacks Essential Vitamins
They are deficient in essential vitamins. Indeed, some high protein diets even require you to take vitamin supplements for the sake of your health.

9. Body Chemistry Changes
They cause potentially dangerous changes in your body chemistry.

10. Increased Chances of Cancer
They run contrary to the latest World Cancer Research Fund Report, entitled
Food, Nutrition and the Prevention of Cancer.

11. Weight Loss is Often Temporary
They deliver temporary weight loss. But a large part of it is water weight and lean muscle mass - not fat. (You lose water because your kidneys try to get rid of the excess waste products of protein and fat, called ketones, that your body makes.) Note: Weight gain is usually rapid when you go off the diet.

12. Odd Calorie-Burning Metrics
Finally, it's worth knowing that while your body burns up 23 calories for every 100 carbohydrate calories it 'digests', it only burns up 3 calories for every 100 fat calories it 'digests'. So a high-protein, low carbohydrate diet makes it easier for you to stay fat!