Fad vs. Fat: Popular diets

Being overweight has been shown to take a considerable toll on our health, from upping our risk of heart disease to diabetes to some forms of cancer. So you'd think it would be wise to lose weight any way you can. But losing weight on an unsafe diet plan or repeatedly losing and gaining weight, as can happen as a result of fad dieting, can also cause health problems.

The vicious cycle of losing and gaining weight is often referred to as yo-yo dieting. While some people may tell you yo-yo dieting can make it harder to lose weight the next time around, a number of studies have shown that to be a myth. But that doesn't mean yo-yo dieting is good for you.

One study that was published in the Journal of the American Dietetic Association suggests that yo-yo dieting may weaken the immune system. The study, which measured immunity by testing the activity of natural killer cells - which fight off viruses such as the common cold, viral pneumonia, herpes, and more - found that postmenopausal women who had ever intentionally lost at least 10 lbs. had weaker immune systems. And the more times the participants had lost 10 or more pounds, the greater the effect. Women who lost weight and kept it off, however, seemed to have stronger immune systems.

There is also some evidence that yo-yo dieting may increase your risk of developing high blood pressure and gallstones. But while many experts say the risks associated with yo-yo dieting shouldn't stop you from trying to lose weight if you are overweight, they do underscore the importance of finding a weight-loss plan that will help you not only lose the fat, but keep it off as well.

And yo-yo dieting aside, fad diets can have other negative effects on your health. For example, many fad diets are effective for quick, short-term weight loss because they require a very low-calorie diet, which has been linked to gallstones in obese patients.

Cutting out particular foods or severely cutting calories may also limit the vitamins, nutrients, and minerals you get from dietary sources, causing a nutritional deficiency. Even if you are losing weight on a more reliable diet plan, you should talk to your doctor, pharmacist or a registered dietitian about whether you need any vitamin supplements.