By Dr. Brian McDonough

By Dr. Brian McDonough, Medical Editor

PHILADELPHIA (CBS) – Crash diets: they are a trend and they are popular but very few can deliver long term results.

Many crash diets prevent you from getting the nutrition your body needs. This is especially true of those that limit or avoid certain food groups.

Without proper nutrients, you can weaken your immune system, increasing the risk for illness. Losing weight quickly – can backfire. That’s because these diets are hard to follow. And people tend to gain back all the weight they’ve lost (or more).

Adding to the problem, weight loss naturally slows the metabolism because you need fewer calories to maintain your weight, making it harder to keep the weight off once you’ve lost it.