Knoxville (WVLT) Many celebrities promote weight loss pills and other products as a quick and easy way to lose weight.

And, as Americans' waistlines continue to expand, more people are turning to rapid weight loss diets.

Medical Reporter Jessa Goddard has more on what these can do to your body.

Diets have changed over the decades, from the grapefruit diet to South Beach.

The goal has not, to drop pounds, and fast.

But weight loss is a case in which slow and steady wins the race.

A very low calorie diet that's less than 1,000 calories a day may have you looking better, faster on the outside.

But what's happening inside your body?

First, your body goes into starvation mode and your metabolism slows to conserve energy.

Registered nurse Vicki Durham says, "we see people focus only on losing weight, not realizing that many behaviors need to be focused on in order tor them to improve their heart health."

Durham says certain tissues need carbohydrates for fuel.

When not available from the diet, the body gets its blood sugar by breaking down proteins, causing you to lose lean body mass.

During this time, only about half the weight you lose is fat, the other half is muscle and the result is a reduced metabolism.

If you're using diet pills or other products to achieve rapid weight loss, you may also be putting your heart at risk.

Durham continues, "most diet pills that are designed to help you lose weight actually increase your heart rate in some way. They're stimulants in some form."

You may also develop mineral and electrolyte imbalances while on a very low-calorie diet and that can be life threatening.

And you lose bone mass which is more risky for women, because they diet more often, and are also at higher risk for developing osteoporosis.

Finally, regaining weight is almost certain.

And the faster you lose, the more likely you are to re-gain.

"A lifelong weight management plan is more realistic, whether you're holding your weight the same or planning on trying to lose two to four pounds."

And remember, regaining weight can be damaging both physically and psychologically.

Because rapid weight-loss diets can be harmful to your health, you are encouraged not to start one without talking to your doctor first.