21 Pounds in 21 Days: Is Steve Harvey's Liquid Diet Unhealthy?

Actor Samuel L. Jackson (L) and Steve Harvey attend the BLUE Scholarship Gala to benefit Spelman College at The Plaza Hotel on October 4, 2010 in New York City. (Photo by Andrew H. Walker/Getty Images)
Andrew H. Walker/Getty Images)
Steve Harvey (right) attending a recent charity event in New York City. (Photo by Andrew H. Walker/Getty Images)

(CBS) Chubby comedian Steve Harvey is halfway through a 21-day liquid "detox" diet, and he says he feels great. Today he tweeted, "Day 11 on the Martha's Vineyard detox I have not chewed food in 11 days that sounds crazy but I feel great and I know I am healthy."

Harvey, 53, the host of "Family Feud" and a syndicated radio show, is following the diet plan outlined in the best-seller "Lose 21 Pounds in 21 Days." The diet is also called the Martha's Vineyard Diet Detox.

Harvey may feel healthy, but nutritionists frown on crash dieting.

The liquid-only diet calls for people to consume only juices and vegetable broths. Protein and enzyme supplements are encouraged, as are coffee enemas, according to the book's website.

But diets like this provide only temporary results, experts say.

"When you go back to eating regular food, having slowed down your metabolism, you'll just gain the weight back," Christine Avanati, the author of "Skinny Chicks Don't Eat Salads," told the New York Daily News.

Not only that, but diets that don't include solid food don't provide the feeling of fullness, so they are hard to stick to, says dietitian Anne Fletcher, the author of "Thin for Life."

"So then the deprivation factor enters into it," she told the newspaper. "How long can you stick with something that deprives you of so much?"