Docs: Be careful when it comes to celeb-endorsed diets

The new year means new goals, new resolutions, and new ways celebrities say they got skinny.

But medical experts warn against turning to TV and movie stars for words of weight loss wisdom. While they may appear gorgeous and glowing on the silver screen and magazine covers, they often aren’t qualified to dish out diet advice.

Take "the cleanse."

Gwyneth Paltrow, Beyonce and Salma Hayek have all raved about the benefits of washing your insides out. But some docs say beware.

“Cleansing is a good thing overall, but can be done badly,” Alan Christianson, NMD Author of The Complete Idiots Guide to Thyroid Disease, told FOX411’s Pop Tarts column. “Many cleanses are little more than stimulant laxatives such as senna or cascara sagrada. These only irritate the intestines.”

Some pros pooh pooh the whole concept of a “cleanse” or “detox.” Beverly Hills-based internal medicine specialist Peter Pressman, MD, told WebMD that the science behind the detox theory is deeply flawed, as the body already has multiple systems in place –like the liver, kidneys, and gastrointestinal tract, for example -- that do a perfectly good job of eliminating toxins from the body within hours of consumption.

Then there are pills.

Newly tiny reality star Snooki is attributing her recent weight loss to hard-core workouts and popping Zantrex-3 diet pills. But some experts are warning that caffeine-containing stimulants like Snooki’s go-to are not the way to go.

“Many different types of stimulants have been shown to have weight loss effects, but at what cost? Caffeine has multiple possible side effects including nervousness, [and] stomach issues like nausea and vomiting,” said Landa. “Caffeine may also increase blood pressure, heart rate and respiration.”

A rep for Zoller Laboratories, the U.S.-based company that formulates Zantrex-3, said that Snooki has been using their product in conjunction with a sensible diet and exercise program, and it works not just to reduce body weight, but body fat.

“A serving of Zantrex-3 Fat Burner (Snooki’s favorite) contains a significantly potent, but absolutely safe, xanthine mixture of about 200 mg,” the company's rep stated.

The “Jersey Shore” star's diet is another thing.

“For breakfast, just have a yogurt," she told WetPaint.com. "For lunch, if you can, just have like, a banana or an apple, and then for dinner, that’s when you can have a big meal of like chicken and rice and broccoli. Once you start doing that, I mean you’re gonna lose like 10 pounds right away. And exercising, just do a lot of cardio.”

But don’t fist-pump to that, warns one doctor.

“This type of diet will actually cause the breakdown of muscle. Since muscle weighs more than fat, one can lose weight quickly but on this diet you will lose muscle tone as well,” Dr. Jennifer Landa, Chief Medical Officer of BodyLogicMD, explained.  “This kind of dieting ultimately leads to more fat and flab, so you can lose pounds on the scale, but actually appear flabbier. This is what I call ‘skinny fat.’”

Supermodel Miranda Kerr, who practices yoga and eats only organic food, also swears by consuming a whopping four tablespoons of coconut oil per day for a flawless complexion. Those four tablespoons equate to 480 excess calories and 54 grams of fat.

“The deal with fat is that we actually need fat to burn fat and have great skin and a healthy metabolism. But she is pushing her fats out of balance going that high,” said co-star TLC’s "Freaky Eaters" and author of “Six Weeks to Sleeveless & Sexy,” JJ Virgin. “That is going a little overboard. Just one tablespoon of coconut milk or coconut oil is great.”

Adriana Lima’s secret to getting taut and tiny in a pinch for the Victoria’s Secret Fashion Show last year was a liquid diet in addition to double daily workouts, but it seems that won’t give us supermodel-esque bodies in the long-term.

“Liquid diets or diets that involve eating only meal replacements don't work because they aren’t realistic. The main thing to understand is that in the long run, diets don’t work,” explained Landa. “True lifestyle change is the only thing I have seen work and keep the weight off.”

The recently released 2011 review from Sense About Science also takes aim at a number of stars for spreading unfounded facts. The report debunked Simon Cowell’s apparent desire for a drip-fed intravenous cocktail of vitamins C, B12 and magnesium by stating that unless one has a “vitamin deficiency, what you eat in food will provide you with the vitamins you need,” and dismissed  Juliette Lewis’s reported claim that coconut water is “about the most hydrating thing you can drink,” by noting that it has “half the amount of carbohydrate but also a different balance of salts than a typical sports drink, and so could be less hydrating.”

So what’s the skinny? Dr. Landa has the last word: “Unless the celebrities are credentialed in the area, they should probably stick to their own area of expertise."