Those are fighting words!

Gwyneth Paltrow has been known to ruffle a few feathers in the past. From voluntarily getting stung by bees to failing her food stamp challenge, Paltrow is no stranger to criticism. Yet lately she's been on the receiving end of a little more flak than usual.

The 44-year-old actress is firing back at critics who are blasting the health advice on her website, Goop. She says, "If you want to f-ck with me, bring your A-game."

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Challenge accepted, says San Francisco-based OB/GYN Dr. Jen Gunther.

In a scathing May 22 blogpost, Gunther slammed the actress — calling her health advice "all around medical bullsh-t that you and your pals at Goop promote and sell."

"Ultimately, what people like Gwyneth Paltrow do is they lower the medical IQ," Dr. Gunther exclusively tells In Touch. "They have this disclaimer on Goop where none of this is advice, but that is not how it is presented."

Debunking some of the "crackpot theories" passed off as fact on Gwyn's site, Dr. Gunther tells In Touch the star "is selling fear."

Idiotic Claim No. 1: Tight Bras Cause Breast Cancer

"I've had patients read this on Goop and worry that they caused their own cancer," Dr. Gunther tells In Touch, adding that the theory "comes from somebody who is not a doctor or cancer researcher. But it was presented as fact."

The doc asks Gwyneth, "What do you possibly have to gain by spreading lies to women about bras causing breast cancer?"

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Idiotic Claim No. 2: Vegetables With Lectins, Like Tomatoes, Are Making Us Obese

"Obesity is caused by processed foods low in nutrition and high in calories," says Dr. Gunther. "But that won't get page clicks!"

Idiotic Claim No. 3: Beware of Latex Condoms, Which Contain Nitrosamines, a Carcinogen

"The only thing between [you] and HIV or gonorrhea is a few millimeters of latex, so glove that sh*t up," Dr. Gunther rages. "If you used a condom a week for 30 years, you would absorb only a minuscule amount of nitrosamines."

What has proven to cause cancer? Alcohol, notes Dr. Gunther, which is featured in Goop's many cocktail recipes.

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