The ketogenic diet is all the rage these days, with an array of celebrities embracing the high-protein, low-carb diet that encourages eating plenty of animal fat while staying away from grains.

However, fitness guru Jillian Michaels says she’s no fan of the wildly popular diet, and expressed her views in no uncertain terms in a new video for Women’s Health magazine.

“I don’t understand,” says the former trainer on “The Biggest Loser”. “Like, why would anyone think this is a good idea?”

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Speaking in the voice of the diet’s creator, she adds, “’You know what we need to do? All fat and animal protein!’ No! Bad plan. For a million reasons.”

As Michaels, 44, explains, the diet may promote weight loss, but will also leave the body seriously deprived of the nutrients it needs to thrive.

“Your cells, your macro molecules, are literally made up of protein, fat, carbohydrates, nucleic acids. When you do not eat one of the three macro nutrients — those three things I just mentioned — you’re starving yourselves,” she says. “Those macro nutrients serve a very important purpose for your overall health and well being. Each and every one of them.”

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Instead, Michaels recommends a more common-sense approach, and urges people to embrace a diet that’s well-balanced and healthy.

“You don’t eat processed sugar, you don’t eat processed grains, and to make a very long story short: avoid the keto diet,” she says. “Common sense. Balanced diet is key.”

However, Michaels took some heat from a pair of celebrity keto fans, with “NBC” weather reporter Al Roker offering an uncharacteristically savage response, calling her out for “bullying, deprivation, manipulation and more” during her “Biggest Loser” days.

Also unimpressed was “Watch What Happens Live” host Andy Cohen, who dubbed Michaels the “Jackhole of the Day” for her keto comments, reports Women’s Health.

“Don’t feel bad, keto diet,” quipped Cohen on his show — although Michaels was quick to point out that Cohen also called Roker’s “Today” co-host “dumb” back in September when she revealed she was on the keto diet.

Michaels then offered a response to Roker, taking to Facebook to share her thoughts in a video. Telling Roker that she respects him “very much,” Michaels adds, “the personal attacks are bizarre. It’s unnecessary, it’s uncalled for, it’s beneath both of us.” Watch: