As many of us learned this January, when we tried to get back in shape for our New Year's resolutions, there are endless debates about which workout plans, methods, and diets work best.

But those fights don't usually turn into nasty public feuds involving celebrities.

A recent spat, all about the popular but controversial keto diet, is continuing to heat up as more and more stars take sides. At the heart of the debate are two unlikely opponents: Today show weatherman Al Roker, and celebrity fitness trainer Jillian Michaels.

The tizzy began when Michaels called out the medical diet, which she claims is unhealthy. The keto diet is best explained as a high-fat, low-carb diet plan, and is normally prescribed to help treat epileptic seizures in children, not for weight loss.

"I don't understand," Michaels told Women's Health about the fad, "why would anyone think this is a good idea?" She went on to call the diet a "bad plan, for a million reasons."

The trainer, who is known for appearing on the weight loss reality show The Biggest Loser, warned that following a keto diet could lead to nutritional deficiencies.

"To make a very long story short: avoid the keto diet," she said. "Common sense."

But plenty of the diet's celebrity devotees took offence to Michaels' interview, and said they're living proof that the keto works.

Watch What Happens Live host Andy Cohen joked, "Don't feel bad, keto diet. A lot of people think Jillian Michaels is a bad idea."

Al Roker, who often shares keto recipes and tips with the Today audience, had an even harsher response for the reality star.

"So @JillianMichaels says #Keto is a bad idea," he tweeted. "This from a woman who promoted on camera bullying , deprivation, manipulation and more weekly in the name of weight loss. Now those sound like bad ideas."

Roker was referencing the sometimes harsh ways Michaels' show, The Biggest Loser, encouraged competitors to lose a huge amount of weight in just a few weeks, something the show was routinely criticized for.

After offering Roker the chance to debate the merits of keto versus her own diet plan, the Six Keys, Michaels fired back at the weatherman in a video message.

"If you want to debate the personal sciences of keto, by all means let's do that," she said. "But the personal attacks are bizarre. It's unnecessary. It's uncalled for. It's beneath both of us."

Michaels cleared the air about the feud with TMZ on Tuesday, saying that her celebrity critics weren't behaving "like adults."

"We don't need to name call, we don't need to have personal attacks," she said. "If we're going to have a debate about keto, let's have a debate about keto. But of course, when I invited them to do that, both ran away with their tail between their legs."

While Roker may not be interested in a debate, he stated his case about the keto diet on Today after his spat with Michaels went viral.

"My point is, what works for you, works for you," he told his co-hosts.

"I think it's up to people, with their doctors, with their medical professional (to make their own decision)."

Roker added that his cholesterol and blood pressure levels have both improved since he embraced the diet.

For the record, Michaels isn't the only person warning that the keto plan poses health risks. Harvard Medical School also says that following the diet plan could cause liver and kidney problems, constipation, and mood swings.

As they wrote, "it's not the type of diet to try as an experiment."

[H/T: USA Today, Fox News]

What do you think of the feud? Have you tried the keto diet yourself?