• Fitness expert and life coach Jillian Michaels criticized the popular keto diet in a video for Women's Health magazine.
  • Today host Al Roker, who has been on the diet since September, called Jillian out on Twitter about her stint on the weight-loss show The Biggest Loser.
  • Jillian apparently responded to Al in an email, however the host didn't disclose what she said and stands by his perspective of the diet.
  • Many nutritionists aren't fans of the keto diet due to its extreme nature.

Jillian Michaels recently told Women's Health how she really feels about the keto diet (which advocates eating more fats and proteins in place of carbs to induce a metabolic process called ketosis). And let's just say Al Roker, who is all about keto, was not having it.

The fitness trainer blatantly told the publication that the keto diet is "a bad plan" and that she "can't understand why anyone would want to do it." What's more, she also recently listed out all the reasons she "hates" the keto diet to Prevention, which included arguments like:

Apparently, Jillian's point of view did not sit well with the Today anchor. To his fans, this isn't too surprising – after all, Al frequently shares his own keto recipes on his social media accounts. But his Twitter response was, in a word, YIKES.

"So @JillianMichaels says #Keto is a bad idea. 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," the weatherman tweeted.

Al is referring to Jillian's stint on The Biggest Loser, a weight-loss show where Jillian was known for her no nonsense approach to losing weight.

On Twitter, many of Al's fans defended him, sharing their own personal stories about how keto helped them lose weight. Not surprisingly, there were also a lot of people siding with Jillian.

Today revealed that Jillian responded to Al's comments in an email, although he wouldn't discuss what she said. He did however, continue to show his support for the diet.

"I've been checking blood work and vitals every month, and my cholesterol has gotten better,'' he said. "It was good to begin with. My blood pressure is great."

So, who's right: Al or Jillian?

It's really not that simple. While there's no one-answer-fits-all when it comes to the contentious diet plan, Jaclyn London, MS, RD, CDN, of the Good Housekeeping Institute says there's one reason she wouldn't recommend keto.

"Any diet that's as extreme as keto — to the point where it's often implemented under the supervision of an entire medical team — won't translate into everyday life," she states. "And when it backfires (as it always does), the shame and feelings of inadequacy hit us even harder when we've put so much darn work into it."

London does state though, that eating habits are personal and that if you want to lose weight, you should follow a plan that works best for you.

"That said, it's still crucial that you look into whether or not you're meeting all of your nutrient needs in food form in order to remain healthy over time," she says. "The fact that there's not much research on the overall sustainability of ketogenic diets is what prevents many nutritionists from recommending it universally."

Wherever you stand on the keto debate, there's one indisputable fact that everyone should agree on: It's best to consult with your doctor before trying any weight-loss plan (and if you're taking meds for diabetes management, it's essential to talk to your endocrinologist before trying keto).