There’s a major smackdown going on between Al Roker, weatherman and presenter on NBC’s CMCSA, -0.70% ”The Today Show” and “The Biggest Loser” fitness trainer Jillian Michaels.

The subject: The fashionable ultra-low-carb “Keto” diet. Roker follows it, along with a host of other celebrities. Michaels says it’s bad news.

“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,” Roker tweeted.

“@alroker how about a civil intelligent debate on The 6 Keys book and keto instead of personal attacks and name calling?” Michaels retorted on Twitter TWTR, +2.03% .

The pair kicked off after Michaels ripped the Keto diet in an online video posted by “Good Housekeeping” magazine.

The Keto diet, which is an extreme version of the low-carbohydrate Atkins Diet, is the latest weight-loss craze among celebrities and their followers. It aims to trick the body into burning up your fat by starving it of carbohydrates.

Roker and Michaels aren’t the first to square off on the subject. The Keto diet, and similar regimens, have been the subject of intense scientific debate for a number of years.

“ A report last summer from the European Society of Cardiology concluded that those who follow the Keto diet are ‘at greater risk of premature death.’ ”

A “meta-analysis,” meaning a study of published medical trials, published a few years ago seemed to give the Keto diet the thumbs-up.

But an alarming report last summer from the European Society of Cardiology aimed to turn that on its head. Those who follow the Keto diet are “at greater risk of premature death,” it warned. “Low carbohydrate diets are unsafe and should be avoided.”

That study examined the relationship between low carbohydrate diets and deaths from a variety of diseases in a nationally representative sample of 24,825 U.S. individuals from 1999 to 2010. “The results were confirmed in a meta-analysis of seven prospective cohort studies with 447,506 participants,” it said.

So who’s right?

We spoke to the Harvard School of Public Health in Cambridge, Mass. to find out the truth.

The elevator summary?

Both sides have a point. But the balance probably tilts towards Michaels.

On the one hand, the Keto diet can work really well for some people short-term. And if you do it right you can eliminate most of the health risks.

But on the other hand, you can’t eliminate those risks entirely. And most people won’t do it right anyway, so it can end up being very unhealthy.

In other words, the Keto diet is probably overrated.

“When an individual adopts the Keto diet, they tend to emphasize saturated fats and animal proteins,” says Jeremy Furtado, a senior research science in nutrition at Harvard’s T.H. Chan School of Public Health. “And both of those, in study after study, have been associated with health risks, [including] cardiovascular disease and some cancers.”

“ The one thing that really works? Having a support network to keep you on track. Best of all are regular face-to-face meetings with a diet counselor. ” — —Jeremy Furtado, a senior research science in nutrition at Harvard’s T.H. Chan School of Public Health

That is, they treat the Keto diet as the cheeseburger diet. One problem lies in their carbohydrate replacements. “If individuals emphasized healthy fat and plant-based proteins, they wouldn’t see so many negative outcomes,” Furtado says.

Yet, ultimately the body needs carbohydrates, he says. Eating whole-grain carbs are especially important for the digestive tract. Harvard itself favors a balanced diet of carbs, fats and proteins that is heavy on plants and cuts out refined carbs and junk.

So both sides have a case. But in the short-term, at least, a healthy Keto diet can help you drop the pounds. “In the short term it can work,” Furtado says. “It is very successful for a lot of people.” It has clearly worked for Roker, and others.

But is it the best diet? A study almost a decade ago found little to choose between the success of low fat and low carbohydrate diets. The best diet is the one you stick to.

The one thing that really works? Having a support network to keep you on track. Best of all are regular face-to-face meetings with a diet counselor, say Furtado. “It’s more psychology than biology,” he says.