Joe Rogan said he is eating only meat and fruit for the next month. His last 'carnivore diet' led to weight loss and diarrhea.

• The UFC commentator and podcaster Joe Rogan said he would eat only meat and fruit for a month.

• He's said the "carnivore" diet helped him lose weight and have more energy. It also caused diarrhea.

• Dietitians don't recommend the diet because it lacks nutrients like fiber.

The podcaster Joe Rogan said he was giving up vegetables, bread, and just about every other food group to kick off the new year.

Rogan said on Instagram last week that he was embarking on a so-called carnivore diet in January (after a final indulgence of pasta for dinner).

"Just meat and fruit for the whole month," he wrote.

It's not clear what his regular meals consist of, though his Instagram suggests ribeye for breakfast is one staple.

Rogan has tried the diet before — he said he lost weight but had severe digestive issues, too. Dietitians don't recommend it because a lack of nutrients can cause side effects like digestive upset.

Rogan's previous meat-only diet led to weight loss, increased energy, and diarrhea

In January 2020, the podcaster said he'd spent 30 days eating nothing but animal products, during which he lost 12 pounds and experienced more energy and relief from some health issues.

He said on Instagram that "lots of aches and pains went away" and that he'd seen "improvements in my vitiligo," a chronic skin condition.

There was, however, a major side effect: Rogan said he had frequent and explosive poops, which he described in graphic detail to his followers.

"I haven't shit my pants yet, but I've come to accept that if I keep going with this diet it's just a matter of time before we lose a battle," he posted on January 11, 2020, with a picture of his dinner of liver and bacon.

The gastrointestinal issues lasted about two weeks, Rogan wrote later.

At the time, Rogan's Instagram suggested a typical day of eating on the carnivore diet involved two meals. Breakfast included six eggs or a steak, and for dinner he would eat another steak, either beef or elk, and occasionally other types of wild game such as bison.

Meat-only diets lack fiber, which can cause side effects like digestive upset

Diarrhea may be a common side effect of cutting veggies, grains, and other plant foods out of your diet. While meat contains important nutrients, it's devoid of fiber, a type of carbohydrate that is slow to digest.

Research suggests fiber can reduce the risk of illnesses like heart disease and aid in healthy digestion.

Many plant foods are also rich in other nutrients, including vitamins, minerals, and antioxidants — and missing them in your diet may cause health issues.

The carnivore diet has been popular for years, but dietitians don't recommend it

That January is known to some, like Rogan, as World Carnivore Month and to others as Veganuary highlights a persistent conflict between meat eaters and vegans about which diet is best.

The diet has been popularized by advocates like Dr. Shawn Baker, an orthopedic surgeon and the CEO of Revero.

"We're trying to simplify. Rather than adding supplements, superfoods, this is the opposite approach, removing irritants," Baker previously told Insider. "It's very simple to follow. No other animal on the planet sits there with a diet manual or a calculator."

The carnivore diet is also compatible with popular keto and paleo diets.

Other carnivore dieters have shared anecdotal stories of weight loss and mental clarity, using hashtags like #MeatHeals, on Twitter and Instagram.

But while Baker is working on research to study the health effects of a carnivore diet, there's no evidence to back up any claims about its benefits.

Dietitians caution against carnivore diets because of potential side effects. Carbs are an important energy source, and eliminating them almost entirely can lead to muscle breakdown and fatigue, experts say. Some carnivore diets include carbs in the form of honey or fruit (which also includes fiber).

Eating red meat has also been linked to a higher risk of heart disease and cancer — though the risks of eating unprocessed red meats might be lower than the risks of regularly eating processed meats. In contrast, diets rich in plants have been linked to a lower risk of illness.

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