Drew Barrymore said she eats mycoprotein to stay healthy on her flexitarian diet. Here's what to know about fungus protein.

• Drew Barrymore said she eats a mostly plant-based flexitarian diet, including fungus-based protein.
• Called mycoprotein, it's a popular meat substitute in foods like chicken nuggets and meatballs.

Drew Barrymore said she follows a mostly plant-based flexitarian diet, and swaps out regular chicken nuggets with a plant-based meat substitute called mycoprotein, she told Woman's World.

The main principle of the flexitarian diet is following a mostly vegetarian eating style, with room for occasional animal products, according to dietitians.

"I don't think I'm rigid about anything," Barrymore said.

The actress has partnered with the brand Quorn, and said that she and her family are "obsessed with the company's meatless chicken nuggets.

"I've never had anything like Quorn. I feel like chicken has been brought back into my life," she told Woman's World.

Amid the increased popularity of plant-based protein options, mycoprotein is gaining attention as a nutritious, sustainable substitute for meat, although rare allergic reactions have been linked to products containing it.

Mycoprotein can be healthy for most people, depending on cooking style and allergies

Mycoprotein is made from fungus, and has a fibrous texture that helps imitate chicken or beef. It's a low fat protein source, with 11 grams of protein in each 85 calorie servings. It's also a more complete protein than many plant based options, with a hefty dose of essential amino acids, protein building blocks needed for health.

Mycoprotein is also rich in vitamins as well as fiber, an important nutrient for hunger management, healthy digestion, and stable blood sugar.

Research also indicates that the fungus, fermented in tanks, has a significantly lower environmental impact than meat, since livestock farming takes up land and water resources and produces greenhouse gas emissions.

While mycoprotein is widely considered to be safe, it can provoke allergic reactions in very rare cases, about one per nine million packages, according to one study. A 2018 review of self-reported adverse reactions found a small number of people experienced nausea or gastrointestinal symptoms after eating mycoprotein, and two people had fatal allergic reactions reportedly linked to the fungus.

While mycoprotein isn't risky for most people, the healthfulness depends on how it's prepared — highly processed foods may still have health risks, including high sodium and oil content, even if they are plant-based, experts previously told Insider.