Method actors tend to go to extreme lengths to get inside the minds of the characters they portray. For Ashton Kutcher, that meant adopting Steve Jobs's fruitarian diet for one month, a regimen based solely on, well, fruit. He's portraying the late Apple CEO in jOBS, a biopic set to hit theaters in April.

All that fruit—must be healthy, right?

Not exactly. "I ended up in the hospital two days before we started shooting the movie," Kutcher told reporters at the Sundance Film Festival. "I was doubled over in pain, and my pancreas levels were completely out of whack, which was terrifying, considering everything." Jobs died in October 2011, after a long battle with pancreatic cancer. His fascination with fruitarianism helped inspire his company's name.

Motivation for adopting the diet varies, but followers are typically swayed by health, religious, environmental, and political factors. Many tout fruitarianism as the original diet of mankind, and believe it encourages simple living and a holistic approach to health. Those who latch on are often propelled by a desire not to kill anything, including plants. The regimen comes with a rich history: Leonardo da Vinci was a fruitarian, and Mahatma Gandhi followed the plan for six months in the early 1900s.

So what's the problem with loading up on apples and bananas? For starters, it's extremely restrictive. Although there's no one fruitarian diet, most followers make sure at least 75 percent of their daily intake comes from raw fruit. Often, they snub anything that was picked, opting only for fruit that fell naturally. Though some fruitarians are more flexible than others, the diet typically revolves around the seven basic fruit groups. These include: acid fruits (citrus, pineapples, cranberries); subacid fruits (sweet cherries, raspberries, figs); sweet fruits (bananas, melons, and grapes); nuts (hazelnuts, pistachios, cashews); seeds (sunflower, squash, pumpkin); oily fruits (avocados, coconuts, olives); and dried fruits (dates, prunes, raisins).

It's perhaps counterintuitive to consider that there's such a thing as too much fruit. Indeed, it's a healthy food packed with vitamins and antioxidants. But "it can't supply many of the building blocks needed to maintain the structure of your organ tissue, muscles, bones, immune cells, and hormones," says registered dietitian Cynthia Sass, author of S.A.S.S. Yourself Slim: Conquer Cravings, Drop Pounds and Lose Inches.

We each need protein, fat, and carbohydrates to keep our bodies functioning properly, and fruit only provides carbs. In addition to supplying too few calories, the fruitarian diet likely won't provide adequate levels of vitamin B-12, calcium, vitamin D, zinc, iodine, and omega-3 fatty acids—which can "lead to a form of starvation and serious health risks," Sass says.

It's unclear exactly why Kutcher's fruitarian diet went awry; details about his case are scarce, and the actor is no longer following the plan. Some experts speculate that the regimen was too taxing on his organs. "Our pancreas secretes insulin when carbohydrates are consumed," says registered dietitian Keri Gans, author of The Small Change Diet. "If all he was doing was eating fruit, he may have been overworking it."

In general, research on the fruitarian diet is lacking, and what little does exist dates back 40 years or so. Most stories of benefits come from the followers themselves. Michael Arnstein, founder of the Woodstock Fruit Festival in Diamond Point, N.Y., for example, has been all-fruit for about five years now. "I've become nearly super-human," he says. "I've evolved into an elite marathon runner, and I recently ran 100 miles in 12 hours and 57 minutes. I also haven't had a cold or a cough during that time."

Fruit does offer plenty of benefits, so there's no need to give up your favorite berries or melons. Research suggests that fruit may reduce the risk of cancer and other chronic diseases, and it's also a good source of fiber and naturally filling. The key is moderation. Stick to two cups or two pieces of fruit each day, says registered dietitian Dawn Jackson Blatner, author of The Flexitarian Diet.

Meanwhile, the Woodstock Fruit Festival—a weeklong event in August—has extended an open invite to Kutcher. "As far as I know, from my extensive experience in the fruitarian community, no one has died or come down with an illness related to a fruit diet,"Arnstein says. "We'd really like Ashton to consider coming." The festival, which is in its third year, has seen significant growth, and more than 700 fruitarians are expected to attend this year.