LONDON -- For the past year, Stuart Adams has been fasting twice a week. While he has lost 15 pounds, the real reason he's depriving himself is to stave off brain disorders including schizophrenia and Alzheimer's disease.
"There's a virulent strain of madness running through my family, and I reckoned my chances of going down that route were pretty high," said Mr. Adams, 43, a freelance translator and interpreter in London who learned of a possible link between Alzheimer's and diet while watching a BBC documentary last year. "Anything that could help with that was of great interest."
Because there is no cure for Alzheimer's, which afflicts more than 35 million people, any possibility of prevention holds huge potential. Mr. Adams was inspired to try the diet last year after the BBC documentary called "Eat, Fast & Live Longer" cited a study in mice that suggested intermittent fasting could delay the onset of cognitive disorders.
The study was led by Mark Mattson, professor of neuroscience at Johns Hopkins University in Baltimore and senior investigator at the U.S. National Institute of Aging. Mr. Mattson is planning a new project to measure how fasting twice a week for two months affects human brain function and early signs of Alzheimer's.
While this and other similar diets are gaining in popularity even as they spawn a steady outpouring of new books on the subject, some experts have doubts.
"This is part of a never-ending carousel of diet books," said Kelly Brownell, former director of the Rudd Center for Food Policy and Obesity at Yale University and now dean of the Sanford School of Public Policy at Duke University. "There will be some buzz and then the diet will go away, never to be heard of again."
Nonetheless, the studies and the books keep coming. Another examination into the fasting-dementia link will be led by Krista Varady, an associate professor of kinesiology and nutrition at the University of Illinois at Chicago. Her research focuses on alternating a normal diet with eating 500 or 600 calories every other day. Nutritionists recommend men consume about 2,500 calories a day and women 2,000 calories.
While research on fasting diets and dementia still has a long way to go, the early evidence is promising. The mouse study led by Mr. Mattson found that intermittent fasting may have protected the function of brain cells, even if it didn't reduce levels of the plaque and tangles that are typical signs of Alzheimer's.
At the same time, fasting is increasingly seen as playing a role in the prevention of other diseases including breast cancer and diabetes. That's paved the way for a flurry of how-to books including Ms. Varady's "The Every-Other-Day Diet," which goes on sale Dec. 24. Competing with that is "The Fast Diet" by science journalist Michael Mosley, who was behind the BBC documentary Mr. Adams watched, and lifestyle writer Mimi Spencer. Their regimen is known as the 5:2 diet.
There's also "The 2-Day Diet" by dietitian Michelle Harvie and Tony Howell, a professor of oncology at the University of Manchester in England. Their approach was developed specifically to help prevent breast cancer, for which obesity is a known risk factor.
Health experts say fasting diets can't substitute for eating healthy foods.
"In general, intermittent fasting is a good thing if it's done properly," said Dean Ornish, a professor of medicine at the University of California at San Francisco and a physician consultant to former President Bill Clinton. "But if you're already eating very healthily, then you may not need to do that."
In a study conducted with Mr. Mattson and published this year, they found the two-day diet led to greater drops in body fat and insulin resistance in women with high breast-cancer risk after three months, compared with a diet where calories are cut every day, suggesting that intermittent fasting is an easier approach to follow.
The bottom line, though, is that any fasting diet needs to be undertaken thoughtfully, including eating healthy foods on non-fasting days, Ms. Harvie said.