significantly overeat on the "feed days" the rest of the week, they will lose
weight in a steady fashion, he says. Mosley didn't find himself overeating on
the feed days.
So what about feeling hungry? "I've gotten used to it. Hunger is one of those things that generally passes," Mosley says.
Some people worry that intermittent fasting will make them unable to focus, he says. "What I've discovered is that it sharpens my senses and my brain."
Before he started intermittent fasting, Mosley, who is 5-foot-11, weighed 187 pounds and had a body mass index of 26, which put him into the overweight category. His waist was 36 inches; his neck, 17. His fasting blood glucose (a measure of diabetes risk) was too high, along with his cholesterol.
After two months on his program, he weighed 168 pounds, a loss of 19 pounds. He had a body mass index of 24, and his waist was 33 inches. His neck size was 16. His cholesterol, blood glucose and other factors fell to the normal range.
"I didn't want to lose any more because my wife, who is a doctor, said I was looking gaunt. These days, I fast one day a week, and often skip lunch on the other days."
One scientist who studies fasting takes exception to the way some of her work was used in the book. "My research on alternate-day fasting has been misrepresented," says Krista Varady, an assistant professor of nutrition at the University of Illinois-Chicago. "He is using my research, which looks at fasting three to four days a week, to support his diet, which encourages fasting two days a week."
But Mosley says he was partly inspired to try the 5:2 approach after reading research done by Michelle Harvie, a dietitian in England who wrote The 2-Day Diet.
U.S. obesity experts say Mosley's plan may work for some, but many questions remain.
"I am aware of only one randomized, controlled trial that compared conventional daily calorie restriction with the 5:2 diet plan," says Samuel Klein, director of the Center for Human Nutrition at the Washington University School of Medicine in St. Louis. "In that six-month trial, weight loss and most health benefits from weight loss were the same in both groups.
"Additional and longer-term studies are needed to fully evaluate the effectiveness of the 5:2 diet approach and to determine which people might be more compliant with intermittent fasting than conventional daily calorie restriction," he says.
Klein says the real question is this: "Is it easier for people to starve two days a week than to reduce their calorie intake every day?"
"We do not know whether intermittent fasting has independent health benefits beyond weight loss alone," he says. "In rodents, alternate-day fasting has metabolic health benefits without a change in body weight." However, alternative-day fasting in people causes weight loss, so it's difficult to separate the benefits of intermittent fasting from those of the weight loss itself, he says.
Tim Church, director of preventive medicine research at the Pennington Biomedical Research Center in Baton Rouge, says, "We know that one diet doesn't fit all. This style of caloric control may work for some people, but we need more research to test the proposed mechanisms and benefits."
The bigger question is whether people can stick with a fasting diet, given the amount of time and energy it takes, he says.
The research into fasting
To learn about the science behind fasting, Mosley interviewed several researchers, including ones with the National Institute on Aging and at several major universities. Much of the research on fasting has been done on rats and mice, but there have been 11 human trials on it, Mosley says.
Some of the medical benefits of fasting involve the hormone insulin-like growth factor 1, called IGF-1, Mosley says. People need adequate levels when they are young and growing, but high levels later in life appear to lead to accelerated aging and cancer, including breast cancer and prostate cancer, he says. Fasting appears to reduce the levels of IGF-1, and it appears to switch on a number of repair genes. The reason it happens is not fully understood, he says.
Marji McCullough, a nutrition epidemiologist with the American Cancer Society, says, "Higher levels of IGF-1 have been linked to several cancers, including breast, prostate and colorectal cancer. Whether reducing IGF-1 levels will lower cancer risk is plausible but not proven."
Mosley believes fasting has "undone" some of the damage he has done to his body over the years and hopes that it will help him live longer and healthier.
He recommends seeing your doctor before starting a fasting program. He says fasting is not recommended for people who are pregnant, those who are underweight or have diabetes (especially type 1), and children and teens who are not fully grown. And he wouldn't recommend it to people who have issues with food, although "there is no evidence it will trigger anorexia or bulimia," Mosley says.
Not everyone is going to get the results they want, he says. "Some people find that they don't lose weight as fast as they thought. That's probably from overeating the other five days. It's not magic."
Drastically cut calories for two days, then eat normally for five, says Michael Mosley.
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