Even though adults need about 2,000 calories a day to maintain their weight, reducing normal calorie intake by 30 percent produces longer lives and better health in every species studied.
"CRONies" — people who practice Calorie Restriction with Optimal Nutrition — may not live significantly longer, but they display striking reductions in blood pressure, cholesterol, blood sugar and other risk factors for heart disease and cancer. The diet also seems to protect the brain from degeneration.
Calorie restriction, however, requires more willpower than most people can muster, so a simpler method known as alternate day has been attracting legions of followers. Men restrict themselves to 600 calories on "fast" days (women get only 500), and then eat whatever they want on "feed" days. Some fast only two days a week, and eat normally the other five. Either way they lose weight and reduce their risk factors for disease.
Mark Mattson, head of the neuroscience laboratory at the National Institute on Aging, has found that rodents subjected to this type of periodic fasting need less insulin to regulate blood sugar, suffer fewer strokes and appear to be resistant to the damage that accumulates in brain cells with age. The diet appears to improve autophagy — the ability of cells to dispose of their own garbage — and repair DNA, he said. It also appears to boost levels of brain-derived neurotrophic factor, or BDNF, a protective protein that declines in Alzheimer's, depression and other brain disorders. Among other benefits, BDNF increases the number of energy-producing mitochondria in brain cells.
"Exercise increases the number of mitochondria in muscle cells," Mattson said. "We're finding that similar things occur in nerve cells in brain."
Without food, the body uses up the energy stored in the liver in 10 to 12 hours. After that the body starts burning fat — a process that produces ketone bodies, which also protect brain cells.
And intermittent fasting, despite periodic hunger pangs, is easy, according to Mattson, who has practiced it for years. "In the studies we've done, people who do it for two or three weeks find it easier than counting calories," he said. "You can make it through today if you know you can eat normally tomorrow."
Intermittent fasting received a huge boost in August 2012 when the BBC broadcast Eat, Fast and Live Longer with host, Michael Mosley, author of The Fast Diet: Lose Weight, Stay Healthy, and Live Longer with the Simple Secret of Intermittent Fasting (see inset). Mosley, who has a family history of diabetes and cancer, reduced his risk factors dramatically in just a few weeks fasting two days a week. (Watch the broadcast at vimeo.com/54089463.)
The day after the program aired, Krista Varady, who was interviewed by Mosley about her research on alternate-day fasting in humans, found 800 emails awaiting her when she arrived at her laboratory at the University of Illinois in Chicago, most requesting more information about alternate-day fasting.
The interest in the regimen was so intense it inspired her to write her own book, The Every Other Day Diet, subtitled The Diet That Lets You Eat All You Want (Half the Time) and Keep the Weight Off.
She said Mosley's plan to fast two days a week will slow weight loss, and may reduce health benefits somewhat. Also, her subjects who fast every other day tend to experience a reduction in appetite that prevents them from overeating on "feed" days. "They don't binge," she said. "They eat only slightly more than usual, but if you fast only two days a week your fast days could be separated by four days, so people may not experience the same appetite suppression."
Varady is conducting a year-long study in which overweight and obese participants will practice alternate-day fasting for six months, and then increase their calorie consumption to 1,000 calories on fast days to see if they can maintain the weight loss.
"So far, we've found people regain only a pound or so," she said. "They are able to sustain reductions in their blood pressure, cholesterol and glucose."
Also, since about 90 percent of the weight lost by people who practice alternate-day fasting is fat, they retain more muscle mass, which burns calories. (The weight lost by traditional dieters tends to consist of 75 percent fat and 25 percent muscle.)
"If you don't lose as much muscle mass you're more likely to keep the weight off," Varady said. "Alternate-day fasting will help you lose weight and keep the weight off, too."
Tom Valeo writes on health matters. Email him at firstname.lastname@example.org.