Running On Empty: The Pros and Cons of Fasting
Fasting restricts calories and may benefit your body. Is it a safe way to lose weight?
February 02, 2009
Los Angeles Times
Something about the way Americans eat isn't working -- and hasn't been for a long time.
The number of obese Americans is now greater than the number who are merely overweight, according to government figures released last month. It's as if once we taste food, we can't stop until we've gorged ourselves.
Taking that inclination into account, some people are adopting an unusual solution to overeating. Rather than battling temptation in grocery stores, restaurants and their own kitchens, they simply don't eat. At least not at certain times of the day or specific days of the week.
Called intermittent fasting, this rather stark approach to weight control appears to be supported by science, not to mention various religious and cultural practices around the globe. The practice is a way to become more circumspect about food, its adherents say. But it also seems to yield the benefits of calorie restriction, which may ultimately reduce the risk of some diseases and even extend life. Some fasters, in fact, ultimately switch from regular, if comparatively rare, periods of hunger to permanent deprivation. They limit calories all the time.
"There is something kind of magical about starvation," says Dr. Marc Hellerstein, a professor of endocrinology, metabolism and nutrition at UC Berkeley, who studies fasting.
Adds Mark P. Mattson, chief of the laboratory of neurosciences at the National Institute on Aging: "In normal health subjects, moderate fasting -- maybe one day a week or cutting back on calories a couple of days a week -- will have health benefits for most anybody." Mattson is among the leading researchers on the effects of calorie restriction and the brain.
Not all nutrition professionals see the merits of fasting. Some think of it as a recipe for disaster, setting up a person for binge eating and metabolic confusion.
Ruth Frechman, a registered dietitian in Burbank and spokeswoman for the American Dietetic Assn., says she frequently sees such extreme strategies backfire. "You're hungry, fatigued, irritable. Fasting is not very comfortable. People try to cut back one day and the next day they're starving and they overeat."
Researchers who study fasting and caloric restriction, however, say the body's hunger cycle ultimately adjusts.
And from a biological standpoint, they say, fasting can be helpful whether someone is overweight or normal weight.
"We're brilliant at this," Hellerstein says, referring to humans' physical reaction to not eating. "We're not good at responding to too many calories, but we're very good at responding to fasting. Fasting, in itself, is not an unhealthy process."
Benefits to body
During fasting, almost every system in the body is "turned down," Hellerstein says. The body changes how it uses fuel. Certain hormone levels fall. Growth stops. Reproduction becomes impossible.
"By the end of three weeks of fasting you are a completely different metabolic creature," he says.
"It affects many, many processes -- but in a somewhat predictable way that takes you toward disease prevention."
Put simply, intermittent fasting appears to offer the same advantages as long-term calorie restriction -- defined as eating at regular times but consuming 25% to 30% fewer calories than what is recommended for that person based on age, size and gender (see accompanying article). People who eat this way tend to do so by filling up on nutrient-dense but low-calorie foods. They get all the protein, fiber, vitamins and minerals the body absolutely needs -- and very little else.
With intermittent fasting, "the idea is that maybe you can trick the system to think it's starving, but not make it starve every day," Hellerstein says.
Researchers aren't sure why the body apparently benefits from a state of mini-starvation. One theory is that the process produces just enough stress in cells to be good. "What our evidence suggests is that nerve cells in animals that are on dietary energy restriction are under mild stress," Mattson says. "It's a mild stress that stimulates the production of proteins that protect the neurons against more severe stress."
What they do know is that occasionally going without food or reducing calories daily makes the body more sensitive to insulin, which helps maintain normal blood sugar levels. And animal studies suggest calorie restriction may reduce the risk of cancer by slowing the growth of abnormal cells.
"We've been finding that putting an animal on a reduced-calorie diet for a couple of weeks dramatically slows cell proliferation rates," Hellerstein says. "This is the case in pretty much every tissue you look at: prostate, skin, colon, liver, lymphocytes."
Intermittent fasting and calorie restriction have also been shown in animals to reduce cognitive decline in diseases such as Alzheimer's disease and Parkinson's disease, Mattson says.
Little research yet
Researchers caution that not many studies have examined humans who are practicing intermittent fasting or caloric restriction. But the little evidence that exists is favorable.
A study published last week in the Proceedings of the National Academy of Sciences found that reducing calories 30% per day increased the memory function of elderly men and women. The study was performed at the Salk Institute in La Jolla.
University of Utah scientists looked at health data from members of the Church of Jesus Christ of Latter-day Saints, who have lower rates of heart disease than most Americans. Mormons typically don't smoke or drink alcohol, and some abstain from food on the first Sunday of every month. After controlling for several factors that protect against heart disease, the researchers found that only fasting made a significant difference in lowering the risk of heart disease. Among 448 people surveyed, intermittent fasting was associated with more than a 40% reduction in heart disease risk. Fasting was also linked to a lower incidence of diabetes. The study was published in October in the American Journal of Cardiology.
Another study showed that asthma patients who fasted had fewer symptoms, better airway function and a decrease in the markers of inflammation in the blood than those who didn't fast or restrict calories. The study was conducted because being overweight is known to worsen asthma symptoms. The study was published in 2007 in the journal Free Radical Biology & Medicine.
"They complied with the diet pretty well," Mattson says. "If people know that tomorrow they can eat whatever they want, today they can eat less."
The National Institutes of Health is now supporting calorie-restriction research at three medical centers. At one study site, Washington University in St. Louis, Dr. Luigi Fontana is following the largest group to date of people who practice caloric restriction or intermittent fasting. So far his research shows that such people are not malnourished and have excellent cardiovascular health.
"Eating less is important because 65% of the American population is overweight," Fontana says. "But another question is: If you are already lean, should you change your diet to improve your health and possibly extend your life span?"
That ultimately may be the strongest selling point of a reduced-calorie lifestyle.
"It does demand more than some other diets," says Joseph Cordell, a St. Louis lawyer who limits his intake to 1,800 to 1,900 calories a day.
"But surely the payoff is dramatically better than anything else. I feel so much better and have more energy. And there is this prospect of living so much longer than you otherwise would."