New research suggests if you don't eat from dinner until breakfast, you'll be less likely to gain weight. • But is that advice really new? • According to researchers at the Salk Institute in La Jolla, Calif., mice fed a high-fat diet for only eight hours a day remained lean, while another group that had access to the same food 24/7 became obese, even though both groups consumed about the same number of calories.
On top of that, the obese mice developed high cholesterol, high blood sugar, a fatty liver and other metabolic problems, while the mice forced to fast 16 hours a day showed virtually no sign of such problems.
Why such a big difference in outcome between two groups eating the same amount of food?
Lead author Satchidananda Panda says the body's internal clock determines when the liver, intestines, muscles and other organs work at peak efficiency. During those periods the organs are primed and ready to deal with the processing of food, but when mice — and possibly humans — eat frequently all day long, they force their organs to deal with food when they're not operating at peak efficiency. For example, measures of digestive hormones, cholesterol and glucose in the fasting mice showed that their liver enzymes had a chance each day to break down cholesterol into bile acids.
"The focus has been on what people eat," Panda said in a statement announcing the results, which appeared in the journal Cell Metabolism. "We don't collect data on when people eat."
The mouse study, he believes, shows that when people eat matters as much as what they eat.
But didn't Oprah adopt the practice of overnight fasting years ago? Her diet and nutrition guru Bob Greene advised her to stop eating by 7 p.m. each day, and not eat again until breakfast, and she credited that with helping her to lose weight.
"It's common sense," said Greene, whose most recent book, 20 Years Younger, was just published.
"I didn't structure this way of eating based on scientific evidence, but we know that your digestion pretty much ends when you reach a certain stage of sleep. I structured my own eating so I wouldn't have much food in my stomach overnight and found that I felt better, and my weight-loss results were better. It's nice to see research supporting that."
Many nutritionists, however, say that overnight fasting only helps control weight because it causes people to eat less.
"A few years ago I had one dietitian come after me," Greene said. "She said, 'It doesn't matter when you eat calories,' and she's right in that an apple has the same number of calories in the evening as in the morning, but the body handles those calories differently."
Of course, both opinions could be true. Throughout most of human history, calories were scarce and snacking was difficult, especially during the darkness of night. Now, however, faced with a cornucopia of rich, inexpensive food available 24 hours a day, eating at night while watching TV has become an honored pastime that provides excess calories when your body is least prepared to digest them.
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"You're more likely to burn off the calories you consume early in the day because you raise your metabolic rate when you eat in the morning," Greene said. "At night, not so much."
Tom Valeo writes frequently about health matters. He can be reached at firstname.lastname@example.org.