Obesity finding turns diet advice on its head
Randy Shore, Vancouver Sun 12.04.2012
A UBC study using mice suggests when you eat — and when you don't eat — matters as much as the amount you eat
DOUG HANSEN / AFP/Getty Images
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Research from the University of B.C. and the Salk Institute in California throws doubt on the value of calorie counting and suggests that popular dietary advice to eat frequently through the day may promote obesity.
The studies suggest obesity may be as closely related to when we eat as it is to how much we eat.
UBC researchers, while studying the effect of insulin on pancreatic cells in mice, inadvertently discovered that normal mice fed a high-fat, high-calorie diet became obese, while mice bred to produce half the normal amount of insulin stayed lean.
Both groups ate the same food in the same amounts, according to the study published Tuesday in the journal Cell Metabolism, .
The rich diet caused normal mice to produce too much insulin, which triggers weight gain, liver disease and inflammation, the study found.
The low-insulin mice were protected from obesity and the ailments that accompany it because they spent more time in a low-insulin condition that mimics fasting, according to James Johnson, an associate professor of cellular and physiological sciences at UBC.
Each time we eat — every meal, every snack — the body produces insulin in response to rising blood sugar.
Johnson believes that extending the time between meals could help to return insulin to healthier levels for longer periods through the day, causing fat cells to burn energy rather than store it.
Eating between meals short-circuits that process, he said.
"We have constant access to very calorie-dense foods like soft drinks and 500-calorie lattes," said Johnson. "We can take in with just a few sips what our ancestors would consume in a whole day."
The body appears to need snack-free time to recover from high-calorie events, such as a typical North American meal.
"There is a growing body of literature that suggests anything you can do to let your [insulin-producing] beta cells rest and keep your insulin levels low for longer periods of time would be helpful," he said. "Of course, we have to have enough insulin to prevent diabetes, the key is not having too much."
Another study published earlier this year, also in Cell Metabolism, lends credence to Johnson's conclusions.
Scientists at the Salk Institute found that mice fed a high-fat, high-calorie diet for eight hours followed by a 16-hour fast maintained a normal weight.
A second group of mice that ate the same diet in the same amount, but spread over 24 hours, became obese and suffered from high cholesterol, high blood sugar and other obesity-related ailments. Without an extended break from feeding, the mice appeared unable to process all the fat, cholesterol and glucose they had consumed.
The mice on the high-fat, feed-and-fast regime also outperformed all the mice in the study on the exercise wheel, even the lean mice in a normal-diet control group.
"I think [the Salk] study is exactly the same result that we got," said Johnson. "I suspect the obesity they observed is due to the hypersecretion of insulin because the mice had constant access to food, snacked all the time and practically ate all through the night."
"That leads to insulin levels that are chronically high and promotes obesity," he said.
The feed-and-fast mice had more opportunity to maintain normal insulin levels for long periods of time, which promotes energy-burning rather than storage.
"The timing of food intake is critical," he said.
Johnson plans to observe obesity-resistant mice over several years to see if they age in a healthy way.
"We want to see if they live longer and we will look at their strength and their cognition in old age," he said.
rshore@vancouversun.com