Bad news for dieters fat fights back: Ottawa researchers find fat cells are resistant to death

Sharon Kirkey
The Ottawa Citizen

Thursday, September 16, 2004

Canadian researchers have discovered the sheer act of dieting appears to sabotage a person's plan to slim down.

In other words, when fat is under attack, it fights right back.

Scientists at the Ottawa Hospital Research Institute examined human pre-fat cells removed from subcutaneous fat below the bellybutton of 10 volunteers before and after weight loss.

The team discovered that, following weight loss, the pre-fat cells were more resistant to cell death and produced higher amounts of a protein that normally sends flat, pre-fat cells down the road to becoming round and full of fat.

The finding, published in the current issue of the journal, Obesity Research, opens the door to finding specific diets, exercise regimens or drugs to stop this process of fat cell maturation.

More immediately, it could help explain why success rates for long-term weight loss are so dismal.

"Many people in the field wonder about what may go on in these people who have successfully lost weight initially, but just can't maintain it," says Dr. Alexander Sorisky, a senior scientist at the Ottawa research institute and one of Canada's leading obesity researchers.

U.S. studies suggest that up to half of all adults are on a diet at any given time. But only five to 10 per cent of people who lose weight manage to keep the pounds off five years later, Dr. Sorisky says.

Many get caught in a chronic cycle of weight loss and weigh gain. "Yo-yo" dieting has been linked to everything from weakened immune systems to heart problems in post-menopausal women.

Some people just stop exercising or fall off their diets. But several body systems also conspire to get people back to their original, heftier weights, Dr. Sorisky says.

One theory is the "set-point concept", whereby the body slows down metabolism, stimulates appetite and invokes "all kinds of changes to try and get the weight to go back up," Dr. Sorisky explains.

It may be a defence mechanism against starvation that developed long ago, when food was scarce -- one that hasn't adapted to our "modern obese-ogenic environment," he says.

As well, the human body contains millions of pre-fat cells, or pre-adipocytes, that are ready to burst into mature fat cells with the right trigger.

"We thought one of the things that might be happening is these pre-fat cells become more trigger happy to become fat cells in the period after weight loss," Dr. Sorisky said.

The Ottawa scientist collaborated with Dr. Robert Dent, director of the Ottawa Hospital's weight management clinic and plastic surgeon Dr. Murray Allen, also of the Ottawa Hospital.

The researchers isolated pre-fat cells from the abdominal tissue of 10 dieters and looked at specific proteins before and after weight loss.

They found an increase in two proteins post-weight loss, one for survival and another the body normally uses to allow pre-fat cells to become full-blown adipose, or fat, tissue.

The team has not yet proven the pre-fat cells erupt into fat cells following weight loss. "But our hunch is they are better able to hang around longer to become fat cells, they're more resistant to cell death and they have higher levels of a protein that normally help these cells become fat cells," Dr. Sorisky says.

If further and bigger experiments prove the hunch right, it could be possible to use variations in diets or certain forms of exercise that alter metabolism, or combine diet and exercise with drugs to keep pre-fat cells at bay, he says.

The story also appeared in the National Post, Times Colonist, Vancouver Sun, Edmonton Journal, Calgary Herald, Windsor Star and the Montreal Gazette.

copyright The Ottawa Citizen

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