Blood test may tell whether low carbs or low fat best for you

One diet doesn't fit all
Blood test may tell whether low carbs or low fat best for you
May 16, 2007
Megan Ogilvie
Health Reporter
Lentil soup or low-fat muffin? A simple blood test could soon
determine which one will help you lose weight.

Researchers at Boston Children's Hospital have found that the amount
of insulin a person produces can predict which one of two diets will
work best for their body.

The study, published yesterday in the Journal of the American Medical
Association, found people who make a lot of insulin lose more weight
on diets low in simple carbohydrates, called low-glycemic load diets,
than on low-fat diets.

The study's lead co-author says the finding partly explains why some
people can lose weight on a conventional low-fat diet, while others
can't.

"You often hear that people aren't motivated or don't have the
willpower (to lose weight) while others who succeed stick with it,"
said Cara Ebbeling, co-director of obesity research at Boston
Children's. "From our perspective, that didn't offer a complete
answer ... so we sought to determine whether biology could offer
another explanation."

To test their theory, the researchers randomly assigned 74 obese young
adults to either a low-fat diet (55 per cent carbohydrate and 20 per
cent fat) or a low-glycemic load diet (40 per cent carbohydrate and 35
per cent fat).

Before starting the diet, participants took a standard glucose
tolerance test, which can be done by a family physician, to determine
whether they produced high or low amounts of insulin.

Insulin is a hormone secreted by the pancreas that helps the body turn
glucose into energy. Eating simple carbohydrates, such as white breads
and sweets, causes insulin levels to spike, which then tells the body
to quickly store the carbohydrates as energy.

Ebbeling says consuming a lot of simple carbohydrates can create a
cycle of overeating thatcan lead to weight gain. That's why the
researchers tested the weight-loss effect of a low-glycemic load diet
that relies on complex carbohydrates, such as fruits, vegetables,
legumes and minimally processed grains.

People who secreted high amounts of insulin and were on the low-
glycemic diet lost an average of 2.2 pounds per month for the first
six months, while those on the low-fat diet lost 0.9 pounds per month.
At the end of the 18-month trial, the same high-insulin secretors on
the low-glycemic diet lost an average total of 12.8 pounds, about 10
pounds more than those on the low-fat diet. "That tells us, not only
did those on the low-glycemic diet lose more weight, they were more
successful at keeping it off," says Ebbeling.

There were no differences in weight-loss between the two diets for
people who produced low amounts of insulin. But all participants on a
low-glycemic diet, regardless of insulin secretion levels, had better
HDL, or good, cholesterol levels at the end of the study. Thomas
Wolever, professor of nutrition at the University of Toronto and an
expert on glycemic response, says the study adds more evidence to the
theory that one diet does not fit all. Wolever said researchers
already knew a low-glycemic diet helps raise good cholesterol levels.

He also cautions against relying on the test to find the right diet
because weight loss is much more complicated than just dieting alone.
Society, he says, needs to change to help people make healthier eating
and exercise choices.

Diva