By Sally Squires
Tuesday, June 5, 2007
Why some people struggle more than others to shed pounds is a mystery that perplexes scientists and frustrates dieters, who are often blamed for lack of willpower.
But a new report shows that biology may be at work and suggests that eating according to something called the glycemic index, or GI, may be a way for some people to overcome this disadvantage.
First a little background: The GI ranks food not by its nutrients, but by how much it raises blood sugar after being eaten. Highly processed carbohydrates -- sugar and white bread, for example -- are considered the benchmark against which other foods are measured. Foods that raise blood sugar rapidly, like these , are considered high-GI foods. Those that raise blood sugar less are ranked as low- or medium-GI foods.
This idea has been popularized in recent years by a number of diet books, from the best-selling "Sugar Busters" series, written by a group of New Orleans doctors, to "The New Glucose Revolution" by University of Sydney researchers.
Here's how it works: Eat lower-GI foods to help keep blood sugar steadier and hunger pangs at a minimum, since fluctuating sugar levels stoke appetite. Scores of books and Web sites give details about the glycemic index of individual foods.
Trouble is, few people eat meals consisting of only one food. So scientists have developed another measure: the glycemic load -- a system that describes the quality and quantity of carbohydrates in a meal or a diet. "It's a hard concept to understand," says David Heber, director of the UCLA Center for Human Nutrition, who has written about it in his latest book, "The L.A. Shape Diet."
Whether taking the glycemic index or load into account is beneficial when eating is still under debate. In recent years, studies have pointed to benefits of low-GI foods not only for controlling blood sugar and body weight but also for reducing levels of unhealthy blood triglycerides and boosting beneficial fat, high-density lipoprotein. (HDL).
Most recently, researchers at Children's Hospital Boston compared the weight-loss benefits of a low-GI diet with a traditional low-fat approach in 73 overweight adults, ages 18 to 35. All participants received the same nutrition and exercise counseling, and all were advised "to eat when you are hungry, before you become famished. Stop eating when you are satisfied, before you become stuffed."
Both approaches produced the same small weight loss -- an average of about five pounds over 18 months, far less than what most dieters dream of. Both diets were equally liked by participants.
But when the researchers analyzed the results further, they discovered a subgroup of super losers, who shed five times more weight than other participants and maintained that loss throughout the study.
What separated the super losers from the rest? How quickly their bodies produced the hormone insulin after eating.
Slow insulin producers lost the same small amount of weight on both diets. Fast insulin producers did even more poorly on the low-fat diet, which included processed carbohydrates. But the fast producers who followed the low-GI diet became super losers when they dined on complex carbohydrates such as fruit, vegetables and whole grains and slightly higher amounts of healthy fat.
The findings could help explain "why some people do very well on a weight-loss diet and others do very poorly on the very same regimen," notes David Ludwig, director of the Optimal Weight for Life program at Boston Children's and senior author of the report, published last month in the Journal of the American Medical Association. "The usual answer is motivation and compliance -- that people just don't stick to their diets. But our findings show that biology determines why some people do well on one weight-loss diet and not on another."
The results may prompt a closer look at taking glycemic index into account, especially for dieters who have not had good results with the traditional low-fat approach. But there's no need to obsess over GI numbers, since low-glycemic fare includes a long list of familiar healthful foods. Low-glycemic foods include the smart choices from whole fruit (rather than fruit juice and dried fruit, which are usually higher in sugar), vegetables, beans, nuts and whole grains. Most dairy products have a low glycemic index. But skip yogurt with added sugar or sweetened fruit. Lean cuts of meat, poultry and fish have a low glycemic load. So do eggs.
High-glycemic foods are generally highly processed, with minimal amounts of fiber and often lots of sugar. Popular snack foods such as frosted cupcakes or bagels with nonfat cream cheese are all high on the GI scale. So are pretzels and graham crackers.
Making just a few adjustments can significantly alter the GI of a snack. So have half a pretzel and add some peanut butter. Or have a glass of milk with a graham cracker.
When in doubt, there's the water test, recommended by Ludwig, author of "Ending the Food Fight: Guide Your Child to a Healthy Weight in a Fast Food/Fake World." Just drop a little bit of a food in a glass of water. If it dissolves quickly, it's got a high glycemic index. If it dissolves slowly, it's likely lower on the glycemic index.
But just because a food has a low GI doesn't mean it's healthy. "Steak and creme brulee both have a low glycemic load," Heber notes. "But they are loaded with fat and calories. You can gain weight on anything if you eat enough of it. It doesn't matter what it is."
Which is why Ludwig recommends hedging your bets by eating a diet moderately low in fat and low on the glycemic index. ·