Jewish World Review March 6, 2003 / 2 Adar II, 5763

HEALTH SENSE: Good carbs, bad carbs

By Judy Foreman | If you haven't heard of it yet, get ready to grapple with the "glycemic index,'' the latest wrinkle in America's endless diet debate. On the surface, the glycemic index is a simple concept -- a way to measure how much blood sugar rises two hours after eating carbohydrates. Carbohydrates with a high glycemic rating, like cake with icing, trigger huge, rapid spikes in blood sugar, followed by steep spikes in insulin, the hormone that escorts sugar into cells. Carbohydrates with low glycemic ratings, like whole grains and fresh fruits and vegetables, trigger more modest, slower rises.

The basic idea is that high-glycemic carbohydrates are bad because they leave the stomach quickly and trigger the rapid rise in blood sugar and insulin, which is soon followed by a crash in blood sugar that prompts renewed hunger. The result can be more calories consumed and more weight gained.

Using the index in real life is dicey. For instance, carrots have a high glycemic rating, but they're good for you. French-fried potatoes could be interpreted as having a better (lower) rating than a naked baked potato because they contain fat, which causes slower emptying of the stomach and, hence, a more modest rise in blood sugar and insulin, according to Karen Chalmers, a registered dietitian and director of nutrition services at the Joslin Diabetes Center in Boston.

But what is important about the glycemic index is its symbolic value as a reminder to ever-fatter, ever-more-confused consumers that carbohydrates, the big "no-no'' of current fad diets, are not a monolithic entity. There are "good'' carbs -- found in whole grains, fruits and vegetables -- and "bad'' ones, found in highly refined baked goods, candy and many processed foods, said Dr. Walter Willett, chairman of the department of nutrition at the Harvard School of Public Health.

In the last several years, Dr. David Ludwig, director of the obesity program at Children's Hospital in Boston, and others have published studies suggesting that obese people put on low-glycemic diets lose more weight than those on reduced-fat diets.

In one such study, Ludwig gave some obese youngsters high-glycemic-index meals and others low-glycemic ones. The number of calories given to both groups was the same. But the children on the high-glycemic diet ate almost twice as much as the others when allowed free access to food. Obviously, more snacks mean more calories and more weight gain.

That said, there are limits to the logic behind the glycemic index. It is incorrect to infer, as some do, that sugar is "addictive.'' Nor is it correct, as some diet gurus say, that carbohydrates turn into body fat more easily than does fat. It's fat that's most efficiently converted into body fat; that is, it takes the fewest calories for the conversion. Carbohydrate is the next most efficient, then protein.

More important, a calorie is still a calorie is still a calorie. No matter what combination of protein, fat, and carbohydrate you eat, if you take in more calories than you burn, you'll get fat.

And getting fat triggers a dangerous cascade of biochemical events. Excess body weight causes the pancreas to work overtime to produce enough insulin, a phenomenon called insulin resistance, noted Dr. Edward Horton, director of clinical research at the Joslin Diabetes Center in Boston.

Insulin resistance, in turn, is associated with a whole cluster of metabolic problems, including elevated triglycerides (fats), low HDL ("good'' cholesterol), high blood pressure, changes in blood clotting patterns and a build-up of plaque in artery walls. High insulin can also raise the level of PAI-1, or plasminogen activator inhibitor, which prevents the breakdown of potentially dangerous clots.

Insulin resistance is also associated with high levels of C-reactive protein, a marker for heart disease. Eating too many calories -- from any source, protein, fat or carbohydrate -- can lead to obesity. But part of the problem today -- two-thirds of Americans are overweight and one-third of these are obese -- is that for years we were all told to cut down on fats.

There's still some truth in this message; saturated fats and trans-fats (like those found in some margarines) are dangerous because they boost cholesterol and the risk of heart disease.

Some fats, though, are good, notably the monounsaturated and polyunsaturated fats found in olive, canola or peanut oils; nuts; other plant products; and fish. These fats can lower the bad kind of cholesterol (LDL) without lowering the good (HDL).

The lesson that most of us have absorbed over the years, however, was not this mixed message, but a starker one: All fat is bad. That, not surprisingly, prompted consumer demand for "low-fat'' foods, and the food industry responded, with a vengeance. In recent years, "the food industry has screwed around with fat-free foods to keep the taste up,'' said Dr. David Heber, director of the Center for Human Nutrition at the University of California at Los Angeles. "They lowered the fat content but raised the sugar,'' he said, noting that many processed foods are now loaded with high-fructose corn syrup, in part because "corn is subsidized by the federal government.'' Indeed, one reason for the current obesity epidemic is all the high-fructose -corn syrup added to processed foods.

So where does this leave us, besides fat and frustrated? It's pretty straightforward, actually. Don't take the glycemic index too literally. It's too complicated, and you could spend hours trying to calculate the glycemic rating for each food on your plate.

But do use the concept as a valid, potent way of remembering that not all carbohydrates are created equal. After all, lumping all carbohydrates together as a diet rationale has clearly not worked to help people lose weight.

Bottom line? Stick to whole grains and fresh fruits and vegetables, and avoid refined carbohydrates as much as you can. Chances are, you'll be less hungry and much healthier.

Judy Foreman is a lecturer at Harvard Medical School. Comment by clicking here.


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