Release Date: January 6, 2004
BUFFALO, N.Y. -- The demonizing of carbohydrates and concern over their potential role in disease has reached a fever pitch, generating mass-media claims and counterclaims for one diet approach or another.
The idea that all carbohydrates are "bad" concerns Christine L. Pelkman, Ph.D., assistant professor of nutrition in the School of Public Health and Health Professions at the University at Buffalo and a specialist in clinical nutrition and metabolism.
Pelkman analyzes the carbohydrate conundrum in a paper published in the December issue of Current Topics in Nutraceutical Research.
"A couple of decades ago we all were worried about fats, and all fats were 'bad,'" said Pelkman. "But now we know that there are different kinds of fatty acids, and that not all fats are 'bad.' In fact, some are 'good.' Now, in this decade, thinking that all carbohydrates are 'bad' will lead us down the wrong path again.
"We need to understand this macronutrient better and be more sophisticated in our analysis," she said. "Carbohydrates can't be stratified merely by structure, as simple or complex, and we shouldn't think of foods high in carbohydrates as 'bad' and those low in carbohydrates as 'good.' The importance of carbohydrates lies in what happens in the body after they are eaten."
In her article, Pelkman specifically addresses the concept of the glycemic index, a measure of how quickly the carbohydrates in a food will turn to sugar in the body, and examines the evidence supporting its role in disease prevention. The glycemic index concept has grown in popularity recently in both scientific circles and the general population, she noted.
A major point of her review is that basing a diet on a food's glycemic index can result in faulty and irrational choices.
"For example, any food with a glycemic index of 70 or above, is considered 'high.' However, carrots have a glycemic index of 131, almost as high as pure glucose and much higher than white bread. Watermelon has a glycemic index of 72, placing it in the high category."
A more telling number, she noted, may be a food's glycemic load: a measure of how quickly and strongly its carbohydrate content increases blood sugar and insulin levels. Both carrots and watermelon have a very low glycemic load, 10 and 6 respectively, and are far more nutritious than many foods with a lower glycemic index, noted Pelkman. Glycemic load takes both type and amount of carbohydrates into consideration, making it a better measure when examining foods in the context of healthy diets, she said.
What happens to a food containing carbohydrates in the body is determined not only by its glycemic index and glycemic load, however. Factors that affect the body's glycemic response to a food (the amount of glucose and insulin produced) also include the type of carbohydrate; the mix of carbohydrates in a food; cooking and processing methods; amount of fat, protein and fiber; presence of micronutrients such as flavinoids and trace minerals; the food's acidity, and an individual's genetic makeup.
All of these components make pinpointing the dietary and health effects of carbohydrates a daunting challenge, Pelkman said.
"There is no one recommendation that fits all," she said "We shouldn't promote a low glycemic index diet to the general public without exception, although it is reasonable to adopt a diet with a little less carbohydrate, as low as 40 percent.
"How many carbohydrates and of what type you should consume depends on the individual health profile and the desired end result," she said. "If a person has elevated blood sugar and diabetes in their personal history, they may want to limit their diet to foods with a low glycemic index. But they still need foods with micronutrients.
"On the other hand, high glycemia (high levels of sugar in the blood stream) may not always be bad, in athletes and growing children, for example. And maybe a constant low-glycemic-index diet will turn out to be damaging in the long term. These are things we are just beginning to understand, and much more research is needed.
"We always come back to the issue of balance in one's diet," Pelkman said. "No nutrient is always 'bad' or always 'good.'"