If saturated fat doesn't adversely affect cardiovascular health, what does? Sorry, Nabisco: We should be giving a closer look to foods with a high glycemic index—a measure that reflects a food's influence on blood sugar levels, based on how quickly it is digested and absorbed. Typically, that means carbohydrates like cereal, bread, chips, and cookies.
In a 2000 study in the AmericanJournal of Clinical Nutrition,Harvard researchers compared the food intakes of 75,521 women with their health over the course of a decade and found that the quintile of women who ate food with the highest glycemic load—a measure that incorporates portion size—had twice the risk of developing heart disease than the quintile who ate food with the lowest glycemic load. A 2008 meta-analysis of 37 studies reported a significant association between intake of high glycemic index foods and increased risk of type 2 diabetes, heart disease, gallbladder disease, and breast cancer. Some studies suggest, however, that the bad effects of high-G.I. foods can be tempered by pairing them with low-G.I. foods. For instance, a piece of white bread smeared with peanut butter may be healthier than a piece of white bread alone.
The link between carbohydrates and heart disease is also supported by LDL particle data. In a 2008 study published in Nutrition Research, researchers reported that subjects who followed high-fat, low-carb diets for eight weeks experienced a 46 percent drop in blood concentrations of small LDL particles, while those who followed a high-carb, low-fat diet experienced a 36 percent spike in them. What's more, processed carbohydrates lower "good" HDL cholesterol, whereas saturated fat increases it.
Just as different fats affect the body in dissimilar ways, it seems that sugars are not all created equal. Though fructose actually has a lower glycemic index, it may be a bit less healthy than glucose, a sugar with the same chemical formula but a different structure. (Sucrose, or table sugar, is 50 percent glucose and 50 percent fructose; high-fructose corn syrup is typically 55 percent fructose and 45 percent glucose.) Research published by Peter Havel, a professor of nutrition at the University of California-Davis, suggests that compared with glucose, fructose incites less of an insulin response, which ultimately results in lower circulating levels of the appetite-suppressing hormone leptin and higher levels of the appetite-boosting hormone ghrelin—so fructose may make you hungrier.
It could also put you at greater risk of heart disease and diabetes. When overweight people supplemented their diets with drinks sweetened either with fructose or with glucose for 10 weeks, fructose drinkers ended up with higher concentrations of small LDL particles in their blood after they ate. They also experienced, on average, a 20 percent drop in insulin sensitivity—low insulin sensitivity is a risk factor for type 2 diabetes—over the course of the experiment compared with the glucose drinkers. (Havel believes that the glycemic index is ultimately flawed and that a "fructose index" might be a better nutrition metric.)
In any case, it seems that processed carbohydrates are America's most deserving nutritional enemy. And our misguided war against fat has just made us more addicted to them, because when people cut out fat, they typically turn to "diet" foods high in carbs—SnackWells, Baked Lays, even low-fat Jif, which contains the same number of calories as the regular version, with less peanut butter and more "corn syrup solids." That's not to say that all carbs are bad; fiber is a carbohydrate, and an important one. And there is still a lot left to be desired about certain fats. Trans fats really are bad for you, and foods very high in omega-6 polyunsaturated fats—such as corn oil and margarine—are not particularly healthy, either. But overall, Americans could stand to start replacing carbs with fat. More bacon, fewer Bacos.
Will this new research on fat and carbs will be reflected in the 2010 Dietary Guidelines? According to Meir Stampfer, a Harvard professor of nutrition and epidemiology who worked on the 2000 guidelines, scientists on this year's committee know perfectly well what the evidence says. But few researchers want to shake the status quo or risk confusing the public. Robert Post, deputy director of the U.S. Department of Agriculture Center for Nutrition Policy and Promotion, admits that when it comes to nutritional recommendations, "simple messages, few messages, targeted messages, are very important." Ultimately, then, policymakers have to choose between keeping the message consistent and actually getting it right.