Good Carbs, Bad Carbs
To paraphrase the band, Led Zeppelin, "Good carbs, bad carbs, you know I've had my share…." Well, in another case of life imitating art, according to a new study published in the Archives of Internal Medicine, women who ate the most "high-glycemic" carbohydrates -- the carbs that cause quick spikes in the level of blood sugar -- had more than twice the risk of heart disease compared to women who ate the least high-glycemic carbs. Plus, among women who followed a low-glycemic diet, those with type-2 diabetes were better able to control their blood sugar levels and rely less on medications than those who ate high-glycemic carbohydrates like white bread and potatoes.
The study followed 47,749 Italian adults -- 15,171 men and 32,578 women. Based on their responses to dietary questionnaires, the researchers calculated their overall carbohydrate intakes as well as the average glycemic index of the foods they consumed and the glycemic loads of their diets.
According to study leader Sabina Sieri of Fondazione IRCCS Istituto Nazionale dei Tumori, in Milan, Italy, "High consumption of carbohydrates from high-glycemic foods, rather than overall quantity of carbohydrate consumed, appears to influence the risk of developing heart disease in women." In other words, not the quantity of carbs but the type seems to be the differentiating factor. The risk is not caused by "a diet high in carbohydrates, but by a diet rich in rapidly absorbed carbohydrates," says Sieri.
As a result of years spent studying the potential for various carbohydrates to raise blood sugar, researchers developed the glycemic index (GI) to quantify the impact of assorted food items. The glycemic index rates carbohydrates based on how quickly they convert to pure glucose in the body, using a scale of 0 to 100. Pure glucose ranks at 100 and high-glycemic foods typically come in at 70 or above. Medium GI foods rate scores between 56 and 69, while low GI foods score 55 and under. The high-glycemic foods associated with heart disease in the study include the usual suspects -- cake, white bread, candy -- but there are some surprises, too. For instance, from the glycemic index standpoint, it's hard to do worse than a baked potato, which has a glycemic index of 85. And while you might think that you should eliminate pasta and turn to brown rice, you'd be dead wrong n terms of GI. It turns out that a two-ounce serving of cooked pasta, which has a glycemic index of 42, elevates blood sugar less than a serving of brown rice, which has a glycemic index of 55 -- keeping in mind that both still score as low glycemic foods.
According to Glycemicindex.com, "Choosing low GI carbs -- the ones that produce only small fluctuations in our blood glucose and insulin levels -- is the secret to long-term health, reducing your risk of heart disease and diabetes, and is the key to sustainable weight loss." The reason this is so is that the rapid increase of blood sugar and the associated rapid release of the hormone insulin damages cells throughout the body, which leads to heart disease, diabetes, and other ills.
As for the results of the new study, there are a couple of wrinkles to consider. First, eating high GI foods does not seem to increase the risk of heart disease in men. According to the study authors, high GI carbs raise the levels of blood glucose and of harmful blood fats known as triglycerides while reducing levels of protective HDL or "good" cholesterol, for both men and women. But only in women did that increase the risk of heart disease. The study authors theorized that adverse changes associated with carbohydrate intake, including triglyceride levels, are stronger risk factors for heart disease in women than in men.
The other wrinkle is that the Glycemic index may not be the best way to understand how carbs affect blood sugar levels. That's why researchers at Harvard came up with a little ditty they call "glycemic load." GI is based on how fast 50 grams -- 1.765 ounces -- of the food in question raises blood sugar levels. Glycemic load "takes into account both the amount of carbohydrate in the food and the impact of that carbohydrate on blood sugar levels." Watermelon is a good example. It has a very high GI (72), but because it contains so little carbohydrate per serving, its glycemic load is quite low (8). From this point of view, brown rice returns to the table as a not-so-bad comestible. In fact, pasta is in a dead heat with steamed brown rice, each of which has a GL of 16. However, boil that rice in excess water for 25 minutes and it becomes a glycemic loser, with a GL of 29. Of the grains, by the way, barley wins, with a GL of only 8, if you use the hull-less variety and boil it for 25 minutes.
Of course, all this nitpicking about high- versus low-glycemic foods becomes irrelevant if you stick to the Mediterranean diet, which emphasizes fresh vegetables, fruits, olive oil, a bit of fish and very little meat. But in the event that you're tempted to wander in the valley of carbohydrate-loading, it's good to know the effects of your culinary indulgences.