Conventional wisdom holds that the way to protect against heart disease is to eat a diet low in fats and high in complex carbohydrates. Such dietary advice has indeed lowered the national intake of total fat—but provoked an increased intake of refined carbohydrates and sugars and the twin epidemics of obesity and diabetes. Everyone agrees that replacing saturated fats with unsaturated fats is good—but citing numerous studies that show an elevated risk of heart disease when carbohydrates replace saturated fats, scientists have been rethinking the role of carbs in cardiovascular disease. Unfortunately, most carbs readily available are highly processed—bagels, pizza, white rice. And their consumption creates what's been called a "perfect storm for the development of cardiometabolic disorders"—namely diabetes and heart disease. More biologically meaningful is to evaluate carbs by their effects on metabolism. There are five factors to bear in mind:
- Carbo Companion One of the the best ways to judge the quality of a carbohydrate is by the company it keeps—specifically, the amount of soluble fiber in the food. Carbohydrate-rich foods such as barley, oats, and rye, which are also high in soluble fiber, are digested at a slow rate. As a result, they release sugar into the bloodstream at a rate that keeps blood glucose levels steady and does not burden metabolic processes, such as production of insulin by the pancreas.
- Metabolism 101 Don't bother dividing the world into simple (bad) and complex (good) carbohydrates anymore. That's a chemical descriptive now disfavored by nutrition researchers because it ignores biology. Some complex carbs, like baked potatoes, disturb blood glucose levels even more than simple sugar does, burdening metabolic systems and provoking hunger and deposition of body fat. By contrast, fruit sugars are simple carbs, but they minimally impact blood sugar levels and insulin production.
- Fast Processing The degree of processing a food undergoes is another important indicator of the quality of the carbohydrates it contains. In highly processed foods, such as white bread, the wheat or other grain is stripped of both the bran and the germ during milling. As a result, the carbohydrates are easily attacked by digestive enzymes, rapidly digested, and then rushed into the bloodstream, where they cause a spike in blood glucose levels and burden insulin production.
- Glycemic Index The glycemic index, or GI, acknowledges that all carbs are not created equal and ranks them 0 to 100 by ability to spike blood glucose levels and thus insulin release. It is a measure of the amount of blood glucose released in two hours after ingestion of a food. Edibles with a low GI (55 or less) are slowly digested, only gradually raise blood glucose and insulin levels, and do not raise blood lipid levels. They also allay hunger—and are now thought to protect against diabetes and heart disease. GI of apple: 38; baked potato: 85.
- Glycemic Load Another good gauge of the biological value of a food is its glycemic load. It represents both quality and quantity and indicates the effect on blood glucose levels of any food eaten by measuring its glycemic index times the amount of carbohydrate in a serving. Watermelon has a high glycemic index (72) but only a small glycemic load (3.6) because it contains relatively little carbohydrate (and lots of water). A baguette slice is a different story, with a GI of 95 and a GL of 48. A GL over 20 is considered high—worth avoiding.