Carbs: Cutting through the confusion

Carbohydrates, along with protein and fat, are the three major nutrients your body needs to function well. A wide range of foods — black beans, bread, and bananas, for example — contain carbohydrates. But the unique mix of fiber, starches, and sugar (the three main components of carbohydrates) in carbohydrate-rich foods can affect your health in different ways.

"Carbohydrates can definitely be confusing, and many of the patients I work with have questions about them," says Nancy Oliveira, a registered dietitian and manager of the Nutrition and Wellness Service at Harvard-affiliated Brigham and Women's Hospital. People who want to lose weight or better control their diabetes often try to cut back on carbs. "But I always emphasize that including some carbohydrate in your diet is important, especially in terms of cardiovascular health," she adds.

The fiber factor

Why? Many carbohydrate-rich foods are good sources of other vital nutrients, such as folic acid, vitamins C and E, and magnesium, says Oliveira. High-quality choices include whole grains, legumes (beans and peas), vegetables, and fruits. But what makes these foods especially healthy is that they're full of fiber. Fiber breaks down in the large intestine, providing food for gut bacteria that produce short-chain fatty acids. These and other fiber components confer a range of health benefits, including lowering cholesterol, blood pressure, inflammation, and body weight.

Sorting out starches

Starches are the most commonly consumed form of carbohydrate. Cereal grains (such as rice, wheat, and corn) and root vegetables (such as white potatoes and sweet potatoes) have a particularly high starch content; so do peas and winter squashes.

Like fiber, starches are considered complex carbs: their complex chemical structure means the body needs to break them down into simpler sugar molecules during digestion. However, Americans tend to favor foods made from highly processed grains (like white rice and white flour), which have been stripped of their fiber and other nutrients.

French fries and potato chips aren't great dietary choices because of the added fat they contain, but there's no reason to avoid potatoes and other starchy vegetables. "I like to microwave baby potatoes to have alongside a piece of salmon and a salad," says Oliveira. Not only are potatoes filling, they're a good source of potassium, which helps lower blood pressure.

Sugar showdown

Unlike fiber and starch, sugars are simple molecules that are digested quickly, which can cause blood sugar spikes and dips. Whole fruit contains natural sugars but also fiber and other nutrients that help moderate those spikes. But that's not the case for the sugar in sodas, candy, and sugary desserts. Occasional treats are fine, but over time, a diet high in sweets can make the body less sensitive to insulin, the hormone that regulates blood sugar. The resulting insulin resistance triggers weight gain, inflammation, and other factors that contribute to the artery-clogging plaque that's responsible for most heart disease.

How much and when?

Unless you have diabetes and need to track your carbohydrate intake for adjusting your insulin dose, there's no real reason to count the grams of carbohydrate you consume each day. "Instead of focusing on numbers, I like to use visual cues," says Oliveira. When you eat carbohydrate-rich foods, aim for a serving size that's about the size of your fist, which works whether you're having grains, beans, a starchy vegetable, or a piece of fruit, she says.

For the main meal of your day, you can fill up to roughly one-third of your plate with foods high in carbohydrates — a combination of a fiber-rich grain or starchy vegetable and a smaller amount of fruit. For breakfast, it's nice to have some carbs to provide energy after your overnight fast, says Olivera. Healthy choices include oatmeal or breads made with 100% whole grain.

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