Just like fat, there are good and bad carbohydrates. Though your choice of carbohydrates doesn’t have a major impact on your LDL cholesterol level, it can affect your triglyceride and HDL cholesterol levels substantially. Carbohydrates encompass a broad range of foods, including table sugar, fruits and vegetables, and grains such as rice and wheat.

The DRI for carbohydrates is 45 percent to 65 percent of your daily calories. But, as the Healthy Eating Pyramid shows, most of these carbohydrates should come from wholegrain foods, vegetables, and fruits.

If most of the carbohydrates you eat are bad carbohydrates (white bread, potatoes, white rice, and other white starches at the top of the Healthy Eating Pyramid), you could end up gaining weight and putting yourself at risk for some serious diseases.

A 2002 report in the Journal of the American Medical Association cited several dozen studies that have found that people who eat a lot of starchy foods are at higher risk for obesity, heart disease, and diabetes compared with people who eat such foods in moderation.

A study in the Journal of the National Cancer Institute in 2002 found that women who were overweight and sedentary and who ate a lot of starchy foods were two and a half times as likely as other women to get pancreatic cancer. The list of bad carbohydrates may come as a surprise. Why are potatoes bad for you?

They’re vegetables, after all. Why are they in the same category as sweets? To answer these questions, you have to consider the glycemic load, a measure of how quickly a serving of food is converted to blood sugar during digestion and how high the spike in blood sugar is.

In general, the good carbohydrates have a lower glycemic load than the bad carbohydrates. The glycemic load of your diet can significantly affect your risk for diabetes, heart disease, and possibly obesity. Foods with a high glycemic load are digested more quickly than foods with a low glycemic load.

Rapidly digested foods can be a problem because they flood your bloodstream with a lot of sugar all at once. Sudden, high spikes of blood sugar trigger a gush of insulin to clear the sugar from your blood. The problem is that this quick surge of insulin can leave your blood sugar too low after just a few hours.

When your blood sugar is too low, you feel hungry; if it’s low soon after a meal, you’re apt to overeat and possibly gain weight. Another problem with a steady diet of meals high in glycemic load is that over many years, your body’s system of responding to insulin could be impaired.

This is called insulin resistance. When your cells are less responsive to insulin, the resulting overload of sugar in your bloodstream forces the pancreas to step up its production of insulin in an effort to move the sugar from the blood into the cells.

If the pancreas is forced into overdrive for a sustained period, it may wear down and eventually stop producing insulin altogether, leading to insulin deficiency and type 2 diabetes— the more common type of diabetes, which typically develops in late adulthood.

Insulin resistance can also cause other problems, including unhealthy cholesterol profiles, heart disease, and perhaps some cancers. The high-carbohydrate foods that are good for you can help protect against these health problems in part because they have a relatively low glycemic load.

They are digested slowly, which means they cause a gradual rise in blood sugar. Building your meals and snacks around foods with a low glycemic load appears to have many health benefits. It may help you maintain a normal weight and protect you against heart disease, diabetes, and some forms of cancer.

As a rule, carbohydrates have higher glycemic loads than do proteins and fats. But the good carbohydrates, such as legumes, nuts, and whole grains, usually have lower glycemic loads than the bad, starchy carbohydrates, such as potatoes. You can estimate whether a carbohydrate is good or bad based on these characteristics:

• How swollen is the starch? The more a starchy food absorbs water and expands when cooked, the faster it is digested and the higher its glycemic load. White rice expands more than brown rice does. Potatoes (white potatoes, russets, red potatoes, and others in this family) expand more than do sweet potatoes (which are not related to white-fleshed potatoes, despite their name).

Pasta has a somewhat lower glycemic load because it is digested more slowly, especially if it is cooked al dente rather than overcooked until it is swollen and soft.

• How heavily processed is the food? One factor in a grain product’s glycemic load is its degree of refinement. In general, the smaller the pieces, the faster they are digested. This is one reason finely ground wheat flour is digested faster than coarsely ground (sometimes called “stoneground”) wheat flour.

Some scientists think that the glycemic load of the average American diet has increased in recent years because we’re eating greater amounts of heavily processed carbohydrates. Processing removes the fibrous casing from grains.

This casing is good for you because it slows digestion and contains a host of nutrients that may lower the risk of some diseases. Studies show that wholegrain foods such as brown rice and barley, which have their fibrous casing intact, are healthier than the more heavily processed refined grains.

In two large ongoing studies, the Nurses’ Health Study and the Health Professionals Follow-Up Study, people who ate the most whole grains were less likely than other people to develop type 2 diabetes, heart disease, and several types of cancer, including cancer of the mouth, stomach, colon, gallbladder, and ovary.

• What proportion of the food is whole-grain? Not all foods in the grocery store that seem to be “whole-grain” really are. “Whole-wheat” bread may include refined, white flour. Look for labels that say “100 percent whole wheat” (or oats or rye).

Read the ingredients list to make sure that the first ingredient is a whole grain. Some wholegrain foods can be easily spotted by their color. Brown rice is a whole grain (it’s brown because its casing is intact), but white rice isn’t.

• How much fiber is in the food? Fiber is the indigestible part of grains, vegetables, and fruits. Its effect is to delay the time it takes for the food to be digested, and some kinds of fiber can lower cholesterol. Whole-grain foods have more fiber than refined foods.

• How much fat is in a meal or snack? Because fats take longer to digest than carbohydrates, the more fat a meal or snack has, the more slowly it will be digested and, possibly, the less detrimental an effect it will have on your blood sugar. Just make sure that the fat is one of the good fats.

Pasta with olive oil and roasted vegetables is far healthier than a burger and fries. A handful of cashews or other nuts is a better snack than a cookie made with butter or trans fats.