March is National Nutrition Month, so it seems like a good time to write about the major nutrients in our diets: carbohydrates, fats, and protein.

These nutrients provide nearly all of the calories we eat (alcohol contains calories, too) and have a large impact on our health.

Given the importance of these nutrients, there tends to be much confusion about the different forms they come in and how much of each we should eat. Let’s start with carbohydrates.

Carbohydrates are an important energy source in your diet. All carbohydrates contain four calories per gram. Grains, fruits, and vegetables are good sources of carbohydrates. Carbohydrates include starches, naturally occurring and added sugars, and fiber.

Carbohydrates are produced as a result of photosynthesis in plants and are stored as complex carbohydrates or starches in grains and many vegetables and as simple sugars in other vegetables and fruits.

When you eat carbohydrates, your body breaks down the starches and converts the sugars to glucose, or blood sugar, which is used for energy.

The extent to which a food affects blood glucose is called the glycemic index. Refined carbohydrates, like white rice, pasta, and flour, and sugars typically have a high glycemic index, meaning they cause spikes in blood glucose level. This can pose a challenge for diabetics who need to regulate their blood glucose.

Whole grains, like whole wheat, whole oats and brown rice, have more of a “low and slow” effect on blood glucose.

This can help with blood glucose control and may affect appetite.

For these reasons, complex carbohydrates from whole grains are called “good carbs,” in contrast to refined grains and sugars, known as “bad carbs.”

Carbohydrates also include fiber, the nondigestible portion of fruits, vegetables, and grains. Whole grains, fruits, and vegetables are rich sources of fiber while refined grains and sugars contain little, if any, fiber.

Fiber comes in two forms, soluble and non-soluble. Non-soluble fiber, also called “roughage,” promotes good digestive health. Soluble fiber, like that found in oats, can actually lower blood cholesterol. Studies show that diets higher in fiber tend to promote weight loss over time.

You should make an effort to reduce your intake of sugars, especially added sugars, in your diet. Even though all sugars have the same number of calories, foods and beverages containing added sugars should be avoided. Look for “corn syrup” and “high fructose corn syrup” on the label to identify added sugars. You may be surprised how much added sugar you consume! Fruits or 100 percent fruit juices are a healthy choice since they are rich in vitamins and minerals, even though they contain sugar.

Carbohydrates should be the major part of your diet. Current recommendations call for 45 to 65 percent of your daily calories to come from carbohydrates, so a person who eats 2,000 calories per day should consume 300 grams of carbohydrate. Sugars should be limited to less than 10 percent of calories, so the majority of your carbohydrates should be complex carbohydrates.

You can meet this goal by reducing your intake of sugars, especially added sugars, and refined grains while increasing your consumption of whole grains, fruits, and vegetables that are high in fiber. When comparing food labels, look for foods that contain whole grains (the first ingredient should be something like “whole wheat flour”) and higher levels of fiber. But be aware that some foods, like many breakfast cereals, contain whole grains but are also high in added sugar.

Brian Parr, Ph.D., is an associate professor in the Department of Exercise and Sports Science at USC Aiken where he teaches courses in exercise physiology, nutrition and health behavior.