What’s the difference between a good and bad carbs?

DEAR DOCTOR K:

In your column you often distinguish between “good” and “bad” carbohydrates. What makes a carb good or bad?

DEAR READER:

Carbohydrates — carbs — occur naturally in a variety of foods, from fruits, vegetables and milk, to breads, cereals and legumes. Carbs are also added to many foods, often in the form of sugar. Your digestive system transforms carbs into glucose (blood sugar). They are your body’s main source of energy.

Whether a carb is “good” or “bad” depends on several factors. Some of the most important are:

  • Whether they are refined or whole;
  • Their effect on your blood sugar level;
  • Their fiber content.

REFINED VERSUS WHOLE. Refined carbs include white flour, white rice, soda, fruit drinks and sweets. The refinement process strips away many of the original carbohydrate’s valuable nutrients, fiber and vitamins.

Good carbs, on the other hand, are intact, or minimally processed. They include whole grains, which lower the risk of heart disease, diabetes and possibly stroke. Other minimally processed carbs include brown rice, oats, whole wheat flour, fruits and vegetables. At the end of this post I’ve put a table with examples of healthy carbs to enjoy and refined carbs to avoid.

EFFECT ON BLOOD SUGAR. Your body digests refined carbs and sugars quickly. This causes blood sugar levels to rise rapidly following a meal. When the pancreas — an organ in your abdomen — senses high levels of blood sugar, it produces bursts of insulin. Insulin lowers blood sugar levels by driving the sugar from the blood into the cells. The cells need it for energy.

So far, so good. The problem is that if your pancreas has to keep responding to sudden surges of blood sugar, many times a day, day after day, it gets pooped. After many years, the overworked pancreas can’t make insulin as well as it used to. That can lead to Type 2 diabetes.

Good carbs take longer to digest. As a result, blood sugar and insulin rise slowly and peak at lower levels. Fruits, vegetables and whole grains tend to keep blood sugar levels steady. The pancreas isn’t overworked, and the risk of diabetes is reduced.

FIBER CONTENT. There are two types of fiber: insoluble and soluble. Insoluble fiber is found in the skin, peels and husks of fruits, vegetables and whole grains. It passes through your digestive tract without breaking down and helps prevent constipation.

Soluble fiber is chiefly found in oats, legumes (beans and peas) and a part of fruit called pectin. Soluble fiber improves blood sugar levels. And it decreases the level of LDL cholesterol in the blood, reducing the risk of heart disease.

Fruits, vegetables and whole grains are good sources of fiber.

For many years, people were told that low-fat diets were healthy. That’s wrong. Just as there are good and bad carbs, there are good and bad fats. Unfortunately, the low-fat diet craze led many people to substitute carbs for fat as an energy source. Even more unfortunately, the carbs people chose were bad carbs. So stick with the good carbs and eat a balanced diet.

Quality of carbohydrates
The quality of the carbohydrates you eat depends on how much they have been processed, the fiber content, the content of bran and germ, and their glycemic load. In this table, more healthful carbs are found on top, progressing downward to the least healthful.
Type Processing and structure Examples
Intact whole grains Whole grain with the bran, germ, and endosperm — which all have important nutrients — from the natural cereal intact Brown rice, bulgur wheat, wheat berries
Minimally processed whole grains Some processing is performed to improve palatability or digestibility, yet the bran and germ remain partially intact Stone-ground whole-wheat bread, cracked wheat, steel-cut oats
Milled whole grains The whole grain, including bran, germ, and endosperm, is milled to fine flour Most commercially available whole-grain breads, whole grain breakfast cereals, whole-grain pasta
Refined grains The bran and germ are removed during processing White bread, white rice, most ready-to-eat breakfast cereals, instant oatmeal, regular pasta
Starchy vegetables Plants that have been bred or engineered to contain high levels of starch with relatively low dietary fiber and micronutrients Potatoes, corn
Refined sugars Natural and industrially produced sugars, including sucrose, glucose, fructose, high fructose corn syrup, maltose, dextrose, and maltodextrin Candies, other sugars added to food
Sweetened refined grains Refined grains with added refined sugars Sweetened breakfast cereals, grain-based desserts (cakes, cookies, pies, doughnuts, sweet rolls, muffins)
Refined sugars in liquid form Natural and industrially produced sugars in liquid form Sugar-sweetened beverages, including sodas, iced teas, sports drinks, and fruit drinks
Adapted with permission from Circulation, June 21, 2011, pp. 2870–91.