Lightly processed whole grains are 'good carbs'

Q: You talk about "good carbs" and "bad carbs" in your column. Since I know new studies sometimes change thinking, I'm wondering if "bad carbs" are still bad - because I like eating them.

A: I've got some bad news for you. If anything, the case against bad carbs is growing stronger.

To refresh everyone's memory, let's distinguish good carbs from bad carbs. Carbohydrates are found in a broad range of foods; some are healthy and some aren't.

Table sugar, fruits and vegetables, and grains such as rice and wheat are all carbs. But they aren't equal in how they affect your body.

What makes a carb-rich food one that should be generally avoided?

One discussion you've heard before in this column involves the "glycemic load." This describes both the amount of carbohydrate in a serving of food and how fast that amount will raise your blood sugar level.

Foods with a high glycemic load flood your bloodstream with sugar all at once. That's not healthy.

Low glycemic load foods, in contrast, are digested slowly, causing a gradual rise in blood sugar, rather than a harmful spike. That is healthy.

How can you tell the difference?

Consider these characteristics:

How heavily processed is it?

Finely ground white wheat flour is digested faster than coarsely ground (sometimes called "stone-ground") wheat flour, because the smaller pieces are digested faster.

Whole-grain foods such as brown rice and barley have their fibrous casing intact. The casing slows digestion and contains nutrients that may lower the risk of some diseases. These include Type 2 diabetes, heart disease and several types of cancer, including cancers of the mouth, stomach, colon, gallbladder and ovaries.

Is it really whole grain?

Not all foods in the grocery store that claim to be "whole grain" really are.

"Whole wheat" does not mean no refined flour. Look for labels that say "100 percent whole wheat" (or oats or rye or another grain). The first ingredient listed should be a whole grain.

How much fiber is in the food?

Whole-grain foods have more fiber than refined foods. Fiber slows digestion and prevents blood-sugar spikes.

I said the evidence for the adverse effects of bad carbs was growing. One example is an analysis that combined information from 37 different studies that collectively included over 40,000 people. Those whose diets had the highest glycemic loads had a greater risk of developing diabetes, heart disease, gallbladder disease and breast cancer.

What makes this particularly worrisome is that over the past 20 years, many people are eating more highly refined carbs. In part, that's because during the late 20th century all types of fats in food - including what we now call good fats - were demonized as unhealthy.

So people gravitated to foods that were carb-rich and fat-poor. Unfortunately, a lot of those foods were rich in highly refined bad carbs. They were readily available, relatively inexpensive, and it was easy to develop a taste for them - as you have.

I'd urge you generally avoid them.

• Dr. Anthony Komaroff is a physician and professor at Harvard Medical School. To send questions, go to AskDoctorK.com, or write: Ask Doctor K, 10 Shattuck St., Second Floor, Boston, MA 02115.