DEAR DOCTOR K: I recently read that fiber doesn't prevent colorectal cancer. So is a high-fiber diet good for you or not?
DEAR READER: Many claims have been made about the health benefits of fiber. Yet studies have disagreed. With all the back and forth, I can understand why people are confused. And why they sometimes tune out and say, "Call me when you've discovered the truth."
Without claiming to have discovered the truth, let me tell you what I think the best evidence shows. First, a word of explanation about fiber. It's a form of indigestible carbohydrate that's found mainly in plant foods.
Fiber was once thought to play an important role in preventing colon cancer. As you've read, that turned out not to be the case. In my view, most of the evidence is against a protective effect, at least in economically developed nations like the United States.
However, diets rich in fiber are still good for your health in many other ways. For example, we know that fiber slightly reduces bad (LDL) cholesterol. It improves insulin resistance (a common precursor to diabetes). And it is linked to a lower rate of heart disease and obesity.
In addition, fiber increases the bulk of foods and creates a feeling of fullness. As a result, fiber may help you avoid overeating and becoming overweight.
You should aim to eat between 21 and 38 grams of fiber daily, based on your age and gender, as follows:
- Men ages 50 and younger: 38 grams/day;
- Women ages 50 and younger: 25 grams/day;
- Men over age 50: 30 grams/day;
- Women over age 50: 21 grams/day.
On average, Americans eat only about 15 grams of fiber a day. So chances are, you could benefit from eating more fiber.
Fruits, vegetables and whole-grain foods such as whole-wheat bread, whole-grain cereals, brown rice, bran and oats are all good sources of fiber. In particular, split peas, red kidney beans, raspberries, whole-wheat spaghetti, pears, broccoli and apples are all good choices.