Q: How can fiber aid in disease prevention?

A: Most foods contain a mixture of soluble and insoluble fiber. Soluble fibers - found in oat bran, nuts, beans, lentils, and some fruits and vegetables - help slow down digestion. Insoluble fibers - in wheat bran, fruits, and dark-green leafy vegetables - reduce constipation and help food pass through the stomach and intestines. A diet rich in dietary fibers can help control numerous health issues. Here are a few:

Colorectal cancer. A high-fiber diet plays an important role in colon cancer prevention. Fiber enters the colon, where it is fermented to produce short-chain fatty acids that may enhance the healthy composition of gut microbiota. Insoluble fiber may reduce potential toxins' transient time in the colon and raise water content in stools, potentially diluting carcinogens.

High cholesterol. Soluble fibers can significantly lower LDL ("bad") cholesterol and total cholesterol.

Cardiovascular disease. Fiber can substantially reduce the risk of coronary heart disease, particularly coronary death in middle-aged men who smoke. Researchers have found that people on a high-fiber diet have a 40 percent lower risk of heart disease and that for every 7 grams more fiber consumed daily, stroke risk decreases by 7 percent.

Obesity. Soluble fiber can help a person feel full and can reduce cravings for snacks by controling blood glucose levels. It also boosts fat metabolism indirectly.

Irritable bowel syndrome. Insoluble and soluble fiber have different effects on IBS. Soluble fiber is the best dietary aid for preventing and relieving symptoms; insoluble fiber can induce IBS and diarrhea.

- Farzaneh Daghigh

Farzaneh Daghigh, Ph.D, is a professor of biochemistry at the Philadelphia College of Osteopathic Medicine.