In addition to being an enjoyable part of life, food provides the essential nutrients and energy that the body needs to function and maintain health. Of course, the process of getting these nutrients out of food is more complex than we might expect. As food is being digested (broken down), it passes through the stomach and then about 20 feet of small intestine, where nutrients are absorbed into the body and then delivered to cells throughout the body.

Cells that line the inside of the small intestine are the major entry point for nutrients to get into the body. These intestinal tract cells have a challenging balancing act. In addition to taking nutrients in, they also serve as a key barrier between the body and naturally occurring or environmental toxins that are commonly in food.

QUESTION: What happens when the intestinal barrier is compromised in some way?

ANSWER: Intestinal cells are replaced by new ones every few days. This process is compromised if intestinal cells run short on an essential nutrient like iron. The integrity of the barrier is lost, and toxins can enter the body too easily. In addition, nutrients might not be absorbed as efficiently as needed. The compromised barrier also can let undigested proteins pass between cells and trigger the closely associated immune system cells to go into action. The result is an allergic response. Depending on the offending food component, the result can be a long-term food allergy causing both inflammation and damage to the intestinal cells lining the small intestine and to cells elsewhere in the body. The most common food allergies are triggered by peanuts, tree nuts, milk, eggs, fish and shellfish, soy and gluten-containing grains (wheat, barley, rye).

Q: Are allergies the same as irritable bowel syndrome (IBS)?

A: No. IBS is a chronic condition with recurrent abdominal pain or discomfort at least three days per month that persists for at least three months. The symptoms include constipation, diarrhea or an alternating combination of the two. Since these symptoms can be associated with serious conditions like colon cancer, internal bleeding, celiac disease and iron deficiency, physicians try to eliminate these possibilities before diagnosing IBS.

IBS is more common than most people realize, affecting an estimated 12 percent of people in North America and 21 percent of the population in South America. Women are more likely to develop IBS than men, and they also are more likely to have constipation as a predominant symptom. IBS with diarrhea is more common in men. It is not clear what causes IBS — a major reason why it is referred to as a syndrome.

Q: How is IBS treated?

A: As a condition that can include a wide variety of symptoms with no obvious specific cause, treatment is complicated and variable. It involves treating symptoms with a variety of symptom-specific drugs, making dietary changes and increasing physical activity.

Q: What other problems occur in the intestinal tract?

A: Harmless polyps can form in the colon, but these are frequently removed due to the risk of them becoming cancerous. Colon cancer also is a serious disease that is life-threatening and challenging to treat.

Keeping the intestinal tract healthy is the priority. This requires eating foods that meet essential nutrient needs and maintaining a physically active lifestyle.

Alan Titchenal, Ph.D., C.N.S., and Joannie Dobbs, Ph.D., C.N.S., are nutritionists in the Department of Human Nutrition, Food and Animal Sciences, College of Tropical Agriculture and Human Resources, University of Hawaii at Manoa. Dobbs also works with University Health Services.