Food is an enjoyable part of living that is intertwined with social life, culture and traditions. But what happens to food after it is eaten is rather mysterious — a mystery worth understanding because health is only as good as the health of the gastrointestinal tract.

When we eat, food starts a fascinating journey through a complex and amazing tube that passes from one end of the body to the other. This tube, known as the gastrointestinal tract, performs many essential functions, with its major action being that of getting nutrients out of food and into the body so they can replace and repair tissues and provide the energy needed for normal function of the body.

When everything is working right, this tube is very efficient and quietly carries out its functions.

QUESTION: What is the gastrointestinal tract?

ANSWER: The gastrointestinal tract, also called the GI tract or digestive tract, specifically refers to the mouth, esophagus (the tube between the mouth and stomach), stomach (the “gastro” part) and intestines. “Tract” indicates that the tube runs through the body.

The role of the GI tract is threefold: digestion of food, absorption of nutrients, and elimination of undigested food components and waste products.

Q: What is digestion, and how does it affect our health?

A: Food starts its journey with physical breakdown in the mouth (chewing), followed by chemical digestion that starts in the stomach and continues in the small intestine. This breaks down food into small molecules that include nutrients and energy sources that can be absorbed into the body and used by cells — including intestinal cells.

Q: What health issues affect the digestion of food?

A: Many things can impair digestion and reduce the supply of essential nutrients to the body. Adequate chewing often is overlooked as an important first step in getting nutrients out of food. For example, research comparing ground meat to steak found that protein components from the ground meat were more thoroughly absorbed. Of course, chewing the steak well could make its digestion and absorption similar to ground meat.

A dry mouth can also negatively affect digestion of foods in a number of ways. Both inadequate hydration and a number of medications can cause the mouth to be overly dry. Saliva produced during eating contains enzymes that start the digestion of starches and fats, and a dry mouth hinders this seemingly simple process. It can also hinder swallowing.

Dysphagia, the inability to swallow or the sensation that food is sticking in the throat, is a clinical condition that occurs more frequently in females and people with anemia or iron deficiency. This condition can change the types and amount of food consumed and lead to malnutrition.

Gastroesophageal reflux disease (GERD), aka heartburn, is an increasingly common condition. Medications taken for GERD decrease the stomach’s ability to digest protein and to prepare nutrients like calcium, iron and vitamin B12 for absorption.

Helicobacter pylori (H. pylori) is a bacteria that thrives in the stomach and is associated with both inflammation and stomach cancer. Many people harbor H. pylori without symptoms, but when there are problems, antibiotic treatment can help.

Countless other problems can occur throughout the GI tract. To reduce the risk of these problems occurring, maintain overall good nutrition and 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.