The human intestinal tract consists of the small and large intestines. The small intestine is approximately 23 feet in length, has a vast amount of surface area, and is where the majority of digestion and absorption of nutrients occurs. The large intestine is only about five feet in length but is significantly wider in diameter than the small intestine.
The large intestine contains microbes that perform a small amount of digestion. Some absorption does occur there, but it primarily serves as a waste elimination organ. Although foods you have eaten have already undergone a significant amount of physical and chemical digestion during about three hours in the mouth and stomach, it will take 20 or more hours to finish the processing in the intestines. This very complex process is amazingly efficient, but at times can have a few flaws.
Digestive enzymes are proteins found in the digestive tract that help break down foods into small enough particles that can be absorbed and used in the body. In the small intestine, several types of digestive enzymes are secreted that act upon fats, carbohydrates and proteins. You can usually tell an enzyme and its function by its name’s root and –ase ending. For example, sucrase breaks down the sugar sucrose and protease breaks down proteins. Aging, genetics and other factors can contribute to a reduced production of one or more enzymes in the digestive tract.
Lactose intolerance is a good example of a condition where the milk sugar-digesting enzyme lactase is lacking, and ingestion of dairy products can cause gastrointestinal upset. Undigested lactose travels to the large intestine and is broken down by colonic bacteria, resulting in gas and bloating. Fortunately, lactase and other digestive enzymes can be supplemented by those with certain food intolerances due to lack of enzymes. Dietary supplements containing specific digestive enzymes—or even a broad range of them—are available and should be taken prior to meals if needed.
The intestinal tract is a long muscular tube that propels ingested foods along by contracting its walls in segments. This is known as peristalsis. This occurs almost continually in the small intestines, but slows to just a few times per day in the large intestine. The large intestine prepares the digested mass for elimination by removing water and solidifying it. If that mass stays in the large intestine too long, too much water can be removed, making waste hard, dry and difficult to eliminate. It is important that the large intestine function properly and move waste toward elimination to prevent constipation. Prescription medication use, stress, travel and lack of exercise can each cause or exacerbate constipation. However, the most common cause of constipation is a diet high in fat and low in fiber, which slows the elimination process. Limiting unhealthy fat intake and increasing fiber intake from foods and dietary supplements (especially those containing psyllium, oat bran and other fibers) is an easy way to maintain regularity. Herbal products that contain natural laxatives such as cascara sagrada bark or senna leaves can help provide relief as well.
Maintaining a healthy intestinal tract involves keeping friendly residents. Several hundred species of bacteria live in the intestines. Probiotics are friendly bacteria that produce health benefits for their host such as improving digestion and immune function. Probiotics in the gut can be increased by eating fermented milk products like yogurt or kefir, taking a probiotic dietary supplement, or consuming foods or dietary supplements containing prebiotics. Prebiotics are fibers and other substances metabolized by colonic bacteria that increase colony growth. Inulin and fructo-oligosaccharides (FOS) are examples of these.