Large Intestine

The large intestine is made of six parts, including the cecum, ascending (right) colon, transverse colon, descending (left) colon, sigmoid colon, and rectum. The small intestine connects to the large intestine at the cecum, which is actually the beginning part of the ascending colon. A small projection attached to the cecum, called the appendix, serves no well-understood function. However, the appendix is predisposed to becoming infected, a condition referred to as appendicitis. The main function of the large intestine is to reabsorb water from the stool and eliminate the remaining relatively dry waste. Food and drink consumption and intestinal secretions result in approximately 5 gallons (19 L) of fluid being placed in the large intestine daily. A failure to adequately resorb this fluid would result in dehydration. The following factors keep a GI tract healthy:

• Adequate dietary fiber (viscous: soluble)
• Adequate dietary fiber (nonviscous: insoluble)
• Optimal bacterial flora
• Adequate fluids
• Regular movement; physical activity
• Balanced diet with adequate folate
• Reduced intake of simple sugars
• Avoidance of bacterial contamination
• Avoidance of antibiotics (disrupt microflora)

The large intestine is populated by bacteria, many of which are essential for human nutrition. Some of these bacteria manufacture vitamin K (an important substance for blood clotting). The bacterial flora is also important for normal large intestine function by creating gas that aids peristalsis and by aiding in the digestion of certain materials. Certain consumed foods may create a healthy bacterial flora, which can help overwhelm "bad" bacteria that try to populate the gut. For instance, live-culture yogurt often contains Lactobacillus bulgaricus and Streptococcus thermophilus,⁸ which convert pasteurized milk to yogurt during fermentation. In addition, some yogurts contain Lactobacillus acidophilus and Bifidobacterium bifidum. The amount of intestinal bacteria varies depending on diet and use of antibiotics but can make up more than half the weight of fecal material. An infection with "bad" bacteria creates an irritation that causes an increase in mucus production and a failure to resorb water from stool, leading to diarrhea. Of course, the use of antibiotics disturbs the bacterial flora in the gut and often leads to abnormal gut function until the "healthy" bacteria return.

Common problems of the large intestine include constipation, diarrhea, diverticulosis or diverticulitis, and colon cancer. Constipation, diverticular disease, and colon cancer risks are increased with low fiber intakes. Currently, Americans consume approximately half of the 20 to 35 grams of dietary fiber recommended to reduce disease risk and maintain healthy gut function. To obtain the recommended level of fiber, athletes would need to consume at least five servings of fresh fruits and vegetables and three servings of whole grain products daily, as well as legumes occasionally. Because of the gas and bloating caused by higher fiber intakes, athletes could experience performance difficulties unless the fiber intake is timed correctly so it does not interfere with training or competition. The issue of food timing is comprehensively discussed later in this book.