Factors Influencing Digestion and Absorption of Nutrients

Any number of factors may result in maldigestion or malabsorption, either of which will diminish nutrient delivery to needy cells. It is important to consider that a problem early in the GI tract (i.e., the mouth or esophagus) is likely to create a cascade of problems later in the GI tract. For instance, the pain associated with esophagitis (an irritation in the esophagus from frequent vomiting, frequent alcohol consumption, or gastric reflux) may inhibit normal drinking patterns to the point of changing normal bowel habits, causing colonic irritation and, of course, dehydration. The most common problem areas include the following:

• Mouth: irritations, dental caries, mouth sores
• Esophagus: irritation of the lower esophageal sphincter from gastric reflux or alcohol
• Stomach: gastritis from alcohol, stress, or overtraining
• Small intestine: malabsorption from celiac disease or Crohn's disease or other inflammation (often from alcohol)
• Large intestine: Crohn's disease irritation, with possible bowel obstruction associated with a fluid and electrolyte imbalance

Diseases of the Mouth Any condition that affects the mouth can have an impact on food intake. Dental caries, cold sores, sensitive gums, and swollen tongues all have the potential of limiting food intake and, therefore, restricting nutrient and fuel exposure to needy tissues. Regular visits to a dentist will resolve the majority of these problems. However, a B-vitamin deficiency (particularly deficiencies of vitamins B2 and B6) may also lead to mouth and tongue problems that inhibit food intakes.

Celiac Disease Celiac disease is an intestinal intolerance of the protein gluten (found in wheat, barley, rye, and oats). It is associated with dermatitis herpetiformis, which occurs in 70 to 80 percent of people with gluten-induced GI tract damage. Celiac disease has a strong genetic association, so relatives of someone who has celiac disease may also develop the condition. Uncontrolled celiac disease results in intestinal damage, with associated malabsorption, and causes diarrhea, steatorrhea (fat malabsorption), iron-deficiency anemia, other vitamin deficiencies, and eventually weight loss. It may be asymptomatic for years before these symptoms occur, or some signs, such as milk intolerance or iron deficiency, may be present without any of the other signs. Recent studies suggest that celiac disease is underdiagnosed around the world, with incidence rates much higher than previously thought. In people diagnosed with iron-deficiency anemia, for instance, 10 to 15 percent have celiac disease.

Individuals with malabsorption, frequent diarrhea, iron deficiency, or any of the other symptoms of GI dysfunction associated with celiac disease should consider the possibility that they do not tolerate gluten. It is quite possible that at least a proportion of those who report feeling so much better on the Atkins diet (a high-protein, low-carbohydrate diet that restricts bread intake) improve because of the elimination of gluten rather than any of the other purported benefits of the Atkins regimen. For those wishing a firm diagnosis of celiac disease, clinically accepted tests are available, often involving a small bowel biopsy, to confirm the presence of the disease. Patients with celiac disease who remove gluten-containing products from the diet are initially distressed at having this limitation in food consumption, but the improvement in bowel function with gluten restriction often allows them to comfortably consume other foods that may previously have caused GI distress. Virtually all celiac patients feel so much better with the restriction of gluten-containing products that they are self-motivated to continue with a gluten-free diet.5 In addition, numerous gluten-free bread products on the market, typically made of rice or corn, are excellent substitutes for wheat and rye breads. There are numerous online resources on gluten-free foods and recipes for readers who wish additional information.

Crohn's Disease Crohn's disease is a regional inflammation of the ileum but may affect the entire small or large intestine. It is associated with abdominal pain and frequent diarrhea, with bowel obstruction a serious problem for the Crohn's patient. This form of irritable bowel syndrome (IBD) causes a thickening of the intestinal wall that reduces the internal transit diameter of the affected portion of the intestines. This reduced interior intestinal diameter is responsible for the bowel obstruction. Crohn's disease equally affects men and women and appears to run in families, although about only 20 percent of Crohn's patients have a relative with the disease. The disease has no known cause, but it is theorized that an immune system reaction against a bacteria or virus causes the inflammation. It appears clear that, unlike some intestinal disorders, Crohn's disease is not related to stress.

For an athlete, Crohn's can have a debilitating effect on the capability to absorb sufficient nutrients, and the associated diarrhea affects fluid and electrolyte balance. The ileum (the main intestinal area affected by Crohn's disease) is the site of vitamin B12 absorption. A failed absorption of vitamin B12 will eventually lead to megaloblastic, hypochromic anemia, which negatively affects oxygen-carrying capacity.

Athletes who have been diagnosed with Crohn's disease are most commonly treated with an anti-inflammatory drug (commonly containing mesalamine; sulfasalazine is the most common of these drugs), along with treatments that aim to correct the nutrition deficiencies and relieve the pain and diarrhea. Treatment with fluids and electrolytes is common for patients who are suffering from frequent diarrhea. Some drugs also reduce the immune response so as to reduce the cause of the inflammation. An irritated GI tract may require that no solid foods be consumed to allow for a reduction in the inflammation and to reduce the chance for a bowel obstruction. Liquid full-nourishment meals are often consumed during these periods. No foods appear to universally increase the GI inflammation of Crohn's disease, but doctors often ask patients to limit the intake of foods that are not well tolerated in large portions of the population or foods that are known irritants (e.g., milk, alcohol, spicy foods).8 In the presence of a vitamin B12 deficiency, consumption of oral supplements or foods high in vitamin B12 (foods of animal origin) does not resolve the deficiency because, regardless of the amount consumed, the absorption of vitamin B12 is sufficiently corrupted that it will not enter the blood. Periodic injections of vitamin B12, which bypass the GI tract, are typically needed to correct the vitamin B12 deficiency.

Drugs Certain drugs may also have an impact on the digestion and absorption of nutrients. Antibiotics destroy the intestinal microflora (bacteria) that assist in digestive and absorptive processes and that are even involved in creating certain nutrients, such as vitamin B12. The commonly prescribed antibiotic neomycin, for instance, causes a malabsorption of fat, protein, sodium, potassium, and calcium. Because of the competitive absorption of divalent minerals (calcium, iron, magnesium, and zinc), a high intake of calcium-containing antacids could, for instance, take up most of the absorption site and interfere with the absorption of the other minerals. Nonsteroidal anti-inflammatory drugs (NSAIDs) that are commonly taken by athletes to resolve the bumps, bruises, aches, and pains of athletic endeavors may create a GI irritation that results in blood loss and an iron-deficiency anemia. These are but a few examples of how drugs can result in an altered fuel intake and utilization. Athletes should be fully aware that virtually every drug taken, including over-the-counter drugs, is likely to have a digestive, absorptive, or metabolic impact that could be a detriment to performance. Athletes should therefore consult with an appropriate health care professional rather that pursue self-diagnosis and self-prescription.