Digestion is the process of breaking food down both mechanically and chemically so the nutrients it contains can be absorbed and used by your body. Optimal nutrition requires a properly functioning gastrointestinal system. A defect in any of several digestive mechanisms can lead to incomplete utilization of the food you eat or, worse, to overt malnutrition.
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Your digestive tract is composed of your lips, teeth, tongue and oral cavity, pharynx (throat), esophagus, stomach, small intestine, colon and anus. Several accessory organs are included in the gastrointestinal system, including the salivary glands, the liver, the gallbladder and the pancreas. When you place food in your mouth, it triggers a cascade of events that include increased secretion of saliva, release of digestive enzymes, stimulation of gastric motility and increased hormone production.
Although your stomach is usually capable of thoroughly mixing the food you eat, inadequate chewing due to weak jaw muscles, poor dentition or haste can make it more difficult for your stomach to do its job. Foods that are inherently difficult to digest, such as carrots or similar high-fiber foods, may not be completely broken down in the gut if they are not chewed well. Fragments of such foodstuffs may traverse the intestine and be recognizable in your stool. Likewise, if your stomach does not adequately mix your food before it enters your intestine – a problem that occurs when gastric motility is impaired by diabetes, for example – the intestine is not equipped to finish the task, and food particles may be eliminated in the feces before they are completely digested. Moreover, if food travels too quickly through your gastrointestinal tract, it may not be thoroughly digested. This may occur during an episode of viral diarrhea, with irritable bowel syndrome or with inflammatory bowel conditions such as Crohn’s disease or ulcerative colitis.
Digestion begins in your mouth, where food is mixed with saliva and enzymes that initiate the breakdown of starches and fats. If you are not producing enough saliva – certain medications, autoimmune diseases or prior radiation treatments of the head and neck can inhibit salivation – your food will reach your stomach without being subjected to this important “pretreatment” process. Once in your stomach, food is normally mixed with hydrochloric acid, which improves the function of digestive enzymes. Insufficient acid production, which occurs in pernicious anemia or with the use of anti-ulcer drugs, can contribute to incomplete digestion. Impaired secretion of pancreatic enzymes or bile, which are complications of pancreatitis and liver disease, respectively, will reduce digestive efficiency, too. Finally, abnormalities of the intestinal lining, which are characteristic of celiac disease, can reduce the absorptive area of your gut and interfere with proper digestion.
Digestion is a complex process that demands more than reasonably normal anatomy and physiologic function. The so-called cephalic phase of digestion is activated by smells, sights and even memories of specific foods. When you are exposed to appetizing stimuli, your stomach begins to growl, you salivate, and your stomach and pancreas begin to secrete hydrochloric acid and digestive enzymes. Conversely, when foods elicit disagreeable memories, you may exhibit the opposite response: nausea and loss of appetite. Perhaps you have experienced problems with digestion during a particularly stressful period in your life. The connection between psychological factors and digestion is not completely understood, but most people have been affected by the interplay in some fashion.
If you notice that your food is incompletely digested for more than just a few days, you should consult your physician. If you are acutely ill, the problem may resolve on its own in a short period of time. A bout of viral diarrhea, for example, usually clears up within two or three days. If you have been diagnosed with pancreatitis in the past, your pancreas may not be producing enzymes as it should, and you might benefit from the use of enzyme supplements. Your physician can recommend a good regimen. Foul-smelling, oily bowel movements may be an indication of celiac disease, which can now be readily diagnosed with blood tests. If you are not digesting your food, and you are also losing weight, you should see your doctor as soon as possible to rule out potentially serious causes, such as inflammatory bowel disease.