This article summarizes the normal digestion process, and discusses how failure of absorption of nutrients leads to symptoms of food intolerance.
What is Food Intolerance?
Food Intolerance is the inability to completely break down food into absorbable components due to lack or insufficient amounts of digestive enzymes. Generally speaking, the body’s immune system is not involved in food intolerance. This differentiates cases of food intolerance from food allergies, where the immune system is activated. Individuals suffering from food intolerance may experience the following symptoms after ingesting the offending substance:
- Nausea
- Stomach cramps
- Heartburn or gastroesophageal reflux
- Diarrhea
- Headaches
- Vomiting
How is Food Digested?
Digestion of food begins in the mouth, with mechanical breakdown of ingested material by chewing. Additionally, food in the mouth is mixed with saliva, which contains a starch-digesting enzyme, known as amylase. This begins the chemical breakdown of food. After chewing, food is swallowed, and enters the esophagus. The esophagus is primarily a conduit to transfer ingested material from the mouth to the stomach – very little, if any, breakdown of food occurs in the esophagus. Food then passes into the stomach, where it is exposed to acid, and additional enzymes promote protein and fat breakdown. Next, food passes into the small intestine, where additional enzymes (primarily from the liver and pancreas) are secreted and mixed with food, to further break down protein and carbohydrates, and to emulsify fats. Additionally, food absorption occurs in the small intestine. If breakdown of ingested material and absorption do not occur normally, symptoms of food intolerance result.
Finally, food passes into the large intestine, where excess water is absorbed, and waste is stored. Very little in the way of nutrients is absorbed by the colon – but if absorption hasn’t occurred in the small intestine, those leftover nutrients will be broken down by the bacteria in the colon, resulting in the symptoms listed above.
Examples of Food Intolerance.
Lactose Intolerance – The most common form of food intolerance, lactose intolerance is the manifestation of the inability to digest dairy products. Lactose, the main sugar in diary products, is broken down in the small intestine by the enzyme lactase. Many older children and adults lack adequate lactase, resulting in incomplete digestion of ingested milk sugar. Colonic bacteria then ferment the sugar into carbon dioxide (CO2), methane (CH4), hydrogen (H2) and hydrogen sulfide (H2S), resulting in the unpleasant gastrointestinal effects associated with food intolerance.
Gluten Intolerance – The inability to properly absorb gluten is probably underreported in the medical literature. In mild form, the typical symptoms result when the affected individual ingests certain grains which contain gluten – wheat, barley and rye. In severe form, the condition is known as celiac disease. Undigested gluten provokes an autoimmune response, which damages the small finger-like projections (villi) that line the small intestine. When damaged and inflamed, the villi are unable to absorb water and nutrients such as vitamins, folic acid, iron and calcium. This causes suffers of celiac to be susceptible to a variety of other conditions related to malabsorption.
References:
