The small intestine is a pink, tube-shaped organ lined with muscle. It is about 20 feet long on average (can vary from 15 to 30 feet) and about one inch in diameter. The top is connected to the stomach, and the bottom is attached to the large intestine. To move food along, the intestines normally contract about a dozen times per minute. Digestion begins with chewing and breakdown in the stomach, but the majority of further digestion and nutrient absorption occurs in the small intestine, where various additional enzymes are introduced to break down nutrients. Food is transformed into glucose (sugar), fatty acids (fats), amino acids (protein), and a myriad of micronutrients. These nutrients pass through the thin walls of the intestine via nutrient-absorbing projections (villi) into the bloodstream. Water-soluble nutrients (carbohydrates, amino acids, water-soluble vitamins) are absorbed through brush border cells via passive and active transport systems. Fat-soluble nutrients (fat-soluble vitamins such as A, D, E, and K, and fatty acids) must first undergo emulsification with bile and are then taken into the lymphatic system for later association with plasma proteins.
For proper nutrient absorption, the intestine’s mucous membrane lining must be healthy. If not, defects in the absorptive pathways can lead to nutrient deficiencies. The mucosal barrier also serves as a defense against unwanted toxins, antigens, and harmful microbes.
Malabsorption occurs when one of the many steps of digestion is disrupted. Causes, which sometimes overlap, include:
- Food not being broken down properly. Problems with the pancreas or liver can reduce the production of digestive enzymes or bile needed for digestion, resulting in incomplete or insufficient nutrient absorption.
- Excessive harmful bacteria in the small intestine, which can interfere with digestion.
- Damage to the intestinal lining, which can impair absorption. Certain drugs, toxins, excessive alcohol consumption, over-processed non-foods, celiac disease, Crohn’s disease, other diseases, and radiation therapy for cancer can cause damage to the lining.
- Some forms of obesity.
- Surgery that shortens the small intestine, reducing the surface area available for nutrient absorption.
Signs of malabsorption include abdominal bloating and gas, weight loss, chronic diarrhea or loose stools, increased stool volume, and excess fat in stools (pale, foul-smelling, bulky, greasy). Other symptoms are specific to nutrient deficiencies. In older adults, symptoms can be subtle and harder to recognize.
Nutritional support for the lining of the small intestine, pancreas, or liver, as well as measures to reduce harmful bacterial overgrowth, can be beneficial. A quality digestive enzyme or bile salt supplement taken with meals can aid digestion, and other problems such as celiac disease, lactose intolerance, or leaky gut require dietary changes. Boosting nutrient intake to compensate for deficits caused by malabsorption and supporting intestinal repair can help correct or prevent serious deficiencies and resultant disorders. Unbalanced diets, typified by the highly processed, low-fiber Western diet, can alter intestinal barrier function and promote leaky gut, leading to further problems. A healthful, whole-food diet rich in non-digestible but fermentable fiber components can definitely help.
Zinc and nucleic acids (such as ribonucleic acid) are among the nutrients that help prevent and heal injury. Glutamine, the most abundant amino acid in the body, plays several important roles in the intestine. For example, glutamine regulates protein metabolism and intestinal inflammation, among other mechanisms.
