Small Intestine

The small intestine is responsible for ninety percent of all digestion. The human body lacks enzymes to digest fiber, so fiber passes through the small intestine undigested. The small intestine handles 90% of all digestion and nutrient absorption. The small intestine requires an alkaline environment to activate its digestive enzymes. The ileum reabsorbs ninety percent of bile salts and absorbs vitamin B12, dietary fat, fat-soluble vitamins, and electrolytes. The small intestine's internal surface area covers approximately 2,700 square feet when fully stretched. Damage to the small intestinal lining impairs bile salt recycling, causing bile levels to drop. Damage to the small intestinal lining reduces absorption of vitamins, minerals, fats, and bile salts, causing systemic deficiencies. Gastric bypass surgery can impair iron absorption because the duodenum is altered or bypassed. The duodenum is the primary site for iron absorption.