Exercise Can Modify the Rate of Gastric Emptying and Intestinal Absorption

Dynamic exercise must be strenuous (demanding more than 70% of the maximal oxygen uptake) to slow gastric emptying of liquids. Little is known of the neural, hormonal, or intrinsic smooth muscle basis for this effect. Although gastric acid secretion is unchanged by acute exercise of any intensity, nothing is known about the effects of exercise on other factors relevant to the development or healing of peptic ulcers. There is some evidence that strenuous postprandial dynamic exercise provokes gastroe-sophageal reflux by altering esophageal motility.

Chronic physical activity accelerates gastric emptying rates and small intestinal transit. These adaptive responses to chronically increased energy expenditure lead to more rapid processing of food and increased appetite. Animal models of hyperphagia show specific adaptations in the small bowel (increased mucosal surface area, height of mi-crovilli, content of brush border enzymes and transporters) that lead to more rapid digestion and absorption; these same effects likely take place in humans rendered hyper-phagic by regular physical activity.

Blood flow to the gut decreases in proportion to exercise intensity, as sympathetic vasoconstrictor tone rises. Water, electrolyte, and glucose absorption may be slowed in parallel, and acute diarrhea is common in endurance athletes during competition. However, these effects are transient, and malabsorption as a consequence of acute or chronic exercise does not occur in healthy people. While exercise may not improve symptoms or disease progression in inflammatory bowel disease, there is some evidence that repetitive dynamic exercise may reduce the risk for this illness.

Although exercise is often recommended as treatment for postsurgical ileus, uncomplicated constipation, or irritable bowel syndrome, little is known in these areas. However, chronic dynamic exercise does substantially decrease the risk for colon cancer, possibly via increases in food and fiber intake, with consequent acceleration of colonic transit.

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Constipation Prescription

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