Case Study: Is Exercise bad for the digestive system?
Most fitness experts and personal trainers assert that exercise is good for the digestive system. Many nutitionists and physicians support this view. It has been shown, however, that many people develop occasional trouble with their digestive systems after moderate to strenuous exercise. Scientifically conducted surveys recently revealed that approximately 30% of all runners suffer from abdominal cramping during practice or after a race. The immediate need to defecate occurs in 30% of these people. Another 25% develop diarrhea during or just after the race. It is not surprising that strenuous exercise could cause intestinal problems at the time of the activity. After all, the parasympathetic nervous system that controls intestinal activity relaxes during exercise. Some physicians believe that this cuts off blood to the digestive system and may produce discomfort if undigested food is in the stomach or intestines.
Scientists now know that it is not the exercise alone that produces many of the intestinal problems. The surveys show that runners who suffer intestinal cramping very likely have digestive system disorders, such as irritable bowel syndrome or lactose intolerance. Those without any underlying digestive system disorders reported having diets that are probably too high in fiber. Almost half of the runners who deficate after a race have a digestive system function that is modified by exercise. Scientists now believe that the condition humorously called "runners' trots" is caused by decrease in intestinal transit time. Intestinal transit time is the amount of time it takes for food to pass through the digestive system. So far, this explanation is not fully supported by research.
Studies have shown that people who start regular strenuous exercise routines have a decreased average intestinal transit time. People who normally took 35 hours to pass a meal from mouth to rectum reduced their intestinal transit time to 24 hours. The researchers did not take into account any significant changes in diet. Other scientists take the traditional argument that blood flow to the intestines is reduced by approximately 80% during exercise. This loss of blood may cause digestive system abnormalities, such as cramping and diarrhea. Then, there are scientists who believe that dehydration associated with execise could be producing the digestive system disorders.
Use the information in this chapter and the Web sites on page 523 in your book to answer ALL OF the following questions about exercise and digestive system health:
- How does the average intestinal transit time affect a person's health?
- Is there enough evidence supporting the negative effects of exercise on digestive system function?
- Should physicians caution people about exercise given the recent evidence supporting its negative effects on the digestive system?
- What warnings about exercise and eating should a personal trainer or physician give to people who are considering an exercise program?
- What, if any, actions should be a person take to avoid intestinal problems during exercise?
- Should people with preexisting digestive system disorders be discouraged from participating in strenuous exercise?
- Follow up question to #6: If people were discouraged to exercise, how would that impact their health?
- Should the government require people or agencies that promote athletic events or regular exercise to provide warnings about digestive system disoreders associated with the activity? (EXPLAIN your answer)
