In similar fashion, exercise speeds up gastrointestinal metabolism, resulting in an increased metabolic rate for the digestive process as well as urinary excretion. This could be expected to remove oncogenic (cancer producing) chemicals which might be metabolities of unhealthy foods eaten. The net result then, would be an expected decrease in colon and other gastrointestinal cancers.

In the last several years, there has been other additional evidence that exercise may reduce the risk of cancer by bolstering the immune system. First, it is more clearly appreciated that ever that the body’s immune system plays a vital role in "walling off" or preventing emergence of cancer. Patients placed onto certain immunosuppressant drugs, such as Cyclosporine, have a higher incidence of certain cancers. Certain cancers seem to follow earlier infections, the result of a compromised immune system. The AIDS epidemic has certainly lent credence to the notion of decreased immunity allowing for the emergence of cancers. Marathon runners have a brief increased susceptibility to the common cold and influenza, for several days post-marathon. However, overall long distance runners have heightened immunity and decreased tendency toward illness in general. There is some early evidence this may result in lower probability of certain cancers as well. It has been shown, for example, that people who are more physically active and exercise regularly produce higher levels of NK-cells (natural killer cells). These white blood cells are probably the "front-line defense" against emergence of certain cancers. It has been demonstrated by physiologists and pathologists that of the trillions of cells in the human body, several sporadic cells at any time multiply improperly, producing a cancer cell. In the vast majority of cases, the body’s immune defenses destroy these abnormal cells in order to maintain homeostasis balanced health in the individual.

If physical activity is at least one important factor in maintaining or bolstering immunity, it becomes crucial for us as rehabilitation practitioners to restore or maintain physical activity levels in the injured and disabled populations. In some patients, who by dint of nature or lifestyle, are sedentary, this might involve strategies to increase the level of activity over the course of the day. This might include using the steps instead of the elevator when possible, encouraging lunch break out of the office, advising purchase and usage of home exercise equipment, and encouraging membership in exercise or health club facilities. It might involve preparing the patient for recreational sports, for gardening and other household chores and tasks, or helping the patient to find special interest groups who can act as support groups to encourage an active lifestyle. In the more active patients who are participants in athletic activities, the strategy might involve much more aggressive rehabilitation efforts to return the patient to the sport on some level. It is up to the creativity of the practitioner to decide upon need for medication, splints and braces, therapy, modification of exercise, injections, or surgery. When taking into consideration the risk benefit ratio of a sedentary lifestyle versus the risks of injury with activity, one must also think about the theoretical risk of compromise of the immune system.