The Importance of Physical Activity and Good Nutrition Chronic diseases accounted for 5 of the leading 6 causes of death in 2002 in the United States. The prolonged illness and disability associated with many chronic diseases also decreases the quality of life for millions of Americans. Much of the chronic disease burden is preventable. Physical inactivity and unhealthy eating contribute to obesity and a number of chronic diseases, including some cancers, cardiovascular disease, and diabetes.