While neither diarrhea nor hard stools are healthy, loose stools are preferred to hard ones, according to The Doctors. Soft bowel movements can be an indication of good health, as long as they don't become watery.
Bowel movements that are too soft or watery are often caused by lactose intolerance or excessive fructose in the diet; changing the diet may change the stool consistency, as The Doctors explains. Diarrhea can also be caused by viruses, bacteria or digestive disorders such as inflammatory bowel disease. Hard stools are typically the result of constipation, which can usually be treated by increasing fiber in the diet or taking an occasional over-the-counter laxative.