The amount you eat may not have a lot of impact on how much stool you produce. Many disorders cause large, bulky stools even in people who don't eat a lot.
The size of your stools has more to do with how well you digest your foods than how much you eat. Some types of foods produce larger stools because they don't break down completely. Some gastrointestinal disorders also cause poor food breakdown and absorption, which leads to large, bulky stools.
Normal Stool and Constipation
People vary considerably in their production of stool. Contrary to the beliefs of many, it's not necessary to have a bowel movement every day. As long as your stools remain soft but formed and pass easily, you have a normal stool pattern, even if you only pass stool three times a week, according to the Michigan Bowel Program of the University of Michigan Health System.
You might become constipated from not passing stool if you hold back from having bowel movements due to lack of opportunity or out of fear of pain from hemorrhoids or other issues. Constipation can cause larger than normal stools, which may be hard and dry. In some cases, your stools may become smaller, not larger, when you're constipated.
What you eat has an effect on how large your stools are. Many raw foods contain both soluble and insoluble fiber. Insoluble fiber, an indigestible type of carbohydrate, found in fruits, vegetables and whole grains, passes through the intestinal tract mostly intact.
Soluble fiber, found in oats, peas, beans and some fruits, absorbs water, creating a soft, large, easily passed stool. If you eat a high-fiber diet, you may have large stools, even if you don't overeat. As long as your stool passes easily, this doesn't cause any health problems.
Diseases that affect the digestive tract can cause large, bulky, often foul-smelling stools. Disorders such as celiac disease, which affects digestion of foods that contain gluten, or cystic fibrosis, which affects the production of enzymes that break down food, can both cause larger than normal stools.
If you have irritable bowel syndrome, you may have alternating bouts of constipation and diarrhea. If you have large, bulky, greasy stools that float, let your doctor know. This type of stool can indicate fat malabsorption. You might develop serious nutritional deficiencies from malabsorption disorders unless you seek treatment.
If your stools become large and hard, try increasing your fluid intake. When nature calls, try not to put off the call. Going when you feel the need helps avoid constipation. If you have other symptoms, such as fever, abdominal pain, blood in your stools or vomiting, see your doctor.