Some of the less common causes of Protruding abdomen may include: 1  Constipation. 2  Chronic constipation. 3  Poor muscle tone.  Poor muscle tone after 1  childbirth. Lactose intolerance.  Food 1  allergies. Food intolerances. 2  Pregnancy. 3  Hernia. Malabsorption.  Irritable bowel 1  syndrome. Colonic bacterial fermentation. 2  Gastroparesis. Diabetic gastroparesis.