Being backed up (having fewer than three bowel movements per week) has at least a dozen possible causes. One that's common: a lack of fiber in the diet. In fact, adults consume just about half of the recommended 38 grams for men and 25 grams for women daily. Magnesium also plays a role in moving stool along, says Wagner. Along with eating more magnesium-rich foods, you may also consider a 120 mg supplement of magnesium citrate and increasing until regularity improves, she advises. And don't forget the fiber. Good choices include lentils, broccoli, and apples. Don't miss the 30 ways to get more fiber into your diet without even trying.