Shoot for about 40-50g of mixed fiber per day, but no more. The absolute lower limit is 20g per day. Your main fiber sources should be (in order of importance): vegetables, beans, nuts, fruit, and grains (like oatmeal). If you eat 1 oz of mixed nuts, 1 apple, 2 cups of kidney beans, and 2 cups of mixed vegetables each day, you’ll be getting 41g of fiber. Also, a small amount of supplemental fiber is okay. You can get soluble fiber from psyllium, guar gum, and apple pectin, and insoluble fiber from flax seeds.