Butter Lettuce is cholesterol free, fat free, an excellent source of vitamin A and a good source of vitamin C and folate. It contains 1 gram of fiber per 1 1/2 cups. While fiber is an essential part of a healthy and well-balanced diet, too much fiber can distress the intestinal tract. If your fiber intake was low prior to your meal and the portion size of fiber was high, it may have contributed to the loose bowels you experienced. The level of fiber you need is based on age, gender, and stage of life. When adding fiber to your diet, do so slowly to avoid intestinal upset.