If you eat Weetabix you're probably aware of the benefits of a high fiber diet. As a high-fiber food, Weetabix should help keep your bowel movements regular and comfortable; however, you may be surprised to learn that eating Weetabix can have the opposite effect. Like most high-fiber foods, Weetabix promotes digestion in the right doses, but too much fiber can block your system nearly the same way a lack of fiber does.
Weetabix is a breakfast cereal made from fiber-rich whole wheat grains and shaped into dry brick-like shapes. One serving of Weetabix consisting of three 18 g biscuits contains about 6.3 g of fiber, according to the USDA National Nutrient Database. That makes Weetabix a relatively high-fiber food. A three-biscuit serving contains approximately 201 calories, though not everyone can eat three biscuits at one meal.
Adult men should get about 38 g of fiber from their diet per day, according to the University of Maryland Medical Center. Adult women need slightly less -- around 25 grams per day. People over 50 need slightly less fiber overall. That means that one three-biscuit serving of Weetabix provides between 16 and 25 percent of your daily recommended fiber, depending on your gender. This large fiber dose could put added strain on your system. In some cases, this might leave you feeling constipated.
As nutritionist Jane Clark explains in a "Daily Mail" article, high-fiber foods don't work smoothly in your system without water. The dry Weetabix biscuits and their fiber content bind water in your colon and draw food particles together. However, if you're dehydrated the Weetabix might harden your stools, making them hard to pass. Make sure that you drink around 8 to 10 cups of water or other liquids per day, including a cup at the same time as your Weetabix. That may help to relieve feelings of constipation.
Most people eat Weetabix in a bowl with milk, which can also lead to dairy-related constipation. If you feel constipated or unwell after eating other types of cereal or other milk products, you may be lactose intolerant -- a condition unrelated to the cereal. You doctor can advise you about a suitable diet for lactose intolerance.