A diet high in fiber is important to human health, when consumed with adequate fluid, reduces the risk of constipation and disease of the colon because stools are softer and less pressure is needed for defecation. A high-fiber diet may also reduce the risk of heart disease, diabetes, and colon cancer.
However, a high-fiber diet or too much fiber consumption can cause problems if fluid intake is not sufficient, or if fiber intake is increased too rapidly. Too much fiber diets also have the potential to affect vitamin and mineral levels and calorie intake.
Consuming fiber without consuming enough fluid can cause constipation. Fiber increases the need for water because it holds fluid in the gastrointestinal tract. The more fiber there is in the diet, the more water is needed to keep the stool soft. When too little fluid is consumed, the stool becomes hard and difficult to eliminate. Intestinal blockage can occur in severe cases when fiber intake is excessive and fluid intake is low. To avoid these problems, the fluid content of the diet should be increased when fiber consumption increases. Even when there is plenty of fluid, a sudden increase in fiber intake can cause abdominal discomfort, gas, and diarrhea due to the bacterial breakdown of fiber. To avoid these problems, fiber intake should be increased gradually.
In some people, a diet high in fiber can increase the risk of vitamin and mineral deficiencies. This occurs for two reasons. First, the increase in the volume of intestinal contents that occurs with too much fiber intake may prevent enzymes from coming in contact with food. If a food cannot be broken down, the vitamins and minerals from that food cannot be absorbed. Second, fiber may bind some minerals, preventing their absorption. For instance, wheat bran fiber binds zinc, calcium, magnesium, and iron, reducing their absorption. Too much fiber diet can contribute to deficiencies when the overall diet is low in micronutrients. High-fiber diets are of concern in children because they have small stomachs and high nutrient needs. Children consuming a diet that is very high in fiber may feel full before they have met all their energy and nutrient needs.