Why Malnutrition Is Common in People With Cystic Fibrosis

Malnutrition is a common cause of poor growth in people with cystic fibrosis

Serving food
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Malnutrition is a common symptom of untreated or poorly controlled cystic fibrosis (CF). Malnutrition leads to poor growth and weight loss, which are often the first symptoms that cause doctors to suspect that a child might have CF.  If your child is not growing because they are malnourished, you may hear your doctor use the term "failure to thrive." This means your child is not developing at a standard pace for their age.

Once treatment is initiated, patients usually respond very well to dietary changes and begin to follow normal growth patterns.

What Causes Malnutrition in People With Cystic Fibrosis?

The simple answer to this question is that without treatment, people with cystic fibrosis use more energy than they have available to use. Essentially, their energy bank accounts are overdrawn. There are three major reasons for the energy imbalance.

High energy requirements.  People with cystic fibrosis have to work hard to breathe and that work requires energy. It is estimated that the work of breathing alone increases the energy requirement to 9 percent more than that of a healthy person with the same body weight.

Poor absorption. Because of the effect CF has on the pancreas, the body is not able to absorb much energy from the food that is eaten. Even if a person with cystic fibrosis eats large amounts of food, most of the potential energy is eliminated, unused.

People with CF tend to have steatorrhea, stools that float and are often foul smelling. This is caused by large amounts of fat being eliminated from the stool. 

Poor intake. People with cystic fibrosis often have large appetites because their bodies are telling them that they need more energy, but appetite alone is not always enough to ensure adequate intake.

Sometimes people with CF have other issues going on that make it difficult to eat, such as acid reflux, breathing problems, or struggles with depression.

How is Malnutrition Treated?

The goal of nutrition treatment in people with CF is to restore a positive balance in their energy bank accounts. Energy requirements cannot be changed so the focus of treatment is on improving absorption and intake, the other two contributors to the negative balance.

Enzymes. Before each meal and sometimes snacks, people with CF must take pills containing the pancreatic enzymes that their bodies cannot secrete. These enzymes help the digestive system to absorb nutrients and energy from food that otherwise would be excreted.

Diet. Nutritionists design individualized diet plans to meet each patient’s needs, but the basic rule of thumb is to consume a high-fat diet that consists of 35 to 40 percent of the total calories from fat. Total caloric intake usually varies from 110 to 150 percent of the recommended daily allowance for a healthy person of the same age and sex. Fiber should be eaten in moderation to prevent constipation, but high-fiber diets should be avoided because they may not provide enough calories and sometimes can lead to intestinal obstruction in people with cystic fibrosis.

Pencharz, P.B. and Durie, P.R. “Pathogenesis of Malnutrition in Cystic Fibrosis and Its Treatment”. Clinical Nutrition 2000 19(6):387-394. 20 June 2008.