Nutrition for Life

ASSOCIATE PROFESSOR HUICHUAN LAI MS’90 PhD’94 BEGAN EXPLORING the link between nutrition and cystic fibrosis in 1994, when she spent a year working in UW-Madison’s pediatric pulmonary center. A registered dietitian trained in biostatistics, she has spent much of her career scouring epidemiological data for trends that explain how diet affects the health and longevity of children with the genetic disorder. Her work led the national Cystic Fibrosis Foundation in 2005 to rewrite its nutritional guidelines, a move that is contributing to a heartening trend toward better nutrition and increased life expectancy among CF patients.

What causes cystic fibrosis?

The basic defect is in the gene that encodes a transport protein for chloride. It affects almost all organs in the body, but the clinical manifestation is primarily in the lungs and in the digestive system. The classic presentation for undiagnosed CF is failure to thrive, meaning that kids don’t grow as they normally would. Because of the problem in the digestive system, they can’t absorb fat, and fat contains a lot of energy. The lung involvement does not manifest until a little bit later in life, and most patients end up dying from respiratory complications.

Nutrition treatments have lengthened survival dramatically. The median age of survival is beyond 40.

What can doctors do?

Because the lung disease is what causes mortality, the treatment now is really focused on that part of it. But there are many anecdotal observations, small studies, that show that if patients preserve good nutritional status the lung disease will progress more slowly. Over the last 10 years more and more emphasis has been placed on treating malnutrition, with the hope that you can slow down lung disease. And nutrition treatments have lengthened survival dramatically. The median age of survival is beyond 40 now. Three decades ago it used to be less than 10.

How is nutritional status measured in these patients?

It’s important to define optimal nutritional status in CF patients because nutrition has such a big impact on lung disease, quality of life and survival, and that’s what my research focuses on.
So the Cystic Fibrosis Foundation publishes clinical practice guidelines—the first one was done in 1992, and then it was updated in 2002 and again in 2005. The guidelines traditionally have been based on how close a patient’s weight is to an ideal standard. So when a patient comes to the clinic, doctors will try to calculate the patient’s ideal weight, and then they will take their actual weight as a percentage of ideal weight. If the result is above 90 percent, they say, “That’s fine. Let’s keep watching.” If it’s below 90 percent, they do something about it. One of my major contributions to the field is that I proved this percentage of ideal body weight guideline is faulty. It’s only correct for children of average stature.

What was wrong with it?

At the extremes (of height), the ideal body weights are wrong. If the patient is short, for instance, the ideal weight is underestimated. So when you do the calculation for a short child, a doctor is more likely to think a child is fine, when in fact he is too thin.

How did you figure this out?

I didn’t just discover it. I was motivated by questions coming from the clinic. I work with dietitians and pulmonologists a lot, and this question was brought by a dietitian who was using this index in the clinic. She had calculated the ideal weight for a child who was particularly short, and it just didn’t seem right to her. She said, “This child is not supposed to be at this weight. It would be too low.”
I also heard about problems with tall patients, where the dietitian would say, “I can’t increase his weight to that level, I think it’s way too high. Why is that the standard?” It’s not only frustrating. It doesn’t make sense to them.
So these comments motivated me to look into whether there was anything wrong with the definition of this parameter. That is how I got started.

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