When it comes to rare diseases for which there is still no cure, the next best thing medicine can accomplish is to ensure maximum quality of life.

One good place to start is to understand how dietary and lifestyle factors impact disease severity and progression. This should be an obvious point, but it is one that is easy to miss. The questions we should be asking in absence of a cure are: Have we explored all angles, exhausted all avenues in understanding the contributing factors that drive disease pathology? What more can be done? Are there any areas that have been overlooked? 

In this article, we will be looking at cystic fibrosis (CF), one of the many diseases with no known cure. Specifically, we will explore the relationship between diet, weight, physical activity, and pulmonary status in patients with CF. 

Implications of Nutritional Status in Childhood 

Nutritional status has always been a cause of concern for patients with CF. “Malnutrition was once thought of as an inevitable consequence of CF,“ Schindler and colleagues wrote in Nutrition in Clinical Practice. “Today, achieving and maintaining optimal nutrition status is viewed as a critical component of CF care.” 

Ashkenazi and colleagues conducted an important study on this very topic, published in the journal Lung. They sought to assess any link between nutritional status in childhood and lung function in adulthood in patients with CF. To do this, they examined medical archives at the Sheba Medical Center in Tel HaShomer, Israel, from 1986 to 2017 to track the progression of CF retrospectively. 

Read more about CF etiology

The research team discovered a statistically significant correlation between body mass index (BMI) at the age of 10 years and forced expiratory volume in 1 second (FEV1) at the ages of 20 and 30. Via logistic regression, nutritional status at 10 years of age was identified as a dominant risk factor for lung transplantation. In addition, their results demonstrated that a BMI Z score lower than -0.75 was a risk factor for lung transplantation.

“This study reports a clear, significant and important correlation for the first time between nutritional status in childhood and lung function for the same patients at adulthood,“ they wrote. “Hence, nutritional status sets a clear trajectory and should be treated aggressively.”

Now that we have illustrated the importance of nutrition and weight monitoring in CF management, we turn our attention to the best way that weight change is measured and its correlation with disease severity. 

Meaningful Methods of Assessment

Scully and colleagues conducted a study with 38 adolescents and adults with CF to assess their dual-energy x-ray absorption entry (DXA) body composition, physical activity, and 24-hour dietary recall. Healthy controls that were age-, gender-, and race-matched were recruited. 

Below are the results: 

  • The DXA body composition analysis revealed that patients with CF had a lower appendicular lean mass index (ALMI) than the control group. BMI was not statistically different between the groups. 
  • Patients with CF reported a higher percentage of calories from fat and a lower percentage of calories from protein. 
  • CF patients reported a higher glycemic index compared to the control group. 
  • Univariate analysis correlation studies revealed that ALMI was significantly correlated with FEV1. BMI was not significantly correlated with FEV1 after adjustment for age and gender. 
  • Physical activity was negatively correlated with body fat in patients with CF. 
  • Pulmonary function in patients with CF was negatively associated with fat mass but positively associated with lean mass. 

At first glance, the results of this study confirm a lot of what we already know about the relationship between diet, weight, physical activity, and pulmonary status. However, this study demonstrated an interesting discrepancy between the measurements of body fat using BMI and ALMI. As the results showed, patients with CF had a lower ALMI compared to healthy volunteers, and ALMI was significantly correlated with FEV1. This was not true of BMI.

Read more about CF prognosis

Hence, an argument can be made that ALMI may be a better measurement of body fat in patients with CF, compared to the standard BMI. The key weakness of BMI? “BMI has been the primary measure of nutritional status in patients with CF for many years, due to its established strong correlation with pulmonary function and mortality,“ Scully et al wrote. “However, BMI does not distinguish between fat mass and lean mass, and may be an insensitive marker of both fat-free mass deficits and excess adiposity in patients with CF.” 

This study also highlights the difference in nutrition between patients with CF and healthy volunteers. Pairing this with the study of Ashkenazi and colleagues on the relationship between nutritional status and pulmonary function, we see why it is so important for nutrition to be optimized in CF patients for a better quality of life and prognosis. 

“Comprehensive nutrition assessment is recommended at CF patient clinic visits, including review of changes to and overall appetite of the patient,“ Schindler and colleagues wrote. “Nutritional interventions in patients with CF include behavioral approaches/interventions, oral supplements, and enteral tube feedings. Appetite stimulants are also commonly used.” 

References

Scully KJ, Jay LT, Freedman S, et al. The relationship between body composition, dietary intake, physical activity, and pulmonary status in adolescents and adults with cystic fibrosis. Nutrients. Published online January 12, 2022. doi:10.3390/nu14020310

Ashkenazi M, Nathan N, Sarouk I, et al. Nutritional status in childhood as a prognostic factor in patients with cystic fibrosis. Lung. 2019;197(3):371-376. doi:10.1007/s00408-019-00218-3

Schindler T, Michel S, Wilson AW. Nutrition management of cystic fibrosis in the 21st century. Nutr Clin Pract. 2015;30(4):488-500. doi:10.1177/0884533615591604