April 2017 Issue

MNT in Cystic Fibrosis Care — What RDs Need to Know
By Carrie Dennett, MPH, RDN, CD
Today's Dietitian
Vol. 19, No. 4, P. 44

Learn how proper nutrition can save loves and boost quality of life for patients.

Cystic fibrosis (CF) is a recessive genetic disease caused by mutations in the CF transmembrane conductance regulator (CFTR), a channel that allows chloride ions to move in and out of the cells that produce mucus, sweat, saliva, tears, and digestive enzymes.1 CF is the most common life-limiting autosomal recessive disorder in whites—two copies of the gene must be passed down. In North America, about 1 in 36 people carry the gene,2 and the disease occurs in 1 in 3,000 white newborns.3

CFTR is found primarily in the epithelial cells of the airways and intestines, as well as in the lining of the pancreatic ducts. The most severe feature—and the main cause of premature death—is respiratory failure,2,4,5 which starts with progressive obstruction of the airways by viscous, sticky mucus. The consistency of this mucus can vary from maple syrup to Play-Doh, says Zachari Breeding, MS, RDN, LDN, a clinical dietitian in the Adult Cystic Fibrosis Center at Drexel University College of Medicine and chair of the CF Nutrition subgroup of the Academy of Nutrition and Dietetics (the Academy) Medical Nutrition Practice Group. The obstruction not only damages the airways but also provides a breeding ground for pathogenic microbes—including antibiotic-resistant bacteria.5,6

Life Expectancy
One-half of CF patients are older than 18 and average life expectancy—currently age 40—has increased steadily due to universal adoption of newborn screening in the United States.7 This allows for earlier diagnosis and treatment.8 Infants born with CF usually are referred immediately to one of the many multidisciplinary CF centers located around the country; these include dietitians who specialize in CF. "If they go to a CF center, they will be seen by the RDN at least once annually," says Vanessa Carr, MS, RDN, LDN, consultant for Kate Farms Nutrition and chair-elect of the CF Nutrition subgroup. Carr and Breeding both spoke on CF at the Food & Nutrition Conference & Expo™ in Boston in October 2016.

Breeding says nutrition is as important as pulmonary medication in treating CF because adequate calories and protein can help prevent the muscle wasting and malnutrition that stem from struggling to breathe. "[Proper nutrition] can promote overall health for them, which can improve pulmonary function. That's huge." He adds that increases in life expectancy mean that the transition from pediatric to adult care is important. In fact, he starts introducing the idea of adult care when patients are very young. "We want them to know that they're going to live to adulthood."

CF Complications
Because of the nature of CF, patients can experience the following complications:

Exocrine pancreatic insufficiency (EPI). Most infants with CF are born with EPI,6 which happens when the pancreatic ducts become blocked, preventing secretion of pancreatic enzymes and the bicarbonate needed to activate the enzymes in the small intestine.4 The result is inadequate digestion and nutrient absorption, especially of fats and fat-soluble vitamins.6 Treatment involves daily pancreatic enzyme replacement with all fat-containing foods, including tube feeds. Failure to supplement will cause malnutrition and can lead to intestinal blockage.6

Carr says she has her pediatric CF patients tested for the fecal elastase enzyme EL-1 every one to two years, because older children and adults with CF who think they don't need pancreatic enzymes can start developing EPI symptoms.

• CF-related diabetes (CFRD). EPI is a significant risk factor for CFRD, the most common complication of CF, because CFTR is an important regulator of insulin secretion by the pancreatic beta cells.2,4 Even though CFRD typically develops between the ages of 18 and 21, with about one-half of CF patients developing it by age 30, children younger than age 10 may have impaired glucose tolerance.2,4 CFRD also is associated with decreases in lung function.4

There are many pathways to CFRD, more than with type 1 or type 2 diabetes.2 CFRD "is like type 1 diabetes and type 2 diabetes had a baby. It has parts to both," Carr says. CFRD is characterized by decreases in pancreatic beta cell function as well as varying degrees of insulin resistance.4,9 An oral glucose tolerance test is widely used for diagnosis.9 Treatment generally involves consistent intake of high-quality carbohydrates and insulin when necessary.

• Gastrointestinal (GI) problems. Even though respiratory function largely is responsible for the shortened life expectancy of CF patients, the GI tract is the site of many of the earliest and most severe complications.6 CF patients often have low-level inflammation of the GI tract and are more prone to increased intestinal permeability and small intestine bacterial overgrowth, as well as a slowed intestinal transit time and intestinal blockages.6 Because the gut microbiota are important for harvesting and metabolizing nutrients for their host, disruptions to the gut microbiota may help explain why nutritional outcomes are both variable and unpredictable in CF.6 In addition, the gut microbiota may play a role in the development of CF-related liver disease, which has become more common as life expectancy with CF increases.6

"There's more and more research to show that a healthy gut microbiota can promote a healthy lung microbiota," Breeding says. Studies suggest that CF patients have alterations in the composition of the gut microbiota, compared with healthy controls, and that potentially pathogenic bacteria may colonize the gut before they appear in the respiratory tract.5 Antibiotics may be one reason why.

"People with CF are more likely to need antibiotics," Breeding says. "When they're on antibiotics, they're getting two or three times the dose as someone without CF, and they need them for two or three times as long." He adds that probiotics are essential during antibiotic treatment—with the best evidence supporting Lactobacillus and Bifidobacteria.10,11 What about probiotics in fermented foods? Breeding says they're fine when a patient is no longer taking antibiotics, especially if they opt not to continue probiotic supplements, but while they're on antibiotics, "There isn't enough yogurt in the world that can save these people."

Protein, Calories, and BMI
Initial dietary recommendations for CF were to reduce fat, because patients weren't absorbing it well. However, in the 1980s, clinicians began to realize that a high-fat, high-calorie diet facilitated weight gain, better pulmonary function, and improved quality of life. Poor nutrient absorption plus increased energy expenditure when breathing and at rest means that individuals with CF have dramatically higher calorie needs—up to 200% of the Recommended Dietary Allowance—especially if they have EPI.12,13

Without adequate calories and protein, patients can become both underweight and malnourished, making it harder to fight off respiratory infections,14 which further increases calorie and protein needs while impairing appetite. "It ends up being a vicious cycle that can be difficult to break and takes daily commitment and, I would venture to say, moment-to-moment commitment," Carr says.

Research shows that lung function in CF optimizes at a BMI of 22 for women and 23 for men.13 "With a higher BMI there has been decreased exacerbations, decreased pulmonary infections, a decreased mortality rate, and overall increased quality of life," Breeding says, adding that around a BMI of 30, lung function may decrease, although realistically most of the time it's difficult to get patients up to the optimal BMIs.

Carr says the ramifications of poor growth during childhood are more severe in children with CF. "Children with CF need their nutrition to be on par with everyone else not only for their bones and brains to grow normally but also to have normal life expectancy." She says it's a myth that children with CF will always be smaller. "They should look just like their siblings without CF. They should be able to grow as beautifully and wonderfully as every other child. They have better genetic potential; let's reach it."

To reach protein, calorie, and BMI goals, Carr says dietitians need to help patients make meals calorie- and nutrient-dense, especially with kids, as they have smaller stomachs. Although they may need to eat more fat, they don't have to eat separate food from their friends and family. That's one reason why oral supplemental beverages like PediaSure, Scandishake, or Boost Very High Calorie should be included in addition to meals, not to replace meals. Carr says CF babies can have breastmilk, but mothers may need to pump their milk so they can add formula to it, increasing the calories to about 24 to 28 kcal/oz.

Due to these nutritional challenges, many patients deal with the following:

• Eating fatigue. "Eat, eat, eat. They're always told to eat, and eating fatigue is common," Breeding says. "They get sick and tired of eating so many calories." The first thing he does is look at patients' appetites, and determine what's preventing them from getting enough calories. He says that a liberalized diet that's high in fat and protein—without ignoring fruits and vegetables—can help, and that he sometimes has to reteach his young adult patients the importance of fruits and vegetables and wean them off fast food. "They were told to eat so many calories in fat that they didn't focus on vegetables because they were so low calorie," he says. "It's reminding them, 'You still need high protein, you still need high calorie, you still need fruits and vegetables.'" Because chronic inflammation is a characteristic of CF,6 a diet inclusive of fruits and vegetables, which contain anti-inflammatory phytonutrients, may be of particular benefit.

Breeding says that even though adult oral supplements can help, there's still eating fatigue. "They get sick and tired of drinking two to three of these a day as snacks in addition to their high-calorie meals. So what I do is generate recipes." Creating different flavor combinations gives patients variety that can help them stick to their nutrition plan. He also suggests using liquid shakes in baked goods to increase calories and protein. "I'm constantly finding ways to put in these calories without them getting too tired, because when they get tired, they stop doing it, and when they stop doing it, they start losing weight and their lung function can go down."

Enteral nutrition (EN). Sometimes, appetite is impaired enough that EN is necessary.12,14 Many CF patients receive supplemental EN through nasogastric tubes or directly into the stomach through gastrostomy. Overnight feedings are common to encourage oral intake during the day and because, as Breeding says, "Adults have lives." While this can improve weight gain, nutritional status, lung function, and possibly quality of life, it's expensive and can have a negative impact on body image and self-esteem.12 More well-designed randomized controlled trials are needed to assess the efficacy and possible adverse effects of supplemental EN feeding, compared with normal oral feeding and oral supplement feeding.12

Carr says CF patients can develop sinus polyps, which affect how food tastes and smells. Kids don't want to spit out their mucus in front of anyone, so they are constantly swallowing it. "They have a sour stomach, and it doesn't feel good."

Other Nutrition Needs
Additional nutrition needs include the following:

• Vitamins and minerals. If someone can't absorb fat, they can't absorb the fat-soluble vitamins A, D, E, and K.13 Iron deficiency and zinc deficiency, which affect appetite and linear growth, also are common. To combat this, Carr says CF patients should take CF-specific vitamins, such as AquADEKs, MVW Complete Formulation, or Libertas, designed for their specific needs.

• Sugar. When a CF patient also has CFRD, the challenge grows. Carr focuses on reducing day-to-day concentrated sweets—such as replacing sports drinks with coconut water or artificially sweetened sports drinks—while recommending that kids be allowed to have sweets at parties or sleepovers.

• Salt. People with CF lose a great deal of salt in their sweat, so they need to salt their food regularly. Carr says a high-sodium diet doesn't appear to cause the same problems for patients with CF as it might for those without CF. Even infants need 1/8 tsp daily, increasing to 1/4 tsp at 6 months.15

• Water. CF patients may need 2 to 4 L of water per day, combined with some type of electrolyte replacement therapy, especially on hot days and during physical activity, Breeding says. Sugar-free electrolyte replacements, coconut water, or even a salted banana are options. "So many adults that I see who don't have CF don't drink enough water. That doesn't change because they have CF. They're still adults who [find it difficult to] drink enough water."

Tips for RDs Without a CF Specialty
When a patient with CF can't get to a CF center or satellite clinic, they may be seeing a general practitioner or pulmonary specialist in their own town. If a patient has an acute health issue, such as worsening lung function, they're likely to end up in their local hospital. Carr says this is the reason she and Breeding created the CF subgroup of the Academy. "We wanted to have resources for those RDNs, because other than the CF Foundation, there wasn't anything else for them to check on how to provide optimal care for these people."

What other resource do inpatient dietitians who encounter patients with CF have when they aren't sure how to proceed? "Ask the patient. If you don't know, I guarantee you that they know," Breeding says. "These patients are professional patients. If they're kids, their parents know what these kids need. Ask them because if you have any questions, you might not work with a doctor who knows CF. You might not work with another dietitian colleague who knows CF."

Breeding offers these additional tips:

• Make sure patients are taking their enzymes and the right dosages of enzymes. "If they're not getting the enzymes into patients, then all the nutritional support just goes right through them."

• Pay attention to oral hydration, even if the patient is on IV hydration. "Oral hydration is just as important, because they aren't going to be on IV hydration when they go home, most likely."

Make sure the diet order is double salt, high protein, and high fat. There are various ways of getting enough salt, including electrolyte supplements and actually putting salt in the tube feed.

Barriers to Change
"A lot of folks want to be 'normal.' They fall into the same trends as anyone else," Breeding says. Sometimes, when patients want to drink nonfat milk because the rest of their family does, or try some type of diet that they think might make them feel better, he has to explain why that's not a good fit for them, given that they have CF.

Breeding also says that the burden of treatment can be a barrier to managing CF. "The same thing that impedes other people from meeting their nutrition needs affects CF patients twice as much." This is where he says motivational interviewing skills are important. "We know the benefits; they might know the benefits, but they just might not care, and so it's our job to make them care."

Carr says one of the biggest challenges in the CF pediatric population is gaining the trust of parents. "It's difficult to convince them that the changes you want to make in their everyday life will be meaningful and make an impact. These families have been dealing with CF day in and day out, and I think as a clinician, you have to go in there with respect for them and for how they go about their nutrition regimen before you can really recommend extreme changes or improvements."

— Carrie Dennett, MPH, RDN, CD, is the nutrition columnist for The Seattle Times and speaks frequently on nutrition-related topics. She also provides nutrition counseling via the Menu for Change program in Seattle.


1. CFTR gene: cystic fibrosis transmembrane conductance regulator. National Institutes of Health, US National Library of Medicine Genetics Home Reference website. https://ghr.nlm.nih.gov/gene/CFTR. Updated March 7, 2017.

2. Barrio R. Management of endocrine disease: cystic fibrosis-related diabetes: novel pathogenic insights opening new therapeutic avenues. Eur J Endocrinol. 2015;172(4):R131-R141.

3. Carrier testing for CF. Cystic Fibrosis Foundation website. https://www.cff.org/What-is-CF/Testing/Carrier-Testing-for-CF/

4. Gibson-Corley KN, Meyerholz DK, Engelhardt JF. Pancreatic pathophysiology in cystic fibrosis. J Pathol. 2016;238(2):311-320.

5. Albenberg L, Kelsen J. Advances in gut microbiome research and relevance to pediatric diseases. J Pediatr. 2016;178:16-23.

6. Rogers GB, Narkewicz MR, Hoffman LR. The CF gastrointestinal microbiome: structure and clinical impact. Pediatr Pulmonol. 2016;51(S44):S35-S44.

7. Diagnosed with cystic fibrosis. Cystic Fibrosis Foundation website. https://www.cff.org/What-is-CF/Diagnosed-With-Cystic-Fibrosis/

8. Pittman JE, Ferkol TW. The evolution of cystic fibrosis care. Chest. 2015;148(2):533-542.

9. Jones GC, Sainsbury CA. A practical approach to glucose abnormalities in cystic fibrosis. Diabetes Ther. 2016;7(4):611-620.

10. Tojo R, Suárez A, Clemente MG, et al. Intestinal microbiota in health and disease: role of bifidobacteria in gut homeostasis. World J Gastroenterol. 2014;20(41):15163-15176.

11. del Campo R, Garriga M, Pérez-Aragón A, et al. Improvement of digestive health and reduction in proteobacterial populations in the gut microbiota of cystic fibrosis patients using a Lactobacillus reuteri probiotic preparation: a double blind prospective study. J Cyst Fibros. 2014;13(6):716-722.

12. Morton A, Wolfe S. Enteral tube feeding for cystic fibrosis. Cochrane Database Syst Rev. 2015;(4):CD001198.

13. Sabharwal S. Gastrointestinal manifestations of cystic fibrosis. Gastroenterol Hepatol (N Y). 2016;12(1):43-47.

14. Schwarzenberg SJ, Hempstead SE, McDonald CM, et al. Enteral tube feeding for individuals with cystic fibrosis: Cystic Fibrosis Foundation evidence-informed guidelines. J Cystic Fibros. 2016;15(6):724-735.

15. Minerals. Cystic Fibrosis Foundation website. https://www.cff.org/Life-With-CF/Daily-Life/Fitness-and-Nutrition/Nutrition/Getting-Your-Nutrients/Minerals/