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Recommendations Summary

CF: Macronutrient Distribution 2020

Click here to see the explanation of recommendation ratings (Strong, Fair, Weak, Consensus, Insufficient Evidence) and labels (Imperative or Conditional). To see more detail on the evidence from which the following recommendations were drawn, use the hyperlinks in the Supporting Evidence Section below.

  • Recommendation(s)

    CF: Macronutrient Distribution

    For individuals with cystic fibrosis (CF) who are not at risk of malnutrition, the RDN or international equivalent may suggest consuming macronutrients (carbohydrates, protein and fat) in the same percentage distribution as is recommended for the typical, age-matched population, since there is no current evidence to suggest benefits from modified macronutrient distribution.

    Rating: Weak

    • Risks/Harms of Implementing This Recommendation

      There are no obvious risks or harms associated with this recommendation, but MNT should be individualized to each person with cystic fibrosis.

    • Conditions of Application

      Individualized MNT. The pathology of CF is complex and variable. Nutrition status, degree of pancreatic insufficiency, prescription for and tolerance of PERT, and other factors affecting malabsorption and digestion in CF requires an individualized approach to nutrition therapy. Some individuals with CF may have very high energy needs, requiring an energy-dense diet. For these individuals, a diet higher in fat may be appropriate in order to attain high caloric intake. Individuals with CF may experience protein energy wasting, which may require higher intakes of high-protein foods. Those with CFRD may require modification of macronutrient distribution, including timing and types of carbohydrate. In all cases, RDNs should regularly assess nutrition status and symptoms of the person with CF and should adjust nutrition recommendations accordingly.  

    • Potential Costs Associated with Application

      This recommendation is not associated with any obvious costs. Foods that optimize health are generally easily accessible, but socioeconomic and environmental factors, including food insecurity, should be considered and addressed when advising individuals with cystic fibrosis how to improve their dietary intake.

    • Recommendation Narrative

      Background. Traditionally, a high-fat diet has been recommended for individuals with CF to achieve high energy intake needs, due to malabsorption of fats and fat-soluble fatty acids resulting from exocrine pancreatic insufficiency and a high risk of malnutrition. This “CF legacy diet” was implemented as a strategy to achieve high energy intakes required for individuals with CF and to compensate for fat malabsorption, as opposed to having a demonstrated, direct physiological effect. This diet was crucial during an era when individuals with CF commonly had major catch-up growth required at diagnosis.  Undernutrition is still a significant concern in the CF population and has serious implications for long term health (Academy of Nutrition and Dietetics 2019).  However, over time, treatment options for CF have improved, and there is a decline in the proportion of individuals with CF that are undernourished (Cystic Fibrosis Foundation Patient Registry 2017). Additionally, survival and longevity have increased for individuals with CF, requiring health care professionals to balance immediate nutrition needs with potential long-term consequences of a diet that contains too many foods that are high in fat, but low in essential nutrients. Currently, it is more realistic for many individuals with CF to consume adequate energy to meet their needs on a mixed diet with less reliance on energy dense-nutrient poor foods than it was in the past.

      Evidence. There is a lack of evidence examining the role of macronutrient distribution on nutrition-related outcomes, and there were no dietary trials for pediatric or adult individuals with CF identified in the systematic review. However, the observational literature that was included demonstrated no relationships between macronutrient distribution and FEV1% predicted in pediatric individuals (Forte et al 2012) or adults (Forte et al 2012, Moen et al 2011, Gordon et al 2007); BMI z-score (pediatrics) (White et al 2007) or BMI (adults) (Gordon et al 2007, Olveira et al 2006); gastrointestinal symptoms including distal intestinal obstruction syndrome (DIOS) in pediatric individuals (Declercq et al 2015, Proesmans et al 2002) or adults (Declercq et al 2015) or various lab measures in pediatrics (Woestenenk et al 2017) or adults (Gordon et al 2007, Ziai et al 2016) over a range of intakes, with mean intakes near population norms. A 2019 cross-sectional study published after the cut-off date for the systematic review supporting this guideline concluded there was no association between the amount of fat, carbohydrate or protein intake and body composition or fasting glucose levels in adults with CF (Bellissimo et al 2019). There were no studies within the specified eligible time frame, even observational, that reported on the relationships between macronutrient distribution and mortality, quality of life, length of hospital stay or antibiotic use. Therefore, the research examined in this systematic review does not indicate a benefit for altering macronutrient distribution without addressing overall energy content, micronutrient composition or diet quality. Instead, RDNs should consider dietary patterns that are healthy for the general population and adjust as is necessary to address energy needs, protein energy wasting, malabsorption, and co-morbidities, such as CFRD. The effects of types of dietary fats, whether beneficial or detrimental, have not been adequately investigated in the CF population (Olveira et al 2006, Woestenenk et al 2017, Colombo et al 2006, Maqbool et al 2012, Moukarzel et al 2017). However, healthy diets suggested for the general population are generally low in trans and saturated fats (United States Department of Agriculture 2015).

      Counseling Individuals on a High-fat Diet. Many individuals with CF have been prescribed a high-fat diet, possibly for many years. For these individuals, RDNs should assess if the individual is tolerating their current diet by assessing the individual’s gastrointestinal symptoms, energy levels, anthropometric and body composition measures and relevant laboratory values, including inflammatory markers, glucose homeostasis measures and blood lipid profile. If a high-fat diet, especially one that is low in essential nutrients, is not being tolerated by the person with CF, the RDN can work with the individual and family to determine how to shift to a more moderate-fat, nutrient-dense diet that is higher in essential nutrients and lower in non-essential nutrients (see General Guidance for Food Intake section). Concerns about shifting dietary intake closer to that of the general population may also be met with concern by individuals with CF who have lower access to resources, since high-fat foods that are low in other nutrients may be less expensive than foods that are high in essential nutrients. When appropriate, RDNs should provide education regarding inexpensive sources of nutrient-dense foods.

      Implementation of this recommendation is feasible, since it focuses on the tenants of a healthy diet that are in line with those for family and friends who do not have CF. RDNs should work closely with individuals with CF, their families and their interdisciplinary health care teams to determine if modification of dietary macronutrient distribution is needed due to specific needs or conditions.

    • Recommendation Strength Rationale

      The evidence supporting the recommendation for macronutrient distribution was graded as Weak/Limited. The understanding of how macronutrient distribution affects outcomes in CF may change with higher quality research including dietary trials and large, long-term cohort studies that follow relationships between dietary patterns and nutrition-related outcomes over time.

    • Minority Opinions

      Consensus reached.