Quality of diet linked to controlling blood sugar among CF patients

Study explores relationship between diet and glucose tolerance in cystic fibrosis

Lindsey Shapiro, PhD avatar

by Lindsey Shapiro, PhD |

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Dietary factors were associated with measures of glucose tolerance — how well the body processes sugar in the bloodstream — among cystic fibrosis (CF) patients in a recent report.

Left uncontrolled, impaired glucose tolerance is associated with the development of CF-related diabetes, or CFRD, where blood sugar levels are very high.

While plant proteins and certain healthy fats were linked to indicators of better glucose metabolism, added sugars were associated with greater impairments across patients with normal blood sugar, somewhat elevated blood sugar (prediabetes), or CFRD.

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“We showed novel relationships linking the quality of dietary fat, carbohydrates, and protein to glucose homeostasis [balance] in adults with CF across the glucose spectrum,” the researchers wrote. “If proven effective … interventions for diet modification represent a non-invasive and inexpensive measure that could prevent or delay metabolic abnormalities for individuals with CF.”

The study, “Quality of dietary macronutrients is associated with glycemic outcomes in adults with cystic fibrosis,” was published in Frontiers in Nutrition.

The buildup of thick, sticky mucus that characterizes CF can affect the pancreas, where insulin — which controls the amount of glucose in the bloodstream — is produced. Patients often experience deficiencies in insulin production and responsiveness that drive high blood sugar, ultimately leading to CFRD.

Still, “whether there are modifiable secondary factors contributing to CFRD development, such as dietary intake, is unknown,” the researchers wrote.

Historically, CF patients were recommended a high-energy, high-fat diet to help offset metabolic and nutritional problems that are common in the disease. To meet these nutritional goals, CF patients commonly consume high-calorie, but nutrient-poor foods with a lot of fats and sugar, according to the researchers.

Diets high in saturated fats — found in meat, dairy, and fried foods — are linked to type 2 diabetes in the general population, but the impact of dietary factors on CFRD has not been explored well.

The recent study examined the relationship between dietary intake and glucose tolerance among 27 clinically stable adult CF patients, mean age 26, who were enrolled at Emory University Hospital in Atlanta, Georgia, from 2014 to 2018.

All patients had pancreatic insufficiency

All participants had pancreatic insufficiency, where the pancreas does not release enough of the enzymes needed for proper digestion.

Overall, 44% of participants were considered to have CFRD, 22% had prediabetes, and 33% had normal blood sugar. CFRD was more prevalent in females compared to males.

In the clinic, participants underwent a blood glucose test, as well as blood tests for levels of insulin and C-peptide, an indicator of insulin production. At home, patients completed a three-day food diary, which was reviewed and analyzed by a dietitian.

CFRD patients had significantly lower C-peptide levels after a period of fasting and higher blood sugar levels two hours after consuming a high-glucose drink, as would be expected with impaired glucose tolerance.

These patients also were found to consume significantly less total fat and fewer monounsaturated fatty acids (MUFA) compared to those with normal glucose tolerance. Considered a healthier type of fat, MUFAs include fats from things like olive oil, nuts and avocados.

In final statistical analyses adjusted for age and sex, higher C-peptide concentrations — reflecting more insulin production — were associated with greater dietary fat intake, as well as intake of MUFAs and polyunsaturated fats, or PUFAs. PUFAs are another type of healthy fats found in foods like nuts, seeds, and fish.

On the other hand, higher C-peptide was linked to lower carbohydrate intake and a lower overall glycemic load, which estimates how likely a person’s diet is to raise blood sugar.

Consistently, blood sugar after consuming glucose was associated with less total fat and MUFA intake. A greater degree of insulin resistance, a feature of CFRD in which cells don’t respond well to insulin, was linked to lower plant protein intake and higher added sugar intake.

Taken together, “our study suggests that modifications to the typical CF diet, with decreased consumption of added sugars and increased consumption of MUFA, PUFA, and plant proteins, may improve glucose tolerance in adults with CF,” the researchers wrote.

Why controlling blood sugar is important

As CF patients live longer, the scientists noted it is critical to understand the long-term impact of diet for these patients, particularly because nutrient-poor diets are linked to chronic health complications in the general population.

Indeed, obesity is on the rise in CF. “Thus, the need for changes in diet quality and recommendations that decrease the risk of chronic disease in the aging CF population are becoming a more urgent need,” the researchers noted.

Larger studies are still needed to further assess the relationship between diet and glucose tolerance in CF.

“Rigorous clinical trials are warranted to determine if modifying the macronutrient quality of the CF diet will influence glycemic outcomes … and ultimately mitigate decline in glucose tolerance among individuals with CF,” the researchers wrote.