Abnormal Glucose Tolerance in Cystic Fibrosis and the Role of Low Glycaemic Index Diets

Abstract

Abnormal glucose metabolism states have increased in prevalence in cystic fibrosis (CF). Hypoglycaemia without glucose lowering therapies is a novel complication, with no unifying definition or hypothesis for its aetiology. Thus optimal management strategies for discomforting symptoms remain unclear. Furthermore, there is little evidence for what might prevent progression of impaired glucose tolerance in CF and modifiable factors such as dietary intake in abnormal glucose tolerance may be useful. Five studies were conducted in this thesis: 1) a systematic review of hypoglycaemia in CF in the absence of glucose lowering therapies; 2) a review of an adult CF clinic describing the prevalence of hypoglycaemia on an oral glucose tolerance test (OGTT) and in free-living situations; 3) an extended OGTT study exploring hormonal responses to and the prevalence of post-prandial hypoglycaemia; 4) a study utilising a semi-structured questionnaire and continuous glucose monitoring (CGM) to report on the prevalence of hypoglycaemia in free-living states; 5) a study describing diet quality and the relationship between dietary intake, including dietary glycaemic index (GI) and glucose load (GL), and glucose dysmetabolism using CGM. The systematic review found hypoglycaemia in the absence of glucose lowering therapies occurred during OGTT and CGM. Hypoglycaemia was confirmed on OGTTs and a sub-group of participants reported symptoms suggestive of hypoglycaemia in free-living states. The prevalence of hypoglycaemia may be unmasked by extension of the OGTT out to 3 hours. Abnormal insulin release appears to have a role in its aetiology. The semi-structured questionnaire and CGM confirmed episodes of hypoglycaemia in free-living situations. A detailed food record and formal dietary analysis provided some support for a correlation between dietary GI, GL and glycaemic response variables on CGM. These studies provide empirical support for randomised controlled trials of dietary intervention in CF related glucose dysmetabolism.