Preliminary in vivo studies have shown that fatty acid composition of membranes, where insulin receptors are embedded, can provide significant correlations for insulin resistance. Docosahexaenoic acid (DHA) is a member of the n-3 polyunsaturated fatty acid family present in the membrane that may modulate insulin action. The aim of the study was to investigate if variation in insulin sensitivity is related to variation in DHA in red blood cell (RBC) membrane.
Thirty participants were included for which ethical approval was obtained - 8 ideal weight normal glucose tolerance (IWNGT) and 11 overweight/obese normal glucose tolerance (OWNGT) and 11 overweight/obese with impaired glucose tolerance (OWIGT). Fat and lean body mass were determined by an impedance method. Blood was analysed for glucose, triglyceride and HbA1c. RBC fatty acid phospholipids were analysed. Insulin sensitivity was determined from homeostasis model assessment (HOMA).
Baseline data revealed that there were significant differences between groups for weight, BMI, fat mass, %fat, HbA1c and triglyceride (p<0.05), but there was no difference in %fatty acid composition in RBC membranes between groups. In all patients, no correlation was found between DHA and HOMA although the HOMA mean value was 1.0±0.4, 3.1±2.1 and 5.6±3.7 for IWNGT, OWNGT and OWIGT respectively. The HOMA value correlated negatively with DHA phosphatidylethanolamine fraction (r=−0.809, p<0.01) in the OWNGT subjects and explained 29% and 42% variation in fasting and 2 hrs HOMA respectively. However, this association was absent for the IWNGT and OWIGT subjects implying that other mechanisms independent of DHA modulate insulin sensitivity in these groups.
In this pilot study there was no overall association between insulin sensitivity and RBC DHA phospholipid concentration. The subgroup inverse association needs confirmation and may indicate that increased RBC %DHA phospholipid may protect against increased insulin resistance in overweight/obese subjects with normal glucose tolerance.