Science

Mario Kratz, Santica Marcovina, James E Nelson, Matthew M Yeh, Kris V Kowdley, Holly S Callahan, Xiaoling Song, Chongzhi Di, and Kristina M Utzschneider

Background:
Plasma phospholipid concentrations of trans-palmitoleic acid (trans-16:1n27), a biomarker of dairy fat intake, are inversely associated with incident type 2 diabetes in 2 US cohorts. Objective: The objective was to investigate whether the intake of trans-16:1n27 in particular, or dairy fat in general, is associated with glucose tolerance and key factors determining glucose tolerance.
Design:
A cross-sectional investigation was undertaken in 17 men and women with nonalcoholic fatty liver disease and 15 body mass index (BMI)- and age-matched controls. The concentrations of trans-16:1n27 and 2 other biomarkers of dairy fat intake, 15:0 and 17:0, were measured in plasma phospholipids and free fatty acids (FFAs). Liver fat was estimated by computed tomography– derived liver-spleen ratio. Intravenous-glucose-tolerance tests and oral- glucose-tolerance test (OGTT) and hyperinsulinemic-euglycemic clamps were performed to assess b-cell function and hepatic and systemic insulin sensitivity.
Results:
In multivariate analyses adjusted for age, sex, and BMI, phospholipid 17:0, phospholipid trans-16:1n27, FFA 15:0, and FFA 17:0 were inversely associated with fasting plasma glucose, the area under the curve for glucose during an OGTT, and liver fat. Phospholipid trans-16:1n27 was also positively associated with hepatic and systemic insulin sensitivity. None of the biomarkers were associated with b-cell function. The associations between dairy fat intake and glucose tolerance were attenuated by adjusting for insulin sensitivity or liver fat, but strengthened by adjusting for b-cell function.
Conclusion:
Although we cannot rule out reverse causation, these data support the hypothesis that dairy fat improves glucose tolerance, possibly through a mechanism involving improved hepatic and systemic insulin sensitivity and reduced liver fat.