Background: Plasma phospholipid concentrations of trans-palmitoleic acid (trans-16:1n−7), 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-16:1n−7 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-16:1n−7 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 β-cell function and hepatic and systemic insulin sensitivity.
Results: In multivariate analyses adjusted for age, sex, and BMI, phospholipid 17:0, phospholipid trans-16:1n−7, 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-16:1n−7 was also positively associated with hepatic and systemic insulin sensitivity. None of the biomarkers were associated with β-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 β-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.
Alex’s notes: It has been previously shown that there is an inverse association between trans-palmitoleic acid (trans-16:1n−7) content and the risk of type 2 diabetes. This fatty acid is a known biomarker for dairy fat intake, and therefore one can hypothesize that diary fat is inversely associated with type 2 diabetes risk. The study at hand aims to confirm this by looking at if dairy fat is associated with glucose tolerance and with major determinants of glucose tolerance, including liver fat, hepatic and systemic insulin sensitivity, and β-cell function.
A total of 32 obese men and women (average 51 years of age) were included in the study, with half having non-alcoholic fatty liver disease (NAFLD). Interestingly, four of 6 plasma biomarkers of dairy fat intake were significantly lower in participants with NAFLD than in controls, and dietary records confirmed that the NAFLD group consumed significantly less dairy in general and butter and cheese specifically.
The consumption of greater amounts of dairy fat was associated with lower fasting glucose concentrations, better glucose tolerance, higher systemic and hepatic insulin sensitivity, and less liver fat. The fact that the relation between biomarkers of dairy fat intake and glucose tolerance was diminished when adjusted for liver fat or measures of systemic or hepatic insulin sensitivity, but not β-cell function, suggests that the relation between dairy fat and glucose tolerance may be largely mediated by greater insulin sensitivity because of reduced liver fat content in individuals consuming more dairy fat. In other words, consuming dairy fat reduces liver fat which increases insulin sensitivity which leads to subsequent benefits.
I want to emphasize that this is only correlative and the above are simply a proposed explanation of why diary fat is beneficial. Nonetheless, this is not the first study to show the benefits of dairy fat on metabolic health and it provide more support to the notion that you should be enjoying your cream, butter, and full-fat milk – pastured and preferably raw, of course.