Mozaffarian has published this nice observational correlation between three markers of dairy consumption and subsequent onset of diabetes over the following 15 or so years.
Circulating Biomarkers of Dairy Fat and Risk of Incident Diabetes Mellitus Among US Men and Women in Two Large Prospective Cohorts
Any of the three markers is associated with a roughly halving of the incidence of diabetes. I sort of like this, living largely on bulk calories from dairy myself. I also like the size of the effect. If you consider how many people are in the process of developing diabetes in the USA alone, halving that incidence might make a significant contribution to reducing suffering.
If you eat a gram of C15:0 fat, what else comes bundled along with it? Well, in Swedish milk fat there is about a gram of C15:0 in 100g of total fat. That total fat is made up of 70% saturated fats, mostly palmitic acid, a decent dollop of stearic and myristic acids plus odds and sods of shorter chain saturates. These fats might be what reduces the diabetes risk. What makes me think that, other than my biases?
If you feed a normal Bl/6 mouse 40% of its calories as stearic acid, what happens to its blood glucose level? Taken from fig 2.3.1 part B. After 10 weeks the blood glucose of a normal mouse will be significantly lower than if it had been fed standard CIAB or 40% of an oleic acid/PUFA mix. That will be the red arrow:
The blood glucose lowering effect even occurs in db/db mice, a routine model used to vaguely represent T2 diabetes, green arrow. That's all fine and gives some sort of suggestion that it might be the saturated nature of dairy which is protective against diabetes. But why should this occur?
I'm drawn back to the perfused isolated pancreas and the insulin response to physiological levels of glucose in the presence of various fatty acids. This is the image I'm thinking of, from The Insulinotropic Potency of Fatty Acids Is Influenced Profoundly by Their Chain Length and Degree of Saturation:
Notice the marked but transient spike in insulin when glucose is raised from 3.0mmol/l to 12.5mmol/l, most obvious in the black squares representing stearic acid as the background FFA (palmitate is the black triangles). After the spike, which I think represents the first phase insulin response, there is a steady climb in insulin, equivalent to the second phase of insulin secretion. Obviously this is needed because it's an isolate pancreas prep, glucose is fixed at 12.5mmol/l in the perfusate. If the first phase insulin response does its job in real life the systemic circulation (and pancreas) would never see 12.5mmol/l of glucose. The surge of insulin would hit the liver and interact with the insulin receptor. Two things follow on from this. Most insulin would be metabolised following interaction with its receptor, so insulin would never flood the systemic circulation. Second effect is that insulin/insulin receptor activation would shut down hepatic glucose output while the Glut2 transporters continue to pretty well clear the portal vein of glucose.
So a first phase insulin response is designed to protect the systemic circulation from both hyperinsulinaemia and hyperglycaemia. That is its job.
If you want to obliterate the first phase insulin response what you need to do is to reduce reverse electron flow through complex I. Just take a peek at the open circles (oleic acid) and, even better, the closed circles (linoleic acid). For a healthy pancreas, from a healthy rat, you can eliminate the first phase insulin response to hyperglycamia just by choosing your background FFA.
Arterycloggingsaturatedfat first phase insulin response 16ng/fraction
Hearthealthypolyunsaturatedfat first phase insulin response 2ng/fraction.
Want to be fat? Use your second phase insulin response in the systemic circulation to pack fat and glucose in to adipocytes. But you must avoid the first phase response because this will keep glucose in the liver as harmless glycogen.
Try using sunflower oil or corn oil as advised by the Food Standards Agency. When you get so fat that your adipocytes start to spew unregulated FFAs, you can be a diabetic (congratulations!). You owe it all to your cardiologist. Or the FSA. Remember who to contact when you get your first diabetic amputation.
Oh, picked up this quote about dairy and heart disease from Tom Naughton's blog:
"Rather than suggesting that the saturated fats in dairy products are harmless, Aslibekyan and co-author Ana Baylin, an adjunct assistant professor of community health at Brown, hypothesize that other nutrients in dairy products are protective against heart disease, for all but perhaps the highest dairy consumption quintile in their study. The potentially beneficial nutrients include calcium, vitamin D, potassium, magnesium and conjugated linoleic acid (CLA)".
The authors are completely wrong in the interpretation of their own data. On every front. Saturated fats are NOT harmless. Shout it from the roof tops. THEY ARE PROTECTIVE.
"calcium, vitamin D, potassium, magnesium and conjugated linoleic acid (CLA)"?
Bollocks. Ask the mice on stearic acid.