This is beautifully illustrated by this paper, courtesy of Tucker. In the study soybean oil was given either orally six hours before an hyperinsulinaemic euglycaemic clamp or as an intravenous infusion over the six hours leading up to the clamp. Each fat load was 900-1000kcal in total:
The summary figure is this one:
The M values are derived from the glucose infusion rate needed to maintain stable blood glucose during the clamp. The lower the value, the more insulin resistance is present. So iv intralipid, oral soybean oil or intravenous lipopolysaccharide all produce insulin resistance compared to the small infusion of glycerol given to the control group.
Clearly all interventions approximately halve the insulin sensitivity of the subjects. I'll come back to the fascinating insulin resistance generated by lipopolysaccharide another time.
So soybean oil, per os or iv, clearly induces insulin resistance.
What we are looking at with the oral dose is this, from a different study. I've kept with the Novotny/Shulman colour scheme for po fat and con:
At the 6 hour time mark an hypothetical clamp would produce what Nowotny and Shulman published:
No arguing. Consuming PUFA gives you insulin resistance. It's obvious by eye at one hour in the Spanish study and is still detectable using a clamp as late as six hours in Nowotny's study, by which time blood insulin and glucose are completely back to baseline in Spain and never budged for Nowotny.
But.
What would have happened if, instead of a PUFA load, there had been a butter load, of equal calories?
We know the answer because it was done in Spain and butter comes out like this:
At the one hour mark, from blood glucose/insulin levels, there appears to be about 80pmol/l more insulin needed in plasma to deal with the small carbohydrate/protein load given with the fat. This represents insulin resistance. More from butter than from the PUFA ingestion.
Had Nowotny and Shulman also done this and then clamped at the six hour mark, would they have found butter caused a lower insulin sensitivity than the PUFA load by this time?
Yes they would. Unless something very strange occurs between one hour and six hours, then butter is, absolutely, going to cause *reduced* insulin sensitivity compared to the PUFA load during the clamp.
Frankly I'm amazed that Shulman didn't do this. It would have been a great butter bashing publication. But then, I don't expect too much from Shulman's group.
So.
PUFA ingestion definitely, absolutely, causes insulin resistance.
The problem is that it doesn't cause quite enough insulin resistance.
The correct amount of fat-derived insulin resistance to normalise caloric ingress in to a given cell is provided by butter derived FFAs, or, better still, those from tallow. Or, in pre-agricultural times, from any animal fat.
Peter
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