Thursday, February 09, 2017

Can linoleic acid keep you slim?

TLDR This is a weird study which might show the insulin sensitising effect of linoleic acid in obesity resistant rats.

Saturated, but not n-6 polyunsaturated, fatty acids induce insulin resistance: role of intramuscular accumulation of lipid metabolites

I deeply dislike this paper on so many levels. I'm not going to go through everything which is wrong with it, I'll just highlight a few aspects which strike me as interesting.

The first (unexpected) finding is that none of the groups of rats on high fat diets were significantly heavier than the chow fed rats. The PUFA fed rats were slightly lighter (you read that correctly) and the SAT fed rats were slightly heavier, but all ns at eight weeks of feeding. Who can buy rats which can eat coconut/lard and not gain weight? Korean rats? Korean lard? Who knows. But neither the safflower oil nor the lard fed rats become obese. I find this very, very odd in a set of "we bought them off the shelf" Wistar rats. But well, maybe. Just seems odd.

Second point (expected) is that not only did the SAT fed rats develop insulin resistance, but the PUFA fed rats did not, in fact they showed enhanced insulin sensitivity when compared to either chow or SAT fed rats. This is compatible with the Protons view of PUFA oxidation in non-adipocyte distended rats.

Third (expected) is that as insulin acted on muscles under PUFA those muscles developed the highest levels of stored triglycerides. This is exactly what you would expect, insulin diverts excess calories to be safely sequestered as triglycerides.

The fourth point (very unexpected) is that while triglycerides were being happily sequestered in to muscle, they weren't being sequestered in to adipocytes. Adipocyte sequestration of triglycerides (obesity) happens routinely in a huge swathe of linoleic acid feeding trials in many different species.

Sooo, can you extract anything from this mass of contradictions? I'm just wondering whether if you happened upon a generally obesity resistant rat strain you might be left viewing the insulin sensitising effect of PUFA oxidation without the insulin resistance generating effect of adipocyte distension.

Maybe it separates out the the opposing drives on the adipocyte under PUFA exposure...




August said...

I think there is research on coconut oil saying it promotes a lower weight. If I remember right people wanted it to fatten up cattle, but it didn't. This must have been a long time ago, because it is research Ray Peat actually believes in.

Anyway, having slim rats eating coconut oil may just be another one of these unforced errors modern researchers make constantly.

Peter said...


Lynn Borzillo said...

Nice post Peter.

I work with many clients on a ketogenic diet. Most lose weight but many don't.

I am wondering if lowering Linoleic acid by changing protein from animal to more plant-based would be of any benefit?

karl said...

From the paper:
In the week before any experimental intervention, animals were given ad libitum access to
standard rodent chow (Samtako, Bio Korea). Food intake was not determined in this study because the polyunsaturated fatty acid diet was too “liquid” to obtain accurate measures of the food remaining in cages.

So they don't really know how much they ate - and I also don't buy that being too “liquid” would keep someone from weighing what was left.

I couldn't find the data sheet for the Samtako diet - it looks like the other diet came from ICN Biomedicals -

and uhh - in real science people only change one variable at a time - that would mean something like using one diet and adding something to it - all from the same mix lot etc which would mean a single company - not two.

The "too liquid" note also has me wondering if the palatability was a factor? Do rats eat as much if the food is liquid?

Peter said...

karl, it has crossed my mind that they simply made up the results. Outside of F3666 linoleic acid always seems to = obesity...