Here is the next step. Mice this time.
Prevention of diet-induced obesity by safflower oil: insights at the levels of PPARa, Orexin, and Ghrelin gene expression of adipocytes in mice
The basic study design was that mice were fed a control diet, a safflower oil based diet or a lard based diet for an initial 10 weeks. At 10 weeks half of the lard fed mice were switched to the safflower oil based diet and feeding continued for another 10 weeks.
Here are the diets
They measured the linoleic acid content by gas chromatography. That is very, very good. We can rough out the LA content of the control diet at around 5% of calories as LA, the lard diet at 11% of calories as LA and the high safflower oil diet at around 38% LA.
Here's what happened to the weights
As expected the lard mice became overweight by 10 weeks. Putting them on to 38% of calories as LA returned their weight to that of control mice or that of mice fed 38% LA safflower throughout the full 20 weeks.
This is not an isolated study showing the benefits of safflower oil, but it's one of the better ones. I find it impressive. It has to be understood.
Towards the end of the discussion in this paper the authors cite another gem which completely contradicts their own findings while providing more insight:
"These results are different to the study that the rats fed on 30% safflower oil and mice fed with 20% safflower oil showed significantly higher body weight, white adipose tissue weight, serum leptin, and hepatic PPARa mRNA expression ."
The paper they cite is this one:
Changes in liver PPARa mRNA expression in response to two levels of high-safflower-oil diets correlate with changes in adiposity and serum leptin in rats and mice
Here are the diets
Wow! Have you spotted it? Thats right. More excellent gas chromatography and suddenly you find out that "safflower oil" and "safflower oil" can be very, very different oils. This batch of safflower oil was 24.1% LA. In the highest fat diet we are looking at 24.1% of the 53.68% of fat calories as LA. That's 13% of calories as LA, bang in the middle of the obesogenic range. That's very different from the 38% which corrects obesity...
It must be sad trying to understand your own results and those of rival labs without the Protons/ROS hypothesis to fall back on. Must be awful.
Currently I don't think there is anything special about safflower oil. I think it is an effect the linoleic acid at very high dose rates. You should, theoretically, be able to do the same with corn oil. Sadly most of the corn oil based high fat diets aim to get in to the sweet spot of 10-20% of calories as LA. They want obesity after all.
If we are trying to generate diets with 40% or more of total calories from linoleic acid it will be much easier with safflower oil at 75% LA than using corn oil at 55% LA.
Interestingly mice appear to rather like corn oil. Let's look at a free choice feeding study next. Chow as pellets or corn oil from a liquid feeder bottle. Let the mice decide how much of each... And see if they get fat.