This is an nice little study from Japan looking at the effect of fat composition of diet on oxygen consumption before and after a meal:
Diet-Induced Thermogenesis Is Lower in Rats Fed a Lard Diet Than in Those Fed a High Oleic Acid Safflower Oil Diet, a Safflower Oil Diet or a Linseed Oil Diet
We can accept changes in oxygen consumption as a pretty good surrogate for the degree of uncoupling.
These are the diets used
The sucrose content is around 5% of calories so no confounder there. Fat is consistently 40% of calories and they measured the composition of the fats used. Like this
This lard is Japanese lard, produced in the early years of the 1990s. It's 7% linoleic acid. With lipids at 40 % of the calories in the diet this means that overall the LA provides 2.8% of the calories. So this is not an obesogenic diet*. However we get very little information about that because the rats were grown under a time restricted, calorie restricted protocol. An energy intake value was chosen as about the amount of food that a hungry rat would eat in an hour. This amount was fed twice a day. So there is no browsing allowed which suggests that some modest degree of caloric restriction is in place and the absolute supply of calories will be the same for all groups, despite each group have differing overall metabolic needs.
*[If the old anecdote about pork consumption in Okinawa is true this lipid profile might explain any possible longevity effect.]
The high oleic safflower oil diet provides 6% of calories as LA, the safflower oil diet provides 30% of calories as LA and the linseed oil diet provides 6% LA but this is combined with 21% as ALA. Alpha linolenic acid, from the ROS/Protons perspective, is an extreme version of LA although hard evidence for this is very thin on the ground. There are many studies using ALA which show that it is marvellous stuff at any dose rate but these studies almost always use "pair fed" or fixed calorie, mildly restricted protocols.
The protocol here also describes confirming that none of the diets generated lipid peroxides before being fed to the rats. The group is quite meticulous, so refreshing.
Here are the oxygen consumptions, indicating the degree of uncoupling present in the immediate post-meal period:
We can see that lard at 2.8 % of calories as LA shows very little uncoupling. Diets with LA between 6% and 30% LA uncouple more, although there is no evidence of a graduated response, and that a mix of 6%LA with 21% ALA uncouples the most, although this latter is only statistically ns greater than for the other PUFA groups, with a group size of six rats.
So. Given a fixed, mildly restricted calorie intake, we can take the lard fed rats as being very close to metabolically "normal", and eating closest to what they might want if fed ad-lib. Then we have three groups of rats, fed exactly the same number of calories, whose diet has been modified to induced a significant amount of uncoupling. All animals are at the same room temperature so obligatory thermogenic needs should be equal. So higher PUFA groups of animals will waste some of their consumed energy and not be allowed to replace it. What happens to body weights?
The low PUFA lard fed rats are the heaviest and carry about 5% more carcass fat than the PUFA fed rats. I consider them to be at normal body weight. Visceral fat, a surrogate for metabolic damage, is identical across the groups, all are free from clinical metabolic syndrome.
I would argue that the heavier rats are the least hungry, the high oleic acid safflower fed rats are a little more hungry and the two high PUFA diet rats are the most hungry. Quite what would have happened if the study had included an ad-lib fed arm we will never know.
So here's some speculation about "what if" there had been an ad-lib arm to the study:
The lard fed rats (this time) are our normal group and would weigh only a little more due to relief from calorie restriction. It would be nice if the ad-lib fed 6% LA group might have ended up with modest excess energy storage as fat gain and shown extra food consumption to match the extra weight gain. The high ALA fed group should have consumed even more food with less or similar weight gain because uncoupling is having a significant effect. Finally the group with 30% calories as LA should have come out somewhere between. The group having 30% of LA calories seems to be just on the border between where the ROS calorie storage effect transitions to the uncoupling effect in terms of dominance. From other studies 45% of calories as LA might have had the uncoupling effect absolutely dominating, so a slim phenotype would show, but that would be impossible in a diet where only 40% of calories are from fat in total.
How does this fit in to cellular "hunger" concept? At levels of linoleic acid where facilitated diversion of calories to storage predominates, excessive insulin signalling is dominant. The cell is dealing with an hypercaloric state.
Under marked uncoupling conditions the cellular state is the opposite. A separate defence mechanism against caloric excess is being activated, whether there is a caloric excess or not, by dropping the mitochondrial membrane potential because the closer a diet gets to 45% LA diet the more it provides a supra-physiological level of LA for the uncoupling protein function to maximise, combined with copious supplies of oxidative products such as 4-HNE to activate those uncoupling proteins.
At this point ROS generation is suppressed because, whatever the FADH2:NADH ratio, high mitochondrial membrane potential is still essential for reverse electron transport. There will be a transition from failure to limit ROS generation (forcing a cellular energy surfeit) to a reduction in insulin signalling as the result of a process which also involves the direct loss of calories by uncoupling (an hypocaloric state). The fact that suppressed insulin signalling releases fatty acids is over ridden by their loss through overactive uncoupling.
So PUFA are able to produce both cellular repletion and cellular hunger depending on the concentration.
It feels counterintuitive that a metabolite should, by one action, generate an hypercaloric state with excess energy storage and yet, by a separate process, go on to produce the opposite effect via uncoupling at higher levels of exposure.
But this appears to be the case.
It becomes much clearer using pharmacological uncoupling, which takes us back to 2,4-dinotrophenol.