Dietary linoleic acid elevates the endocannabinoids 2-AG and anandamide and promotes weight gain in mice fed a low fat diet.
Raphi sent me this link early in the New Year. It’s nice. It demonstrates, at some level of complexity, that omega 6 PUFA at 8% of calories are obesogenic in mice, even if they are fed otherwise fat free CIAB. It’s all about endocannabinoid ligands and receptor activation. Potentially useful when folks get round to starting class actions against the cardiological community and any other health advisors warning against saturated fat. If you limit fat to 30% of calories and saturated fat to 10% you still have 20% PUFA/MUFA in your diet. That’s easily obesogenic. Your cardiologist made you fat. Sue now.
But all of this endocannabinoid stuff is what I call high level signalling. At the core mitochondrial level we know that omega 6 PUFA fail to limit insulin activity under situations where a saturated fat would shut down insulin mediated calorie ingress. In an adipocyte this means that, during oxidation of omega 6 PUFA, insulin continues to signal and fatty acids (and glucose) fall in to the adipocytes, stay there, and you get really hungry. Modified chemicals derived from this system of omega six fatty acids are overlaid on top of the core mitochondrial signalling. A modified derivative of arachidonic acid becomes an endocannabinoid ligand and makes you hungry and fat. The system takes something basic and develops an overlay of enormous complexity, this is what I call higher level signalling.
I hate higher level signalling. Give me the core process anyday.
On this front people may realise I have issues with omega 3 PUFA fats. From the ETC perspective they are worse than omega 6 PUFA and should be more obesogenic. But, in general they’re not. In fact there is a massive industry showing us how good they are for us. But there are suggestions that the core process which makes omega 6 PUFA obesogenic really do apply to the omega 3s. Bear in mind that we are only talking about linoleic and alpha linolenic acids here. Longer fatty acids go to peroxisomes for oxidation and have little influence on core mitochondrial processes, though they do perform a great deal of high level signalling. Here we go:
Sucrose counteracts the anti-inflammatory effect of fish oil in adipose tissue and increases obesity development in mice.
Notice the obesogenic effect of fish oil only shows when sucrose is present in the diet. Replacing sucrose with protein eliminates the effect. Fructose is an unstoppable source of cellular energy intake which needs insulin resistance to limit insulin signalling facilitated ingress of glucose. As insulin continues to act, fat cells sequester calories. Fish oil combined with sucrose is the worst, corn oil is intermediate and, without sucrose, none of the fats are obesogenic.
This makes me happy. I can see the core process at work, never mind what EPA and DHA say to g-protein coupled receptors.
There is another paper which shows a similar effect and I like it rather a lot because the cognitive dissonance, which shines through every word of the text, is rather entertaining. How can you get a life-sustaining source of funding if your data show that omega 3 PUFA are grossly obesogenic? They improve insulin signalling exactly as the ETC effects would predict. The cost of improved insulin responsiveness in adipocytes is obesity. Here we go again:
Adipose tissue inflammation induced by high-fat diet in obese diabetic mice is prevented by n-3 polyunsaturated fatty acids.
The values to look at begin with the weight gain. All we have to do is to subtract weight at the start of the study period from weight at the end (perhaps the authors don't do arithmetic?). Low fat group gained a gram, added saturated fat group gained 0.6 g, added omega 6 group lost* 2.4g and omega 3 group gained 10.4g.
Ten point four grams.
These are db/db mice which lack a functional leptin receptor. They are diabetic and I feel their chronic hyperglycaemia represents a similar drive to obesity as the fructose loading in the last study, ie an unregulated source of calories which drop in to adipocytes and which require insulin resistance to shut down whatever further caloric ingress it can practically do. Free fatty acids, a reasonable surrogate for the action of unmeasured insulin, are low so this suggests adipocyte sensitivity to insulin is high, hence the weight gain.
Weight gain in the alpha linolenic acid group was over 17 times that of the saturated fat group and 10 times that of the low fat group. Notice saturated fat protected (admittedly ns) against the weight gain seen on the low fat diet. The logic is obvious. What do the authors say? Well, I can find no mention in the discussion of this massive weight gain in the omega 3 group. Zilch. This is the quote from the only mention it gets, in the results section:
"Body weight at the end of the study was somewhat higher in db/db mice fed HF/3 compared with HF/S (Table 1)".
There is no other mention of the hard fact that omega 3 fats are obesogenic. Also note that in relatively normal, non hyperglycaemic db/+ mice, the omega 3s are not obesogenic. Much the same as for non-fructose fed mice in the previous study.
Now look at the * I put in above. The omega 6 diabetic group LOST 2.4g. Ouch, at the core mitochondrial function level! How can this be? This needs no mention at all in the paper because p is greater than 0.05 (in the twisted stats used by the authors). But brownie points if you have noted the oddity about this particular group of mice.
Well done! Yes, in a group of 5 animals the standard deviation at the end of omega 6 feeding is 8.6. No other group had a standard deviation greater than 3 at any time. How do you get a standard deviation of 8.6? These are diabetic mice. Four gained weight, one became ill and this one lost a lot of weight. That's my guess, just trying to reverse engineer information out of the data supplied by a group of dissonant thinkers...
So, I went to an on-line standard deviation calculator and fed in various options where 4 mice gained some weight and one mouse lost a tonne of weight. Using a 2g gain for 4 possibly healthy mice and a 20g loss for the fifth poorly mouse we get four mice at 44g and one at 22g. This gives a mean weight at the end of the study of 39.5g to with an SD of just over 9. I think something like this is what happened. Would this group notice one skinny mouse in with four fat ones? Hahahahaha!
Summary: When PUFA are being oxidised in the mitochondria of adipocytes, those adipocytes are unable to resist the signal from insulin to distend with fat. The more double bonds in the PUFA has, the greater the effect. Linseed oil should be used for making varnish.