FAB RESEARCH COMMENT:
This elegant study shows that increasing the dietary intake of the main omega-6 polyunsaturated fat found in vegetable oils (linoleic acid, LA) causes obesity in mice.
It also provides evidence that an omega-6-rich diet promotes obesity by increasing endocannabinoid substances that increase appetite.
The endocannabinoid 2-AG promotes increased appetite, and this substance is made within the body from the long-chain omega-6 AA. As predicted, levels of both omega-6 AA and its derivative 2-AG were significantly higher in mice fed a diet rich in omega-6 LA.
Importantly, this high omega-6 LA diet (providing 8% of energy/calories as LA) was chosen to match the current dietary intake of US humans.
Furthermore, the researchers also showed that the obesity-promoting effect of the high omega-6 LA diet was counteracted by adding the long-chain omega-3 EPA/DHA (found in fish and seafood) at just 1% of energy/calories.
These findings show that obesity can be caused by just the kinds of changes in dietary fat intake that have taken place in human diets over the 20th century - particularly in recent decades. Modern, western-type diets - rich in highly processed foods made with vegetable seed oils - have a very high omega-6 / omega-3 ratio relative to any traditional human diet.
Specifically, this study shows that such high intakes of omega-6 fats from vegetable oils, together with low intakes of the long-chain omega-3 fats found in fish and seafood, directly promote appetite and weight gain via known biochemical mechanisms.
Rigorously controlled and detaled studies like ths one are not possible in humans for obvious reasons. However, the findings both match and help to explain the current obesity epidemic as a predictable result from the uncontrolled dietary experiment that has been going on in humans along with the increasing industrialisation of our food supply.