The effort to eliminate trans fats from our diet may have more benefits than expected. There is near unanimous agreement that trans fats increase the risk of heart disease but eliminating them may even have an effect on the obesity epidemic. It isn’t because trans fats are any higher in calories than other fats, it’s a question of the company they keep, namely specific polyunsaturated fats. Vegetable oils such as corn, cottonseed and soybean cannot be repeatedly reheated without decomposing, so they are not a good choice for frying in commercial food production. Neither do they impart the texture or taste to baked goods that can be had with saturated fats. But saturated fats like lard, butter and palm oil, which are stable at high temperature, and which have the desired mouth feel and taste characteristics, are burdened with being linked to heart disease.
The food industry’s answer to this conundrum was the introduction of partially hydrogenated vegetable oils which seemed to be a happy medium between saturated and polyunsaturated fats. However the hydrogenation process also resulted in unintended side products, the notorious trans fats. That was bad, although of course this was not known at the time. Hindsight is always easy. But since the vegetable oils were only partially hydrogenated, there were still a lot of unreacted polyunsaturated fats in the mix, with linoleic acid dominating. Essentially then, the replacement of saturated fats in the diet resulted not only in exposure to trans fats, but also to an increase in linoleic acid intake. And that’s where the obesity connection comes in.
We get a lot of enjoyment out of eating, in fact sometimes so much that we forget to stop. And that may well be due our pleasure centers in the brain being stimulated by compounds called “endocannabinoids.” That term may sound vaguely familiar to anyone who recalls that the active ingredient in marijuana is tetrahydrocannabinol. Have you ever wondered why a chemical that occurs naturally in a plant should have an effect on the human brain? Well, it is because it just happens to chemically resemble the endocannabinoids, compounds naturally produced in the human body. These stimulate the production of dopamine in the brain, a compound linked with pleasure sensations. And guess what the body uses to make the endocannabinoids. Yup, linoleic acid. An increase in linoleic acid intake results in the overproduction of endocannabinoids which in turn results in a pleasurable sensation. And why stop eating if you are getting pleasure?
Interestingly, the trans fat problem is causing producers to look for replacements for hydrogenated fats. One approach has been the genetic modification of soy beans to produce an oil that is mostly composed of oleic acid. This is a monounsaturated fat that is stable to oxidation and can be used in frying. It is the same fat as found in olive oil, but that oil is way too expensive to use commercially. The increase in oleic acid content, up to 80%, also means that the linoleic acid content was cut from 50% to 3%. While this was not the goal of the genetic modification, it could turn out to be a very welcome effect. The use of the high oleic acid soya oil by the fast food industry and its use in processed foods could lead to our brain not being continually stoned on endocannabinoids. And that could have an effect on obesity.