Feeding your genes: the omega-6/omega-3 ratio

By Sonia Tandon

You’ve likely seen the news headlines and the countless product advertisements – take fish oil or omega-3 supplements to improve your cholesterol, fight inflammation, and reduce your risk of cardiovascular disease and dementia. But what exactly are omega-3s and why are they so important for health?

First of all, here’s a quick primer on fats – a fat molecule consists of two parts: a “head” and a fatty acid “tail”. The “head” is composed of a glycerol molecule, and the fatty acid consists of a long chain of carbon atoms. Fatty acids are classified by the length of their carbon chains and by their saturation. Saturation just means that all of the carbon atoms in the fatty acid have single bonds, while unsaturation means that at least one double bond exists. If a fatty acid has one double bond, it is a monounsaturated fatty acid. If it has two or more double bonds, it is a polyunsaturated fatty acid (PUFA).

Essential fatty acids are types of PUFAs that are needed to support normal function but cannot be made by humans (we lack the necessary enzymes). This means that we must consume these fats through our diets. Essential fatty acids include the omega-6 fatty acid linoleic acid (LA) and omega-3 fatty acid alpha-linolenic acid (ALA). They’re classified as ‘omega-6’ and ‘omega-3’ according to the position on the carbon chain where their first double bond exists. Importantly, they can be converted within the body to biologically active long-chain polyunsaturated fatty acids (LC-PUFAs); however, the rate of conversion is low.

The omega-3 and omega-6 fatty acids considered most relevant for human health are summarized below:

200330 Sonia Picture 2

*Of note, DHA/EPA can also be obtained through vegan sources such as algae. In fact, fatty fish are such a good source of DHA because it accumulates in their tissues as they consume phytoplankton!

Although it is most effective to consume foods or supplements containing LC-PUFAs, they’re also synthesized in the body from LA and ALA. The rate at which this bioconversion occurs is regulated by our genes. This is an example of nutrigenetics, the study of how genetic variations affect how we respond to nutrients.

LA and ALA compete for conversion to their LC-PUFA forms by enzymes in the fatty acid desaturase (FADS) gene cluster. Two distinct patterns of variation in FADS genes have been identified across different populations. The “efficient” variation, observed in African populations with diets low in LC-PUFAs, is associated with higher conversion to LC-PUFAs. Meanwhile, the “inefficient” variation, associated with lower conversion, is present in Greenland Inuit populations that typically consume diets high in LC-PUFAs. The efficient variation likely emerged as a genetic adaptation to a shift from hunter-gatherer diets rich in LC-PUFAs to plant-based agricultural diets. That is, populations with poor access to dietary LC-PUFAs developed genetic variations over time, allowing them to more efficiently synthesize LC-PUFAs from LA and ALA.

 

This seems like a beneficial adaptation, right? Not exactly. 

There have been major changes in the food supply over the past 100 years. Advances in food technology and agriculture have contributed to widespread adoption of a western diet high in saturated fats, refined sugars and cereals, and vegetable oils. During paleolithic times, humans consumed a diet that was equal in omega-6 and omega-3 fatty acids; however, the ratio of omega-6 to omega-3 in the modern Western diet is approximately 16:1. While both classes of fatty acids are necessary for human health, omega-6s are largely considered pro-inflammatory while omega-3s are anti-inflammatory. Because omega-3s and omega-6s compete for bioconversion by the same FADS enzymes, excess consumption of omega-6s can block metabolism of omega-3 fatty acids. Human observational studies show that individuals and populations with the efficient variation have higher concentrations of LC-PUFAs. In the context of the western diet, this means increased production of omega-6 LC-PUFAs relative to omega-3 LC-PUFAs, a profile that has been associated with increased risk for metabolic syndrome and coronary heart disease. Although individuals with variants in FADS genes may be at increased risk of chronic disease, their genetic information can potentially be used to tailor personalized diets to optimize health.

While the idea of using nutrigenetic approaches to prevent disease is certainly exciting, additional high-quality research is needed before we can translate research to practice. For now, experts generally agree that, to achieve better balance, everyone can benefit from eating more omega-3s.

 

Peer-edited by Leah Chapman 

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