Why “good” and “bad” are irrelevant when talking about genes and nutrition
From the desk of: Mihai Niculescu, M.D., Ph.D.
…“How to override your bad genes with food.” “Can Exercise Override Bad Genes?” “Good Nutrition Can Overcome Bad Genes”…
We are bombarded by media with these kinds of messages. The main theme, of course, is that many of us may have “bad” genes that would put us at risk of a certain poor health outcome unless we eat less of “this” and more of “that.” Knowing myself as a bearer of several such genetic variations, I almost feel, at times, guilty that I am harboring such “bad” genes, albeit without my consent.
Here is why such thinking is wrong, and why the paper I have read recently is a good example of how the public should understand what nutrigenomics is, and why there are no such things as “bad” or “good” genes when it comes to nutrition (except for very few documented cases). And here I am talking about those genetic variations (changes in our genetic code) that are quite frequent (being present in up to 50 percent of us).
First, let’s establish a couple of things. 1: Genetic variations that are at high frequency in a population are the result of Darwinian selection. If such genes are (still) frequent in the human population, all this means is that individuals who carry them had no troubles in reproducing and in disseminating their genes through their offspring. This only tells us that those individuals were okay in the environment (including nutrition) they used to live in. 2: Scientists discovered that, in many cases, genetic variations across one or more genes are not randomly combined, but rather they exist in only several combinations (called haplotypes). These combinations of genetic variations are inherited by descendants.
THE STUDY
The study by Ameur and colleagues (see link below) looked at how these haplotypes, or combinations of genetic variations, evolved during human evolution for those genes responsible for processing omega-3 and -6 fatty acids acquired from vegetable oils. When comparing the present European populations with archaic hominins and distant primates, they concluded that a certain combination of such variations (called Haplotype D), appeared after the split from Neanderthals (around 500,000 years ago). Moreover, this means that the Haplotype D, being enriched in more recent populations (Africa, Middle East, Asia and Europe), while quite rare in the Americas, indicates that the Haplotype D shows positive selection (its frequency increases in more recent populations), meaning that it brought some type of survival advantage in the environment from Africa, Asia, and Europe, but not in the Americas.
WHY IS THIS IMPORTANT
Interestingly, the researchers also measured how Haplotype D influences the omega-3 and -6 metabolism, and they concluded that the Haplotype D accelerates the conversion of omega-3 and -6 fats from vegetable sources, into molecular species that are found mainly in fish oil (DHA and EPA), and also into arachidonic acid (main omega-6 component). Note: DHA and EPA have many health benefits, while arachidonic acid is a pro-inflammatory molecule. So, by all means, Haplotype D carriers were at an advantage during the development of the human race in the Afro-Eurasia continental mass. Is this, then, a “good” haplotype? “Definitely,” would answer the proponents of the “good” and “bad” genes concept.
But here is the catch! The same Haplotype D (so beneficial during our evolution) proved to be a problem when it comes to our modern lifestyle and nutrition habits. It turns out that the Haplotype D actually increases the risk of having coronary artery disease, but only because we eat more omega-6 oils than we should (and not enough omega-3 oils). Because Haplotype D carriers are so efficient in converting omega-6 precursors to arachidonic acid, they have an increased inflammation status, which contributes in turn to the coronary artery disease. This is “bad,” isn’t it?
WHAT THIS MEANS FOR YOU
So how should we interpret these findings, and how do we know what we should eat? This study is a good example of how we can tackle individualized nutrition. It suggests that those people who have the Haplotype D should increase their intake of omega-3, and decrease the omega-6 intake.
“Good” and “bad” genes? Hardly. Rather, we should focus on how fit our environment (nutrition included) is for our genes. This is a much more productive approach, allowing us to reshape our lifestyle to what each of us needs.
Reference: Genetic Adaptation of Fatty-Acid Metabolism: A Human-Specific Haplotype Increasing the Biosynthesis of Long-Chain Omega-3 and Omega-6 Fatty Acids (Am J Hum Genet. 2012 May 4; 90(5): 809-820)
