DNA; it’s remarkable that this “small” molecule carries all the information organisms need to develop and function. Since DNA in many ways is at the root of all life on earth, I strongly believe that understanding the interaction between our environment and lifestyle and our genetic material is a key to optimizing health. In terms of genetics and life on earth, a long-standing discussion revolves around the relative importance of nature and nurture. Are we the way we are because of our innate qualities, or because of our personal experiences throughout life? In the field of health & fitness, the question of genetics vs. environment is highly debated, but a general belief is that genetics hold the gun, while environment pulls the trigger. In other words, the genes you inherit from your parents determine your susceptibility to disease, but whether you get a certain disorder or not is largely determined by your environment and lifestyle. This is where we get into the field of epigenetics. While it’s long been known that a healthy diet and lifestyle to a great extent can dampen the effects of “poor genetics”, it’s only recently that we’ve begun to understand the mechanisms and extent of this relationship.
Epigenetics is defined as heritable changes in gene expression that are not due to alterations in the DNA sequence. The epigenome is “above” the actual genome in the sense that it consists of chemical compounds that modify or mark the genome in a way that influences gene expression. In a broader perspective, this statement by Boris A. Shenderov and Tore Midtvedt summarizes how our view on human genetics is changing:
It is now generally accepted that the ‘central genome dogma’ (i.e. a causal chain going from DNA to RNA to proteins and downstream to biological functions) should be replaced by the ‘fluid genome dogma’, that is, complex feed-forward and feed-back cycles that interconnect organism and environment by epigenomic programing – and reprograming – throughout life and at all levels, sometimes also down the generations (1).
So, basically what we’re learning through this fascinating area of science is that although we aren’t able to change the actual DNA sequence, we do have great control over gene expression. In other words, even though the genetic code stays the same throughout our lives, it’s our environment and lifestyle that determine which genes are highly active and which ones that are suppressed. Even more interestingly, some of these epigenetic marks are heritable, meaning that your children (and possibly generations after that) not only receive your genetic code, but also your epigenome.
The fact that our environment impacts the epigenome means that some of the epigenetic marks we inherit from our parents might be passed on to future generations, while others are not. At this time we don’t really know how long these marks can linger throughout generations. Studies in agouti mice have shown that a special gestational diet turned off disease genes for 3-4 generations, but as studying these types of effects in humans takes a long time, there isn’t a lot of infromation on transgenerational epigenetics yet (2). It’s well known that certain epigenetic marks pass down to your children, but it’s still unclear to which extent your grand children and great-grand children are affected by your lifestyle choices.
Epigenetics: The bridge between genotype and phenotype
Although we’ve known about the epigenome since the 1970s, it’s only during the last couple of decades (and especially the last couple of years) that we’ve started to understand the important implications epigenetics has for medicine, nutrition, and human health. Epigenetics is in many ways the missing link between environment and genetics, as it can help us understand how humans can adapt to a wide range of different living conditions. Also, it can help explain many phenomenons that fall outside the classical view of human genetics.
We know that most of the so-called diseases of civilization, such as obesity, type-2 diabetes, and cardiovascular disease, have a genetic component. However, we also know that the prevalence of most of these disorders have increased dramatically over the last several decades. In combination with the studies showing that these conditions are/were virtually unheard of in hunter-gatherer populations and many non-westernized populations, this suggests to me that epigenetic processes are more important than the specific human genes you inherit from your parents.
Since our environment has such a profound impact on the epigenome, one of the reasons many chronic diseases are now on the rise is that we’re putting down epigenetic marks that are passed to future generations. This maladaption to the modern environment, a habitat characterized by easy access to highly palatable and calorie dense food, pollutants, and little demand for physical activity, is something I’ve talked a lot about on the blog, and it’s no doubt that chronic degenerative diseases primarily result from a mismatch between our genome (which was forged in an ancestral natural environment) and the modern diet and lifestyle.
Studies of identical twins have been an important part of the process of understanding epigenetics. Identical twins are born with the exact same DNA and epigenome (epigenetic marks inherited from parents), but as we know that environment impacts gene expressions, this epigenome doesn’t stay constant throughout life. So, although twins have the same genotype, their actual gene expression throughout life depends on their environment and lifestyle. In other words, if one of the twins is exercising regularly and eating a nutrient-dense diet, while the other one is sedentary and consumes primarily refined food, their gene expression will be very different. These epigenetic processes explain why twins can develop different diseases even though they have the exact same DNA.
Turning your good genes on
Although epigenetics is still a young science, we already know that dietary components, smoking, pollutants, stress, physical activity, and several other factors impact gene expression (3,4). Basically, by making the right lifestyle choices we can turn our “good genes” on and our “bad genes” off. This might sound like a far-fetched idea to those that are used to the concept of DNA as a static machinery, but the science is actually clear-cut; pretty much all aspects of our lifestyle have an impact on how we express our genes; whether it’s sitting down for some yoga, eating some greens, or going for a run (3,5,6).
Although there’s definitely still a way to go in terms of understanding exactly how we can tweak this gene expression to our advantage, I would say that we already have the knowledge we need to make the right lifestyle decisions. As I’ve repeatedly highlighted in my articles, combining an evolutionary perspective on human health with modern science can help us understand what types of inputs our genome “expects”. Basically, we have to provide the type of stimuli that are needed to promote a normal phenotype (the observable physical or biochemical characteristics of an organism). As with pretty much everything else related to health and fitness, it comes down to these essential components: diet, stress, physical activity, sun exposure, sleep, exposure to microbes, and exposure to pollutants.
In terms of nutrition, studies have shown that broccoli, green tea, cauliflower, kale, and other plant-based foods seem to have a positive effect on gene expression (3,4,7). However, while most of the focus has been on polyphenols and other specific compounds found in food, I firmly believe that focusing on specific food components is too narrow. Yes, eating a lot of fresh vegetables is certainly not a bad idea, but it’s the overall diet that matters.
Recent animal studies have even shown that “small amounts of occasional indulgences may produce significant changes in gene expression that could negatively impact physiology and health” (8). This is not to say that you should get compulsive about your diet, as healthy living is definitely about finding the right balance between “optimal” and “enjoyable”. However, it does suggest that even small changes in diet have an impact on the epigenome.
The idea of epigenetics might be a unwelcome thought for some, as it means that pretty much all bad lifestyle choices we make alter epigenetic processes that not only affect ourselves, but also future generations. However, the fact that we can influence gene expression is also immensely empowering in the sense that DNA is not destiny…
Did this pique your interest in epigenetics? I hope it did, as this is an extremely fascinating subject. If you want to learn more, take a look at the two videos below…
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