Welcome to Nutrition Bites. The no nonsense podcast where you get the truth about food so you can eat what you want and be healthy. I’m your host Maggie and welcome to the series! If you’ve ever been frustrated at the mismatch between the way you eat, and how you look on the outside, or feel on the inside, you’ve likely blamed the scapegoat of human variability - genetics. On the menu today, DNA-based diets.
As a child I was a terribly picky eater. For some reason, I hated flavour, texture and pretty much anything that involved more than one taste bud. I lived off of plain, neutral-coloured foods like white bagels with butter and pasta with no sauce. I also had a crazy sweet tooth. As a teen I would consume a full box of Froot Loops cereal and 2L of mango juice whenever I competed in a volleyball tournament. The fact that I didn’t have an issue with weight or blood sugar is incredible. And that’s the strange thing. For all intents and purposes my diet was problematic, but I was considered healthy, with no health issues on the horizon. So what gives? Well while the basic principles of nutrition are generally true for everyone, our individual requirements and responses to food are highly varied. That’s because our unique lifestyle, environment, gut microbiome, and genetics all influence our health. But while you can adapt your lifestyle, modify your environment, and influence your gut microbiome, you can’t change your DNA. And the genetic diversity between people means there is no “one-size fits all” approach to nutrition. An eating pattern that works for your friend may be terrible for you. So the idea of analysing your DNA, and prescribing a diet based on your unique genetic code, seems fantastic. But is it even possible to do? And is it actually the nutrition solution some make it out to be? Let’s find out.
To truly understand the power and intersection of nutrition and genetics, we first have to dust off the old noggin and recall some basic high school biology. But instead of cracking open a dilapidated textbook, we can now use Reddit as a resource to provide a TLDR on such a complicated topic. At a high-level genetics is all about providing instructions to your body on how to function. The genome is what we call the overall genetic map of an organism, like an instruction book for how to make a human. The genome is made up of structures called chromosomes, each of which act as a group of instructions. Think of them like pages in a book. These chromosomes are made up of thousands of genes. Genes are instructions for building specific materials in the body - all our proteins, hormones and every other molecule. In this book analogy, genes act like sentences on a page. Genes are composed of a particular sequence of DNA. DNA is a molecule that codes for the instructions, and in this analogy they are like individual letters in a sentence. So to summarise, DNA are the coding blocks that make up genes, and genes instruct the body to make literally everything. Genes are stored together on chromosomes, and your entire genome, which dictates how to make a human, consists of multiple chromosomes.
Now while the general base code of all genes in the human body is the same, slight differences in the order of the DNA molecules can cause big changes. Think of it like swapping letters around in a sentence - a letter added or removed can make the difference between protagnoist Dan feeding his dog, dogs, or frogs. Now let’s apply this logic back to real humans. We all have a gene called “OCA2” which helps code for eye colour. While the majority of the DNA in this gene will be the same between all of us, differences in the DNA code can cause OCA2 to instruct for brown eyes or blue eyes. These variations in our genetic code, which are a result of natural processes, are responsible for the incredible variety in how humans look and operate.
Importantly, our genetic variety doesn’t just cause external changes - it has significant internal impact as well. A fairly relatable variation is in the gene that codes for the lactase enzyme. One variation can mean we exist in a world where “ice cream is nice”, while another variation equates dairy with a doomed trip to the bathroom. But generally speaking, our differences are rarely the result of DNA changes to one single gene. And that’s because many biological processes and physical traits are controlled by multiple genes. Even the OCA2 gene is not solely responsible for eye colour. It is thought to be just one of 16 genes that influences the exact shade we wind up with. And when you think of complex processes related to nutrition and health, genetic variation can be a billion piece puzzle to sort out.
The field of nutritional genomics, often called nutrigenomics, and sometimes, for the hell of it, nutrigenetics, aims to explain how and why our bodies respond to what we eat and drink. The ultimate goal is to use this knowledge to help inform food choices so your body’s unique nutritional requirements are precisely met. Let’s use caffeine as a simple example of how our genes, and their variations, influence our digestion and reaction to this molecule.
As of today, scientists have discovered two genes which dictate how caffeine is broken down in the body. Together, these genes influence how much, and for how long, caffeine circulates in your bloodstream. Variations in either of these genes can lead to two outcomes. One is that you are a quick metabolizer, meaning your body rapidly breaks down caffeine. Quick metabolizers are the types of people who need three espressos before starting the day, and never fail to remind you about it. Other variations in these genes may cause you to be a slow metabolizer, meaning caffeine stays in your blood for longer, and one sip of coffee can be enough to power you into the evening. A separate gene involved in caffeine metabolism is thought to be responsible for transporting the molecule from the blood to the brain, which is where it exerts its energising effects. Variations in this gene may result in more or less caffeine reaching your brain, therefore impacting the magnitude of its effects on you. And finally, two other genes have been discovered which influence anxiety levels after caffeine reaches the brain. Some variations of these genes are thought to cause heightened anxiety.
Knowing there are multiple genes, with different variations, that can impact how one metabolises and reacts to caffeine, let’s now imagine the following scenario. Say your DNA is analysed and you are confirmed to be: a slow caffeine metabolizer, with a high transport to the brain, and are likely to have heightened anxiety after ingesting this molecule. This information can now be used to help guide your decision making about consuming caffeinated items. And this is the whole point of nutrigenomics - arming people with information about their unique biology so they can make better decisions for their health and wellbeing.
And sure, you may be able to tell from a life of coffee and Redbull experimentation that caffeine is not your friend, but having this confirmed by your DNA can be very powerful. And this is particularly important with chronic health conditions like diabetes, obesity and heart disease. Knowing your family history is one thing, but having a geneticist tell you that your DNA suggests a high likelihood of a heart attack, can really motivate you to make some lifestyle changes. And it’s this idea of being able to better control your future health which is driving the recent trend of direct-to-consumer nutrigenomics tests.
Before 23andMe existed, analysing your DNA was an incredibly expensive, complex, and lengthy process. It was really only used to test very specific health conditions, and support CSI style crime investigations. But with recent, incredible, advancements in technology, “just-for-fun” genetic tests, like from 23andMe and Ancestry.com, became a reality. While once quite popular, buying these tests today to discover your ethnic background, or any long lost relatives (family drama not guaranteed), seems to have lost their appeal. Data privacy is a big concern, and we don’t want to send our genetic details to a company unless the results can really change our lives. Which is why it’s not surprising that the once genericized consumer genetic tests are becoming more niche. With health being the biggest focus of them all.
Multiple companies now sell direct-to-consumer nutrigenomics tests. And no matter who you buy from, the process, and promises, are the same. Spit in a tube, mail it off, and receive personalised information to help you take control of your health. Nutrition Genome is one of the more popular nutrigenomics testing companies. For $359 US dollars you will receive over 20 reports outlining your specific health-related genetic traits - like how sensitive your blood sugar levels are to refined carbs, and what your optimal micronutrient requirements are. Not only that but you’ll also receive a customised grocery list, and a catalogue of foods and ingredients to avoid, all based on your DNA. After listening to enough of these podcast episodes, your spidey senses should be tingling right about now. Because if it sounds too good to be true, it usually is.
Critics are quick to point out that the nutrigenomics tests which exist today are incredibly flawed. And it’s for one simple reason. We just don’t know enough about our genes to make personalised dietary recommendations. Evaluating and understanding human genetics is an extremely new field. We just didn’t have the technology required until a few decades ago. The Human Genome Project, which was a massive global initiative to sequence the entire human genome, kicked off in 1990, and only finished, in full, 6 months ago. That’s right. It took over 30 years to determine the base code for the roughly 30,000 genes that make us human. And remember most, if not all, genes have some level of variation to them. So a company trying to sell you DNA-based recommendations for health is very premature. And keep in mind, Nutrition Genome only evaluates 100 genes. Considering how complex our entire body is, looking at such a small portion is like claiming you’ve read an entire book when really you’ve only glanced at the cover art. This means you’re more likely to receive generic good-for-you food advice, than a DNA-based diet tailored to you.
Another flaw with current nutrigenomics tests is a general problem with genetics: they mostly just make predictions. Now there are cases where having a particular gene variant will guarantee an outcome, like with Cystic Fibrosis, but for the most part, a genetic variation often results in an association with a health outcome. And it’s these associations that makes nutrigenomics a tricky field to make recommendations in. Let’s use obesity as an example.
The FTO gene is the it girl gene in nutrigenomics - scientists just can’t stop talking about her! This gene helps regulate fat metabolism, and in 2007 scientists discovered a specific variation that was associated with an increased risk of obesity. In the study, 40,000 Europeans had their FTO gene analysed, and researchers discovered that the presence of a unique variation was associated with increased weight, and a high likelihood of developing obesity, compared to someone who didn’t have the variation. For nutrigenomics, this was a groundbreaking finding. After all, if you could test for the genetic risk of developing obesity, you could guide people with the risky variant to adopt preventative habits earlier in life. But in the 15 years since that publication, there hasn’t been development of an obesity genetic test. Moral implications aside, the primary scientific reason why this hasn’t happened is that just because a genetic variant may be associated with a particular trait, doesn’t mean that someone with that variation is destined to develop that condition. Obesity is influenced by multiple factors including nutrition, physical activity levels, and mental health status. And each of those factors is what we call polygenic - meaning that tens to hundreds of genes, with multiple variants, play a role. So guaranteeing the development of obesity based on one variation of one gene doesn’t add up. And as much as we’d like a genetic scapegoat when it comes to things like weight gain, it’s just not that simple.
The future of nutrition is definitely moving towards genetic precision, and at some point in your lifetime, you may be recommended to take a DNA test to help inform recommendations on what you should eat. But this Gattaca-level aspiration is very much a future state. There is just so much more science to be done to build the evidence required to provide individual, DNA-based nutrition guidance. And even still - genetics is only one factor that influences your overall health. Your environment, behaviour and the makeup of your gut microbiome (those sneaky buggers), will also need evaluation and attention. So at this point in time, let the scientists keep on with their science, and save your money for genetically testing your adopted dog rather than yourself.
That’s been the bite for today, stay hungry.