As a kid, I remember hearing that one in three people would get cancer in their lifetimes. It terrified me – cancer is almost undoubtedly the most feared illness in Western countries. But I consoled myself with the thought that almost no-one in my family had ever developed cancer. Maybe we just weren’t genetically predisposed to it.
My best friend, meanwhile, had lost several family members to cancer. She often gloomily proclaimed that she was probably destined to get it too.
Only later in life, when I became more educated about health, did I realise how disturbing it is that so many of us hold these sorts of views. In reality, there are many factors that influence our health outcomes more than our genes do.
Toothless paper tigers
Renowned physician Dr Caldwell Esselstyn once said that “…coronary artery disease is a toothless paper tiger that need never, ever exist. And if it does exist it need never, ever progress”. And yet in many developed countries, heart disease is our number one killer. It’s not uncommon for several members of one family to succumb to it. Isn’t this proof that it’s genetic?
Not necessarily. In his groundbreaking book How Not to Die, Dr Michael Greger states that “The primary reason diseases tend to run in families may be that diets tend to run in families”. He points out that for most fatal diseases, at least 80 to 90% of cases are not caused by genes. Diet is a major factor, and so are other lifestyle-related factors like stress, exercise, smoking, drinking and getting enough sleep.
How do we know this is the case? Dr Greger points to migration studies as proof. We know that in some cultures such as Japan, rates of chronic illnesses like heart disease are much lower than in Western countries like the US. But when Japanese people migrate to the US and adopt an American diet and lifestyle, they are just as likely to develop chronic illnesses as Americans. This shows that Americans are not more genetically predisposed to these illnesses than the Japanese.
Similar studies have been done for a variety of diseases and cultures, and the outcomes are the same. It has long been observed that in societies which eat their traditional diets, chronic disease is often rare or nonexistent.
Do genes have any role at all?
This isn’t to say that genes have no effect, but the effect is probably smaller than you imagine.
We may have genes predisposing us to certain illnesses, but whether these genes are expressed is largely dependent on our lifestyles. Studies of identical twins show that two people with identical genes can have radically different outcomes; a twin with a healthy lifestyle is far less likely to get sick than their less healthy sibling. Some diseases are primarily genetic, but these tend to be rare. In reality, we have a lot of control over our health outcomes.
Our mental state can have a huge impact on our physical health. In her book Mind Over Medicine, Dr Lissa Rankin explains that those who are part of a close-knit community have better health outcomes than those who aren’t.
She also discusses the power of language. For instance, if people are told that their illnesses are serious, they tend to lose hope and rapidly become sicker. But if told that it’s possible for them to recover, they tend to do better. And the placebo effect is further evidence that the way we think about something can have dramatic physical manifestations.
Genes and mental health
Mental illnesses like depression also seem to run in families, and many people assume that this is down to genetics. But psychologist Oliver James disagrees. In his book Not in Your Genes, he points out that no genes have ever been found to increase the risk of mental illnesses like anxiety and depression. Instead, these illnesses tend to run in families because of similar ‘patterns of nurture’ – the way children are raised. For example, if our parents push us far too hard at school, we may become stressed, anxious and depressed. But because we’ve internalised the idea that academic achievement is very important, we may go on to push our own children in the same way. As a result, they may develop the same mental illnesses that we did.
More serious mental illnesses may also have little to do with genes. According to James, schizophrenia is only about 3% heritable – in other words, 97% of its causes have nothing to do with genetics. Rather, it is usually caused by trauma.
Don’t believe the fear mongering
The takeaway here is that we have tremendous control over our health outcomes. After reading about these issues, I no longer have any fear of developing chronic diseases. I know that by looking after my body and minimising stress, I can drastically reduce my chances of getting ill.
Likewise, if you already have a chronic disease, you can likely halt or even reverse its progression. Drs Greger and Esselstyn both discuss how heart disease and type 2 diabetes can often be reversed with a whole food plant-based diet. The same is sometimes true of cancer. Our bodies are not inherently flawed – they don’t malfunction without reason. In fact, they have an incredible capacity to heal themselves. This knowledge should be incredibly empowering to us all.
- How Not to Die by Dr Michael Greger
- Mind Over Medicine by Dr Lissa Rankin
- The China Study by T Colin Campbell
- Not in Your Genes by Oliver James
- Preventing and Reversing Heart Disease by Dr Caldwell Esselstyn