What is more important for health?

Maybe you know a smoker who never sports and lives happily into old age. Or maybe you’ve read about a vegetarian marathon runner who had a heart attack in middle age.

These kinds of stories can’t help you, but make you think: if your health is simply written in your genes, then what’s the point of all that exercise and healthy eating? Why not just do what you want?

But, says Laura Zimmermann, MD, medical director of the Rush University Prevention Center, these stories stick with us because they’re unusual. They are examples of what scientists call ‘outliers’.

The reality is that for most people, lifestyle habits like eating healthy foods and getting regular exercise have a big effect on age-related health problems like heart disease, type 2 diabetes, cancer and Alzheimer’s disease, Zimmermann says.

So it’s all about lifestyle then? Not exactly.

“Staying healthy is mainly a matter of the choices we make.” — Donald Lloyd-Jones, MD

Epigenetics: Where Your Genes Are in Your Lifestyle

Your genes, Zimmerman says, can increase your risk for many diseases. But they usually don’t work alone. And it is rarely a single gene that determines whether you get a disease or not. More often you inherit some genetic characteristics that make you more plausible to get a disease, she says.

And even that is not written in stone. That is, these genetic traits (genetic predisposition) may not affect you at all, unless they are caused by certain aspects of your environment (environmental factors) or your lifestyle.

These “epigenetic changes” affect the way your genetic material, or DNA, works in your body. An epigenetic change occurs when lifestyle or environmental factors cause a particular gene to go “on” or “off”. In the case of cancer, for example, such changes can turn on a gene that makes abnormal cells grow. from a gene that would suppress their growth.

To complicate matters further, each gene does not have just one switch. Or even half a dozen switches. “There could be hundreds or thousands of them,” says John Kelly, MD, MPH, president of the American College of Lifestyle Medicine.

This complexity makes it more difficult for scientists to figure out exactly what epigenetic change is causing it and how exactly it increases your risk of a particular disease. But experts believe that lifestyle factors, including poor diet, smoking and lack of exercise, play an important role. “They’re basically driving gene expression into negative territory,” Kelly says.

They play such a large role in so-called “diseases of aging” — such as diabetes and heart disease, Kelly says, that they might be better described as “diseases of a toxic lifestyle over time.”

Epigenetics and Nutrition

For example, heart disease is the No. 1 killer of both men and women in the US. Still, some studies show that it may be possible to prevent 80% of heart disease. Why?

“I have a colleague who says cardiovascular disease is a foodborne illness,” Kelly says. ‘And he’s right! For the vast majority of people, it is caused by food and can be reversed by food.”

Food affects your health directly through diet. It also has an indirect link through cardiovascular disease risk factors, such as obesity and high blood pressure. For example, there are more than 300 genetic variants that can increase your risk of high blood pressure. But even with high-risk genes, you can often reduce your risk of heart disease by a third with a healthy diet and regular exercise. (You may also need medication to lower your blood pressure – check with your doctor.)

For optimal heart health, experts recommend a plant-based diet. That doesn’t necessarily mean you have to go vegan or even vegetarian, Zimmermann says. “The goal is to replace some processed foods with whole foods, including fruits and vegetables.” Look for whole grains, lean proteins (including nuts and seafood), and check the package for added salt and sugar. Talk to your doctor if you’re not sure how to design your own heart-healthy diet.

Other lifestyle factors: exercise and smoking

For exercise, experts recommend 150 minutes of moderate exercise per week. That’s 2 hours and 30 minutes a week – less than 30 minutes a day. And you don’t have to run the Boston Marathon. A walk around the block, or a little gardening or even dancing should suffice.

Putting in this bit of time can help reduce your risk of a number of diseases, whether you have a genetic predisposition to any of them or not. And yet, says Zimmermann, most people just don’t do it.

Smoking is one of the biggest risk factors for heart disease. And that’s true whether you’re genetically predisposed to heart disease or not. If you smoke, consider quitting, especially if you have heart disease or are at risk.

Your doctor can also help you find a program to help you quit smoking.

Your health habits and environment similarly interact with your genes for other conditions, including type 2 diabetes, obesity, high blood pressure, and to a lesser extent, some cancers.

Type 2 Diabetes

Type 2 diabetes tends to run in families. There are several genetic variations, including KLF14, ENPP1, and many others that increase the risk of developing diabetes by up to 30%. But dietary factors, such as how much alcohol you drink, whether you’re a smoker, and how active you are, can all tip the balance in some way, perhaps turning a gene on or off.

It is estimated that 9 out of 10 cases could be prevented through a healthy lifestyle change.

The groundbreaking Diabetes Prevention Program found that people could reduce their risk of developing diabetes by about 65% with careful diet and exercise, compared with just 35% with the blood sugar-lowering drug metformin.

Cancer

There is little doubt that genetic factors play a role in many cancers. For example, women who have a BRCA1 or BRCA2 gene mutation have a 45%-72% chance of developing breast cancer in their lifetime, which is much higher than average. But many women without known genetic mutations also develop breast cancer.

Perhaps more importantly, there is some evidence that good lifestyle habits can lower cancer risk for people with and without genetic predisposition to various cancers.

While a healthy lifestyle alone will not prevent all cancers, mounting evidence suggests it plays an important role. A study led by Cancer Research UK found that around 4 out of 10 cancers can be prevented through smart lifestyle choices such as not smoking, maintaining a healthy weight and following a healthy diet. Restrictions on red meat, sugar, alcohol, and time in the sun may also help.

Alzheimer’s disease

It is true that certain mutations in the APOE gene increase the risk of Alzheimer’s disease. If you have one copy of a version called APOE4, you are two to three times more likely than average to develop this condition. People who have inherited two copies may be at 12 times the average risk.

But it is possible and even common to get Alzheimer’s disease if you don’t have an APOE mutation. While other undiscovered genetic factors may play a role, research suggests that lifestyle is a big factor. A meta-analysis of several studies, published in the lancet neurology, found that about a third of cases are caused by factors you may be able to control, such as diet and regular exercise.

Again, research shows that diet and exercise are very important. While most healthy diets should help, the MIND (Mediterranean-DASH Intervention for Neurodegenerative Delay) diet — which emphasizes brain-stimulating foods like vegetables, berries, fish, and olive oil — seems to be the best.

You can do everything right and…

Scientists still have a long way to go to unravel the complex interplay between your genes and your environment. Zimmermann points out that the impact of these factors varies between diseases and from person to person. There’s no question, she says, that in some cases you can do everything right and still get a serious illness or disease.

The best thing you can do, Zimmermann says, is try to change the factors you can control, such as diet, exercise, regular medical checkups, and taking your medication as prescribed.