Your aunt died of heart disease at 52. Your father has diabetes. Your grandmother had Alzheimer's. And here you are, waiting for your turn, because "it runs in the family."
That belief may cost you more than the genes do.
Look at what happened to people whose genes were against them. Among 55,685 adults, those in the top fifth for inherited risk of heart disease had 91% more heart attacks and other coronary events than those in the bottom fifth. The genes are real.
Then the high-risk fifth was sorted by how they lived. Four plain things were counted: not smoking, not being obese, regular activity and a healthy diet. Those who managed at least three had 46% fewer coronary events than those who managed one or none. In one of the groups followed, that took the share who had an event within ten years from about eleven in a hundred to about five.
Same inherited risk, about half the heart trouble. The genes were as bad on both sides of that sum. The dinners were not.
So the family history is worth knowing. It tells you where to look. It does not tell you how it ends.
What the 2% measures
You may have met the claim that genes control 2% of your health and your choices 17%. The numbers are real. The sentence around them is wrong. It is a good number attached to the wrong noun.
They come from 492,567 British adults, and what was measured was who died early. On top of age and sex, the conditions and habits of a person's life explained a further 17 percentage points of the differences. Inherited risk scores for 22 major diseases explained less than 2.
Disease by disease the picture changes, and this is the part the claim leaves out. For diseases of the lung, heart and liver, the way of living explained more than the genes did. For dementia, and for breast, prostate and bowel cancer, the genes explained more.
So for your aunt's heart, the odds favour what you do. For your grandmother's Alzheimer's the genes carry more weight, and even there the way of living shows. 8 Smart Ways to Fight Cognitive Decline with Food has the figures for people at the highest genetic risk of dementia. And in a two-year Finnish test of diet, exercise and mental training, 362 of the people taking part carried a well-known risk gene for dementia. The benefit to thinking showed in the carriers too.
Genes against habits
Now put the two side by side for the length of a life. 353,742 British adults were scored twice: once for the genes that go with a short or a long life, and once for how they lived. They were followed for about thirteen years.
Genes for a short life went with a 21% higher rate of death than genes for a long one. An unfavourable way of living went with a 78% higher rate than a favourable one. People with both against them died at twice the rate of people with both in their favour.
Each counted on its own, and the habits counted for more than three times as much.
One caution covers most of this page. These people were watched, and no one assigned them a way of living. People who live well differ from people who do not in ways no score catches. Further down, the findings in which people were assigned to change carry more weight, and each is marked.
What the belief does
The belief itself has been put to the test. 223 people had their DNA read for a gene tied to the risk of obesity. Then each was told, at random and whatever the real result, that they carried the "high-risk" version or the "protected" one.
One group of 116 then took a running test. The other 107 ate a meal. What they had been told showed up in their bodies: in how their heart and lungs performed and how long they could run, and in how full they felt after the same meal and the chemistry behind that feeling. The effect ran in whichever direction the result pointed, and it was sometimes larger than the effect of the gene they carried.
They were handed a story about their genes, and their bodies went along with it.
So should you buy a gene test? Across 18 tests in which people were given their DNA-based risk of a disease, the news changed nothing: their smoking, eating and activity stayed as they were. Most of those tests were weak ones, so the question is not closed. A result on paper did not make people live better. What it can give you is a story about yourself, and the running test shows what a story can do.
Hardware and software
Your genes are hardware. Your lifestyle is software. The software decides which programs run.
That is a figure of speech with chemistry under it. Genes carry chemical tags that help set whether a gene is read or left silent. The DNA stays the same. The tags can change.
The field is called epigenetics. C. H. Waddington coined the word in 1942, when no one yet knew what a gene was made of. The hardware itself is modest: between 19,000 and 20,000 genes that code for proteins.
Identical twins show the tags changing. They begin with the same DNA, and in the early years of life their tags cannot be told apart. Older twins carry "remarkable differences", enough to change which of their genes are active. Same hardware, decades of different software.
What that shows is that the tags drift over a life. It does not show which habit moved which tag.
One case does name the cause. In the winter of 1944–45 the German-occupied Netherlands went through a famine, the Dutch Hunger Winter. Six decades later, people who had been conceived during it carried fewer tags on a gene involved in growth than their own brothers and sisters who had not been exposed. A few months before birth could still be read on their genes sixty years on.
Key Factors That Speed Up Aging (And How to Slow Them Down), linked below, has what one habit did to twins' faces: judges could pick out the twin who smoked.
When one gene decides
Everything so far concerns diseases built from many genes, each with a small say. A few conditions hang on a single gene, and the title of this page does not stretch to all of them.
Huntington's disease is the hard case. A person who inherits the gene will develop the disease, and each child of an affected parent has a 50% chance of inheriting it.
Phenylketonuria points the other way. It is a single-gene condition too: a baby born with it cannot break down phenylalanine, a building block of protein, which can then build up to toxic levels. Untreated, it can lead to intellectual disability and seizures. The treatment is a diet low in phenylalanine, begun as soon as possible after birth and kept for life. People who are found early and keep to it can have normal health and a normal lifespan, which is why many countries test newborns for it.
One gene, fully inherited, and what decides the outcome is on the plate.
The four things that matter
Back to the common diseases, the ones built from many genes. 23,153 Germans aged 35 to 65 were followed for about eight years, and four things were counted at the start.
Never smoking. If you smoke, this is the one that comes first, and stopping pays. Among 202,248 American adults, smokers lost more than ten years of life against people who had never smoked. Those who stopped between 35 and 44 lived about nine years longer than those who carried on, and those who stopped between 45 and 54 about six.
A body mass index under 30. That is the line where obesity begins.
Activity. Three and a half hours a week or more, which is half an hour a day. Walking counts. Activity also blunts the strongest known gene for obesity: among 218,166 adults, each copy of its risk version raised the odds of obesity by 30% in inactive people and by 22% in active ones. A modest difference, and it runs the right way.
Diet. Here "healthy" was scored as plenty of fruit, vegetables and whole-grain bread, and little meat. This site's version of the fourth habit is different: real food, with meat, fish and eggs at the centre and the sugar taken out.
People with all four had 78% less chronic disease than people with none: 93% less type 2 diabetes, 81% fewer heart attacks and 36% less cancer. Strokes were halved as well, on numbers too small to be sure of.
People who did all four lived like they had different genes. About one in eleven did all four. The door is open, and ten in every eleven people were standing outside it.
Those Germans were watched. The same idea has been tested with lots drawn, and with the genes read afterwards. 3,234 adults whose blood sugar was raised, short of diabetes, were assigned to one of three things: a programme aimed at losing 7% of their weight and at regular activity, the drug metformin, or a dummy pill. Over about three years the programme cut new cases of diabetes by 58%, and the drug by 31%.
Then came the genes. Among 3,548 people from that test, those carrying two copies of a variant strongly tied to type 2 diabetes went on to diabetes 81% more often than people with none, on the dummy pill. In the programme group the figure was 15%. The gap between the groups was not statistically firm, so take it as a strong hint: the gene counted most in the people who changed nothing. The programme set targets for weight and activity, and it was not a test of any one diet.
Can it be turned back?
Prevention is one thing. Your father already has diabetes, so here is the harder question.
The heart, tested small. Dean Ornish assigned 48 people with moderate to severe coronary heart disease to his programme or to usual care. The programme was five things at once: a vegetarian diet of whole foods at 10% fat, aerobic exercise, stress training, stopping smoking and group support. Cholesterol-lowering drugs were left out.
After five years, the narrowing in the programme group's arteries had eased by 7.9% in relative terms. In the usual-care group it had worsened by 27.7%. There were 25 cardiac events among the 28 people on the programme, and 45 among the 20 who were not.
It was small: 35 people had the final scan. And it was a bundle, and a bundle wins or loses as a bundle. Nothing in it can say whether the diet, the exercise, the calm or the end of smoking did the work, and the diet is not the one this site would choose. What it showed is the thing that matters here: narrowed arteries moved the other way when people changed how they lived.
Diabetes, tested without drawing lots. 262 adults with type 2 diabetes joined a programme built on a ketogenic diet, with carbohydrate cut low enough for the body to run on fat and their medicines adjusted as they went. After a year their long-term blood sugar marker had fallen from 7.6% to 6.3%. They had lost almost 14 kilos on average. The share taking diabetes medicines other than metformin fell from 57% to 30%, and insulin was cut or stopped in 94% of those who had been using it. Among 87 people on usual care, there was no significant change.
The limits are plain. People chose their group, and the work was paid for by the company that runs the programme, where several of the authors work. Anyone on diabetes medicine who cuts carbohydrate needs those medicines reviewed as they go, because blood sugar can fall fast. How to Fix Blood Sugar Spikes Naturally has what low-carb, keto and carnivore eating do to the spikes. A shows both numbers at home: the blood sugar, and the ketones that say the body is running on fat.
What families hand down
Families share more than DNA. They share a table, a street and a set of habits.
Among 257,620 families, the share of type 2 diabetes put down to inheritance fell from 37.7% to 28.4% once the place the family lived was taken into account. For obesity it fell from 53.1% to 46.3%. Part of what looks inherited is the neighbourhood, down to its air.
Kitchens are harder to measure, and the same logic applies. You inherited the way your family eats along with its genes, and only one of the two is fixed.
Two kinds of family show it from opposite sides.
Adopted children carry one family's genes and live with another family's habits. 960 families with a child born in the 1920s and adopted early in life were followed. When a biological parent had died before 50, the adopted child's own risk of an early death was 71% higher, and four and a half times higher for deaths from the heart and blood vessels. For cancer it ran the other way: the risk followed the adoptive parent, at about five times, with a wide margin of error. The pattern was weaker when the parent had died before 70 than before 50: the younger the relative, the louder the signal. One family's genes, another family's dinners: it is the closest thing to an experiment that family life allows.
So a relative lost to her heart at 52 is a signal to take seriously. It is also the same risk that was cut by about half at the top of this page.
Husbands and wives are the reverse case: shared habits and no shared genes. Across 75,498 couples, a husband or wife with diabetes went with a 26% higher risk of having it yourself.
A whole community shows what shared habits can add up to. 34,192 Seventh-day Adventists in California were followed for twelve years. Their church advocates a vegetarian diet and discourages alcohol and tobacco. At the age of 30, Adventist men could expect to live 7.3 years longer than other white Californians, and women 4.4 years longer. Among the Adventists themselves, the best and worst combinations of diet, exercise, weight and smoking were up to ten years apart.
The habits are tangled together there. Nothing in the count says how much belongs to the diet and how much to a life without cigarettes or drink. What it does say is how large the sum can be.
Change the habits, change the outcome.
Stress and the cell's clock
Each strand of your DNA ends in a cap called a telomere, which wears down as cells divide. Among healthy women, those who felt under the most stress had telomeres shorter by the equivalent of at least ten extra years of ageing.
Can that be undone? One small test tried. Thirty-nine people caring for a relative with dementia were assigned to a short daily yoga meditation or to relaxing music, for eight weeks. In the meditation group the activity of telomerase, the enzyme that rebuilds the caps, rose by 43%. With the music it rose by 3.7%. Mood improved more with the meditation as well.
That is an enzyme, in 39 people, over eight weeks. The caps themselves were not measured. It is a reason to deal with stress. It does not show the damage erased.
There is a second clock, which reads the speed of ageing from a blood sample. Among 220 adults, two years on a diet set at a quarter fewer calories slowed that speed, by a small amount. The ageing article linked below has how the measure was built.
Heat and cold
A little stress is a different matter. It can leave a body tougher. The name for it is hormesis, and the short version is "what doesn't kill you makes you stronger". The evidence comes in three sizes.
Sauna, linked. 2,315 Finnish men aged 42 to 60 were followed for about twenty years. Of those who took a sauna once a week, 49% died in that time. Of those who went most days of the week, 31% did, and they had about a third of the dementia. The men chose their own habits, and a man who can sit in a sauna most days may be the healthier man to begin with.
Cold showers, tested. 3,018 adults were assigned to end their showers cold for a month, or to shower as usual. The cold group took 29% fewer days off sick. They were ill on just as many days. They went to work anyway. Whether that is health or stubbornness, the count cannot say.
Cold, breathing and meditation, tested small. Twelve volunteers were trained for ten days in meditation, breathing techniques and cold exposure. Then they and twelve untrained volunteers were injected with a bacterial toxin that brings on flu-like symptoms. The trained group produced fewer inflammatory signals and felt less ill. Twelve people and three techniques at once: it cannot say which of the three did it.
Two claims, put right
Your gut bacteria. The claim is that they switch your genes on and off. What was found runs the other way. Among 5,959 Finns, 567 links turned up between a person's gene variants and the bacteria living in their gut. Your genes help choose your bacteria. Food chooses too, and fast: when volunteers ate only animal foods or only plant foods, their gut bacteria shifted quickly, by enough to swamp the differences between one person and the next.
Your eating window. Squeezing meals into fewer hours is sold as a reset for your genes. Intermittent Fasting: What It Does and When It Works Best has what the window did when it was tested, and Why Snacking and Small Meals Can Sabotage Your Weight Loss has the case against eating little and often.
What to do with a family history
The word "gene" was coined in 1909, from the Greek for offspring. A family history is the oldest gene test there is, and it costs nothing. Three steps make it useful.
Write it down. Who had what, and at what age: parents, brothers and sisters, grandparents, aunts and uncles.
Weigh the ages. A heart attack at 52 says more than one at 82. Among the adopted children, a parent's death before 50 was the louder signal.
Match the habit to the disease. Heart disease in the family: the four things, with smoking first. Diabetes: the sugar and the starch, and your weight. Dementia: the genes count for more, and the same habits still showed in people who carried the risk gene.
Read that way, a family history stops being a sentence. It is a list of where to put the effort.
How long it takes
Knowing and doing are different animals. The figure that gets repeated for how long a change takes is 21 days. It goes back to Maxwell Maltz, who wrote in 1960 that people who had had plastic surgery took about 21 days to get used to a new face. When habits were measured, the average was 66 days, and people ranged from 18 to 254. Why Motivation Fails — and What Keeps Habits Going After It Does, linked below, has the whole story.
So when you quit after three weeks, you are not weak. You were working from bad information.
Start stupidly small. Want to meditate? Start with one breath. Want to exercise? Put on your shoes. BJ Fogg built a method on it in , and James Clear's "two-minute rule", from , is the same idea.
Missing a day doesn't ruin anything. Using one missed day as an excuse to quit ruins everything.
Pick ONE thing
Go back to the family in the first paragraph. Your aunt's heart: people with the worst genes for it had about half the trouble when they lived well. Your father's diabetes: among people who already had it, the share on extra medicines nearly halved within a year of changing what they ate. Your grandmother's Alzheimer's: the genes weigh more there, and the way of living still showed.
Your father's diabetes can end with him. Your aunt's heart was her story. Your family's medical history is just that: history.
Pick ONE thing. If you smoke, it is that. If you do not, take the sugar out, or walk for half an hour a day. Give it 66 days, and when you miss one, do it the next.
The hardware is yours for life. The software is open for edits.
Choose it today.
Curious what ages one twin faster than the other? Key Factors That Speed Up Aging (And How to Slow Them Down) — the sun, smoke, sugar, stress and sleep, and how much each one adds.
Want the one thing to last past week three? Why Motivation Fails — and What Keeps Habits Going After It Does — why the first burst runs out, and what carries a habit once it has.
Do you know someone who is waiting for the family illness to arrive? Send them this, and tell them to pick one thing.
Disclaimer: This article is general information. For advice about your own health, talk to a qualified health professional. If you take medicine for diabetes, have it reviewed before you cut carbohydrate.
Affiliate Disclosure: This article contains affiliate links. As an Amazon Associate, All For Life earns from qualifying purchases, at no extra cost to you. We only link to products we would recommend without the commission.
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