In a Native American community in Arizona, where type 2 diabetes is common and families had been followed for decades, there was a rare chance to tell genes from the womb. Some mothers had developed diabetes partway through their childbearing years. So their children came in two kinds: those born before the diabetes, and those born after.
Same mother. Same father. Same genes on offer. The only difference was the womb. Nature rarely sets up a cleaner test.
The children born after their mother's diabetes had 3.7 times the odds of developing diabetes themselves. The ones who had escaped it so far were heavier too. And when it was the father who had become diabetic, the children born before and after showed no such difference.
A good deal of what runs in families is not genetic. It gets handed over in the womb, at birth, through feeding and at the table.
Ahead, what your mother passed on that was never in your genes: what crosses the placenta, the ice storm that reached children not yet born, where the egg that became you was made, the 300,000 Dutch conscripts who carried a famine into adulthood, the poison the placenta gathered instead of blocking, the bacteria a baby picks up on the way out and the milk sugars meant only for them, the colic that came from the mother's milk jug, the flavour a baby learns before birth, what a father's waistline does to his sperm, and why none of this is anyone's fault.
The womb
The baby gets what the mother eats, drinks and carries.
Alcohol crosses the placenta and the umbilical cord, and the unborn baby breaks it down slowly, so it stays longer than it would in an adult. Smoke sends in carbon monoxide, which takes the place of oxygen in the baby's blood, while the nicotine narrows the vessels of the placenta itself. Babies of smokers are born on average about 200 grams lighter. A small bag of sugar, missing. Fertility Herbs: Which Work, and What Matters More has caffeine's version: it crosses the placenta, and a developing baby can barely break it down, so it builds up.
Her blood sugar crosses too. That is what the Arizona siblings show. A baby who spends nine months in high blood sugar is set up for weight problems and diabetes later, over and above whatever genes it inherited.
Some of what matters is what she runs short of. Nutrient Deficiencies: Who's at Risk and Which Test to Get has why pregnancy and breastfeeding raise the need for iron, folate and iodine at the same time, and why folate matters before a pregnancy begins, because the baby's brain and spine start forming in the first weeks, often before anyone knows. Iodine is the easy one to miss. Sea salt and pink salt carry little of it, so it has to come from fish and seafood, eggs and dairy.
Even stress crosses, in its way. In January 1998, an ice storm left 3 million people in Québec without power, some for as long as 40 days. Of 89 children whose mothers were pregnant through it, those whose mothers went through the most hardship had lower IQ, verbal IQ and language scores at five and a half. How upset the mothers said they felt made no difference. What counted was how much they actually went through.
And the inheritance runs back further than one pregnancy. A girl's eggs are made before she is born: about seven million by 20 weeks of pregnancy, down to one or two million at birth. So the egg that became you formed inside your mother while she was still inside her own mother. Your grandmother's pregnancy was, in a small way, yours too.
Smoke shows how far back it reaches. In southern California, children whose grandmother had smoked while pregnant with their mother had twice the odds of asthma. And the children of mothers who had quit before their own pregnancy carried no extra risk at all.
Hunger leaves a mark
In the winter of 1944 to 1945, the German-occupied western Netherlands starved. The adult ration fell to 1,000 calories a day by November 1944, stayed between 500 and 900 through the winter, and hit 400 in April 1945. The children conceived and carried through it have been followed ever since.
At 19, the boys turned up for military service, and 300,000 of them were examined. The timing mattered. Those whose mothers starved in the first half of pregnancy were more likely to be obese. Those exposed in the last months of pregnancy and their first months of life were less likely.
There is a name for what was going on. In 1990, David Barker of Southampton proposed that a baby short of food in the womb builds a body ready for scarcity, and in 1992 he and Nicholas Hales called it the thrifty phenotype. It is a fine plan for a hungry world. In a world of plenty, the bill comes later, as type 2 diabetes and heart disease.
Around the age of fifty, those exposed early in the womb had three times the odds of heart disease of people born just before the famine or conceived just after it: 8.8% against 3.2%. Exposure later in pregnancy made no such difference.
And when the exposed were measured in middle age against their own brothers and sisters of the same sex, the women carried more weight and more fat. The men did not. Same family, same famine, different bodies.
Your Genes Aren't Your Destiny, linked below, has the other half: the chemical tags on a growth gene that still marked them, against their brothers and sisters, six decades on. The famine did not change their genes. It changed how the genes were read.
What the body stores
Some of what a mother carries, she carries for years.
In Minamata, in Japan, a chemical factory released methylmercury in its wastewater from 1932 to 1968, and the fish carried it into the town. Then children began to be born with what looked like cerebral palsy. Their mothers had few symptoms or none, and the children had never eaten the fish. It took years, and the autopsies of two children, to show that these babies had a congenital form of Minamata disease. Everyone had assumed the placenta would protect the baby. With this kind of mercury, it did the opposite. It drew the mercury out of the mother's blood and gathered it in the baby. The bodyguard turned out to be a collector.
None of this makes fish the enemy. Minamata was a factory's poison, not the sea's. When 11,875 pregnant women in Bristol were followed, the children of those who ate no seafood had about one and a half times the odds of a low verbal IQ, compared with the children of mothers who ate more than 340 grams a week, and lower scores for social skills, communication and fine movement. It was an observation, not a test, but it points one way. Fish carries the fats a growing brain is built from.
Factory chemicals that dissolve in fat take the other route. PCBs, dioxins, DDT and other old pesticides build up in a mother's fat over a lifetime and can come out in her breast milk. The hopeful part is in the same records: where those chemicals have been banned, their levels in breast milk have fallen.
Birth
At birth, a baby meets its first big crowd of bacteria, and they become its starter kit. Nobody chooses their first flatmates.
When newborns were swabbed within minutes of birth, those born vaginally carried bacteria that resembled their mother's vaginal bacteria. Those born by caesarean carried bacteria that resembled skin.
A larger look, at 596 babies born in British hospitals, found what the caesarean babies were missing: the mother's own Bacteroides, a key gut bacterium, often failed to pass on, and in its place came bacteria that live in hospitals, Enterococcus, Enterobacter and Klebsiella among them. The same pattern showed, more weakly, in babies born vaginally whose mothers were given antibiotics around the birth, and in babies who were not breastfed in their first weeks.
Breast milk is built for that job. It carries sugars the baby cannot digest at all. They are there to feed the baby's gut bacteria, bifidobacteria above all, and a gut full of those leaves less room for the harmful kind.
A caesarean can save a life, and often does. It still changes what a child starts with.
Natasha Campbell-McBride takes this further than the tests do. In she argues that a mother's gut flora is the first inheritance she passes on, and her diet, built on meat stock, animal fats and fermented food, is meant to put the gut right before it is handed on.
Breast milk
Breast milk carries what the mother eats, including some things she would rather it did not.
In 1983, 66 mothers of breastfed babies with colic cut cow's milk out of their own diets. In 35 babies, the colic went away. In 23 of them it came back each time the mother had cow's milk again. Then came the blind test: mothers took capsules of cow's milk whey protein or dummy capsules, without knowing which. Of the ten babies who saw it through, nine reacted with colic after their mother's whey.
So for some colicky breastfed babies, the problem is not the baby, and not the breastfeeding. It is the protein from the mother's milk jug, travelling through her milk. A milk problem, delivered by milk.
Taste starts before birth
The flavours of a mother's food reach the amniotic fluid the baby swallows, and later her breast milk.
In one test, pregnant women drank carrot juice or water for a few weeks late in pregnancy, or while breastfeeding. When their babies started solid food, the ones whose mothers had drunk carrot juice, in either period, took to carrot-flavoured food more readily. Persuaded before they had teeth.
A baby arrives with a sense of what food at home tastes like. That is where the table begins.
Fathers count too
A father hands over half the genes and, it turns out, a little more.
When the sperm of lean and obese men was compared, the way the DNA was packed looked alike, but the chemical tags on it and the small molecules carried with them were markedly different. In obese men who then lost weight after surgery, the tags on their sperm were reshaped, notably near genes that control appetite.
Habits leave a mark on sons. Fathers who had started smoking before the age of 11 had sons with a higher body mass index at 9. And in Överkalix, in the far north of Sweden, where harvests, births and deaths were recorded for generations, how much food a paternal grandfather had in his own childhood showed up in his grandsons' death rates.
The Arizona siblings keep this honest. A father's diabetes did not carry into his children the way a mother's did. The womb is the bigger door. The father's is real, and smaller. Still worth a look in the mirror before the honeymoon.
The table
Then comes the table, where taste, portion size and habits are learned long before anyone questions them.
Your Genes Aren't Your Destiny also has the adopted children who carried one family's genes and lived with another family's habits. For early death from the heart and blood vessels, the biological parents counted. For cancer it ran the other way: the risk followed the adoptive parents. The house you grow up in is an inheritance of its own. Recipes are hereditary too.
Not fixed, and not blame
None of it is fixed, and none of it is blame. Mothers ate what they were told to eat.
The famine mothers had no food to give. The Minamata mothers had no idea what was in the fish. The British mothers in 7 Simple Changes to Improve Your Health, Starting Today, linked below, ate sugar as soon as rationing ended, and nobody told them it would show in their children's blood sugar decades later. The mothers of the colicky babies were drinking ordinary milk.
What it does mean is that a family history is not a verdict. Much of what you inherited outside your genes, you can still change, and what you change now is what you hand on.
It runs both ways, too. Cells from a baby cross the placenta into the mother and can live on in her for decades. Cells carrying a Y chromosome, the male one, have been found in the brains of women. Some mothers keep a little of their children for life.
The first diet
Back to those Arizona siblings: same parents, different odds, because one child spent nine months in a different womb from the other.
The first diet anyone ever had was their mother's.
If you are planning a child, start with your own plate, both of you, before the pregnancy begins.
Worried about what runs in your family? Your Genes Aren't Your Destiny: How Much of Your Health Is Up to You — what the famous "2% genes" figure measures and where it fails, what a famine left on the genes of people conceived during it, what adopted children reveal about family risk, and what to do with a family history.
Want the plain changes that count? 7 Simple Changes to Improve Your Health, Starting Today — the minute on the stairs, the food to build every plate around, what the end of sugar rationing in 1953 did to the babies who came after it, and how much sleep you need at seventy.
Know someone who believes their health was decided at birth? Share this with them.
Disclaimer: This article is general information. For advice about your own health, talk to a qualified health professional, especially before changing what you eat in pregnancy or while breastfeeding, or before cutting a food out of your diet for a baby's colic. Decisions about how a baby is born belong with you and the people caring for you in pregnancy.
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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