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Ultrasound at 18 weeks (Globe files/Globe files)
Ultrasound at 18 weeks (Globe files/Globe files)

Part two of two

A new prime suspect behind the global upsurge in obesity and diabetes: the womb Add to ...

In the 1980s, back when obesity and diabetes were considered problems, not plagues, a British researcher dished up a wild idea to explain the diet-related ills of the world.

While studying the causes of death for England and Wales, David Barker, an epidemiologist with the University of Southampton, stumbled upon the fact that, in the 1970s, deaths due to heart disease were highest in poor regions that 60 years earlier also had the highest rates of infant mortality.

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Prof. Barker considered that curious, since coronary disease was thought to be the result of rich living. He went on to trace the fate of 15,000 people born before 1930 in the English county of Hertfordshire and discovered that those with the lowest birth weights, presumably because their mothers were malnourished, again had the greatest risk of heart disease.

Prof. Barker, who published his initial findings in The Lancet in 1986, eventually came to the conclusion that a mother's nutrition can shape the metabolic future of her baby - affecting the child's lifelong risks for heart disease and all the health problems related to it.

At the time, the idea seemed almost absurd. The prevailing view held that susceptibility to disease was something chiselled into your genes from prehistoric times, not dictated by a pregnant woman's diet. The theory of the thrifty gene ruled the day, with the idea that former hunter-gatherer populations faced steady pressures of feast and famine that gave them fat-storing genes to survive the lean times - thrifty genes that made their descendants, aboriginal people in particular, obese and diabetic in the modern world.

But 25 years on, science, and society, have evolved.

With failed efforts to find a thrifty gene, or any genetic explanation for the rapid global rise in obesity and diabetes, Prof. Barker's hypothesis, better known today as the developmental origins theory, has emerged as a leading explanation. It's also a more attractive one: If correct, it suggests that something can be done to turn the tide.

Rewriting nature's script

Support for the developmental origins idea has grown alongside epigenetics, a budding branch of biology that is forcing a radical rethinking of genetic science as it reveals how the environment can alter DNA.

Dramatic experiments have shown that even small environmental changes can have a powerful, and permanent, impact on the way genes work: Tweaking the diets of pregnant rats, pigs, guinea pigs, rabbits and sheep can induce obesity and a range of other metabolic ills among the offspring. In one case, it changed the colour of a mouse.

The implication is that DNA may be the script that nature provides, but nurturing determines how that script will be performed - and, according to the origins theory, rehearsals begin in the womb.

"It's almost a sensing system of what's going on in the environment, so that a fetus can adapt," says Rosanna Weksberg, an epigenetics researcher at Toronto's Hospital for Sick Children. Problems can arise when the world outside the womb is dramatically different - "there's an epigenetic memory of nutrition."

Growing in a woman who is malnourished - either from eating too little or receiving too few nutrients - primes the fetal DNA to hoard every calorie available, only to be vulnerable to obesity and diabetes in a postnatal world of caloric overload. At the end of the Second World War, for instance, children born to women pregnant during the Dutch "hunger winter" proved susceptible to diabetes, obesity, heart disease and other health problems.

The theory is "such a powerful explanation for what's happening," says Daniel Benyshek, a bio-anthropologist at the University of Nevada, Las Vegas.

"Look at India, where diabetes is growing faster than anywhere else in the world."

Many Indian women grew up hungry in poor villages, he says, only to move up and into urban centres, where they suddenly find themselves - and their children - battling diabetes, an epidemic threatening to undermine all the gains of the country's newly minted middle class.

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