A child in the womb is not just some hapless creature waiting to be born into a world of experience. It is preparing. Through its mother, it senses the conditions of the world outside and its body plans its growth accordingly.
There is strong evidence that people who are under-nourished as embryos grow up to have higher risks of heart disease and other chronic illnesses. For example, people born to women during the Dutch Famine of 1945 had higher risks of coronary heart disease as adults.
We might nod our heads at this as if it were expected news, but it's actually quite a strange result. After all, during the early stages of pregnancy, the embryo is actually relatively undemanding. Any embryos that get off to an early slow start can easily catch up during the foetal stage, and they can certainly do it after birth. But Jane Cleal and colleagues from the University of Southampton have found, from studying sheep, that catching up may actually be the problem.
She divided several pregnant ewes into two groups and fed one on half the calorie intake of the other during the first quarter of their pregnancy. As expected, they put on less weight. Pregnant human teenagers often go through the same thing because they tend to be more active than older expectant mothers.
Lambs born to undernourished mothers weighed about the same as those whose mothers had it easy, but they packed on weight more quickly. And when the lambs were deprived of food between their third and sixth months of life, those that experienced poor nutrition in the womb bounced back faster than those that had it easier.
These results supports a theory that developing foetuses prepare for the world outside by using the health of their mother as a sort of nutritional barometer. If mum isn't getting much nutrients, the foetus steels itself for a life of hardship.
In the case of the lambs, those that were under-nourished in the womb went through an initial growth spurt to give them a reserve to draw upon in times of anticipated hardship. And sure enough, they proved to be more resilient when such hardship did occur.
This is all perfectly sensible from an evolutionary point of view - after all, if mum can only afford to eat for one-and-a-half, life on the other side of the uterus is hardly going to be rosier.
But problems crop up when the foetus's intel is wrong - when nutrition before and after birth don't match up. Right from birth, it is poorly adapted to the world around it. The malnourished foetus that is born into a world of plenty is like a karaoke singer thrust into the spotlight at the Royal Opera House - unprepared and likely to do badly.
Cleal found that lambs that had poor nutrition before birth and plenty of food after it, might grow faster but not always in the right way. By their third year of life, they showed signs of poor blood pressure control and cardiac hypertrophy, a thickening of the heart's walls linked to a higher risk of heart disease and hypertension. Even their kidneys showed signs of weakness.
The potential harm of mismatched pre- and post-birth nutrition is particularly relevant for countries going through large spurts of economic development, or people emigrating to more affluent parts of the world. These mismatches could be made even worse by feeding newborn babies on calorific, high-fat diets, or weaning them onto unhealthy foods.
Other studies support Cleal's concerns. For example, Indian children who are small at birth and heavy at 8 years of age have higher levels of cholesterol later on in life, and higher risks of heart disease and diabetes. And children who are small at birth and put on lots of weight during development have higher risks of chronic diseases that those who are born heavy but grow more steadily.
Pre-adapting to the outside world has served us well in our evolutionary history. But in today's rapidly changing world, it might be contributing to the rising levels of heart disease, diabetes and other metabolic diseases in the Western world. The important next step is to find out exactly how this process works.
Reference: Cleal, Poore, Boullin, Khan, Chau, Hambridge, Torrens, Newman, Poston, Noakes, Hanson & Green. 2007. Mismatches pre- and postnatal nutrition leads to cardiovascular dysfunction and altered renal function in adulthood. PNAS doi:0610373104.