When pregnant with me Mum craved bananas and with my sister it was chocolate. As a child, I decided that this was why my sister had beautiful light brown skin and I was pasty and got sunburnt so easily. I reasoned that the brown from the chocolate had somehow got into her and changed her skin tone. Of course now I accept that I was wrong, but research suggests that a woman’s diet whilst pregnant does have lasting effects on her unborn child.
Everyone is different and what causes this are the different genes that we inherit from our parents. On top of this genetic difference, the environment that we live in and our experiences mould us into something completely unique. On a basic level we can imagine a baby being born looking and behaving exactly as it’s genes intended, then as he/she grows up the environment determines which ‘turns’ along the path they will take. That is not strictly true though, environmental effects are there much earlier – in fact right from the very beginning.
Scientists have discovered that during development there are specific windows of time when the environment can affect characteristics of the embryo – this is known as ‘foetal programming’. Here I’m going to describe its effects on nutrition.
Our body’s ability to function relies on it being able to gather information from its surroundings and act accordingly. Too hot? Start sweating and take off a jumper. Tired? Go to sleep. Thirsty? Have a drink. All of these require a fixed point that is recognized as normal. As these systems form in the uterus, factors outside the embryo help determine where that fixed point will be. This makes good sense when you think about it, being able to sense and adapt for the conditions you are about to be born into is very helpful!
When expectant mothers eat a high calorie diet this causes the brain of their offspring to produce more of the chemical that makes us feel hungry and less of the chemical that make us feel full. In other words the ‘normal’ signal has moved along the scale, closer to hungry and after birth that child will feel hungry sooner. As humans our motivation to eat is more complex than simply satisfying our hunger, eating palatable food triggers the reward centre in the brain. Hence why, at the end of a rubbish day you are more likely to choose chocolate than a salad. This part of the brain is also affected by maternal diet, so that over nutrition during pregnancy causes offspring to strongly prefer high fat and sugary food.
Alongside this, fat produces a hormone called Leptin, which acts to suppress appetite. The more fat your body stores the more leptin you produce. This acts as a messenger to your brain, telling it to reduce your appetite as fat reserves become larger. When the foetal brain is exposed to over nutrition during development it detects lots and lots of leptin coming from its mother. As a result of this overload brain cells become less sensitive to leptin and this is maintained after birth.
So the effects of eating a high sugar, high fat diet during pregnancy are three-fold. The foetus perceives hunger at a higher level of nutrition, it gets more pleasure from eating a high calorie diet and it doesn’t sense feedback from the body telling it to reduce it’s appetite. What’s the solution then? Just wait a second before you dash for the celery.
Remember I said that the aim of this mechanism was to prepare the foetus for its future environment? A study in the Netherlands looking at people who were born during the post-war famine (ie their mothers were undernourished during pregnancy) showed that they too had a much higher chance of being overweight. Why is that? Well during development that group of people were programmed to survive without much food and to make the most of the calories they ate – in other words to be ‘thrifty’. As they grew up post-famine, in the same convenience food era as we live in now, they were still extracting the most nutrition possible from their food – only now it wasn’t helpful any more.
The healthiest offspring are produced when their pre-natal and post-natal environments match. So if you are pregnant eat chocolate biscuits or some fast food but mix it in with the green stuff. Provided your child has a similar healthy, balanced diet as they grow up and become adults they will be less likely to be overweight, have diabetes or heart disease than if you eat mostly junk food.