But how far is that inheritance down to genes, and how much is due to the family’s lifestyle? And if the link is genetic, which side of the energy equation are the inherited genes affecting?
Much of the current research into the link between genes and weight concerns the behavior of individual genes and how they affect our appetite or the way we turn food into energy. There have been some exciting developments: for instance, it has been shown that in very rare cases, severe obesity is caused by a genetic mutation that causes the failure of a hormone called leptin, which regulates appetite in the brain. Children born without leptin will eat uncontrollably, but their appetite and weight will return to normal once they receive leptin injections.
Our Caveman Inheritance
Eventually, research into leptin deficiency and some other specific gene mutations may lead to effective treatments for what scientists now call ‘common obesity’. However, whereas only a very few people are unlucky enough to have faulty genes, none of us can escape the genetic pattern that has been handed down to us over millions of years.
Our earliest human ancestors evolved in an environment where food supplies were scarce and sporadic. Our strongest food preferences and cravings – for sweet, fatty and salty foods – are a reminder of the times when sources of glucose, essential fats and minerals were hard to come by. Energy conservation in time of famine was vital, so those human beings who had ‘thrifty genes’ – who were most able to convert food to fat and store it effectively – were the most likely to survive, breed and pass on those genes.
Old Genes, New Environment
Unfortunately, the genetic make-up that suited us so well for survival in prehistoric times is very unhelpful today in our modern environment. Instead of eating fatty, sweet or salty foods only rarely, we now have access to them 24 hours a day, seven days a week, if we want. When we do eat excess fat and sugar, our ‘thrifty genes’ ensure that we store it very efficiently as fat. And instead of foraging and hunting to find our food, we only have to drive to the supermarket, pick up the phone or log on to the internet.
So how can a history lesson help us to lose weight? One vital thing it teaches us is that weight is not a moral issue. People do not put on weight because they are essentially greedy, 1azy or sinful. On the contrary, gaining weight is the natural human response to life in a food-rich and activity-poor environment. If our ancestors had had the choice between hunting for their food or going to the supermarket, which one do you think they would have chosen?
As we are discovering, the fact that our genes have not yet caught up with our environment is bad news for our health. So the other lesson that history teaches us is that, as we cannot change our genes in order to stay thin and healthy, we need to adapt our environment – with small changes to diet and lifestyle that can swing the energy balance back in our favor.