obesity: nature or nurture

Written by Colin Thomas, based on a lecture by Prof Steve Jones

You may or may not be surprised to hear that two out of three of us will die because of something related to our genes. Now that sounds like pretty grim news. Although if we go back just a few hundred years, I can guarantee that 2 out of 3 of you reading this article would already be dead! Let’s keep a hold of the positives.

If I asked you what kills us these days I’m sure you would answer with things like cancer, heart disease, diabetes and the like. You would be correct. These are diseases that your family doctor will tell you have a strong family history. So if your father has type 2 diabetes for instance, you are at an increased risk. Your doctor will also tell you that your risk increases from a lack of exercise and poor diet. So what is the cause? Is it genetics (nature) or is it lifestyle (nurture)? This age old question exists for all of the aforementioned diseases as well as obesity and sporting prowess. Think of Andy and Jamie Murray. Are they genetically primed to be tennis superstars (nature) or did Judy create the perfect environment for them to develop (nurture)?

We all have recognisable family traits whether we like it or not. The colour of your hair or eyes, the size of your nose or ears, your height, your build, your humour, the list is endless. As the saying goes, “the apple never falls far from the tree.” Most people would tend to agree that obesity also runs in families. We probably all know a family like the one in the picture below. 

​This would tend to suggest that obesity runs in families and hence making it a gene trait, ie nature. However, most of the obese families I know also have a family dog or cat looking like the one below. (crude I know but stick with me).

I can’t guarantee it, but hopefully the family genes are not being passed on to the family pet!

In fact we are living in a generation that for the first time, the children that we have are more likely to die before us. Life expectancy in The United States is a lot less in the young than what it is for the older generation. The UK always follows suit and is in fact already the most obese country in Europe. It is also the first time in history that the rich people are thin and the poor people are fat!

Despite the obese family pet theory, a number of genes have been identified that link people to obesity. For instance, the Leptin deficiency gene. Leptin is a hormone that switches off hunger. Without this gene, a child born with this deficiency is constantly hungry. This situation is however curable. Then we have the FTO gene which has been significantly studied in mice. Mice have 99% the same genes as humans. It is clear that those with the FTO gene put on significantly more weight that those without.

Now what about testosterone? A hormone which is regularly abused, creating dangerous situations. Testosterone is typically described as being the hormone that makes a man a man. We need it to build muscle and grow beards. It is also critical for reproduction. Testosterone is the reason why men die sooner, they die from having accidents, and getting struck by lightning and even get murdered more. You could say that testosterone gives you balls. Men also murder a lot more than women and testosterone is often blamed as the cause of this rage. Incidentally murder rates are lowest in countries such as Singapore and Iceland with 0.2 and 0.5 per 100,000 respectively. Generally peaceful countries with low levels of crime or gang warfare. Higher rates of murder in countries such as the US and South Sudan are 5.1 and 12 per 100,000. Yes you guessed it, high levels of gun activity and gang warfare. So the testosterone is present (nature) but it requires the correct environment (nurture) for it to thrive.
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So back to the original question, obesity: nature or nurture? Whether we are genetically disposed to obesity or not, unfortunately we have created an environment for it to thrive. Nature and nurture have to work in tandem to create such extreme results and if we continue to drive along the same path of obesity trends, the end result is simple – Disaster straight ahead!