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Event Review: Is obesity a choice?

25 November 2019
Appeared in BioNews 1025

Dr Giles Yeo at the University of Cambridge is on a mission to change the common conception that obesity is a choice. He certainly succeeded in changing my opinions on the subject during his recent talk 'Is Obesity a Choice?' at the Royal Society on 1 November 2019. 

The evening began with Dr Yeo addressing an apparently common concern – that by discussing the genetic causes of obesity researchers are giving people with obesity an 'excuse'. He explained that in his view obesity is a disease just as cancer is a disease and so in order to treat it, we must think of it as such. However, he did also point out that our genes are not deterministic and while we can't choose our genes, we can choose what we do with them.

Based in the Department of Neuroscience, Dr Yeo is a geneticist who is interested in how the brain controls body weight. His presentation style was engaging and energetic, so I was not surprised to discover that he also moonlights as a science presenter for the BBC, in addition to his academic research. 

During the event, Dr Yeo presented us with a convincing argument as to why obesity is, in fact, not a choice, but the result of subtle variations across hundreds of genes. To back up this argument, he described a range of different genes that influence body weight.   

First, Dr Yeo talked about leptin. Leptin is a hormone that plays a critical role in the control of food intake and, therefore, body weight. Researchers found that mutations in the leptin gene resulted in heavier mice. When they then discovered in the late 1990s that injecting leptin in humans with a deficiency resulted in them losing vast amounts of weight, researchers thought they had discovered a 'cure' for obesity.  As it turned out, however, leptin acts to inhibit hunger, so for people with a functioning leptin system injections were no help.   

To help us understand what it is like to have leptin deficiency, Dr Yeo asked the audience to imagine that we had survived a plane crash and were stranded, starving, in a remote location. He concluded that in such a situation we would all probably eat anything we could find to survive. Dr Yeo explained that this starvation response is constantly 'switched-on' in the brains of people with leptin-deficiency; they constantly feel like they are being starved so must eat anything available. This was just one of the many analogies Dr Yeo used and I think it made the audience more empathetic towards people with obesity. 

Another gene discussed was MC4R. Mutations in this gene have been linked to obesity and one percent of people classed as 'obese' based on their Body Mass Index (BMI) have a mutation in this gene. Interestingly, Dr Yeo also told us that Mexican cave fish with mutations in the MC4R gene will eat all fish available to them. Similarly, another gene that has been linked to obesity in humans, called POMC, has also been shown to be associated with obesity in Labrador Retriever dogs. 

Dr Yeo used parallels with animals to demonstrate that we all have hardwired tendencies in our genes which can be linked to obesity. This shows, he argued, that obesity is not just the result of bad habits or 'lack of morality'. Dr Yeo emphasised that we would never assume fish are making bad choices, so should not make that assumption about humans either. The genetic factors involved mean that people with obesity are fighting their own biology.  

During the talk, I was surprised to learn that height has a heritability of 85 percent, whilst body weight has a heritability of 70 percent. This really made me question common views of obesity. We would never say that a tall person chose to be tall but if the heritability of the two phenotypes is so similar, why is it that we think people with obesity choose their body weight?  

At one point, we were shown a graphic, which was used by The Washington Post to demonstrate how the average BMI of Americans changed between 1984 and 2014. It was clear that more people are now classed as 'overweight' or 'obese' based on their BMI. However, the distribution also changed over the time period. Our genes have not changed since 1984, so Dr Yeo explained that this implies there are other factors at play as well; obesity is not entirely a genetic problem. 

These other factors involved in obesity were not discussed in detail during the event as the focus was on genetics. Socio-economic factors and other influences were touched upon during the questions at the end, but I think it would have been a more balanced discussion if the talk had included some of these as well.   

Overall, the event was very informative and easy to follow – even for people without a background in genetics. He is giving a similar talk with the same title at King's College London on 27 November and I would thoroughly recommend attending. Dr Yeo's closing remark, which I thought was pertinent, was that an understanding of the role genetics play in obesity should urge us to work towards finding treatments for the disease rather than blaming sufferers.

Dr Yeo's talk from 1 November will be available to watch on the Royal Institution's YouTube channel in the coming months.

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