All in the genes
The role of genes in the development of diabetes is an exciting new frontier of science and could lead to treatments tailored to a person’s individual biology. By Caroline Wood.
Many Kiwis are overweight, we have the third highest rates of obesity in the world. But why do some obese people develop type 2 diabetes and not others? And if diabetes is a lifestyle disease, why do skinny people get T2 as well?
In New Zealand, Pacific Islanders and Indians are three times more likely than Europeans to develop type 2 diabetes. Māori are also disproportionately affected. Why are these groups most at risk? Could it be a result of their genes?
Our genes play a major role in determining who puts on weight, or develops a disease. Increasingly research shows that our genes can also determine how a specific individual responds to treatment, including medication.
The challenge for scientists is to better understand the role that genes and biology play so we can tailor treatments to fit the individual. In future, perhaps it may be possible to even predict who is likely to become obese or develop diabetes in later life.
Dr Giles Yeo is a geneticist and obesity expert from Cambridge University and a popular BBC presenter. He recently toured New Zealand raising awareness about the role of genes in obesity and diabetes.
He argues that people shouldn’t be fat-shamed for being overweight – or stigmatised for having type 2 diabetes.
The heritability of body weight is 70%, he says. This means our weight range, or BMI, is pretty much set by our genes. The rest (30%) is down to environmental factors, which can be changed. For comparison our height is 85% inherited and 15% influenced by the environment.
“The control of body weight is not just about willpower, there’s a biological process going on behind it,” says Dr Yeo.
The trouble is a lot of people, including some doctors, think that type 2 diabetes and obesity are a “lifestyle choice” and therefore 100% curable. This is not helpful, he says.
Finding and eating food is one of our prime directives in life. Unfortunately it also means that everyone is an “expert”.
“We eat every day, we buy food every day, we judge. How come she eats like that? I don’t do that. We judge people, how they look and how they behave.
“If you eat more than you burn in calories, you put on weight. But biologically we are asking the wrong question.
“We should be asking why people behave differently in the same food environment. How come some people can resist eating chocolate and others can’t?
“There’s got be a biological variation. If the problem lies in the physics, then education should work – ie eat less, move more, and you will lose weight. This is correct but it’s not working.
“But if we ask the question: Why do some people eat more than others? Then we may get some useful information.”
Dr Yeo explains how the world is getting heavier, it’s a global problem. The average BMI in 1984 was 22, but it is now 27. But some groups of people are heavier than others.
For example, the Cook Islands have the highest rates of male obesity in the world at 60%. But in Bangladesh, which has the lowest rate of obesity, fewer than 1% of adults are obese.
“People are behaving differently in the same [food-rich] environment because there is biological variation and that is something to be studied – a lot of the variation will be down to your genes,”says Dr Yeo.
“I can’t blame a single gene on my BMI, which is 27 [overweight], there’s going to be lots of genes involved. There are genes that influence waist to hip ratio, ie, where you put your fat.
Other genes impact on BMI, ie, how much fat you have, others impact on the brain,” he explains.
Every ethnicity will be different, depending on their biology and genes. Some people are genetically more skinny and others are more likely to be fat.
Can you identify people who are not yet obese but at risk of it? No we can’t, we don’t understand the biology enough to do a personalised intervention.
But you can change the environment, he says.
“Your genes are like a hand of poker. You can have a bad hand of genes or a good hand of genes, you can win with a bad hand although it’s more difficult.
“I can’t run as fast as Usain Bolt but if I train I can run faster. Your genes will cap you within certain limits but with your choices you can make a difference.
“I’m not trying to give anyone an excuse [to blame their obesity on their genes], I’m trying to educate people, and also let medical people know that if they can motivate someone by explaining their biology, it can help them.”