What twins think about the Carb-digesting Gene

PenGenetics1“Carb- digesting obesity gene discovered!” screamed a recent media headline. It was in fact referring to a major breakthrough into the cause of obesity discovered here at the Department of Twin Research together with collaborators at Imperial College and Lille in France. Together, we found that obesity is related to the number of copies that people have of a gene coding for a carb-digesting enzyme called amylase. The findings, published in Nature Genetics , show for the first time that how well we digest carbs varies widely between us due to our genes and suggests that personalised dietary advice based on an individual’s genetic blueprint may be the way forward in the fight against obesity.

Professor Spector invited three pairs of twin volunteers who took part in the study to the department for a chat so that he could find out what they thought of these results. The twins were all fraternal (non identical), sharing 50% of their genes but sharing the same upbringing and home environment for their first 18 years. They were particularly interested in our results as each pair had a weight difference of at least 2 stone between them. Please read on to read Professor Spector’s account of their visit to the Department….

Frances and Linda, Michelle and Georgette, Margaret and Nora all jumped at the chance to talk to me about what the findings meant to them, not only as twins, but as research volunteers as well. They come from different backgrounds and parts of the UK – but their stories are quite similar. Their weight differences were mostly present from infancy – with one describing themselves as the ’tubby twin’, and the other the ‘skinny twin’. None of them could think of a reason why they had different weights from infancy. They all agreed that as kids their Mums’ had given them the exact same foods and portions – and one twin had just put on the pounds and the other hadn’t. None of them had any major illnesses, food allergies, preferences or medications to explain this.

The weight gaining twins all reported immense frustration that their twin could eat the same without any effects on their weight. In Linda’s words “I just had to look at food to put on weight”. Surprisingly, this difference in adult weight could have been even greater still, as the heavier twin tended to exercise more than the lighter twin, in order to try and lose weight.
The twins were all fascinated and excited by the findings of this research and agreed that it gave them another perspective from which to look at their weight differences. They did not reject the effects their diet and environment had on their weight completely, but they all agreed that a genetic difference such as our latest discovery could go a long way to explain their weight differences. The twins remarked that what their children and husbands ate affected their weight in terms of having fussy or big eaters or vegetarians in the family.

The twins were asked whether they would take a genetic test, if it became available on the NHS, to find out whether they were predisposed to putting on weight. All of them agreed that it would be generally useful, although Margaret wasn’t so sure. Frances thought that the twins with the smaller copy numbers (with greater risk of putting on weight) could feel “fed up and frustrated” by this genetic lottery. She thought the individual could use it as an excuse not to make any effort to lose weight and blame it on their genes. Michelle disagreed, “knowledge is always worthwhile” to which her sister Georgette added that “genes can be a reason but not an excuse”. The group agreed that the genetic information could have the positive effect of helping them to focus on adopting a healthier diet and therefore achieve a bigger weight loss. Michelle and Georgette explained how, in their case, the twin that had less of a weight problem when young ended up gaining more weight than her sister as she never felt the need to control her food intake. They thought that this suggests that these genetic tests should only be given to individuals with a weight problem; otherwise a negative test could provide a false feeling of security. Michelle and Georgette’s story was a nice illustration of how we do not need to be slaves to our genes but we can, by our actions, reverse the natural tendencies of our bodies.

It was generally thought by both the twins and the researchers that personalised genetic testing for weight could be very helpful if it was clinically shown that avoiding or reducing particular food types helped to improve metabolism and weight.

Current research also shows that our gut bacteria can affect our tendency to gain weight and I explained how I thought it may be influenced by this ’carb-digesting gene’. I posed some delicate questions about whether they would be prepared to receive a faecal transplant from their healthier twin, if it was found that it could improve their metabolism through receiving a ‘healthier population of bacteria’. Two out of three pairs said they would consider it, and the third said only if she had some more major health problems.

As we wrapped up – I offered everyone some biscuits or fruit before they left. I was the only one to have a biscuit and a couple took the bananas – which I (annoyingly) explained was a genetically modified sterile fruit with more sugar in them than the biscuits!

It seems everyone these days is interested in what we should eat. Hopefully using our ever-useful TwinsUK registry, we can find more gene variants that determine how we metabolise a whole variety of foods that determine our individual weights. Who knows, the next gene we discover could determine whether we can stay slim while eating six bananas daily and a carb only diet!……

CLICK HERE for a press release by King’s College London

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