Mark Henderson, Science Editor
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Nature, and not nurture, is the chief reason why some children put on weight while others stay slim, according to research that suggests parents are not entirely to blame for the epidemic of childhood obesity.
British scientists have found that genes account for more than three quarters of the differences between children’s waistlines, with lifestyle factors such as diet and exercise playing a much smaller role.
The results, from a study of 5,092 pairs of twins aged between 8 and 11, indicate that different family environments explain only a little of the variation in obesity between today’s children. Those who get fat tend to do so because they have a genetic predisposition towards obesity.
It raises questions about the recent decision by Alan Johnson, the Health Secretary, to notify the parents of five-year-olds who are found to be obese. Such children are more likely to be putting on weight because of their genes than any influence their family and home environment has had on their lifestyle.
“This study shows that it is wrong to place all the blame for a child’s excessive weight gain on the parents,” Professor Jane Wardle, of University College London, who led the research, said. The findings, however, do not mean that environmental factors play no part in obesity. Despite the strong influence of susceptibility genes, their prevalence has not altered in recent decades and it is environmental change that has driven the rise in childhood obesity across the population.
What studies of lifestyle have failed to explain are the differences in individual children’s responses to their “obesogenic environment” — factors in the environment that encourage sedentary behaviour and overeating.
In the study, which is published in the American Journal of Clinical Nutrition, Professor Wardle and Susan Carnell looked at Body Mass Index (BMI) and waist circumference in pairs of twins.
As identical twins share all of their genes while fraternal twins share only half, and they share broadly similar environments, comparisons between twins who live together or grew up in the same families can tease out the relative contributions of nature and nurture.
The results, showed that identical twins were considerably more likely than fraternal twins to have similar patterns of obesity. For both BMI and waist circumference, genes accounted for about 77 per cent of the variation between individuals, and environmental factors for 23 per cent.
“We looked at identical pairs of twins who share all their genes and compared their measurements with non-identical pairs of twins who only share half their genes,” Professor Wardle said.
“Contrary to the widespread assumption that family environment is the key factor in determining weight gain, we found that this was not the case.
“These results do not mean that a child with a high complement of ‘susceptibility genes’ will inevitably become overweight, but that their genetic endowment gives them a stronger predisposition [to being overweight].
“In today’s environment — which provides unprecedented opportunities for all children to overeat and be sedentary — it is not surprising that these tendencies result in weight gain.”
BMI, which is the standard measure of obesity, is calculated by dividing a person’s weight in kilograms by the square of their height in metres. A score of 25 is the threshold for overweight, and 30 for obesity.
According to the latest government figures, 30 per cent of children are either obese or overweight by this measure. Obesity among children aged 2 to 10 has risen by 7 per cent in the past decade.
Though the results point to genetics as a key factor in childhood obesity, they also indicate the importance of public health policies that encourage children to eat less and to take more exercise, experts said.
Sarah Hiom, director of health information for Cancer Research UK, which partly funded the study, said: “This research highlights the importance of doing all we can to encourage children to eat healthily. If genetic influence is strong we must try to counter these inherited tendencies by providing the healthiest possible environment, and educating parents on the importance of a well-balanced diet and an active lifestyle.
“Our genes have not changed and yet childhood obesity is rising, and the major challenge is tackling the obesogenic environment that we all share.
“That includes looking at education, transport, town planning and so on, and not blaming parents for genetic susceptibilities that are not their fault.”

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Yes, genes haven't changed, yes obesity is rising. This study isn't saying that genes cause all obesity. It is saying there is sometimes a genetic disposition to obesity, sometimes there isn't, and obesity is rising, therefore there must be an environmental factor at work
Kathryn Jackson, Swindon, UK
i like that you should keep eating because when i was not eating i was sick and coughing up blood
samantha , st. helens, engaland
I come from a family of big people. I ate good sized portions of food & was a very active kid yet i gained weight. as soon as i started going to school, i dropped the weight and was a slim child up until i left school and am now working. I eat healthy food and hit the gym 3/7 but cant lose the weigh
Miss Dee, Sydney, Australia
McDonalds,Coke,Cake etc all mean if a child has a sweet tooth then they are up against it. Playstations, PCs and the like mean children are sedentary much more than they used to be.
Parents are not properly educated about the amount of calories a child needs and the amounts in popular foods.
If your child is overweight it is because they intake more calories than they need. This is Possibly worse due to a 'sweet tooth'/'fat gene' whatever, if you are responsible for feeding your child then its YOUR fault!
There wasn't a overweight Japanese POW because they were all under nourished and forced to work every day, if there is a 'Fat Gene' then there would be a podgy guy sat amongst the skeletal rest saying "what can i say its my genes".
L.King, colchester, essex
I don't believe a word of it.
I used to eat enough for 2 people and never put weight on because I was always very active. An injury caused me to slow down and immidiately I started to put on weight [not too much] and I have noticed many times that fat people tend to be slow moving and inactive.
Mr G, Leeds, UK
When I was a young fella helping myself to the family food without my mothers consent was a dangerous idea a view shared by all my young friends. I ate what I was given, a sensible ration for my size.Refusing to eat was greeted by a kind inquiry about my health never seen as an opportunity to make my own choices or demand a change of diet ,the idea of my mother giving in to pressure from me was an absurdity.Following my mothers sensible approach I have remained slim though I confess in my middle age exercise has helped keep me so.
I read during this early era "Lord of the Flies" more absurdity;contemporary I believe with Crick and Watson's weaving of the double helix. Who would have thought that the cutting edge of our science would have provided a solution to these ideas from long ago with such clarity.
Dave, Gloucestershire,
strange but kinda obvious, for example i can eat like a pig, 4000 calories a day, not do exercise and still be slim and never put on a pound.
its because of my genes and also my race for sure.
some people are just unlucky.
yaz, london, uk
We are merely battery chickens in the foul shed of a malign economy that not only profits from making us ill but also keeps us ill so that Big Pharma can make even more money. Politicians should be banned from acting as 'consultants' for the food industry. Their jobs are merely golden shackles to ensure that the desperately needed legislation to reign in the food industry will never be passed.
The behaviour of an individual is determined by the environment ( social, cultural, economic ) in which they live. If we want healthy behaviours then we need to have a healthy environment.
Dr Colin Guthrie, Glasgow, Scotland
I'm confused, 77% of the reason for being fat is due to gene's then they say 'gene's have not changed', but life stlye has. Which one is it? And if its down to our gene's why has there been a massive increase in obesity, couldn't be because people eat all the crap food thats on offer and thick parents feed their kids with it? Understanding Fat is easy, if you consume more calories that you burn off you put on weight. Simple.
Deb, Manchester,
Of course this is a no brainer. I have one adopted daughter and one biological daughter, 11 months apart. They've eaten the same things growing up, and have had the same activities. My adopted daughter is thin, while my biological daughter weighs more. It's got to be the genes.
Linda, Miami, FL
Absolutely stupid. I can see it with myself - if I stuff myself with crisps and cake, I gain wait. If I follow a well-known slimming system's advice and move more, I lose weight.
Rocket science? No. Common sense.
I loathe the way that everyone blames something or someone else for things that are in their control. If I slap someone for being stupid, can I claim that I couldn't help it because it was my genes that made me do it? I'd love to know - then I'd slap these stupid scientists.
Martina, Dusseldorf, Germany
This is evidence not of genes but of eating the wrong food. It means that the anthropologists are right : we should be eating a hunter-gatherer diet: low in carbs and sweet fruits, higher in protein and fat.
Greg Lorriman, Leatherhead, UK
As reported, this makes no sense at all. The population has essentially the same genes that it always did.... but its only now that obesity has become a problem. The difference is diet and exercise (lifestyle) and not changing genes.
Neil, Glasgow, Scotland
So what is different to the genes of yesterday and today?
Why when I was at school in the 60s and 70s there was only one or two fat kids per class?. Now a good half of them are over-weight. When I was at school chocolate was a weekly treat for most kids and never in packed lunches. Burgers and take-aways were eaten occasionally.
I am not convinced by this research. But it must be a relief to all those parents of obese children - to be told that allowing them to eat rubbish has not caused their life-threatening illness. It's their genes afterall.
Ray Harrington-Vail, Newport, Isle of Wight
Why is it that we are always trying to blame 'someone' or 'something' for our laziness, over-eating, murder, gambling, etc. etc. other than who we should be blaming - ourselves. What is the next study - why are people who exercise and eat well 80-90% of the time and splurge once a week maintain a healthy body weight -hmmmm that is going to take many studies to figure out that 'no-brainer'
Linda, Harrison Twp, MI
Like with most things the answer is not black and white... Some children can have absolutely terrible diets yet not seem to gain weight while others will pile on the pounds. However 99.9999% of children when fed and exercised properly will have a healthy body weight. Some will be able to get away with a bad diet, others will have to be more careful with these things
TA, Lincoln, Lincolnshire
Like....Duh!....Why do you think obese children often have skinny siblings. How much of my tax was spent on this "research"?
megaL, London, UK
This report is unhelpful because it appears to give the message to parents that they have no control of the process of weight gain.
Nor does it seem to take into account lifestyle/diet changes since our early ancestors had to evolve these traits in order to gain a survival advantage.
Simon, Ascot, Berkshire
Our grandparents did not have either the wealth nor the easy access to foods that contribute to obesity.
The study does not say that the environment has no influence, but rather than genes are the dominant factor in variance between different people. I.e. some people are significantly more succeptible to weight gain than others and must thus avoid lifestyle choices that cause others few problems.
Bill, Falkirk, Scotland
If genes account for more than three quarters of the differences between childrenâs waistlines then explain why children were much slimmer and fitter in the days before they were chauffered around by parents.
Anybody with an ounce of common sense will see that it is today's lifestyle that is the cause of so much child obesity.
Tim, Bangkok, Thailand
Then it IS the parent's fault then...why on earth did anybody spend so much on research to discover the bleeding obvious? Our ancestors went through feast and famine. Some humans - today's fatties - put on weight at the sight of food and coped with famine well. Today's skinnies, no doubt better hunters, flourished in better times. By constantly varying offspring to cope with feast and famine humanity survives.
It's just unfortunate now that anybody who has these genes will have to be starved and give their grub to thinner me.
Dave, Slough,
If childhood obesity is genetic, why has it only appeared in such numbers in the past decade or so? Our grandparents
had the same genes!
Rachel, London,
Tell us something we don't know... this is not science but common sense. Of course some people put on weight more easily than others, like the animals that are bred for fattening. They are the ones that have to watch how much they eat while some amomg us can eat anything and everything and not put on weight.
David De Burgh, Hereford, UK
Yes I agree its in the genes. The 'I'm lazy, can't get off my backside, TV watching, pop drinking, rubbish food eating gene'. Face the facts, if calories in > calories out, then you put on weight. Simple.
Walking and running is free, so there is no excuse for not getting the exercise you need if you still wish to eat and drink rubbish.
Lets stop funding these ridiculous studies, and instead increase by 100 times, the funding for kids and youth activities. Give everyone the chance to do something, to get involved, to be part of a project - anything to give them some motivation, pride, etc. Realise that life happens outside of the television - not inside it. If this happened, I bet the youth crime figures would come down too. Everyones a winner.
Chris, Bristol,