Thinness and obesity: it's in the genes
As many people have long suspected, the genetic dice are loaded in favour of thin people when it comes to staying slim.
Some people seem to be able to eat all the burgers and chips they like and and stay the same size, shape and weight all their life. Researchers at Cambridge University have discovered that they have a genetic advantage over their overweight friends who live and eat in the same way that they do.
Prof Sadaf Farooqi at the Wellcome-MRC Institute of Metabolic Science recruited 2,000 healthy but thin individuals into a study called Stilts (Study Into Lean and Thin Subjects) to find out whether there was something particular about their lives or their genes. All had a BMI of less than 18, which is technically underweight, but they were healthy and did not have an eating disorder. The identification and recruitment of this unique cohort was supported by the National Institute for Health Research.
The study, published in the journal Plos Genetics, looked at the DNA of nearly 1,600 members of the thin cohort and 2,000 people who were severely obese, comparing both with a further 10,400 people of normal weight.
The team found several common genetic variants already identified as playing a role in obesity. In addition, they found new genetic regions involved in severe obesity and some involved in healthy thinness. They calculated a genetic risk score from their findings.
“As anticipated, we found that obese people had a higher genetic risk score than normal-weight people, which contributes to their risk of being overweight. The genetic dice are loaded against them,” said Dr Inês Barroso at the Wellcome Sanger Institute, whose team did the genetic analysis.
The thin people, on the other hand, had a much lower genetic risk score. Three out of four of them came from families whose members also had a tendency to be thin and healthy.
“This research shows for the first time that healthy thin people are generally thin because they have a lower burden of genes that increase a person’s chances of being overweight and not because they are morally superior, as some people like to suggest,” said Farooqi. “It’s easy to rush to judgement and criticise people for their weight, but the science shows that things are far more complex. We have far less control over our weight than we might wish to think.”
Other scientists pointed out that genes were not the only answer. Tom Sanders, emeritus professor of nutrition and dietetics at King’s College London, said it was “an important and well-conducted study confirming that precocious severe obesity is often genetically determined and showing convincingly that those who are very thin are genetically different from the general population.
“However, most obesity is acquired in adult life and is linked to the obesogenic environment we live in (a sedentary lifestyle and abundance access to calorie-dense foods). Furthermore, genetic differences are unable to explain the large rise in the prevalence of obesity in children under six years old, which may have its origin in pregnancy and early infancy when appetite is programmed in the offspring.”
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