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Slim people have a genetic advantage when it comes to maintaining their weight
In the largest study of its kind to date, Cambridge researchers have looked at why some people manage to stay thin while others gain weight easily. They have found that the genetic dice are loaded in favour of thin people and against those at the obese end of the spectrum.
Slim people have a genetic advantage when it comes to maintaining their weight. 
While it is well known that changes in our environment, such as easy access to high calorie foods and sedentary lifestyles, have driven the rise in obesity in recent years, there is considerable individual variation in weight within a population that shares the same environment. Some people seem able to eat what they like and remain thin. This has led some people to characterise overweight people as lazy or lacking willpower.
Studies of twins have shown that variation in body weight is largely influenced by our genes. To date studies have overwhelmingly focused on people who are overweight. Hundreds of genes have been found that increase the chance of a person being overweight and in some people faulty genes can cause severe obesity from a young age.
In this new study, the team compared the DNA of some 14,000 people –1,622 thin volunteers, 1,985 severely obese people and a further 10,433 normal weight controls.
Our DNA comprises of a sequence of molecules known as base pairs, represented by the letters A, C, G and T. Strings of these base pairs form genetic regions (which include or make up our genes).
Our genes provide the code for how our body functions and changes in the spelling – for example, a C in place of an A – can have subtle or sometimes dramatic changes on features such as hair colour and eye colour but also on a person’s weight.
To see what impact these genes had on an individual’s weight, the researchers added up the contribution of the different genetic variants to calculate a genetic risk score.
They 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.
Importantly, the team also showed that thin people, had a much lower genetic risk score – they had fewer genetic variants that we know increase a person’s chances of being overweight.
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. We have far less control over our weight than we might wish to think. (University of Cambridge)
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