His work reveals the existence of recently discovered genetic regions that are linked to thinness.
The international team says that their findings confirm the idea that, for some people, being slim has more to do with inheriting a set of "lucky" genes than with following a perfect diet or lifestyle.
The study was published in the scientific journal of open access PLOS Genetics.
In the last decades, several researchers have discovered hundreds of genetic changes that increase the possibility of a person being overweight.
However, it has put much less focus on studying the genes of people who are thin.
To conduct this research, scientists in the UK used DNA samples of 1,600 healthy and thin individuals, who had a body mass index (BMI) of less than 18.
They compared these samples with those of 2,000 people with severe obesity and those of 10,400 people of normal weight.
They also used and analyzed lifestyle questionnaires to rule out, for example, the existence of eating disorders.
The researchers found that people who were obese were more likely to have a group of genes related to overweight.
In the meantime, people who were raw not only had less genes related to obesity but also exhibited changes in the genetic regions recently associated with healthy primacy.
The main researcher, Professor Sadaf Farooqi, from the University of Cambridge, asked people to be less prejudiced about the weight of others.
"This research shows for the first time that the raw and healthy people are generally lean because they have a lower charge of genes that increase their chances of being overweight and not because they are morally superior, as some people suggest," he said.
"It's easy to hurry to judge and criticize people for their weight, but science shows that things are much more complex."
"We have much less control over our weight than we would like to believe."
Scientists say the next step is to identify the exact genes involved in healthy health.
Your long-term goal is to see if this new knowledge can help you set up new weight loss strategies.
Tom Sanders, Emeritus Professor of Nutrition and Dietetics at the King's College in London, said on the research: "This is an important and well-done study that confirms that precocious severe obesity is often genetically determined" .
He added that "convincingly shows that those who are very thin are genetically different from the general population."
However, he clarified: "Most of the obesity is acquired in adulthood and is related to the obesogenic environment in which we live: a sedentary lifestyle and abundant access to dense foods in calories ".
Professor Tim Spector, also from the King's College in London, noted that, in spite of this, about one third of people in most countries managed to stay thin.
"Part of this is due to genes, but other factors, such as individual differences in lifestyle or intestinal microbes, are probably also responsible," he considered.
Health experts point out that, in any case, regardless of the size of your body or your genetic makeup, the old advice to follow a good diet and make a healthy amount of exercises is the most advisable.