Every day we choose which meals, snacks and drinks we want to eat.
But instead of this choice being entirely within our control, genes could dictate what and how much we eat.
One of them, called MC4R, is essential for regulating body weight.
Although everyone has two copies of it, some people with a mutated version find it much harder to resist the urge to eat.
Research shows that people who wear the variant weigh almost 20 kg more than their peers.
One gene in particular, called MC4R, is essential for regulating body weight. Although everyone has it, some people with a mutated version find it much harder to resist the urge to eat
Melanocortin-4 receptors (MC4R) have been associated with obesity since the 1990s.
When it works properly, it produces a protein that signals to the brain's appetite sensors when the body has stored enough fat and therefore when it is full, experts say.
However, if one or both copies of this gene are defective, it can falsely signal to the brain that it has a lack of fat storage, fueling the desire to overeat.
NHS genetic tests for severe early obesity can detect the mutation and some online tests, costing up to £800, claim to detect the mutation too.
A 2021 study by researchers at the The University of Bristol and the University of Cambridge have revealed just how much of an impact this genetic quirk can have.
They looked at data from 5,724 children born in Bristol between 1990 and 1991.
The results showed that 17 (0.3 percent) had mutations in one of their copies of MC4R, which caused their brains to perceive that they had less body fat than they actually had.
According to the findings, at age 18, those with the mutation were on average 17.8 kg heavier than those who did not have the mutation.
They also had a BMI score that was 4.8 points higher and carried 14.8 kg more fat.
The scientists, who shared their results in the magazine Naturopathywarned that those who carry the variant are at risk of entering adulthood with a 'substantial burden' of excess fat.
They suggested the so-called obesity mutation could affect as many as 200,000 Britons and 1 million Americans.
Professor Giles Yeo, a geneticist who studies obesity at the University of Cambridge and co-author of that study, discussed the research at a Royal Society conference this week.
He said, 'You cannot magic energy into your body and you certainly cannot magic energy away.
'The only way you can gain weight is by eating more than you burn, so the only way to lose weight is by burning more than you eat. Obviously your body weight is a function of physics, but that's the way it is.
“Where the biological variation lies, where the interesting things we can do and think about lie in the why – why do people behave so very differently when it comes to food?”
He said genetic modifiers, such as MC4R mutations, go through the entire process of food intake, which is controlled by the brain.
While discussing whether obesity is a choice, he said, “Am I giving anyone an excuse? Hopefully the answer is no.
'But I think you should think of your genes as a hand of cards: you're going to be dealt bad hands.
“And the only people you can blame are your parents, because that's where it comes from. But you can win with a bad hand, it's just more difficult.'
Professor Yeo said: 'We don't lose weight or gain weight overnight. We just don't do that. Each meal, no matter how large, will not noticeably change your body weight. Your body weight is a function of thousands of different nutritional events over the years.
“But imagine if, because of your genetic card hand, you are a few percentage points less likely to say no (to overeating) – five percent.
“Five percent over thousands of eating events is hundreds of thousands of calories.”
He added: 'Until we understand in society that it will always be harder for people who are obese, they are fighting their biology, we will never be able to solve the problem.'
A special one study suggested that mutations in the MC4R gene fuel unhealthy food choices.
Researchers in Cambridge recruited people who were healthy weight and obese, with some of the latter having MC4R mutations.
They were presented with three bowls of chicken korma and three bowls of Eton rubble – each of which had a low, medium or high fat or sugar content – and were told to choose the option they liked best and eat as much as they wanted. wild ones.
Those with the mutation ate almost twice the amount of high-fat curry than their slimmer counterparts and 65 percent more than others who were obese but did not have the genetic quirk. However, they ate significantly less of all the Eton mess variations compared to the other two groups.
The team concluded that people with the gene prefer high-fat foods without realizing it, a habit that contributes to their weight problem.
They suggested that the MC4R mutation could be a way for the body to protect itself against famine by encouraging the consumption of high-fat foods.
Research has also suggested that MC4R is involved in the development of obesity-related health problems, such as type 2 diabetes and high blood pressure.
Scientists think this is due to the molecule playing a role in maintaining healthy insulin levels and blood pressure.
Still, obesity can lead to both conditions and may be a simpler explanation.
However, studies also show that there are nine mutations in the MC4R gene that can help people stay lean and dodge type 2 diabetes and coronary artery disease. It is believed that about six percent of people carry them.