The pesky gene that could make you 20kg heavier: Leading expert reveals how mutation can leave you addicted to junk food… but insists getting dealt a ‘bad hand’ doesn’t mean you’re destined to be fat

Every day we choose what meals, snacks and drinks we would like to eat.

But rather than these choices being entirely under our control, genes can dictate what and how much we eat.

One in particular, called MC4R, is vital for regulating body weight.

Although everyone has two copies of it, some people who have a mutated version have a much harder time resisting the urge to eat.

Research shows that people who carry this variant weigh nearly 20 kg (3 2 lb) more than their peers.

Melanocortin-4 receptors (MC4R) have been associated with obesity since the 1990s.

When it works correctly, it produces a protein that signals the brain’s appetite sensors when the body has accumulated enough fat and therefore when it is full, experts say.

However, if one or both copies of this gene are faulty, it can mistakenly tell the brain that it is low on fat stores, fueling the desire to overeat.

NHS genetic tests for severe early-onset obesity can detect the mutation, and some online tests costing up to £800 also claim to detect it.

A study conducted in 2021 by researchers from The universities of Bristol and Cambridge have found out what impact this genetic feature can have.

They looked at data on 5,724 children born in Bristol between 1990 and 1991.

The results showed that 17 (0.3%) had mutations in one copy of MC4R, causing their brains to feel like they had less fat than they actually did.

According to the findings, at age 18, people with the mutation were on average 17.8 kg (39 lb) heavier than those who did not have it.

They also had a BMI score that was 4.8 points higher and carried 14.8kg more fat.

Scientists who shared their results in the journal Natural medicinewarned that carriers of the variant risk entering adulthood with a “substantial burden” of excess fat.

They suggested that the so-called obesity mutation could affect up to 200,000 Britons and 1 million Americans.

Professor Giles Yeo, a geneticist who studies obesity at the University of Cambridge and co-author of the study, discussed the findings at a Royal Society conference this week.

He said: “You can’t magically put energy into your body and you certainly can’t magically take it out.

“The only way to gain weight is to eat more than you burn, and therefore the only way to lose weight is to burn more than you eat.” Obviously, your body weight is a function of physics, but here’s how.

“Where the biological differences are, where the interesting things we can do and think about are why…why do people behave so differently around food?”

He said genetic modifiers such as MC4R mutations run through the entire eating process, which is controlled by the brain.

Discussing the question of whether obesity is a choice, he said: “Am I giving anyone an excuse? I hope the answer is no.

“But I think you should treat your genes like a hand of cards—you have bad hands.”

“And the only people you can blame are your parents, because that’s where it came from. But you can win with a bad hand, it’s just more difficult.”

Professor Yeo said: “We don’t lose or gain weight overnight. We just don’t do it. Any meal, no matter how large, will not lead to a noticeable change in your body weight. Your body weight is a function of thousands of different feedings over the past few years.

“But imagine that because of your genetic card combination, you are a few percentage points less likely to say no (to overeating)—five percent.”

“Five percent of a thousand meals are hundreds of thousands of calories.”

He added: “Until we as a society understand that people who are obese will always have it harder, they are fighting their biology, we will never be able to solve this problem.”

Separate study suggested that mutations in the MC4R gene contribute to unhealthy food choices.

The Cambridge researchers recruited healthy-weight and obese people, some of whom had MC4R mutations.

They were given three bowls of chicken korma and three bowls of Eton porridge – each of which had 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.

Those with the mutation ate almost twice as much fatty curry as 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 Eton porridge variants compared to the other two groups.

The team concluded that people with this gene prefer high-fat foods without even realizing it, and this habit worsens their weight problems.

They hypothesized that the MC4R mutation may be the body’s way of protecting itself from starvation by encouraging the consumption of high-fat foods.

Research has also shown that MC4R is involved in the development of obesity-related diseases such as type 2 diabetes and high blood pressure.

Scientists believe this is because the molecule plays a role in maintaining healthy insulin levels and blood pressure.

However, obesity can lead to both conditions and may be a simpler explanation.

However, research also shows that there are nine mutations in the MC4R gene that may help people stay thin and avoid type 2 diabetes and coronary heart disease. It is believed that about six percent of people carry them with them.