I’ve got the ‘fat gene’ – but at 42 I’ve finally beaten it

For every person I know who says things like “I only have to look at a croissant to gain half a stone”, I know another who can seemingly eat exactly what they want, without ever breaking a sweat, and yet somehow maintain a slim physique. 

I’ve definitely always been in the first category – and it means that I have to make a choice between accepting my fluctuating weight, or throwing myself into vigorous exercise to stay at a size I’m happy with while still eating a few delicious things. So, why is this? Could my genes be at least partly to blame?

Over the past few decades, scientists have been researching “the fat gene” extensively, to try to get to the (curvy) bottom of why some people, across different genders, cultures and social groups, seem to struggle with their weight more than others – and the impact this might have on their health. 

One of the most commonly cited and fascinating examples is the fact that the Pacific Islands have the highest rates of obesity in the world, with 75 per cent of residents of American Samoa considered medically obese – considerably more than the US which, contrary to its image as a nation of fast-food-devouring couch potatoes, doesn’t even make the top 10. 

Dr Andrew Jenkinson, author of Why We Eat (Too Much): The New Science Of Appetite, explains that this is because the first ever settlers to this remote part of the world originally had long and arduous journeys to get there across the waves of the Pacific – and so sadly only the strongest survived. 

“There was therefore automatically a huge selection bias for anyone settled there,” Dr Jenkinson explains. “Those people who had enough fat reserves before the journey, or those with metabolisms that could shut down in the face of starvation, had a much better chance of surviving the long journey. The sailors and passengers who did not have this insurance perished and did not have the opportunity to pass their genes onto the next generation. It was extreme selective breeding.”

So, if they were optimum physical specimens when they arrived on the islands thousands of years ago, what went wrong? Well, this fighting fit population gradually started adopting Western-style diets, rather than eating fresh, native food, causing their genetically sturdy physiques to balloon.

While most of us have less dramatic reasons for our varying builds, it’s a vivid illustration of the clash between genes and the differing environments they exist in and why it makes it difficult to get to the root of someone’s weight issues – let alone do anything about them, should they wish to. Giles Yeo MBE is professor of molecular neuroendocrinology at the University of Cambridge, and an expert on the topic.

“The top line is that between 40 to 70 per cent of obesity is going to be down to your genes – but simplistically the reason there is a range is because the environment is so volatile,” Yeo explains. “A way of actually viewing this is to take one of the classic environmental factors, poverty. We know that in middle-class households, there are some levels of obesity. But if you go to the poorest households, people are more than twice as likely to end up with obesity over their lifetime.”

But it’s not that the less affluent members of the population are somehow genetically less healthy; it’s more that the world they’ve been born into makes it harder to eat a balanced diet. “I live in a leafy village, where there is no takeaway, no corner shop and no Deliveroo deliveries,” Yeo says. “So if I’m hungry – say, genetically, I’m more hungry on a Sunday night – and I open my fridge, I have carrots and hummus, so that’s what I eat. 

“If you looked exactly like me, but you were poorer, and you lived right in the middle of town somewhere, instead of carrots and hummus you suddenly have a chicken shop next door, which is cheap. That’s a classic example of your genes being relevant, but the environment influencing your diet.”

And of course the biggest impact on a person’s chances of being obese or overweight is the weight of their parents – which is why studies of identical twins can be a great way of getting to the bottom of genetic versus lifestyle factors when it comes to defining weight. 

This is something I often wonder about when it comes to my own body. While nobody in my immediate family is super-skinny, my two siblings, who are both more than a decade older than me, seem to be “naturally” slimmer. Now I wonder if this is less down to genes and more down to the fact that they were brought up frugally in the 1970s and early 1980s, while my 1980s/1990s childhood was fairly affluent, with meals out, convenience food and takeaways more readily available – all of which then felt normalised to me when I left home for university.

Dr Zoe Watson, a GP and wellbeing coach at Wellgood Wellbeing, cites that studies of twins of differing weights show BMI determination to be 60 to 85 per cent down to genetics, and 15 to 40 per cent down to environmental factors, meaning that if two genetically-identical people happen to lead different lives, they could easily look quite different. 

She explains that there are essentially two broad categories of genetic cases of obesity: monogenic obesity, caused by a single gene mutation, and the more common polygenic obesity, caused by the cumulative contribution of a large number of genes amplified in an obesogenic – weight gain-promoting – environment, with a total of around 600 genes implicated in causing obesity.

“While some of those genes are to do with all the stuff going on internally that you’re not aware of, some of those genes are actually to do with food preferences and human behaviour,” says Dr Watson. “There are literally genes that determine how much sweet, salty or fatty foods we like to eat, as well as how much physical activity we are inclined to do.”

The genes contributing to obesity susceptibility are broadly split into four groups: food intake (hunger, appetite and cognitive restraint – better known as willpower), fat cell differentiation and fat storage levels, physical activity (both spontaneous and intentional) and thermogenesis (which we know better as metabolic rate). They explain why some of us can happily go about our day knowing there’s a bar of Lindt in the cupboard but not giving it a second thought, while others – unfortunately, like me! – will be able to think of nothing else. 

While it’s hard to “hack” how we store – and burn off – fat, other factors are within our means to control, if we’re so inclined, by restricting the foods we keep at home, and developing positive habits around exercise. But if we ban biscuits from the house, will those of us who suspect we have a genetic propensity towards obesity end up seeking them out and bingeing on them when we get the chance? It’s this sort of behaviour that explains why diets often fail.  

“Obesity is caused by a complex interaction between genetics, epigenetics, environmental factors and the resultant hormonal changes,” says Dr Watson. “It is a chronic, relapsing and progressive disease – which results in that person constantly battling against their own body as it repeatedly hoodwinks them to try and get back to a previous ‘metabolic set-point’ – which is why any weight lost is often regained.”

When you hear it explained like that, it does make it sound like many of us could be fighting a losing battle – what chance do I have resisting another Hobnob if 600 genes want me to eat it? But Dr Watson says it’s not as simple as that, and that we’re putting too much emphasis on weight alone as an indicator of health.

“We shouldn’t all throw our hands up in despair and say “well there’s no point in eating vegetables or doing exercise because I’ll always struggle with my weight”, she insists. “Doing those things has a positive impact on our health regardless of weight, and just using weight or BMI as a measure of health is pointless as it tells us nothing about body composition, nothing of cardiovascular health, nothing about genetics and family history and nothing about physical activity levels.”

It’s also crucial to remember that excess weight has more of a health impact on some people than others, depending on their cultural background. Giles Yeo explains: “We can all store different amounts of fat safely, and that is also a genetic influence. On the cutting edge of things, people are trying to work out whether or not they can use genetic tests to make some predictions, but we’re not there yet. Famously, we know that South Asian communities can’t get as large as other populations before becoming ill. So, if you’re a doctor, you need to make different decisions based on this – so there is already some level of using ‘genes’ to influence clinical advice.” 

So, if we believe we might have “fat genes” – and Yeo is confident this is something we will soon be able to find out ourselves through testing – what can we do about it? Well, a good starting point is to differentiate between our body shape and body size. “Your body shape is very genetic,” says Yeo. “If you carry weight on your hips, this will be the case if you are overweight or skinny. You just happen to have a big bum, and it’s why ‘booty booster’ fitness classes and the like won’t work – it’s nigh on impossible to direct where weight loss comes from.”

While a huge research project of over 18,000 Chinese people showed that, of all forms of exercise, jogging had the most impact on genetic predisposition to obesity, with some benefits from walking, dancing and yoga too, it also showed that all exercise had health benefits – even if it did not fight obesity in itself.

The good news for anyone who thinks they might have “the fat gene” sabotaging their efforts to stay slim is that scientists are learning more and more about it every day – but that doesn’t mean it’s going to go away. Either way, it seems like throwing our energy into eating a varied diet and living a generally active life, regardless of the lot we might have been given genetically, will have much more of a positive impact on our physical and mental health than yo-yo dieting or exercise fuelled by self-loathing. 

It’s a lifestyle I’m finally finding my groove with at 42 – and, for me, going for a 10k run through London’s beautiful parks and still enjoying a cappuccino and some banana bread afterwards is definitely more appealing than moving somewhere without Deliveroo. 

How to ‘hack’ your fat genes

Scientists say we’re not far off being able to routinely test our own genetic tendency towards obesity – but, until then, we might just have our own suspicions. So, how can we get around them? The key is in making changes to the things we can control: lifestyle, environment and habits… 

Plan ahead

If you’re susceptible to fluctuating willpower and cravings, meal planning, and batch cooking can be great ways to ensure you have healthy meals on tap (think protein first, as it will fill you up more, plus lots of fresh fruit and veg), without succumbing to the lure of convenience foods and takeaways, even if you live in an environment where they’re readily available. 

Join a community

People who regularly exercise in groups, for instance at yoga classes or free community events like parkrun, are more likely to form habits that stick – partly due to the accountability that making a date with friends, or even strangers, gives us, and partly due to it simply being more fun. Since habits take an average of 66 days to form, committing to (and paying for!) a six or eight-week course in a type of movement you enjoy can make it much easier to get to and maintain a weight you’re happy with. 

Find your triggers

Do you binge when tired or stressed? Does alcohol make you comfort eat? Or are you the type who “forgets to eat” when busy and then reaches for the nearest sugary snack? All of these can be down to genetic factors – but they’re within your control. It’s impossible to never be tired or worried, but making sure food is on hand that makes you feel good, longer term, rather than quick fixes, can help. 

Avoid the dreaded yo-yo

We all know that crash diets don’t tend to work – and yet still we succumb to them. If you’re considering a diet, or even one of the now readily available prescription weight-loss drugs (most of which work by suppressing your appetite), try to think beyond it: if the weight comes off, and there’s plenty of evidence to show that it will, how will you maintain it afterwards? Work on cementing those healthy habits while you’re losing the weight, not after.   

Understand your environment 

Rather than resenting your mum for passing on her big bum (and her resenting your granny before her!), analyse habits from your upbringing – perhaps you always dug into the biscuit tin after school – and think about how they impact your eating now. Can you adapt and break the cycle by role-modelling healthier attitudes for your own family, if you have one?  

Accept your genetic fate 

Acknowledging that you might never be skinny, but can still lead an active, healthy lifestyle that you enjoy, is ironically often the key to maintaining a weight you’re happy with – even if you’re still technically overweight on the much-criticised BMI scale. Finding positive role models doing just that – and unfollowing anyone who makes you feel rubbish – can be a great start.