In my diabetes clinic, I’m so often asked by my patients: “Why have I got type 2 diabetes? My friends are all fatter than me and they don’t have this disease.” The answer is this: we all have a different degree of susceptibility to fat. Type 2 diabetes is caused by an individual acquiring more fat than they personally can cope with – something I demonstrated in my work as a diabetes researcher a decade ago. When it comes to this illness, there is no one size fits all approach to the question: how fat is too fat? This week, a study by researchers at the University of Michigan found the number of people around the world who are living with diabetes has more than quadrupled since 1980. Today, almost half a billion people globally have the disease, and 90 per cent of them have the type 2 version. The frightening part is most don’t even realise it. As someone who has studied type 2 diabetes for many years, these new findings don’t surprise me at all. There’s no mystery surrounding the reason for such an explosion in the condition, which causes the level of sugar in the blood to become too high and can lead to complications such as heart disease and stroke, vision loss and kidney problems: it’s a sickness of modern lifestyles, in which we cook less food from whole ingredients and buy more of it ready-prepared. But the correlation between type 2 diabetes and obesity is less straightforward than you might think (hence those puzzled patients of mine). Almost three-quarters of those with a BMI of over 45 (in other words, those who are morbidly obese) actually don’t have type 2 diabetes. Meanwhile, 10 per cent of those with the disease have a BMI of under 25, meaning their weight is theoretically healthy. But in the case of these people, crucially, their weight isn’t healthy for them. Our genes determine how much weight each of us can carry before we enter the danger zone, and for some it’s far less than for others. Our diets have changed dramatically in recent decades. As a result, both men and women are approximately 10kg heavier today than they were 30 years ago. The problem is not the hugely obese people; it’s that most people are walking around with a few extra kilograms they shouldn’t have. The finger of blame often points towards ultra-processed foods, and rightly so: these foods are designed to fill us up less and leave us craving more. Thirty to 40 years ago, most people were cooking more meals from scratch, and our shift to prepared food has had a disastrous effect. Exercise plays a part too, of course, but to a lesser degree. If a large man does a good workout, he could still regain all the calories burned by eating some chocolate. Exercise is important for keeping your weight healthy in the long-term, but nothing beats diet when it comes to shedding pounds fast. So how do you know if you’re one of the unlucky many who’s walking around without knowing you are diabetic? The short answer is you don’t. This is a disease that creeps up on you silently, not making itself known until it’s well on its way. If you’re passing more urine than usual, feeling thirsty, tired, or succumbing to more skin infections, then yes you should get yourself checked. But by the time these red flags appear, it’s likely the disease has already been present a while. It is, however, possible to know if you are at risk before the symptoms appear. If you come from a family with a history of the disease, you stand a fair chance of developing it if your weight goes above a certain level. It’s a genetic predisposition, but it never happens unless a person becomes too heavy for their own body.