According to new research carried out at University College London by the Health Behaviour Research Centre of the charity, Cancer Research UK, and published last week in the American Journal of Clinical Nutrition, there really is such a thing as a fat gene. Researchers who studied 5,000 sets of twins found that genetics has more of an influence on weight than upbringing, exercise and diet. Scientists said parents should therefore not be blamed if their child is fat, as three-quarters of the variations in children’s weight and waist measurements were determined by their genetic make-up.

The long and the short of it is, America may be the most obese nation in the world – Britain is not far behind – but it’s not anyone’s fault. Nothing at all to do with them. Fat genes, you see. More pie? Frappuccino with sweet whipped cream to wash it down?

I hate to blithely dismiss a whole swathe of scientific findings but I don’t believe a word of this. Fat gene, my foot. Funny how it seems to manifest itself only in the prosperous, cake-guzzling carb-and-sugar-laden West. Where are the obese Sudanese toddlers? The porky Ethiopians?

There has been an eightfold rise in prescriptions for obesity drugs – I don’t believe in obesity drugs either, although I do believe in getting a grip – over the past seven years. A million of these are now being written out annually at vast cost to the health service. Nothing to do with fizzy drinks and processed carbohydrates, if we’re to believe these findings – and, of course, nothing to do with self-control: that is, changing your diet and maybe considering dumping the chips and biscuits or, you know, going for a brisk walk every now and then. No: keep at the chips, keep your lardy bottom firmly in your car and demand obesity drugs as your right because it’s not your fault, it’s your genes.

Meanwhile, we are, the government tells us, in the grip of an obesity epidemic; the problem’s magnitude is “comparable with climate change”. According to last year’s Foresight report (the document on which government policy is based), almost two-thirds of British adults and a third of British children are either overweight or obese. The report predicts that by 2050 just 10% to 15% of the population will be at a healthy weight. Britain is the fat man of Europe. We spend £1 billion a year treating obesity-related health problems such as type 2 diabetes (which used to be called “adult onset diabetes”, but got a name change when so many fat children started getting it), strokes, high blood pressure, heart disease, damaged joints and so on. By 2050, according to Foresight, the cost will have risen to about £50 billion, including medical bills, incapacity benefits and lost working days.

The excuses that people make for their own fatness drive me mad (I know whereof I speak and am not wholly unsympathetic: I was very fat myself at one point), and you can just see the mileage they’re going to get out of being told that it’s all down to genes. It’s not. It’s down to taking control of your life and down to choice: you can choose to be fat or choose to be normal. You can choose to make sacrifices or choose to be lazy – and if you choose to be lazy and remain fat, then fair enough, but accept that it’s your own doing and take responsibility for it.

Having written a diet book explaining how I lost my five stone, I also have a diet website that acts as a support tool. I’ve lost track of the number of people who, having read the book and familiarised themselves with its no-sugar, few-carbs principle, still come on and say things such as “I literally can’t live without Coke, is it okay to keep drinking it?” or “I don’t think I can give up biscuits, can I keep eating them?”

There are three things to realise about fatness: a) you made yourself fat (and therefore can make yourself unfat); b) if you want to shrink, you have to dump the kind of eating that made you fat in the first place; c) nobody is mysteriously fat for no reason. The last is the most important: it’s only when you look at yourself honestly and stop making excuses (“but I’ve had a terrible day and this doughnut is cheering me up”) that your diet is going to work. Irritatingly, the diet industry and, to an extent, government advice and guidelines tend to ignore c) completely.

Being fat is as much a mental state as a physical one and until this is addressed I don’t see any reduction in the size of the problem occurring any time soon. It’s no good wailing about rising levels of obesity if you show no interest whatsoever in trying to understand why people overeat in the first place. People overeat for psychological reasons, not physical ones.

There is no such thing as an obese baby – well, there might be a baby with weight problems if it suffers from a certain syndrome or genetic condition, such as Prader-Willi syndrome, of which this is a symptom. But generally speaking, obese newborns simply don’t feature. It’s what you feed your children that makes them fat. In the days when it was considered normal to top up formula milk with a couple of spoonfuls of porridgey baby food, babies got incredibly fat – because stodge makes people fat.

The fat kids you see waddling around aren’t fat because their genes just made them that way – they’re fat because they take very little exercise and are fed a great deal of fattening food which, to add insult to injury, contains very little that’s of any nutritional value. It’s not rocket science. Give your child sugar-laden “juice” and batter-covered chicken, chuck in industrial quantities of “food-product” stodge, dole out sweets as “treats” and raise them to be suspicious of vegetables, and voilà: you can start your own obesity epidemic. Especially if you blame their chafing thighs on their genes.

To be fair, the so-called fat gene identified by researchers needs to be triggered: having it will not automatically result in having three chins. This is the bit that’s going to get lost – the bit that says that if you have a genetic predisposition to fatness, you need to be extra vigilant. However, drowning as we are in nutritionally bereft, fattening everyday foodstuffs, everyone needs to be vigilant about their diet – and their children’s diets. The fact that people clearly aren’t, and that appallingly fattening foods with giant marketing budgets are not only widely available but also constantly touted as being “healthy”, is really reprehensible.

We need to educate ourselves about nutrition and we need to read the label. Above all, we need to get to grips with the fact that fatness is a personal choice, one that can’t be blamed on anybody – or anything – other than our own greedy behaviour.

india.knight@sunday-times.co.uk

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