Fitness fanatic by Martin RowsonThis is the year that everything changes for you. New year, new body! You will transform your diet. You will transform your exercise regime. You will transform yourself from a slouchy carb-stuffed potato sack to a cleansed, lean, immortality machine.

Except, you won’t. That’s not just because New Year’s resolutions are a notoriously flaky way of changing your behaviour, though they are: as Oliver Burkeman explains, “Willpower is a unitary, depletable resource, which means investing energy in any one such goal will leave less remaining for the others, so your resolutions will, in effect, be fighting each other.” Even more than that, though, it’s because as soon as you start trying to make these changes – exercise more, eat better – you’ll run into a mass of unhelpful advice, unsubstantiated claims and downright shysters aiming to lighten your pockets rather than your frame.

So let’s start – as these things so often start – by going shopping. Running is often pitched as the easiest, most accessible form of exercise to take part in. All you need is some pavement, some shorts, a T-shirt and a pair of trainers. And it’s the trainers that cause the trouble. An entry-level pair of running shoes will set you back about £40, but spend any amount of time browsing the display in a sports shop, and feature creep starts to set in. Cushioning. Stability. Breathable mesh fabrics. The promise of a more natural gait. And with every promise, the possibility that pushing the budget a little will push your own abilities as a runner – isn’t that worth a £170 price tag?

But many of the shoes in stores won’t do you any good at all. Dr Casey Kerrigan has been studying the interaction of biodynamics and footwear for decades as a researcher at the University of California using barefoot as the control, and her research consistently showed the same thing: anything you put on your feet makes things worse than wearing nothing at all. She recalls taking her research to shoe manufacturers around 2002 along with a proposal for a better shoe design, and facing being asked by companies whether the model she was proposing would be stabilising, arch-supporting or cushioning – the only designs they seemed comfortable with. Meanwhile, says Kerrigan, “I’m just plugging away showing that each one of those … and any kind of foam cushioning increased those same forces.”

Ten years later, and the trend in running shoes has moved dramatically to accommodate the findings of Dr Kerrigan and other researchers working in the same field. The book Born to Run by Christopher McDougall, published in 2009, was hugely influential in popularising the barefoot movement – that is, the theory that humans are evolved for running and any shoe is likely to inhibit the natural reflexes that produce good running form and protect the joints from injury. Since then, running shoes have increasingly been sold on their ability to imitate … nothing at all. The most expensive shoe you can buy is the one that promises to seem as if it doesn’t exist. (Kerrigan herself has left research to produce her own line of shoes that promise to reduce joint torque compared to barefoot, though she hasn’t made a running model yet.)

Looked at in a certain light, this is a somewhat rum state of affairs, even if it is always nice to have something between your skin and the broken glass and dog mess that decorate city streets. But is running alone enough? The NHS recommends a mixture of aerobic and muscle-strengthening exercises – vigorous running, swimming or cycling three times a week, complemented by weight lifting or yoga twice a week, for example – to balance the benefits to cardiovascular fitness, bone density and muscle mass.

However, a quick skim over the websites of some popular training plans offered by gyms could convince you that might as well eat a Big Mac and fries as run a 10K, such are the perilous qualities they attribute to aerobic exercise. “[A]erobic exercise increases oxidative stress, chronically elevates cortisol, and has been shown to lower testosterone levels in men,” warns one terrifying website that happens to promote a programme of anaerobic weight lifting (and, inevitably, a line of pricy supplements).

Once you enter the world of gyms and the idiosyncratic system of training schemes, certain words become familiar as the nightmare creatures menacing your health and wellbeing. Cortisol, for example, is regarded in some quarters as a very bad thing, and anything that is believed to encourage its production is advised against. The fact that this steroid is a normal and necessary part of human biology is neither here nor there: it’s become a part of the semi-science of fitness. “Inflammation” is another vague nemesis of wellbeing, and certain foods or exercises can be rated as more or less inflaming.

A personal trainer once told me with absolute sincerity that I should avoid oats because they were very “inflaming” and would “elevate my cortisol levels” leading to “reduced muscle mass”. Despite some searching, I never managed to locate the research paper demonstrating that oats would make me waste away, and I recklessly decided to stick with my morning porridge; amazingly, I haven’t succumbed to its alleged wasting powers yet.

It’s not always true that the conventional wisdom is on the side of right, though – particularly when it comes to diet. And that’s particularly true when it comes to carbohydrates, most of all the refined types (rather than my porridge). For some three decades, the dietary mantra has been to load up on carbs and avoid fat. (You might remember this from the “food pyramid” that was common to home economics lessons, where a vast base of bread, pasta and potatoes holds up ever diminishing layers of vegetables, then protein, then a teeny-tiny crown of fat at the top.) Fat consumption has indeed fallen, but fatness has not: the same period has seen a huge increase in obesity as refined carbohydrates and sugar have become increasingly prominent.

This is a particularly cruel trick when sugar is incorporated into low-fat, allegedly healthy eating foods. Robert Lustig MD, an expert in childhood obesity, is unambiguous about what sugar is doing to us: he calls it “poison”. It’s not just that sugar, like fat, is exceptionally high in calories: it’s that the extraordinarily digestible form of the sugar molecule means your body can break it down rapidly into energy (that’s the familiar “sugar rush” knocking you off your feet when you scarf a Twix) and store it as fat (that’s the regrettable obesity and diabetes epidemics).

In which case, what is sugar doing in products that are specifically marketed as healthy? There was some kerfuffle last summer when joint research by Panorama and the British Medical Journal found that not only were the health claims made by sports drinks based on astonishingly flimsy evidence, but their incredibly high glucose content made them a major culprit in the sugar epidemic. For some, this amounted to an attack on sacred truths: sports drinks and gels are a fixture of sports events. The major brands such as Lucozade and Gatorade sponsor road races. They’re given out from the rehydration stands along with the bottles of water en route, and they appear in your goody bag at the end, blazoned with sciencey talk about improving your performance.

Lucozade Sport, for example, claims to “deliver the right fuel before, during and after exercise”. They couldn’t appear more legitimate and integral to healthy pursuits. And they do remarkably little: Dr Carl Henegan, who led the Panorama/BMJ research, commented that “the quality of the evidence is poor, the size of the effect is often minuscule and it certainly doesn’t apply to the population at large who are buying these products.”

That point about the population at large is key. A 500ml bottle of Lucozade sport contains 130 calories. Although that’s probably a trivial mouthful to Lucozade-sponsored Mo Farah, by my fairly rough calculations it’s only a third of what I might burn in a half-hour run. In other words, there’s no evidence that the sweet stuff will make me run better, and a very compelling case that – if your aim in exercising is to create a calorie deficit that induces weight loss by forcing your body to burn fat reserves – sipping an energy drink while jogging is not going to help you very much at all. At best, it might displace a more nutritious post-exercise snack; at worst, you’ll simply be adding a high-calorie drink to your usual diet, in the mistaken belief that this sort of sugar water is somehow sporty because the packaging says so.

There’s only one time in my life that I’ve ever felt that what I really needed was a dose of Lucozade, and it was after I’d cycled 100 miles across Europe for the third day in a row and felt like my head had turned into a balloon and was about to float away to Dieppe. For general fitness purposes rather than calorific emergencies, I’ve always managed quite happily on a scientifically calibrated mixture of bananas and peanut butter on toast.

At this point, you might start to feel somewhat despairing. You can’t resolve your way fitter. The expensive trainers won’t walk you into the kingdom of the fit, gyms will tell you nonsense and sell you jumped-up protein shakes, pasta is not your dietary ally after all and sports drinks won’t make you sportier. Why bother with any of it? But the benefits of being fitter are substantial: not just a longer lifespan, but one that’s likely to be much more pleasant overall. And not simply in the sense that you’ll get your reward – well, not in heaven, but certainly just before you end your acquaintance with the earth’s surface and get cosy with the undersoil, when you’re old enough to smugly appreciate the superior cardio fitness and increased bone density you cultivated while young, as you watch your less fitness-savvy peers totter over wheezing and smash their limbs to dust.

No, the reason to eat better and exercise more now is because it will make you feel better, now. It’s fun to pick up a heavy thing that, a few months ago, you’d have eyed suspiciously and wondered if you should get a man in to shift it for you. It’s fun to know that you can run for miles if you want to, and escape to barely passable paths where birds sing and your mobile phone can’t be roused. It is, despite a popular consensus that the best food is the food you feel guilty about, fun to eat a meal and feel pleasantly sated afterwards rather than sugar-drunk and overstuffed. It is fun – I don’t think we need to be coy about this – to put away the fat trousers and wear our thin ones instead.

And the best way to make all these clearly desirable things happen is probably to stop wanting them so badly. The higher you set your standards, the more likely you are to fail and find yourself even less committed to your own improvement than you were before you made that resolution. But if you can’t recast your whole personality and lifestyle, you can acquire new habits with practice and without putting too much pressure on yourself. Rather than resolving to exercise more, give yourself three set times a week to go out running: if you feel better for actually doing it, that’s more incentive to continue than the miserable tongue lashing you might give yourself for failing to do more of some vague, non-specified exercise.

Screw up the resolutions. Ditch the New Year detox. Embrace the fact that you’ll never do something just because you think it would be good for you, and instead trick yourself into doing what’s good because you’ve lost the habit of doing what’s bad.