Want to lose weight? Try sex and shopping

A hi-tech armband can help you count every calorie you eat – and those you burn. Jo Payton put the device to the test, and discovered that the most energy-intensive activities are not always the ones we expect

Information is a diet we thrive on. In the internet age, having the world at our fingertips feels as vital as food and water. But in our quest to know everything about anything, we've lost touch with something closer to home: our own bodies.

Whatever size or shape you are, an information overload of weight-loss fads, exercise crazes and celebrity-endorsed diets has made it harder for an individual to work out the needs of his or her own body. Factor in our obsession with the "ideal physique" and it's no wonder there's confusion whenever we look in the mirror.

My body has always been a mystery. I don't diet, work out or watch what I eat, but apart from a brief dalliance with whaledom (aka pregnancy), I've always been slim. I've weighed eight stone since I was 21 and, well into my thirties, nothing's changed.

At 5ft 4in, I'm a healthy weight and any BMI calculator will tell you the same, but it's hard to convince well-meaning friends and relatives that a desk-bound writer (with an aerobics aversion and an unquenchable passion for pints) isn't secretly crash dieting or enslaved to bulimia.

I harboured a sneaking suspicion that my hectic 21st-century lifestyle was responsible for my waistline, but apart from the odd magazine snippet about how washing up burns the same number of calories you'd encounter in a Kit Kat finger, I've never been able to substantiate the theory.

When I was offered the chance to gather such evidence, I jumped at it. I was invited to trial a Ki Fit lifestyle armband, a gadget using sensors to measure continuously motion, steps, body temperature, heat flux and galvanic skin response.

The technology was developed for clinical environments, to check that intensive-care patients were consuming the correct number of calories, but now it's available as an informational tool, designed to help people to lose weight, bulk up, or simply gain access to personalised data that can help them understand their bodies.

As with all fitness-related gadgetry, the Ki Fit comes at a price. It retails at £99.99 and there is a further £10.88 monthly website subscription. The good news is that this membership gives you access to a team of human beings: nutritionists and trainers who answer questions and offer advice. Detailed fitness plans and feedback come with an additional price tag.

I wore the band around the clock on my left arm, where it monitored my daily calorie burn, activity (including the ironing), number of steps and sleep quality. At the end of each day I plugged it into my computer via the USB port, downloading the data onto the Ki Fit website, much like synching an iPod.

Then I could see, plotted on a graph, exactly what my body had been up to over the past 24 hours, with clearly defined spikes showing my most energetic outbursts. The only manual hassle is inputting your meals, which gets tiresome and a tad obsessive.

Given my size, I targeted a daily burn and consumption of 1,700 calories to keep my weight stable, 30 minutes of exercise and eight hours sleep. But for me, the armband was less about goals and more about understanding the information it collects. That information was revealing, and often surprising. Although my daily target was 1,700, my actual calorie burn is around 2,200. Even on a quiet day, chained to my desk, I still shed around 1,900 calories, giving credence to the theory that stress keeps the pounds at bay.

During a manic shopping trip – I just had to have that jumpsuit – I was seeing off three-and-a-half calories a minute, the same rate as at my weekly line-dancing class. I always knew shopping was good for me. Sex sheds calories too: an extended session of rumpy-pumpy with my beloved waves goodbye to 3.7 calories per minute.

I'd wondered if watching a buff Jake Gyllenhaal in Prince of Persia would have any calorific benefit, but even with my pulse raised, sitting down in the cinema slowed my burn right down to 0.9 a minute.

Usually, however, I go through calories at a steady rate until bedtime: meeting deadlines, taking small people to parks, lugging shopping bags home on the bus, running late to meet friends for drinks. Relaxation is worryingly absent from my regular routine.

To really put the armband through its paces, I did the unthinkable and enrolled in a "beach body" work-out class. This torture would probably make an aesthetic difference to my bottom in the long run, but apart from a five-minute spike of 5.7 calories a minute (when I was on the verge of heart failure), my average burn during 45 minutes of suffering was only four calories a minute. Given the evidence, I'd rather be trying on harem trousers in Topshop.

I wasn't keen on logging meals, which was laziness combined with a reluctance to own up to the chips and chocolate-based puddings. But the activity manager drew attention to my erratic eating: I unwittingly skip meals then eat like a hog on holiday.

Most days end with either a calorie deficit or surplus. My weight balances itself, but the unstable calorie intake explains my heightened stress levels. As for my sleeping pattern, I rarely burn less than one calorie a minute and either toss and turn like a whirling dervish for six hours, or I am out cold for eight hours – further proof of my chaotic lifestyle.

So can this very detailed information actually be put to good use? Ken Way, a sports psychologist and author of Mental Mastery: Tried and Tested Techniques for Enhancing Sporting Performance says the device could certainly help people individualise their diet and fitness.

"When people strive for outcome goals, usually to get fit or lose weight, they only have one or two variables to test their success: jumping on a pair of scales, or arbitrarily taking their blood pressure," he says. "If they get negative results, they either give up or carry on with a regime that probably isn't suited to their individual needs.

"A device like the armband gives people more variables, helping them engage with their own bodies to get where they want to go," he adds. "By getting valuable, personalised feedback, they have easier access to what we call process goals – clear, achievable targets you can meet on a daily basis. And process goals give you a focus, and motivation to stay on track."

For the overweight, then, the message seems clear, and the news is moderately good. The more we move, the more calories we burn. You don't have be working out to be using energy. Taking the stairs instead of the lift, walking up escalators and building walks and activities into your day really does make a difference.

Wearing the armband certainly gave me focus. I'm now balancing the way I fuel my body, eating regularly to stabilise my energy levels. My calorie-busting shopping trips are a huge bonus, but I understand now that stressing out at my desk is not a productive use of the energy at my disposal, and it disrupts my sleep.

I'm lucky to be on the small side, but the armband made me realise that I've been confusing "slim and active" with "fit and healthy". With the data now at my disposal, I've purchased a pair of (very chic) trainers and been on a power-walk or two.

This isn't rocket science, but in a mass-information age, the look into my daily routine really has opened my eyes.