The calorie/kilojoule/cardio/counting conundrum

17 Apr 12 11:00AM EST
Post by Sam Butler

If you live in NSW, Queensland, SA or the ACT chances are you’ll have seen or will start seeing kilojoule (kJ) counts next to items on fast and snack food menus. That’s because state and territory governments are introducing or have passed legislation making kilojoule labelling mandatory for most larger chains such as Bakers Delight, Subway and, of course, the homes of Colonel Sanders and Ronald McDonald.

I’m a much less frequent customer of KFC than I was in days of old but I can’t deny occasional trips to Subway or other nutritionally questionable restaurant chains, particularly after a long day at work. Unfortunately, I can also see as I get older that the body becomes increasingly intolerant of high-energy food, and most treats need to be either cut out or countered with some joule-burning exercise. After all, energy in, energy out – it’s a pretty simple equation.

But how can you tell how many kJs you’re burning? And isn’t energy measured or spoken about in calories rather than kilojoules anyway?

Waste of energy?

I found myself pondering these questions a while back when I first started using the rowing and cross-trainer machines at my local gym. A display once told me I’d burnt 340 calories after a 20-minute workout on the cross-trainer. I was feeling pretty proud of myself, until it occurred to me I had absolutely no idea how many kilojoules (kJs) that equated to or what percentage of my lunch had been burnt.

One brief Google excursion later, and I was informed: 1 calorie = about 4.2 kilojoules. 

You may know that 8700 is the magic number when it comes to kJs – that’s how many the average Australian adult consumes each day and the benchmark for the percentage daily intake figures for energy displayed on many packaged food labels. So, put very simply, people who want to maintain or lose weight should expend as many or more kJs than they consume. 

The typical Australian adult has about 2071 (8700/4.2) calories to play with every day. And you don’t even need to be in a gym using an apparatus to check how much energy you’re burning during exercise – like most things these days, there’s an app for that.

But there are a few issues that make the energy in, energy out approach less straightforward than it appears.

The first is that 8700kJ only relates to the typical energy needs of the average Aussie person. For a female colleague of mine it’s closer to 7600kJ, or 5600kJ if she wants to lose weight. But for me it’s closer to 10,400kJ. Fortunately, the NSW government has set up, a site where you can work out your ideal personalised kilojoule intake based on your age, gender, level of daily activity and so on.

The second problem is that digital calorie counters built into exercise machines are only a broad indication of energy burnt – they’re based on a general formula that the machine has been calibrated to work out and, like the 8700kJ figure, have been averaged across different age, gender, body and activity types. Where one machine might tell you you’ve burnt 340 calories on one cross-trainer for 20 minutes, another cross-trainer might give you a different reading for the same amount of exertion.

The third problem is: why do food packet labels and now menus refer to kilojoules when exercise machines, much of the media and Tic-Tac ads talk of calories? Calories are a non-metric unit of energy, yet Australia has been referring to metric units since the 1970s. So why hasn’t the advertising industry – not to mention gym machine manufacturers – caught up?

The gym machine makers may have a valid excuse. Exercise machines can be imported into Australia from countries that aren’t fully metrified, such as the US, and so their energy units will be calories rather than kilojoules. But marketers and the Australian food marketing industry really has nowhere to hide – there’s no logical reason to talk in calories when everyone else is talking in kilojoules, as the revised food menus make patently clear. Presumably the ad folk prefer calories to kilojoules as one calorie sounds a lot smaller and simpler than 4.2 kilojoules when it comes to what’s in a can of Diet Coke.

Easy answer

Confusion around food labelling is nothing new, whether it’s to do with country of origin or nutrition. That’s why CHOICE continues to push for effective nutritional labelling on the front of food labels, such as the traffic light approach, which has been proven to be more effective at informing consumers than the grocery industry’s preferred percentage daily intake approach.

Similarly, there’s a simple solution to the calorie/kilojoule conundrum – discourage use of the word calorie in all relevant marketing material in Australia, ensuring only kilojoules is used instead, and also ensure all pieces of gym equipment made in or imported here are calibrated in kilojoules.

Gym machines aren’t an exact science when it comes to determining the second part of the energy in, energy out equation, but at the very least the units of measurements should be the same on either side of the ledger.

Have you been confused by the interchanging of calories and kilojoules?


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