The pleasure of eating a chocolate bar lasts only a few minutes. Burning off the kilojoules it delivers can take nearly three-quarters of an hour.
To lose one kilogram through exercise, you need to burn approximately 33 000 kilojoules. It can take days of moderate exercise to do this, so if you intend to lose weight, a better strategy should involve both exercising and cutting kilojoules.
Although exercise by itself isn’t the fast track to weight loss, it does offer important benefits beyond cancelling out kilojoules. It slightly increases the rate at which you burn kilojoules even when you’re not working out. And kilograms lost through boosting your activity level consist almost entirely of fat, not muscle.
Do the maths
A massive 33 000 kilojoules are stored in a kilogram of body fat. You can use this fact to calculate how you can lose that kilogram, whether it is through exercise, cutting kilojoules, or both.
- Walking or jogging uses roughly 260kJ per km. (Precisely how many kilojoules you’ll burn depends on a number of things, including your weight and how fast you walk.) So you’d lose a kilogram for every 127km you walk — provided you keep food intake and other activities constant.
- If you walk briskly (at a pace of 6.4km per hour) for 30 minutes on five out of seven days, you’ll log 16km a week. That means it would take eight weeks to lose one kilogram if the number of kilojoules you consume stays the same.
- If you alter your diet and cut back by 1 050 kilojoules a day (one 50g bar of chocolate or two sugar-sweetened fizzy drinks), you’d lose a kilogram in one month.
- By eating 1 050 fewer kilojoules and walking for 30 minutes a day, it would take two weeks to lose one kilogram. Reducing kilojoule intake even more and increasing exercise would further speed the process.
Eat it, burn it
- To burn off a 55g bar of chocolate, you need to walk/jog for about 5km.
- To burn off a small packet (30g) of chips, you need to walk/jog for about 3km.
- To burn off a can of coke (340ml), you need to walk/jog for about 2km.
If you ate one of these items on every day of the week, you need to walk/jog 23km to burn off the energy you have taken in. If you walk or jog for 30 minutes a day, it would take seven days of exercise to burn off the kilojoules taken in.