the secret to weight loss: maths

UPDATE: I’ve now lost 12 kgs in 12 weeks doing this.

I have discovered the secret to weight loss and it’s surprisingly simple: maths. Forget diet shakes and the abdomi-whatsernamer. Weight loss comes down to one very simple mathematical equation:

energy in, minus energy out.

To maintain your weight, you must consume the same number of calories (units of energy) as you expend in a day. To lose weight, you must expend more calories than you consume. When you do this, the body is forced to tap into the energy stored in fat cells to meet your daily energy needs.

It is a stunningly simple formula, but harder to achieve in practice. Unfortunately, our bodies are not walking calorie calculators but rather remnants of our caveman and woman ancestors. Despite our new, sedentary lives, we continue to hunger for energy-dense sugary and fatty foods. So to lose weight these days, you need to get a little bit cluey and a little bit organised.

You will need the following equipment: a heart-rate monitor (to measure calories burnt while exercising), access to the internet (for calorie-counting websites such as calorieking, a calculator and digital scales (to see the results).

You also need to know the magic number: 7500. It is magic because it is roughly the calorie deficit you need to build to lose one kilogram of weight. Quite why this number isn’t taught in schools and printed on the side of buses, I do not know.

I found the magic number while doing an online weight loss program. I defy you to follow a program which includes shopping lists, calorie-controlled recipes and exercise, and not lose weight. I have lost exactly 8.5 kilograms in exactly 8½ weeks.

So how does the equation work exactly? First you calculate how many calories you burn in a typical day without any vigorous exercise.

Type “basal metabolic rate calculator” into Google to find out how many calories your body burns just performing basic functions like breathing. This varies with height, weight, sex and age. Then add in a bit more, say 300 calories, for incidental exercise, such as walking to the shower, car, etc.

A woman aged 40, 160 centimetres tall and weighing 70 kilograms will have a rate of about 1500. If she does no vigorous exercise, she will probably burn about 1800 calories a day.

If this woman restricts herself to a diet of just 1200 calories a day, she immediately opens up a daily calorie deficit of 600 a day (1800-1200), or 4200 a week. To get to the magic number of 7500 and lose one kilo a week, this woman must burn an extra 3300 calories a week in exercise.

The good news for overweight people is the 7500 number is the same for everyone. And because overweight people have higher basal metabolic rates – it takes more energy to undertake their body’s basic functions – they open up a wider calorie deficit than a lighter person by sticking to the same “1200 calories in” rule. Even better, when an unfit person starts to exercise, they have a higher heart rate and burn calories faster, also helping to build a bigger calorie deficit.

But you do need to ditch the Easter eggs and get moving.


Calorie deficit you need to build to lose one kilogram.

Calories a 40-year-old woman, 160 centimetres tall and weighing 70 kilograms will burn in one day doing light, incidental exercise like walking.

Calories this woman could burn in one hour of brisk walking (at a pace of about 6.5km/h)

Common suggested calorific intake for women looking to lose weight.

Calories she would burn in one hour of slow jogging (at 8km/h) — yes, you burn double the calories by slow jogging instead of brisk walking!

Daily calorie deficit this woman would build each day just by sticking to 1200 calories a day and doing no vigorous exercise.

7 days
For this woman to build a calorie deficit of 7500 if she ate 1200 calories a day and did the equivalent of one hour’s slow jog for six of the days.

Days it would take her to lose one kilogram doing this.

Calories in one 34-gram Cadbury Creme Egg.


This entry was posted in Behavioural Economics, Fitness, Fun, My New Year's Resolution. Bookmark the permalink.

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