How To Really Lose Weight

If you lose 1 kg of body weight, where does it go? Physicist Dr Tony Heyes explains why the amount you eat is far more important to your weight than what you eat. With thanks to Ruben Meerman and Radio National’s ‘Ockham’s Razor’.

Physics of Fat

Based on an Occam’s Razor talk given by Rubin Meerman on 29 January 2017. Rubin deserves all the credit for this but I know he would be happy for me to present it

Meerman asked 150 health professionals, doctors, physios, health and fitness people, the following question.

“If you lose 1 Kgm of body weight, where does it go?”

Only 3 people got the answer correct!!!

Most said: burnt off as energy, as poo or converted to muscle!

Let us consider these:


The formula is well known: E=mc^2

Put the numbers in and one finds that the energy equivalent to 1 Kgm is equivalent to 1,426 Hiroshima atomic bombs. Yes, 1,426.


No, poo is the waste part of our food intake
which does not get taken up by the body.

Converted to muscle

In your dreams.

And the correct answer….

84% is expelled as CO2 the rest as water
Body fat is essentially a hydro carbon comprising atoms of 55 atoms of Carbon, 104 atoms of hydrogen and six atoms of oxygen.

In normal respiration one loses approximately 9 mgms of Carbon per breath.
Let’s do some calculations:

Between 12 and 20 breaths per minute is normal for resting.

Let us say 16. We therefore lose
9 mgms X 16 = 144 mgms per minute = 8.64 gms per hour

207 gms per day

1.45 Kgm per week

And the supporting evidence…

People on hunger strike lose weight and the rate of 1.45 Kgm per week. See graph below:

The young Thai football players who spent a week trapped in a flooded cave were each 1.45 Kgms lighter when they came out.

So if you wish to lose weight the take-home message is to keep breathing. It really does not matter what you eat; just don’t eat too much of it.

Exercise is clearly good for bodily fitness, but it is of little use if the goal is to lose weight. Except for the fact that your respiratory rate may well increase during exercise.