When I lose weight, where does the fat go?

Fat into muscle?



Does fat become poo or turn into muscle?

When scientist Ruben Meerman asked doctors, dietitians and personal trainers the question "When somebody loses weight, where does the fat go?", the vast majority of them answered that fat becomes energy (something that is only possible with a nuclear reaction), faeces or muscle, with all answers being wrong, of course.

In fact, basic, high school-level chemistry explains that whenever an organic chemical is "burned" (oxidised), it ends up as carbon dioxide and water - as simple as that.

So after being "burned" in the body and releasing energy - NOT becoming energy - fat ends up as carbon dioxide and water. The carbon dioxide is exhaled by the lungs and the water is expelled as sweat and urine. Nothing becomes faeces, nothing becomes muscle and - thank God - no nuclear reaction occurs in our bodies to transform matter (fat) into energy.

However, I am not surprised by such myths, given the fact that most doctors and aesthetic practitioners believe that we have a set number of fat cells in our body throughout our life (which is totally incorrect) or that liposuction permanently removes fat from a given area (also incorrect).


How do we excrete the fat that we store in our body after oxidising it?

Going back to the question of what happens to the fat after being burned with diet and/or exercise, Ruben Meerman actually conducted some research and found out that to completely burn 10 kg of fat, we require to breathe in 29 kg of oxygen and to breathe out 28 kg of carbon dioxide and sweat away or urinate 11 kg of water!

So in summary, we lose most of our fat through our lungs, in the form of carbon dioxide, and through our skin and urinary system, in the form of water.

Ruben has published these facts in the British Medical Journal and at the closing paragraph of his paper he stated: "We recommend these concepts be included in secondary school science curriculums and university biochemistry courses to correct widespread misconceptions about weight loss."

I couldn't agree more.



  • Paper: When somebody loses weight, where does the fat go
  • Link: http://www.bmj.com/content/349/bmj.g7257