Where does the fat go when you lose weight?

Written by Olivier

So you have been noticing the number of the scale slowly coming down in the recent months due to your hard work. Could it be your New Year resolution finally paying off? Or simply your day-to-day healthy lifestyle getting you where you want to be. If that’s the case: GREAT! Keep it up 🙂

Did you ever wonder where those lost pounds go??? Before I give you the answer, here are some possible choices (go ahead and test your peers, health professional or family doctor). “Where does my fat go when I lose weight?”

Is it?

  1. Converted to muscle
  2. Excreted via urine or feces
  3. Lost via heat production
  4. Evacuated in the air
  5. Used as energy in the body

…and the answer is________.

Wait a minute, first let’s recall the ultimate goal in mind: to lose weight while maintaining muscle mass. Perfect let’s move on, what happens when you over consume carbohydrates and protein? The excess is converted/stored as triglycerides in adipose tissue (fatty reserves). The triglyceride formula is C55H104O6 (as you can see it is composed of 3 atoms: carbon, hydrogen and oxygen, remember your chemistry courses?). In order to lose weight, we must metabolize the triglycerides and as shown below, when you completely burn/oxidize a triglyceride molecule you are left with:

C55H104O6 + 78O255CO2+52H2O+energy.

There you have it, when metabolizing fat (or during weight loss if you prefer) you end up with carbon dioxide, water and energy. The authors explained that for 10kg of fat oxidized, it requires the inhalation of 29 kilograms of oxygen, producing 28 kilograms of carbon dioxide and 11 kilograms of water. They add that of the 10kg of fat metabolized 8.4 kg were exhaled when we breathe as carbon dioxide (CO2) and 1.6 kg became water (H20). The right answer to our question is a combination of answers #2-5 but mainly answer #4 and 2. Exhaling evacuates 84% of the fat molecule’s and 16% is lost via water means such as excreted in the urine, feces, sweat, or other bodily fluids.

So the take home message is to be more Active! Replace your sedentary time with light physical activity and include a lot of exercise that make you out of breath (i.e. cardio is really important as you just learned that your lungs are a key player in losing fat). Lastly, is it imperative to continue your strength training as you need to maintain your lean muscle when losing weight 🙂

Source: BMJ 2014;349:g7257

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