When somebody loses weight, where does the fat go?

The TLDR:

> Physical activity as a weight loss strategy is, therefore, easily foiled by relatively small quantities of excess food.

> Our calculations show that the lungs are the primary excretory organ for fat. Losing weight requires unlocking the carbon stored in fat cells, thus reinforcing that often heard refrain of “eat less, move more.”

"Eat less, move more." If anyone isn't aware of that by now, I don't know what to say.

I am confused by this...

> We suspect this misconception is caused by the “energy in/energy out” mantra and the focus on energy production in university biochemistry courses.

I understand from the article that chemistry (Which I can't understand) tells you that it is converted on CO2.

But still. Clearly I can move because I have energy that I acquire from food. How is this wrong ?

The fat molecules burned usually have about twice as many hydrogen atoms as carbon atoms so you end up with about as many CO2 molecules as H2O molecules. Carbon weighs about 14 times as much as hydrogen and most of the oxygen in both comes from the atmosphere. So when you lose weight, 7 parts go to CO2 and 1 part goes to water. A very very tiny proportion goes to energy with mass-energy equivalence.

I can't help but groan at some of the "obvious" health and weight loss platitudes that get smugly thrown around.

"Calories in, calories out!"

"You can't outrun a bad diet!"

"Weight is lost in the kitchen!"

Sure, things ultimately boil down to intake-vs-expenditure. However, it IS more complicated than that in practice. As software developers, we complain when management makes decisions based on inadequate or poor metrics. But likewise there so many more benefits to physical exercise that aren't captured by a diet and exercise tracking app.

During times when I've been 100% sedentary for long periods, I experience overwhelming cravings for sugar and crappy foods. When I force myself to take up any consistent exercise, even just a 30 min walk in the morning or lunchtime... then the cravings subside and regular meals are sufficient. This is fairly common.

Exercise has so many physical and mental health benefits. But even just looking at weight management alone, exercise tends to ramp up your metabolism for hours after each exercise session. Something that doesn't get captured by your tracker app or wearable gadget.

So often, when I hear somebody smugly minimizing the importance of exercise to health and weight management, it's a person who is too-clever-by-half. They're constantly dabbling with soylent shakes or paleo/keto fad diets... because the truth is they're just lazy and don't want to get off their ass, and look to rationalize that.

EDIT: At least half of these replies are completely missing my point altogether. I'm not saying that there is a binary choice to be made between "good diet" OR "exercise", and that you should make the latter choice rather than the former. I'm saying that treating this as a binary choice in the first place is ridiculous.

Exercise correlates with proper eating, it's not incidental or ancillary. It's ineffective to tell someone to "go the gym" without changing their eating habits? Well sure, but telling them to "go keto" without worrying about physical activity will be no more successful a year out. It's the pretense that most people can consistently stick with one of these things, and not both together, that is absurd.

"For anyone coming straight to the comments looking for an answer to the question: it turns into CO2 (and a bit of water) and you breathe it out."

That is why you weigh less when you wake up in the morning (pre-bathroom -/+ yes some sweat).