When You Lose Weight, Where Does It Go?

It doesn&#x27;t surprise me at all...<p>I&#x27;m an MD. I don&#x27;t remember this specific piece of information being mentioned during my training. However, all the information need to reason about it was included...<p>What really blows my mind is how many people get it wrong, including my colleagues and especially dietitians (&quot;they had one job&quot;).

And the reverse biochemical process is equally misunderstood. I used to teach high school Science and everyone thought a tree&#x27;s mass came from the soil.<p><a href="http:&#x2F;&#x2F;youtu.be&#x2F;2KZb2_vcNTg" rel="nofollow">http:&#x2F;&#x2F;youtu.be&#x2F;2KZb2_vcNTg</a>

The question is somewhat badly phrased.<p>I think many people interpret it as &quot;Why do I lose weight?&quot; or even &quot;Where does that fat go when I lose weight&quot; and answer correctly: your body uses up your fat stores as fuel when there&#x27;s no easy sugar available. Calling that a wrong answer is a bit unfair, there&#x27;s nothing technically incorrect about it.<p>However, that&#x27;s not what was asked - the question is where does the mass go? After all, if you light a fire inside a box, the box doesn&#x27;t get lighter.<p>The trap is that there are by-products from the chemical reactions which have to go somewhere, and that somewhere is typically through respiration (and excretion).

I thought it was ironic to find this statement in an otherwise solid article:<p>&quot;(So wrong. Mass cannot be converted to energy except through nuclear reactions)&quot;<p>This is, of course, wrong. All energy has mass. A charged battery has more mass than an empty one. A chunk of fat weighs more than all of the byproducts that come from metabolizing it.<p>It&#x27;s <i>almost</i> true, because the conversion factor between mass and energy is <i>huge</i>, so the change in mass for more mundane quantities of energy is far below what&#x27;s reasonably possible to measure. But there&#x27;s nothing special about nuclear reactions aside from the quantity involved.

Great calculation, wrong conclusion. Exercise does not cause any significant weight loss, of course unless you are doing it 6+ hours a day. All major weight loss typically comes from controlled diet. This means eliminating non-complex carbs. This is a major misconception in general public and people just don&#x27;t seem to get it. Exercise helps build muscles, metabolism and endurance, but for weight loss your only practice option is diet control. The major energy expenditure for body is not walking or moving but just staying warm and brain. The reason people gain weight is not lack of exercise but because they eat all these fast burning carbs that rapidly gets deposited as fat instead of getting used up for body&#x27;s energy need. If you want to lose weight rapidly, just make sure to add lot of fat and protein in your diet with as little carbs as possible and watch the weight drop.

This appears to have been copied without attribution from <a href="https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=4pkSLKucVbM" rel="nofollow">https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=4pkSLKucVbM</a>

Detailed discussion:<p><a href="http:&#x2F;&#x2F;physics.stackexchange.com&#x2F;questions&#x2F;2605&#x2F;how-does-mass-leave-the-body-when-you-lose-weight" rel="nofollow">http:&#x2F;&#x2F;physics.stackexchange.com&#x2F;questions&#x2F;2605&#x2F;how-does-mas...</a><p>I was suprised this was not linked in the post.

6 billion people, each burning 2000 calories per day equals 12 trillion calories.<p>6,000,000,000 * 2,000 = 12,000,000,000,000<p>But wait, those are Kcals.<p>6,000,000,000 * 2,000,000 = 12,000,000,000,000,000<p>1 calorie is the energy required to raise 1 gram of water 1 degree C. There are about 4404.8838 grams in a gallon.<p>12,000,000,000,000,000 &#x2F; 4404.8838 = 2,724,248,934,784.61<p>So this is enough to raise 2 trillion gallons 1 degree, or raise 1 gallon by 2 trillion degrees Celcius.<p>2,724,248,934,784.61 &#x2F; 100 = 2,724,248,934.78461<p>Or boil away 2 million gallons of water. Per day.

What about rubbing? I mean, when you rub against stuff (even wind), some of your cells get taken off. I&#x27;m all for peeing, pooping, and breathing, but how much weight do we lose just through simple friction? And if it&#x27;s significant, should we employ more rubbing in our daily exercise routines?

The url leads to the home page of the blog, this should be instead - <a href="https:&#x2F;&#x2F;mitchkirby.wordpress.com&#x2F;2015&#x2F;04&#x2F;21&#x2F;where-does-weight-go&#x2F;" rel="nofollow">https:&#x2F;&#x2F;mitchkirby.wordpress.com&#x2F;2015&#x2F;04&#x2F;21&#x2F;where-does-weigh...</a>

tl;dr - &quot;The surprising answer to this question is that we breathe it out.&quot;<p>O₂ in, CO₂ and H₂O out

A quick proof that the answer isn&#x27;t &quot;you poop it out&quot;: when you work out more, you don&#x27;t poop more. (You do, however, breathe more, which points towards the correct answer.)

I&#x27;ve had even worse luck trying to convince people that trees are mostly made from air and water.

&gt;It Gets Converted to Energy (So wrong. Mass cannot be converted to energy except through nuclear reactions)<p>This is not true. There is energy in chemical bonds, and that energy is released when the bonds break. When you burn gasoline, the mass of the resulting molecules adds up to less than the mass of the original gasoline. A tiny, tiny fraction less, but still less. Because there was energy in those bonds, and energy has mass.<p>It&#x27;s wrong in another way, too, because even in nuclear reactions mass isn&#x27;t converted into energy. Mass is mass, but energy also has mass. No mass is lost in a nuclear (or chemical) reaction, it just goes somewhere else. There is no &quot;conversion&quot; going on.

I was thinking about this a couple of weeks ago, expiration that is. This question raised itself and I&#x27;ve not focussed on answering it yet - if you breathe more then, like forced breathing, can you accelerate carbon loss [beyond that expected by the increased exercise involved in such breathing]; like fanning flames I guess.<p>Thinking now I suppose an [close] equivalent is probably can you increase carbon dioxide production by increasing oxygen saturation of the air inspired?<p>There&#x27;s probably enough in that idea to sell oxygen masks and little tanks and a book for a new fad &#x27;diet&#x27; ...

When your car loses weight (fuel), where does the weight go? The exhaust, of course; your breath is your exhaust.

Just asked my wife and daughter what the answer was, and they both thought you excreted the mass. Then I asked my son, who is home from Uni, studying a Biology degree, he said it was released as energy. FFS.

Please embrace my willingness to look foolish, I really want to be able to explain this properly; can someone explain to me why fat doesn&#x27;t get changed into energy, and disappear through heat?

What&#x27;s most interesting to me is that in most cases we don&#x27;t gain or lose muscle or fat cells.<p>They just grow and shrink in size.

Movement, CO2 and urine.

It gets dumped into the universe as heat.

How would respiration be surprising to anyone with a high school level education?<p>&gt; This analysis makes it clear why exercise is so powerful in the weight loss equation.<p>There are many reasons to exercise, but it&#x27;s quite clear weight loss isn&#x27;t one of them. I mean, you need to exercise to get your abs to pop, but not being a lard-ass is totally about avoiding excess calorie intake and exercise really doesn&#x27;t enter into it. People don&#x27;t realize what a trivial amount of calories working out burns.

&gt; Mass cannot be converted to energy except through nuclear reactions<p>This is wrong enough to make me stop reading.

Nice try. Everyone knows that there are nuclear reactions that take place in the digestive tract and that we poop out small unobtanium lumps which are gathered in the night by underpant gnomes. that&#x27;s the unknown middle step revealed.<p>you heard it here first.