I just read an article that most of the fat lost during weight loss is removed through exhalation over time. However, I also thought that you don't gain or lose fat cells, but that they simply expand or contract with fluctuations in weight. What happens to fat cells during weight gain or loss?

2 Answers 2


Fat cells make up adipose tissues. Most fat in our body is stored in adipose tissue.

It is true that we do not lose fat cells. Fat cells would only shrink in size.

We do respiration all the time, and we need glucose to do it. The sources of glucose include: direct intake, conversion from other sugars, conversion from lipids.

If we intake small amount of sugars and do vigorous exercise, our body will run out of glucose, and thus start extracting lipids from fat cells, and convert them to glucose for respiration. Therefore, fat cells have less content and would shrink.

The whole process is:

lipid from fat cells -> glucose -> undergoes respiration -> carbon dioxide and water -> exhaled

You may refer to this for more details.

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    If you'll add official source it would make the answer much better. Thanks. Commented Dec 31, 2018 at 9:43
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    My understanding of converting lipids in fat cells to glucose for energy and respirated is that the lipids are extracted from the cells, making them smaller but not removed. The fat cells are then left to store lipids later when required. Where is the evidence that fat cells are actually lost? As @ShadowWizard states, sources add clarity and substance. Commented Dec 31, 2018 at 12:34
  • @Szeto, your claim that we lose fat cells is misleading, at least, and unsupported by any evidence. According to this PubMed study, the number of fat cells can increase during childhood and adolescence and remains constant in adults: then it neither increases or decreases anymore despite gaining or losing weight. It seems that about 10% of fat cells dies each year and is renewed by new ones, but, in summary, this is not an increase or decrease.
    – Jan
    Commented Jan 4, 2019 at 11:43
  • @Jan It seems like the reference I used is not reliable. You may consider informing the moderators to delete this answer, as I am not permitted by the system to delete it.
    – Szeto
    Commented Jan 4, 2019 at 12:13
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    Oh, no, no, no...You just edit your answer on your own and you can use the evidence I found, or you can find another one, and you are all fine. It's only this single bit, which we are talking about: "Actually, we do lose fat cells. "
    – Jan
    Commented Jan 4, 2019 at 12:17

Does not really answer your question regarding where fat cells go when you lose weight as it has been already discussed previously by the previous posts, but I had to share the link to the video on "Where does fat go when you lose it?".

The biochemistry behind it is:

Fat + Oxygen -> Carbon Dioxide + Water

C55H104O6 + 78O2 -> 55CO2 + 52H2O

Please refer to this video for a very detailed explanation from a Tedx talk: Mathematics of Weight loss

Please refer to this for the article (same author and topic as as the video): When somebody loses weight, where does the fat go?

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    Welcome to MedicalSciences.SE. We work differently than most SE sites in that we have a strict policy that all answers should be answers &backed up with reliable references so that the answer can be independently verified regardless of the reader's background. See this list of reliable sources. If you still have trouble with this, feel free to visit the help center or Medical Sciences Meta. Unreferenced claims can lead to answers being deleted. Commented Jan 8, 2019 at 16:47
  • @LangLangC Thanks I was planning to add a comment, but I couldn't do so unless I had 50 reputation. I'll delete and post at another time
    – Pherdindy
    Commented Jan 8, 2019 at 16:49
  • @LangLangC Cool the guy in the video actually created an article regarding it will just add it. Feel free to edit/remove for any issues
    – Pherdindy
    Commented Jan 8, 2019 at 16:53
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    Now, add a bit of quote from that article, and it's a go. (Although the body of OP asks about the fat cells as well. Room for improvement) Commented Jan 8, 2019 at 17:28
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    To provide the bigger picture: TAG (or fat) doesn’t decompose when oxygen is present, imagine all the real-world fatty acids, they‘d need to undergo combustion constantly because oxygen is always present in the atmosphere. The process is far more complicated and involves a fair amount of enzymes. Each TAG is broken down into acyl-CoA, which is reduced to citric acid which then enters the citric acid cycle and eventually becomes CO2. That Wikipedia article is actually quite comprehensive.
    – Narusan
    Commented Jan 8, 2019 at 22:45

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