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?
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.
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?