Hi. I'm not a doctor, but I can opine as a biologist.

The transplanted cells have blood vessels, because all cells need a supply of oxygen to avoid expiring. If they didn't have a supply of blood, they'd quickly turn necrotic.

When you deplete your short term energy stores, the body converts fat molecules within fat cells into sugar, then shuttles those through the body in the blood stream.

The body doesn't draw on fat stores within the body in a totally even way, so I don't know how quickly it would draw from the transplanted cells, but it works presumably still burn fat from these cells when needed.

And the reverse is true as well: when excess sugar is available, the body would generate new fat molecules to fill those cells, and if necessary make new fat cells as well.

I have no knowledge of Brazilian Butt Lifts specifically, but here is some related information about how fat works in general, which I hope is a good starting point:

Fat cells don't die easily. They just shrink. See: https://news.yale.edu/2015/03/02/study-new-fat-cells-are-created-quickly-dieting-cant-eliminate-them

When performing skin grafts, fat cells retain the characteristics of the original skin location. For example, here is a paper that shows a soldier who had a skin graft from his stomach to his hand, and later developed a kind of "beer gut" on his hand. Content warning: graphic images of open surgery in related articles section if you scroll down. If you are even a little squeamish, do not scroll down. https://journals.lww.com/dermatologicsurgery/citation/2006/03000/does_transferred_fat_retain_properties_of_its_site.12.aspx

I can't answer the question directly, but this may be related.

Back in the 90s when the cable channel TLC wasn't shit, they had a series showing actual surgical procedures. I watched one where a woman had previously had a mastectomy, and this follow up was essentially rebuilding her breast by moving fat from her belly into her chest.

It's not just cutting out one lump of fat and putting it somewhere else. The blood supply had to be kept intact, so it was more like a slide puzzle. Lots of stuff moved only as far as it could without interrupting the various veins and arteries.

Interestingly, they made sure to point out that the fat being shifted around still thinks it's belly fat, so gaining and losing weight that would normally affect the belly would show up in the one reconstructed breast

Presumably this other procedure is similar. Fat is moved from the legs in such a way that by moving a relatively small amount, the butt gets bigger and the legs get smaller, making the butt look even bigger by comparison.

I don't have any answer for you but I'm curious if you are considering one

TL;DR is yes, but typically slowly. So the BBL won't last forever but for most people it can last quite a while.

I have seen claims from 5-10 years. But it will depend on your lifestyle. I have seen some sites saying that if your weight is fluctuating it will dissipate faster than if you keep a fairly stable amount of body fat.

If they didn't have blood supply they'd start rotting.

And yes if you burn fat via cardio or whatever, it will pull from anywhere in the body. Your expensive procedure just went up in smoke.

The fat cells behave the same as before they were transferred. The number of fat cells mostly stays the same when you lose weight, just depleting the fat reserves within the them. So yeah, you'd mostly re-gain it in the same cells.

IANAD, but it’s my understanding that how people store and lose fat is unique to their biology. That said, it makes sense (to me) that one of two things would happen:

1. They burn more fat in the area they augmented (ie their butt), because they didn’t have a lot to there begin with
2. They gain/burn their fat faster elsewhere in their body, leaving their butt safe for a while

I do not have any proof to back that up, other than my own personal experience with my body.