Why isn’t fat transferred in large amounts at once?

In fat transfer consultations, I’m often asked, “If you put in a lot at once, won’t more of it stay?” Intuitively it seems that way, but in reality it’s often the opposite. The reason lies in how transferred fat survives its first few days.

When fat is harvested and placed somewhere else, it has no blood vessels connected to it. Until new blood vessels grow in, it has to survive on oxygen and nutrients seeping in from the surrounding tissue. In 2012, Japanese researchers transferred fat in mice and observed it for 2 weeks. Most of the fat cells began to die from the first day after transfer, and only the cells within 0.3 mm of the edge survived. Farther in was a zone where the fat cells died but stem cells survived and turned into new fat, and farther in still was a zone where both died.

A 2014 study followed the same process for 3 months. New fat cells were produced most at about 4 weeks, and regeneration was complete by around 12 weeks. Areas that failed to regenerate remained as scar tissue or oil pockets (oil cysts). When fat is placed in clumps, the center is likely to end up this way.

A study the same year worked this out by calculation. It predicted that if a strand of transferred fat had a radius greater than 1.6 mm, its center would become necrotic. It also suggested that once pressure in the tissue reaches about 9 mmHg, adding more sharply reduces blood flow. In other words, putting in more raises the pressure, so less of it stays.

That’s why fat is placed in thin, noodle-like strands, divided along paths in many directions. The aim is for each bit of transferred fat to touch as much of the surrounding tissue as possible. Not exceeding the amount the recipient site can handle is for the same reason. In breast fat transfer, I aim for about 1 to 1.5 cup sizes and don’t recommend a much bigger change, and this also comes from that principle.

However, the cell-level results come from animal experiments, and 1.6 mm and 9 mmHg are values obtained by calculation. They can’t be applied directly to people. Even so, multiple studies point in the same direction: the result of fat transfer depends more on how the fat is placed than on how much is placed.