The fat organ converts FFA and glucose to triglyceride, the storage form of fat, within the cell. Everything has a cost, and our body has a pecking order for it's energy demand. First choice is glucose, fresh glucose. Then glucose from storage, then FFA and free triglyceride, ( some split into ketone bodies), then ometal fats, and lastly stored fats.
When we ingest excess glucose and overflow glycogen storage, it goes into fat storage first. So fat is first in, (after current demand), last out, if we are eating carbohydrates. It is no wonder we get fat with all the excess carbohydrates around that are really great tasting poisons to us easily fattened low activity persons.