Blobs of fat are not meant to be in the bloodstream, and can be harmful when they are. For example, fat embolization syndrome is a well-known sequela of orthopedic injuries. Someone breaks their femur, and little pieces of the marrow enter the bloodstream, showering the lungs with numerous emboli, and even causing neurologic symptoms, likely secondary to toxic chemical reactions associated with c-reactive protein.
Along the same lines, it's well-known that accidental intravenous injection of oil-based medications like testosterone can cause major problems. If a patient accidentally injects intravenously instead of intramuscularly, all of the oil immediately goes to the lungs. The patient typically gets transient shortness of breath, followed by a reprieve, followed by even more severe and prolonged shortness of breath. Corticosteroids may be needed to reduce lung inflammation.
With these things in mind, I began to ponder what exactly happens to all the oil we inject. It's not metabolized on site. It doesn't break down. Rather, it is slowly absorbed into the bloodstream, either directly or via the lymphatics. Either way, the next stop is the lungs. Might even slow absorption from intramuscular or subcutaneous depots cause problems?
Well, here is a study I found where they did intramuscular injections of sesame oil in dogs:
http://onlinelibrary.wiley.com/doi/10.1111/j.1600-0773.1979.tb02404.x/abstract
In dogs which received unlabelled sesame oil (0.45 and 1.0 ml/kg) or Viscoleo (0.45 ml/kg) intramuscularly once a week for six months and finally an injection of [SUP]14[/SUP]C-labelled oil, pulmonary oil microembolism was seen in all three groups and most markedly after the higher sesame oil dose. The iliac lymph nodes in both sesame oil dose groups were highly enlarged and appeared cystic due to presence of oil. The lungs from the dogs receiving Viscoleo were seat of small mononuclear interstitial cell infiltrations sometimes present in the vicinity of oil microemboli. In the sesame oil groups oil was additionally found extravascularly in the lung interstities together with accumulation of macrophages and leucocytes and focal hemosiderosis in the lungs occurred on the highest dose level. In the sesame oil groups of dogs pulmonary oil microembolism was found microscopically in a higher number than that seen on autoradiograms. The embolisation obtained at one injection may thus not disappear before the next injection. Except for presence of very few oil microemboli and small focal areas with interstitial oil deposits the lungs were normal in dogs examined three months after six month chronic weekly injection of sesame oil. Small oil deposits were still present at the injection site and in the iliac lymph nodes of these dogs, but the lymphoid tissue of the nodes had partly recovered.
Now, in this study, they injected a hefty amount (1 ml/kg), but I wonder if the same principle might apply to lesser doses.
