Bodybuilders seeking to enhance their physique by injecting natural oils risk lasting damage and even death, doctors have warned.
They fear that a case in west London, in which a 25-year-old man suffered scarring and restricted function after injecting coconut oil, may be the "tip of the iceberg".
Instances have been recorded in recent years of bodybuilders using other oils, including sesame oil, walnut oil and paraffin, which are less costly than other synthetic compounds, in the hope of boosting muscle size and definition.
There has been little medical literature on the subject, but a paper published in BMJ Case Reports last Thursday said the practice is well documented among the Arab and Middle Eastern communities.
The 25-year-old man was referred to Ealing Hospital in west London because of pain and loss of function in his right arm. He had injected the coconut oil into his arm over several months.
An ultrasound scan showed a rupture in his triceps - a rare condition in young patients - and multiple cysts within the arm muscles.
Surgery to repair the rupture was successful but he was left with scarring and limited elbow flexion.
Dr Ajay Sahu from London North West Healthcare NHS Trust, who co-authored the report, said: "He has lost significant function in his triceps and he is right-handed."
He added: "If he had injected the coconut oil into one of his veins by mistake, it could have been fatal. It could cause an embolism in the heart, the lungs or the brain. You need to think about the implications."
The case was difficult to diagnose because the patient did not initially admit what he had done. Dr Sahu said he was not aware that injecting oils was something people did to build muscle.
But he said that resorting to such drastic measures was symptomatic of an increasing concern among young men about how they look.
He added that people did all sorts of things to gain muscle and this was often not reported. "These people will never come to the doctor and say all the things they do. This is just the tip of the iceberg."