I saw this film on TV in the late 70s-early 80s.

The premise is a Western businessman ends up on a remote Polynesian island where the natives are all very happy. The businessman discovers the secret to their happiness is a bar made from eucalyptus leaves. He sees this as a way to make his fortune, so he steals the recipe and finds his way off the island. Unfortunately, eating the eucalyptus bar makes people gain weight at an alarming rate, so his plan for wealth fails. I think there is also an active volcano on the island and this plays a part in destroying the businessman’s dreams.

I have tried Google and IMDB with no luck. I don’t recall any of the actors, just these fragments of the story line. Can anyone help please?