Robert Downey Jr. has a nasty parasite to thank for his super-svelte shape in new movie Sherlock Holmes - he lost weight after contracting a bug in Japan.

The 44 year old was in the Far East last year promoting the first Iron Man movie when he fell ill.

The sickness was so severe he dropped five pounds, and the star saw it as an initiative to keep on dieting to achieve a buff body for the upcoming detective movie.

He tells Rolling Stone magazine, "I was in Japan promoting Iron Man, and I went to a restaurant where I contracted a parasite and got really sick for three days. I started losing weight and thought to myself, 'Hey this is a nice jump-start!' It just gave me a nice little head-start with the first five pounds and then I kept going until I was thin. I felt as though I may float away."

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(This news article provided by World Entertainment News Network)