I believe that this is true -- and that fat can offset bitterness the same way that sweet can. For example, raw cacao nibs mixed with cashew nuts taste sweet and chocolatey.
"We know that the human tongue can detect five tastes -- sweet, salty, sour, bitter and umami (a savoury, protein-rich taste contained in foods such as soy sauce and chicken stock)," Russell Keast, from Deakin University, said Monday.Australian researchers say fat is 'sixth taste' (via Kottke)
"Through our study we can conclude that humans have a sixth taste -- fat."
Researchers tested 30 people's ability to taste a range of fatty acids in otherwise plain solutions and found that all were able to determine the taste -- though some required higher concentrations than others.
(Image: Beale's Open Kettle Rendered Pure Lard, a Creative Commons Attribution photo from Steve Snodgrass' photostream)
I write books. My latest is a YA science fiction novel called Homeland (it's the sequel to Little Brother). More books: Rapture of the Nerds (a novel, with Charlie Stross); With a Little Help (short stories); and The Great Big Beautiful Tomorrow (novella and nonfic). I speak all over the place and I tweet and tumble, too.