|MadSci Network: Agricultural Sciences|
According to Dole Food Company, who sell quite a few bananas here in the United States, bananas contain no fat. The Dole Banana Nutrition Site contains some other interesting information regarding bananas, including a complete nutritional label according to United States government specifications.
Though the above is certainly true, bananas do contain "banana oil." This is not a fatty oil like olive oil or canola oil, though. It is a chemical compound called isopentyl acetate, abbreviated as CH3CO2CH2CH2CH (CH3)2. This compound, which is a type of ester, is what gives bananas their distinctive smell. There is a good picture of this molecule here. This site also gives an experimental procedure whereby banana oil can be synthesized, or created artificially.
So you see, you and your friend are both somewhat correct. Hope that helps!
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