Good question. Bruce was reputedly very careful with his foods and experiment with different protein supplements, juices etc. Certainly he didn't get and maintain that physique by eating crap everyday.
One of my favorite quotes on the subject of nutrition by Bruce is as follows:
"When you are a martial artist, you only eat what you require and don't get carried away with foods that don't benefit you as a martial artist".
He certainly ate a predominantly Asian diet, which is the same I recommend in my Samurai Strength program, where I have two giant volumes on nutrition.
One other point I find amusing...there is a rumor that during the filming of Enter the Dragon, the film in Bruce Lee's physique is at it's peak, that this peak was attained as Bruce had dysentery, an infection of the intestines resulting in severe diarrhoea. This left him very dehydrated and showing high muscle definition.....allegedly.
But nutrition is VITAL in building a healthy body. This is a fundamental truth in both Western and Eastern mentality. Sort your diet. ;-)