I have heard that you are not meant to eat any food in the two hours before you go for Bikram yoga -

Whenever you are doing any exercise, yoga or anything else, it's not advisable to do it on a full stomach. This is for two reasons: firstly, if you exert yourself on a full stomach you will probably make yourself feel sick, and secondly, because when your body is digesting, it needs to send it's energy to digesting the food, not on building muscle. Hence the suggestion to leave 2 hours between eating a meal and practicing yoga.