It really depends how long you've known them.
Also according to your profile you aren't sure; I wouldn't be telling anyone much (and kept it between me and my wife at first) until you have a formal diagnosis, and even then I'd be careful.
You can get away with saying your the type of person that does this or that, or that routine helps you keep to healthy sleeping patterns etc, but don't go spraying the A word around until you are diagnosed, and are sure the people you tell understand and will support you.
You also have the other option of saying you have a medical condition, and need to strictly keep to regular meal times to avoid any problems with dropping of blood sugar levels - that might be easier than explaining a condition that is of little concern on holidays, but may come back to bite you when you return to work and the rumour mill starts up about you.
Just make sure whatever you tell them that you really know them, have a good rapport with them, and can trust them, otherwise there may be tears before bedtime.