In reply to mypyrex:
I've has similar experience and I draw this parallel:
If I get engrossed in some serious DIY, I feel no desire to stop and eat at I time I would normally. Nothing significant happens as a result of this, other than I may get a bit grumpy later on.
On a walk of several months, the same sort of thing happened- off on my adventure, and it took time to get into the routine. I 'forgot' to eat. On a practical level, as the trip progressed, I became increasingly aware that if I didn't refuel adequately, the trip would come to a premature end. So the routine developed. I made time to eat, and worked to get enough in.
As regards liquids, the reminder to drink enough comes much earlier
On a walk of a few days, or a week, most people can undereat and get by on the body's reserves.