If they're busy working on a project (like the beach), they won't acknowledge it and their action won't say anything about a meal. The food item just disappears. I am assuming they are eating though.

After a few days or about a week of not eating, the peep's behavior changes a little. It's different in each case, but they slow down, get tired a lot, and so forth. I had to start one of my games over and right away got a really rude townie. My residents are working on the town projects while getting hand fed. The ones who are getting food are staying active and cheerful even if they don't acknowledge the food while they are at work.