I have a project: encourage & help my team to stop eating lunch at their desks

Where I used to work we had a weekly "group hug". We met in our atrium, had a 50/50 draw, lorttery pool, announced birthdays (not always a good idea), and monthly we used the 50/50 funds to purchase a cake or other dessert. Others also would offer homemade treats. It was also a place to make some work related announcements, and for round table questions, but it was very casual. It was very successful until we had a change in location and leadership. For a while we had nothing. People complained and asked why did we stop. Moral sunk to new lows. Then it was decided we would have a "pizza day". But instead of an inviting space, it was decided to have the pizza inside a large conference room. Big mistake. It felt as though we were in a mtg. People did not want to attend, but were "forced". It was a total disaster, but it was bad leadership that made the difference.

Sounds like micromanagement to me. Bring pizza in and put in a conference room or some other shared space where team members can come and get it. Also make sure you're there the entire time and making yourself available to socialize. Don't force them to be social, just get the pizza and be there.

I have to agree with Keith. One other point I will add is that sometimes that break where you don't talk about work is just enough to ruin a productive flow. I often prefer to take lunch at my desk because I am most productive in the mornings and if that gets interrupted my afternoons will sometimes suffer. Don't sacrifice good quality work for social time. I like the people I work with a lot, and sometimes will agree to go have lunch but I always reserve the right to cancel if inspiration strikes. I don't want that to be held against me as a friend or colleague just because I opt out.

Simon,
I won't argue that a change of pace does not make people more productive. There is an underlying assumption, there however that getting away from the desk is in fact a change.

Consider someone who spends all their working time interacting with other people away from their own desk. In the case of the introvert in particular, the change of pace may be getting away from people and having some quiet time away from interacting with others. Mindfulness and mediation fits into this same situation. We have lunchtime yoga clubs at work where people gather, but there is not any real discussion going on.

For different personality types and job roles, a change of pace can mean different things. I often spend my lunch looking for new recipes, planning personal projects, interacting with virtual friends, and other things that have no relation to my work at all, before I go back to meeting rooms, hunting people down at their desks, and hallway discussions between one destination and the next.