What Do You Say?

Here's a moral question I don't think Socrates ever addressed.
   What do you say when someone you haven't seen in a month shows up and they're easily 20 pounds heavier?
   This happened to me this week, and I didn't say a thing, just ignored it as if the guy looked exactly like he had back in October. But he really didn't, his face was puffier, his stomach was wider, he looked pale. And the man boobs... It's obvious he had more than an extra few helpings of mashed potatoes, we're talking some serious overeating and serious non-activity to get that much bigger in such a short amount of time.
   But is it better not to say anything and spare their feelings, or to say something - however tactful yet painful - and let them know they're making a mistake?
   And for that matter, what's a tactful way to say 'hey, Tubby, lay off the Snickers bars?'