Yes, I do feel much better after eating; no sadness at all.

Yet I hope you realize that I was also making an ironic statement about Jack's argument while buying some time to think about it.

While depression leads our thoughts to existential and nihilistic angst (and bad poetry and suicidal thoughts) our feelings of happiness, meaning and purpose also depend upon our beliefs. Accurate or inaccurate, beliefs affect how we feel.

So my response to Jack's argument is that if I believe that the purpose and meaning of my life depends upon objective value, then I will feel depressed if I believe that there isn't any (even if I'm not clinically depressed). So I still need to examine these beliefs: whether feelings of purpose and meaning really do depend upon objective value as a necessary condition (for myself only, I understand this is not universal) and whether or not objective value exists.

If the first, and not the second, then this would mean that accurate beliefs and feelings of purpose and meaning are simply not compatible for me.