I feel like your comment is evidence that you are insufficiently acquainted with various flavors of cult-like behavior and wingnuttery. There are in fact people who sincerely believe that you don't have to eat [1], who believe it so fervently that they risk and sometimes lose their lives for that belief.

Humans are social creatures. We are biologically inclined to follow charismatic leaders, even off a cliff. In most people, the susceptibility to suggestion is much stronger than the strength of their rational beliefs. Just look at American politics, for example.

All of this is to say that if Andreessen said, "I don't eat food," there would be a small but vocal group who would see that as validation of their beliefs; there would be a think-piece in the Atlantic about the history of breatharianism; Hacker News comments about what does "food" mean, really, etc. Yes, people would take it seriously. Just because he's rich and has therefore bought a loud megaphone.

[1] https://en.wikipedia.org/wiki/Inedia