Huh? Were I to find out that Big Mac is people I would tell the press with the clear intent to damage McDonald’s brand name and profitability. Is that also libel? I would hope, anyway, that true claims are never libel.
In the US, truth is usually considered a defense against claims of libel. Not so elsewhere, such as the UK, if I recall correctly. (IANAL)
I would at least hope there's a legal difference between true-and-in-the-public-interest claims like "Big Macs are made of people" and true-but-scurrilous claims like "<closeted gay celebrity> has gay threesomes with rent boys".