I've been binge-watching this guy's videos lately, and came across this:
It turns out that HM is a low-carb fan ... although mainly, it seems, as a cunning plan to offset the indulgence of afternoon tea. Skip through to 8:23 if you don't have time for the whole thing.
I'm not sure why he describes her diet as "bizarre". At 95, she's presumably doing something right, and it all sounds very tasty.