"Ok I love productivity tools but if you're seriously feeling sluggish in the afternoon you probably need to check your diet vs installing new software" – this 100%. Crazy how proper diet is a productivity hack nowadays.
Author here - actually the tip that you should have a proper diet and exercise regularly came up quite often in the research! It's hard to feel productive if you don't feel physically and mentally 100% first.
My point exactly. It should be self-evident even for people who are throwing software at every problem. The Levels alternative recommended seemed promising though.