[yn37]

Just wrote a quick article about this -- http://claudiu.dragulin.com/2017/03/07/two-simple-tweaks-to-...

The main points are:

1. Pay attention to what you eat. In my case, eliminating potatoes from my lunch had a massive impact on how productive I was afterwards.

2. Pay attention to how much you eat. I noticed that the usual approach of eating until full doesn't serve me well in terms of focus and ability to concentrate afterwards. When I ate slightly less (until I felt about 70-80% full), I had more energy and a more focused mind for the rest of the day.

Of course, these are not hard rules (if they worked for me, they may not work for you). But take them as a rough guide and experiment on your own.