Wihtout any guarantees:

You could try skipping a lunch or only eating half of what you usually eat.

I myself tend to eat a lot more than I actually need to. A full stomach will actually drain your batteries for a few hours.

While intermittent fasting (the way I did it - 2/5) was nothing I would do for a regular work week, skipping a lunch once a while or eating just enough to not get really hungry gives me an incredible boost.