For max productivity I usually try to manage my diet strictly. It's all about what you eat, as well as how you treat your body.
Following a few guidelines for myself ensures that I'm feeling the most energized and crisp:
It's all about feeling out your body. I know a lot of people that prefer fasting, or thrive in an environment with only 2-3 large meals a day. Depends on your personal metabolism, activity levels, environment, etc.
Experiment with your foods, record them and the effects in a log to keep track. And try mixing things up. If you get sleepy after lunch and changing the food doesn't help, maybe consider going on a walk to encourage digestion and get your blood pumping. Dedicating 30 minutes to something like that could help snap you back, as opposed to losing a couple hours feeling catatonic and nodding off 👍