It depends on your age or health I guess. I'm now 34 and I am learning some types of food will tend to make me sleepy while others will help me stay away and focused for longer (or maybe they just don't make me sleepy?)
Basically avoiding any type of heavy carbohydrates does the trick to me. Bread, spaghetti, potatoes, milk (in your coffee).
If I do get sleepy, also not sitting straight after lunch helps, I recently got a standup desk and I stand the first 30 min after lunch for work, really helps.
Also avoid any kind of sugar at all costs. Candies, dessert, ice cream, chocolate, sweetened coffee, and counterintuitively even some fruits such as bananas may give you a sugar crush.
2 cups of coffee (1 with breakfast, one mid morning). Small lunch.
10-20 minutes eyes closed/nap. Tea. Earl Grey. Hot.I try to take cat naps, but you would be amazed at how big a difference just closing your eyes for 10 min makes. Mid day brain haze completely gone!
I lay down on couch for 20 minutes.
When I work from home. In the office I can not manage to rest even on the couch.
Exercising has really helped with this, and getting better sleep (the 2 go together I think)
I try to eat less the next time. I find that there is an optimal amount of food that prevents me from being hungry that doesn't causes tiredness.
Can't speak for others but I notice I only feel sleepy if I have a huge meal. A normal sized meal followed by a fruit usually keeps me going till home time.
Most people (that can get away with it) basically just check out after lunch. In a 9-5 job the majority of work happens in the window of 10-12.
