THis is probably late for your exams but here is my input:
So far every comment is missing the point.
Food is not placebo... food has a palpable and measurable effect on brain chemistry. Food is therapeutic in many psychiatric disorders, not to say many other diseases. THis is established.
If you have adhd, that's different from just not being able to "focus," sounds like you have something like that, chatter brain.
Someone else said all food does is similar to caffeine and l-tyrosine, this makes no sense and is overly simplified.
THe best strategies are however mental. Start relaxing and focusing your mind through some from of meditation.
Here are some dietary strategies:
-Try lowering the carbs for a day, or a meal at least. This promotes more GABA in the brain which calms it down.
- skip breakfast and start fasting, this enhances brain function tremendously
- eat meat
- chia seeds/hemp seeds or other omega-3, I prefer the plant omega-3 because they have other minerals that produce noticeable increases in focus. Fish oil is good but many products are impure
- eat clean, this means real food
- green tea
- if your brain feels too chattery, take some chamomille, or other anti-stress herbal teas like white tea, passionflower/valerian, or any blend that says "calm down" tea.
- herbs like roobois are commonly found and are good for brain, turmeric is quite potent, cacao powder as well