While productivity is a mostly mental thing, there's also a large physical aspect. If you're body just isn't feeling up to it, there's no way you'll be able to get anything done. Below are a few additions you should make to your diet to help you boost your productivity.
Not all sweets are bad. A little dark chocolate might be just what you need to get through the work day. Cocoa has a compound called flavanols that sends a surge of blood to your brain. This helps you become more alert and better able to get things done. Citrus fruits are an absolute must. Even a quick sniff will make you more alert.
And, you've got to keep yourself hydrated. Too many people spend their days dehydrated, which makes even the simplest of tasks seem difficult. Drink plenty of water to ensure you are focused and your short-term memory stays on point. To get an energy boost throughout the day, have a cup of coffee or tea. The caffeine will make you more alert and boost your cognitive performance. I recommend tea over coffee because it has a few extra health benefits, like a reduced risk of cardiovascular disease. Plus, tea also helps boost your mood and focus.