DAY TO DAYNutrition is a reasonably broad topic with some somewhat divisive opinions around specific areas and fads, so we will try and keep it brief and prioritise the key areas.
Calories in vs calories out is king, don't worry about timings or fads. If you want to maintain weight – eat as many calories as you burn. If you decide to lose weight, do it slowly, consistently with a small calorie deficit. Close to race day, or on big training camps is not the time to cut calories as you risk illness or injury.
Daily intake is much more important than protein type, timing, or any other fad. As an endurance athlete during hard training blocks, you should be aiming to consume 1.4 - 1.8g of protein per body weight kilo a day (although try to space it throughout the day if possible).
These are good for you… But not all of them! Look at getting you fat from lean meats, nuts, seeds, eggs, fish, avocados and olive oil. And try to avoid trans fats wherever possible.
Vitamins & Minerals
Without targeting any specifics, try and make your meals as rich in vitamins and minerals as possible. Incorporating any form of fruit or veg in your meals and snacks is the best way to do this. As an athlete, you risk running down your immune system, so five portions of fruit and veg a day is the absolute minimum you should be consuming.
Do not try anything new race day, test any new intervention in training before the big day!
Have a good breakfast - high carb, something relatively easy to digest. A typical go-to for most athletes is oats, with some form of dried fruit or berries. It may sound basic, but anything like toast or cornflakes won't fuel you properly.
When racing you should be aiming for 80-90g of carbs per hour (although this takes some practice to stomach).
Caffeine is a fantastic supplement to aid training and racing, 1.5-3mg per body weight kilo is a decent dose (although this can be spread out). It takes 60 minutes to peak, so there is no point taking it 20min from the finish line. Just remember while caffeine can aid performance, it doesn't make you superman so keep to your pacing strategy even if the caffeine makes you feel better.
Don't neglect recovery post-race, try to have a recovery based drink made up ready, with 20-30g of protein, and have 60g+ of hi-gi carbs through food or drink. Aim to consume this within 30 minutes of finishing.