Nutrition
When it comes to nutrition break it down into two distinct areas:
Fueling: All nutrition taken before, during and after exercise
Daily Meals/Snacks: Everything eaten between workouts, major meals and snacks
Nutrition is a "must have" component of performance and recovery. Without it, you will never reach your full potential.
When it comes to fueling any workout over 60 minutes must be supplemented with some type of nutritional support. (under 60 minutes just water is fine) This not only helps you jump-start your recovery going into your next workout, but also allows you to perform to your best ability during that specific session. A good starting point is 3-3.5 Kcals per/kg of body weight, 60-80 grams of carbs per/hr (example: 150/ 2.2 = 68kg, 68kgx3= 204-238 Kcals per hour) Some people can handle larger volumes of food than others and I usually recommend a "front loading" approach to all long course athletes. This entails a larger volume of calories the first 2-8 hours of an event, then slowly decrease the amount as your body becomes less receptive to absorbing calories. This is something that needs to be practiced in training and refined as you get closer to your A race.
Daily meals/snacks: I usually recommend periodizing your nutrition to match your training load and intensity. i.e., When training levels are high, intake must also be higher. When in major training blocks a 30% protein, 30% fat, and a 40% carbohydrate approach is a starting point that you can experiment with. This like many things isn't a one size fits all, some people do better with a higher carbohydrate intake than others and should be something that you refine as you go through training blocks. The MAJOR problem that I see with many athletes is not consuming enough calories to complement there training load. If you are under-consuming it will lead to under-recovering, thus resulting in under-performing, and eventually leading to burn out, injury, and many other potential issues.
Use MyFitnessPal to track your nutrition for one week to see where you are currently at. Then adjust as needed. Re-track your nutrition every few months to make sure you are on point with the adjustments made, and your current activity level.