Malcs.. there is a lot of conflcting debate in sports nutrition about diets for athletes... I don't really know much about it and when reading one paper that directly contradicts another its hard to form any opinion at all about which is 'correct'.
Just for clarification, but saying 'diet' I don't imply losing weight. When I started on my training for my first Iron Man tri back in 2007 I was 2 stone (nearly 13kg, 28lbs) lighter in weight than I am now. Looking back, I was clearly under-weight for what I wanted to do and achieve and I am now much happier with my weight and how it works for my running. Putting on weight, primarily muscle, has helped me enormously.
Through a process of continual refinement and many 'lets see what happens' runs, I have started to learn what works for me. I used to do the 'carb loading' thing just like most other runners. Not any more.
However, by sheer fluke on one of my experimental runs, I found that by taking protein on during the run it really made a difference. I think I was doing a 50 mile run back in 2010, or thereabouts, when I was experimenting with eating cubes of steak and fish. Many times, I've been happy to stop at a McD's for a burger and fries and we've often laughed on here about the buffet of food I'll consume and still be able to run without digestion issues.
The protein discovery made me think more about it and it has been important to the muscle development. Obviously I do still eat carbs... I eat anything. The switch from being vegan for 18 years to being a meat eater back in the summer of 2010 was a profound lifestyle change. Since then I have learned what works for me and what doesn't.
I think we are all different and we need to learn about our bodies. There are some similarities in our nutritional needs to remain healthy, but when exercise and endurance is concerned I think we need to experiment and see what works. Some things will, some won't.
Fluids are hugely important too.. excessive loss of electrolytes, which you'll soon know by the swelling of your fingers, will affect your performance. It's not just a question of gradual de-hydration. I have experimentted with different volumes of fluid intake too.
I need to go now.. I'll write some more later.... hope this is interesting and thought provoking for how you approach your own life and training.