One of the most common questions I receive is about nutrition. While I am not a nutritionist, I will share insights from my years of running and coaching experience, so take this with a grain of sea salt (pun intended!). Poor nutrition is the largest cause of "hitting the wall" - when your glycogen, or storage of carbohydrates, is depleted. The amount of glycogen you have in your muscles has been shown to be directly correlated with how long you'll last on a treadmill test to exhaustion. Good running nutrition should keep you healthy and fuel your training!
Your ideal running diet should focus on foods like organic fruits and vegetables, whole grains, healthy fats like nuts and avocados, fish, and grass-fed (whenever possible!) meat and limit or avoid refined grains, fatty meat, highly processed sweets or added sugar, and fried food that deplete glycogen faster and can lead to weight gain. I love plenty of good carbs (60-70% target of your diet), and the absolute amount should also be proportional to training load; more/less carbs with more/less miles during your peak/taper periods. Make sure to get protein within 30 minutes of finishing a workout or race as protein helps your muscles heal faster and accelerate growth.
On the question of being vegetarian or "pescetarian", I have experimented with both and found it hard to get sufficient protein from tofu, beans, and eggs or sufficient iron from spinach and lentils. Iron builds the red blood cells that carry oxygen which muscles require, especially as you increase the intensity or distance of your runs. You should also be aware that the ideal diet I described often produces gas in the GI track. It can't stay there forever, and the runner's code allows you to pass gas freely when you run! Pretend the gas is propelling you forward like a booster rocket.
For race day nutrition, I almost always have a bagel with Justin's almond butter and a banana, ideally 1.5 - 2 hours before the race. Before a training run, my stomach has become accustomed to eating as soon as 15 minutes before, but it's usually something small and delicious - a Honey Stinger waffle, UNREAL peanut butter cup, or piece of fruit like Marathon Mangos (wink!). Avoid experimenting with anything you're not used to. A lot of dairy doesn't sit well prior to running. The most important ritual is to hydrate as early as 48 hours before a race, water plus electrolytes like Maurten, NuuN, or Zym, to prevent dehydration, cramping, and heat-related conditions.
Have a nutrition plan during the race and stick to it: a gel like PowerGel plus water every 5 miles or 30-45 minutes. Sports drink every 2 miles after the first gel. Electrolyte salts like SaltStick at miles 12 and 18. I ran my first 8 marathons with gels that had half the sodium and without any additional salt and felt I was about to cramp or did cramp by miles 18-20. Switching to gels with more sodium and supplemental electrolytes has eliminated that feeling!
Finally, try using caffeine strategically, by avoiding it a few weeks before a race and then using it on race day for an extra kick. You will discover the right amount of caffeine to suit you and your stomach. Academics believe caffeine lowers perceived effort by shutting down brain receptors that detect adenosine, a molecule associated with mental fatigue. Some also say caffeine enhances muscle contraction while others say it enhances fat oxidation to give you more energy. To me, the mental effects are enough!
Practice your nutrition plan during training, even if you feel like you don't need it. If you sweat a lot or if it's warmer, be more liberal. You'll find what works for you, but only if you train your nutrition too!