After you’ve expended all of your energy on a long run (whether on race day or on a training run) your plan is to rehydrate and re-nourish yourself beginning as soon after the race as possible.
Like all of the recommendations I’ve offered, these are based on general principles, and ideally you’ll adapt them to your individual circumstances, based on your body weight, fitness level, the length of the event, the temperature and humidity, and individual variability. The more opportunity you have to plan ahead and field-test different strategies before race day, the better.
However, I can offer some general guidelines to get you started.
Drink 2 cups of fluid for every pound that you lost during the activity. If you don’t weigh yourself before and after the race to know exactly how much weight you’ve lost, just keep drinking! Water is good, but a sports drink, coconut water, chocolate milk (yes, chocolate milk), or, in fact, any source of fluid is good too.
Begin eating within 15-30 minutes after the event, and plan to consume about a 3 or 4 to 1 ratio of carbohydrate to protein. If possible, your protein source should be particularly rich in branched-chain amino acids (BCAA.) Leucine is one of the primary BCAA’s. Dairy products are high in leucine and other BCAA’s, but there are other sources too.
You need the carbs to replenish your energy stores, but the protein is needed to rebuild muscles that may have experienced some overuse/breakdown during the event. Branched-chain amino acids are doubly important because they serve as protein building-blocks for muscle synthesis, but they also serve as hormone-like messengers stimulating the body to produce more protein and muscle in the first place.
Over the first hour or two after the event, plan to consume about 0.5 gms of carbohydrate per pound of body weight and the coinciding amount of protein, about 0.15 gms per pound of body weight.