There are many myths about what runners should and shouldn't eat and whether they need to eat more than non-runners. As with many questions, my answer is: it depends. All your nutritional decisions should be made based on your goals. Are you trying to run faster? Are you trying to lose body fat? Are you training for a 5K or a marathon? How active are you throughout the day? Once you assess your intentions, you can start to decide how much to eat and when.

A balanced approach

Generally speaking, I recommend that most people stick to eating every four to five hours and eating healthy, balanced, regular-sized meals. By balanced I am referring to meals consisting of an appropriate amount of protein, fat and carbohydrates. This will help you eat an appropriate amount of calories throughout the day while maintaining good satiety (fullness) levels. Eating more frequently can actually have the opposite effect that many diets claim, and can lead to an increased desire to eat.¹

If you are training for your first 5K or 10K, or regularly running three or four times per week, then you likely do not need to add additional calories to your day to maintain weight with this activity level. If you are training for a marathon and will be running five times a week or more and maintaining a high weekly training volume that is greater than what you are used to, then you may need to increase your total overall calories to maintain energy levels.

If you decide to snack or eat between meals, you need to first identify the goal of that snack. Is this to tide you over until your next meal, to get you through a hard workout or to help you recover post-workout? A little bit of planning and scheduling can help ensure that you are timing your meals appropriately around your workouts so you minimize the need for additional snacks.

What to eat pre-workout

If you are doing a hard or long run, you should eat something two to three hours prior to your workout so that you have the energy to get through the workout. This meal should be fairly substantial and contain some carbohydrates and protein—for example, a bowl of lentil and squash soup or three ounces of chicken and half a cup of quinoa.

What to eat post-workout

Most people don't have to overthink their post workout meal. Don't fret too much about it being a 3:1 or 4:1 carbohydrate-to-protein ratio. Rather, think about eating high quality foods like vegetables and lean protein within two hours of finishing your workout—for example, a large salad with three ounces of salmon and some chickpeas.

If you've had a very hard or long workout session (lasting longer than two hours) or you have a second workout later in the day, then the post workout meal is a high priority. In these cases, try to have some easy-to-digest carbs and protein immediately to help enhance recovery for the next workout. A good example would be a smoothie consisting of some fruit, a little high quality protein and some greens. Liquids digest faster than solids, so if you are trying to recover faster this can be a great strategy.

What to eat or snack on between meals

If you have a large gap in your day (more than seven hours) between lunch and dinner, a snack or small meal may help you meet your energy needs. Consider something protein-rich like a hard-boiled egg, plain Greek yogurt or some veggies and hummus to bridge the gap. Avoiding simple carbohydrates like crackers, breads, cereal, dried fruits or other sources of sugar will help keep your blood sugar levels more stable.

Overall, you need to consider the intensity of your exercise program before starting to eat more. Remember, increased training does not give you a free pass. The calories you consume should be of high nutritional value—rather than junk food— in order to fuel your body for the increased demands of your training program.

References:
1. OHKAWARA K ET AL. OBESITY (SILVER SPRING).
2013 FEB;21(2):336-43.