The best diet for runners is going to be very similar to the best diet for non-athletes, with just a few minor tweaks.
Whenever anyone hears "running" and "diet" in the same sentence, they immediately think of carbohydrates. Being a runner, however, does not give you permission to load up on carbs and get a free pass when it comes to good nutrition and subsequent weight loss or weight gain.
Remember that there are good carbs (complex) and bad carbs (simple), and runners are just as likely to suffer the consequences of eating bad carbs in excess as non-runners.
3500 calories = 1 pound
1 mile = 100 calories
"Bad" Carbohydrates = sugars, white flour, some starches
"Good" Carbohydrates = fruits, vegetables, whole grains, low-fat dairy
A widely accepted "rule of thumb" or formula for runners is to plan a diet that consists of 50-65% carbohydrates, 15-25% protein, and 20-25% healthy fat. While the carbs provide the fuel for running, the protein and fats keep you feeling full and satisfied--making weight loss possible.
To begin your diet for runners, you'll need to determine your daily caloric goal. Simply take your current weight and multiply by 13. This number factors in the calories you need for your bodily functions and your usual activity. To lose weight, say one pound a week, you would have to cut those calories by 500 each day (7 x 500 = 3500), assuming you didn't change your normal activity level.
A diet for runners would obviously have to factor in the calories spent running. Again, as a "rule of thumb" running one mile = 100 calories. Yes, that amount varies depending on size, weight, gender, age, etc., but it's a good starting point. So to lose weight, you can cut some calories from food, while cutting more calories through running.
So now to lose one pound each week, while running 2 miles per day, you could cut 300 calories from your diet, and burn an additional 200 calories through activity, giving you the 500 daily caloric-deficit you need. It's simply a game of numbers when it comes to a diet for runners...grab a calculator and figure out what works best for you.
Current weight: 200 pounds x 13 = 2600 calories (current need)
Desired weight loss: 2 pounds per week
Caloric-deficit needed each week: 7000 (3500 x 2)
Caloric-deficit needed each day: 1000 (7000 / 7)
This deficit can be achieved in any combination through decreasing food & drink, and increasing activity, especially running.
Calories needed daily: 1600 (2600-1000)
Distribute your calories according to the runner's formula:
50% x 1600 = 800 calories of carbohydrates
25% x 1600 = 400 calories of protein
25% x 1600 = 400 calories of healthy fats