The number of calories you should eat to fuel your running is a highly individual decision. While there is a general recommended daily amount of calories, finding the right number of calories requires trial and error over weeks and months. But there are several guidelines in finding the types and amounts of calories that work for you as a runner.
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"The Complete Book of Running" by Jim Fixx says you burn approximately 100 calories per mile of running, with carbohydrates as your main muscle fuel. The Sports Fitness Advisor says your body can store up to 2,000 calories of carbs, with the best formula found by multiplying 15 grams of carbs per kilogram -- or 2.2 pounds of your body weight -- with 4 calories per gram. The Cleveland Clinic's Calorie Calculator says a 150-pound runner burns 588 calories during a 6-mile run. With this in mind, eat a similar amount of carb calories to restore your body weight.
The Sports Fitness Advisor says fat calories contain twice the amount of potential energy that carbs do -- 1 gram contains 9 calories of energy -- but your body can't convert fat into immediate muscle fuel as quickly as it can convert carbs. Monique Ryan's "Sports Nutrition for Endurance Athletes" suggests that your daily diet should include at least 25 percent fat calories. Eat nuts, avocados or oily fish to add fat calories to your diet. Keep in mind, however, that you need carbohydrate calories to burn during your run.
The Sports Fitness Advisor says endurance athletes such as marathon runners need up to 2 grams of protein per kilogram of body weight to perform well. At 4 calories per gram, registered dietician Suzanne Girard Eberle recommends that you consume 15 to 20 percent of your daily calories in the form of protein. Hammer Nutrition says a 154-pound runner needs 98 grams or 392 calories of protein a day for good muscle health. Eberle emphasizes that your protein intake is especially important immediately after running.
When keeping track of your total daily caloric intake, make sure to count those coming from your sports drinks. You may drink anywhere from 20 to 80 ounces of sports drinks during a run, depending on the duration and distance of the run. Girard Eberle says most sports drinks can contain 50 to 80 calories per 8-ounce serving. While many of these calories are burned during your run, it is important to factor them into your overall daily calorie intake.
Finding a Balance
No two runners will have the same caloric needs. Finding the right balance of the amount and types of calories to consume daily is key in helping you run your best, day after day. Finding the right balance can only come through experimenting with your diet. Monique Ryan suggests keeping a daily food journal to track what works best for you.