If you're running a marathon this spring, you're about to enter the most critical – and difficult – four weeks of training, when 1) your weekly mileage is at its peak; 2) your motivation may be flagging; and 3) you're most likely to get sidelined
-depleted state. Ever since carbohydrate-loading caught on decades ago, carbs have been the focus of nutrition advice for marathon runners. You can burn 2,300 calories on a 20-mile run, and the carb is the most readily converted fuel source, so it makes perfect
