The New Rules of Marathon Nutrition

Old Rule: The high-carb diet recommended to runners in the 20th Century was a mistake.

New Rule: The current carbohydrate-moderation fad in running is a mistake.

Back in the 1960s, Swedish researchers discovered a high-carbohydrate diet increased muscle glycogen stores and thereby boosted endurance running performance. The practice of pre-marathon “carbo loading” was born out of this research. Subsequent studies revealed a high-carbohydrate diet also increased runners’ capacity to absorb heavy training loads day after day. Sports nutritionists have recommended high-carb diets for runners ever since.

Well, most sports nutritionists recommended high-carb diets for runners almost ever since. Lately, some experts have suggested a low-carb diet is better, arguing when runners maintain a low-carb diet their muscles become better fat burners, an adaptation that spares muscle glycogen in marathons and thereby pushes back the wall.

Studies have shown that low-carb diets do indeed increase fat burning during running. However, this effect has not been linked to improved endurance performance., Meanwhile, new research has reconfirmed that runners aren’t able to train as hard on a low-carb diet because it produces chronically low glycogen stores.

A study conducted by Asker Jeukendrup and colleagues at the University of Birmingham, England, compared the effects of a 41 percent carbohydrate diet and a 65 percent carbohydrate diet during an 11-day period of intensified run training. On the low-carb diet, performance levels decreased and the runners’ self-reported fatigue levels increased. On the high-carb diet, performance and energy levels were maintained.

Take-Away Tip: The amount of carbohydrate a runner needs to handle his or her training is tied to the amount of training he or she does. Use this table to determine how much carbohydrate to include in your diet.

Average Daily Training Time (Running and Other Activities) Daily Carbohydrate Target
30-45 minutes 3-4 g/kg
46-60 minutes 4-5 g/kg
61-75 minutes 5-6 g/kg
76-90 minutes 6-7 g/kg
90 minutes 7-8 g/kg
>120 minutes 8-10 g/kg

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