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Old Rule: Carbo load before a race.
New Rule: Fat load, then carbo load before a race.
Earlier I said a low-carb diet — specifically a high-fat, low-carb diet — increases fat burn during running, but this benefit comes at the cost of reduced training capacity. For this reason, it’s not recommended runners use such a diet as their normal training diet. However, research has shown that a short-term high-fat diet that immediately precedes the traditional pre-race carbo load offers the best of both worlds. 10 days of fat-loading are enough to increase the muscles’ fat-burning capacity, while the subsequent three-day carbo load ensures muscles also have plenty of glycogen available.
In 2001, Vicki Lambert, an exercise scientist at the University of Cape Town, South Africa, tested the effects of 10 days of fat loading followed by three days of carbo loading on endurance performance in cyclists. After warming up with two hours of moderate-intensity cycling, Lambert’s subjects were able to complete a 20K time trial 4.5 percent faster after using this protocol than they did when carb loading was preceded by their normal diet.
To get these benefits in your next marathon you’ll have to get 65 percent of your calories from fat every day for ten days starting two weeks before your race. This means virtually everything you eat will need to be high in healthy fats. Recommended staples for fat loading are avocadoes, Greek yogurt, cheese, eggs, nuts, olives and olive oil, salmon, and whole milk.
Take-Away Tip: Switch from fat-loading to carbo-loading three days before your marathon. Aim to get 70 percent of your total calories from carbs during this period.