Some say yes

By Michelle Hamilton

Steaming bowls of pasta and rice are the staple of any endurance athletes’ pre-race ritual. But once your glycogen stores are full – i.e. your muscles have packed in as many carbohydrates as they can – is there a benefit to eating lots of carbs race morning? Could eating more fat instead prolong endurance? A new study published in the journal Nutrients suggests yes.

“Carbo loading is important, but on race morning, it is misunderstood,” says Hiroaki Tanaka, Ph.D., who directed the research. Tanaka and his team of exercise physiologists at Fukuoka University in Japan hypothesised that high fat consumption would jump-start fat metabolism during exercise, thereby preserving the body’s carbohydrate stores for use later during a race or long run.

The researchers had eight male collegiate distance runners carbo-load for three days. The men ate 10,725 kilojoules a day consisting of 71 per cent carbohydrates, 19 per cent fat, and 10 per cent protein. They limited exercise in order to maximise glycogen storage. Four hours before a treadmill test, the athletes were randomly served either a high-fat meal (4185 kilojoules of 30 per cent carbs, 55 per cent fat and 15 per cent protein) or a high-carb meal (4185 kilojoules of 70 per cent carbs, 21 per cent fat and 9 per cent protein). Three minutes before the test, they ate a small amount of maltodextrin jelly or a placebo. Maltodextrin is an easily digestible carb found in various sports drinks and gels; it replaced the carbs used in the four hours between the meal and the treadmill test.

The athletes ran for 80 minutes at marathon pace, then for as long as they could at a faster pace, around 16km race pace. Blood samples were taken to ensure exhaustion was due to a depletion of carbohydrates rather than the accumulation of lactic acid. Gas exchange was measured to monitor fat versus carbohydrate metabolism. Each subject participated in three trials, with at least one week separating tests.

The athletes who ate a high-fat meal and the carb jelly increased their endurance on average by 10 minutes – that is, they sustained the faster segment after the 80-minute warm-up longer. Time to exhaustion for runners who ate the high-fat meal but the placebo jelly was not statistically relevant, but all but one runner prolonged endurance by two to eight minutes – significant for runners interested in improved performance.

The study concludes that “following three days of glycogen loading, a high-fat meal and subsequent ingestion of a small portion of carbohydrate jelly prior to exercise enhances performance of athlete endurance running.”

So should you add a thicker layer of peanut butter to your pre-race bagel? Tanaka believes all runners can benefit from eating more fat before events or hard workouts lasting 80 or more minutes, such as marathons, half-marathons and long runs with several kilometres at marathon race pace. “If I were running a marathon, in the morning I would take a double cheeseburger,” Tanaka says, adding that hamburger has the right ration of carbs, fat and protein.

Tanaka emphasises, though, that the high-fat meal is effective only if your carb stores are full. The study cites improper carbo-loading as one key reason several previous studies concluded that high-fat pre-race meals did not extend endurance. Adequate digestion time is also important.

Leslie Bonci, a sports dietitian who specialises in distance running, isn’t a fan of fat-loading. Her concern is that it remains unclear if the additional fat actually preserves carbohydrate metabolism or impairs it. Plus, fat is harder to digest than carbs, making it a less prudent choice before exercise.

“But distance runners sometimes do consume a diet that is too low in fat,” she says. “So rather than a 55 per cent fat meal, even 25 to 30 per cent fat would work.” Ideal fat choices include nuts, nut butters, seeds and avocado. “But always test the gut in training,” says Bonci. “Not on race day.”

Writer Michelle Hamilton is a Runner’s World contributing editor.

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