There was one other wrinkle in the study design. Three minutes before the start of the running test, the subjects consumed a gel that contained either 400 calories of maltodextrin (a carbohydrate commonly used in sports drinks) or no energy at all (placebo). Specifically, subjects got the maltodextrin gel on the day when they had the high-carb breakfast and on one of the two high-fat meal days. They got the placebo gel on the other high-fat meal day. Distance runners often consume a gel packet minutes before the start of the race in order to give the muscles an extra source of energy from blood glucose; this helps to conserve muscle glycogen. Tanaka and his colleagues wanted to see if this extra measure made any difference between the two trials involving high-fat meals. As it turned out, it did.
More: The New Rules of Marathon Nutrition: Fat
On average, the subjects were able to run for 90 minutes in the trial in which three days of carbo loading were followed by a high-carb pre-race meal and a fake energy gel taken three minutes before running. They lasted two minutes longer on average in the trial in which carbo-loading was followed by a high-fat breakfast and a fake energy gel. While this difference is not statistically significant (meaning it could have happened by chance), seven of the eight subjects lasted at least one minute longer in this trial than they did in the high-carb trial.
When the subjects were given a high-fat breakfast and a carbohydrate gel before running, they lasted an average of 100 minutes, which is both statistically and practically significant. Seven out of eight subjects lasted at least four minutes longer (the other lasted two minutes longer) in this scenario than in the high-carb meal trial.
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Measurements taken during the three runs revealed that the subjects burned the most carbs and the least fat after eating the high-carb meal. They burned the least carbs and the most fat after eating the high-fat meal and the fake gel. So it would appear that the combination of a high-fat meal and a carbohydrate gel maximized performance by sparing the subjects' glycogen stores in two ways: by increasing fat burning and supplying an alternative source of carbohydrate fuel.
The authors of this study did not report exactly what the subjects ate, but it isn't hard to construct a breakfast that roughly matches the nutritional composition of the high-fat meal used in it. Here's one example: two scrambled eggs, half a bagel with cream cheese and a small glass of orange juice.
More: The New Rules of Marathon Nutrition: How Many Carbs?
Before you rush off and eat this before your next marathon, consider a few precautions. First, previous studies with similar but not identical designs have not found that a high-fat meal enhances endurance performance compared to a traditional high-carb pre-race meal. Further research is needed to determine if a high-fat meal that includes some carbs plus a carbohydrate gel is truly superior. In particular, we need to see if the apparent benefits of this approach are wiped out when a high-carb breakfast is combined with a carbohydrate gel, or when carbs are consumed during the run (as they were not in this study).
More: 5 Common Pre-Race Nutrition Blunders
Finally, if you do wish to test out the race-day nutritional protocol that got the best results in this study, be sure to do it before a long workout or a low-priority race before using it on a day when you're chasing a marathon PR. You don't want to find out the hard way that it doesn't work for you when there's a lot at stake.
More: How Athletes Can Choose the Best Dietary Fats
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