Never assume that your diet is already good enough.
Former U.S. Secretary of Defense Donald Rumsfeld once famously said the following: “There are known knowns; there things we know we know. We also know there are known unknowns — that is to say we know there are some things we don’t know. But there are also unknown unknowns — the things we don’t know we don’t know.”
This statement is famous not for its poetry but for its convolution, but the point that Rumsfeld was trying to make was pretty simple: The things you don’t know you don’t know are more dangerous than the things you do know you don’t know.
This principle applies to the domain of sports nutrition as much as it does to any other domain. Consider the specific example of carbohydrate intake. It’s better to know that you don’t know whether you’re getting enough carbohydrate in your diet than to have no clue that you’re not getting enough. If you are aware that a diet with inadequate carbohydrate hampers training, and you are aware that your diet may lack sufficient carbohydrate, all you have to do to ensure that lack of carbohydrate does not hamper your future training is find out how much carbohydrate you should be eating, calculate your current level of habitual carbohydrate consumption, and make an adjustment if necessary. But if the thought never even crosses your mind that you might not be getting enough carbs, you are likely to continue to train with suboptimal results without ever realizing it.
Wait: without ever realizing it? Yes. There is a tendency to assume that problems in an athlete’s diet always manifest themselves in obvious ways: injuries, anemia, overtraining syndrome, etc. But this is not always the case. Some diet problems can simply cause you to get a little less benefit from your training than you would otherwise get. You still get fitter, and you still feel good overall, but you don’t know that you could perform even better if your diet were fixed.
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This truth was demonstrated in a recent study conducted by researchers at Australia’s Charles Sturt University. Ten healthy male volunteers participated in a two-day intervention. On day one the subjects performed a long workout designed to deplete their muscle glycogen stores. That same evening, they were fed either a high-carbohydrate meal to replenish their muscle glycogen stores or a low-carbohydrate meal to keep those stores low. But the subjects were not aware that their meals were being manipulated in this fashion.
The following day the subjects completed another workout. This one was a 60-minute run that included a 15-meter sprint every minute. The subjects who had been fed a low-carbohydrate meal unknowingly started this workout with almost 47 percent less glycogen (i.e. fuel) in their muscles than those who had been fed the high-carb meal. They also covered 4.9 percent less total distance in the 60-minute run and 8.1 percent less distance in the sprint segments of the workout.
In addition to measuring performance, the scientists overseeing the study took ratings of perceived exertion from the subjects as they performed the workout. Interestingly, those ratings were the same between the two groups. Even though they were getting their butts kicked, the glycogen-depleted subjects felt that the workout was no harder for them than the glycogen-replenished subjects felt it was for themselves. In other words, the glycogen-depleted subjects had no idea their performance was being compromised by their diet.
If the design of this study had been a little different, such that the subjects were forced to try to cover just as much distance in a glycogen-depleted state as they had covered previously in the same workout performed in a glycogen-replenished state, it would have been a different story. In that case the subjects would have found it much harder to match their previous numbers and would have ultimately failed in the effort. But the workouts in this study were self-paced. Free to regulate their running pace by feel, both the glycogen-depleted and the glycogen-replenished groups chose the same level of perceived effort. But because the glycogen-depleted athletes had only half as much fuel to work with, the same level of perceived effort was associated with a much lower level of performance.
This is how a poor diet can compromise your training without your ever realizing it. What’s the solution? Don’t assume your diet is good enough. Always be on the lookout for ways to improve how you fuel your body. Also consistently measure your performance in training so that you have a basis to determine whether a particular changes helps or not. If a dietary change has no effect, so be it. But if does—well then, you now know what you didn’t know.
About The Author:
Matt Fitzgerald is the author of Iron War: Dave Scott, Mark Allen & The Greatest Race Ever Run (VeloPress 2011) and a Coach and Training Intelligence Specialist for PEAR Sports. Find out more at mattfizgerald.org.