In its simplest form, the study is aimed at discovering the role diet plays in how our bodies metabolize fat vs. carbohydrate during exercise. The complete study will be released later this summer, but I can at least share with you some of my personal results.
One portion of the study was a VO2 Max (maximal oxygen uptake) treadmill test. VO2 Max is the maximum amount of oxygen that an athlete's body can utilize during exercise, and is a partially determining factor in an athlete's aerobic endurance. It is important to note that VO2 Max is not necessarily the point at which you have to stop running; the measurement is is a general indicator of endurance at best: Some folks are able to push on well past hitting their VO2 Max, while others almost immediately cave upon reaching it. I guess this is where mental toughness and guts come into play.
During the test, the researchers gradually increased both the speed and incline on the treadmill until I could no longer continue, and my rates of fat and carbohydrate metabolism at various intensities were measured. In order to be consistent with all testing subjects, they had to use the same method of VO2 Max testing, increasing both speed and incline. Personally, I'd like to try the test again with a program that just increases speed, as my training is more specific to flat, fast surfaces at this time. This makes a difference in the VO2 Max, which is why everyone has a different VO2 Max score for each sport. (Like I said, they did it the way they did for methodological purposes; this is just me being a data geek.)
My VO2 Max came in at 66.1. As I suggested above, this number is of rather little importance by itself, as it really doesn't say too much about what I can do on the racecourse. However, with the rest of the data from the study, I can pinpoint where my fat metabolism and carbohydrate metabolism peak at varying intensities, and I can see the ratio between the two at any given percentage of my VO2 Max.
Analyzing the data was wonderfully reassuring to me. My fat metabolism peaked at 1.57 grams/minute. At this point in the test, my VO2 uptake was at 49.4. By dividing this number by my eventual VO2 Max of 66.1, I can calculate at what intensity I burn the most fat: 74.4%. At that intensity, I was burning 98% fat 2% carbohydrate (1.57 fat grams/minute and .07 carb grams/minute). To put this into perspective, 65% of my VO2 Max had me running approximately a 7:15 per mile. Even when I increase my speed to around 7:00 per mile, I was still burning nearly all fat! Of course, as the intensity moves up, these numbers begin to shift a bit, but you would be surprised at how efficient at fat burning one can be, even at increased intensities.
Take a look below at a few more of my personal data points from my VO2 Max test:
% VO2 Max
As you can see, even when I start reaching some pretty high (for ultrarunning) intensities (80%+ VO2 Max), I am still metabolizing way more fat than carbs. This is an important takeaway for me, especially as I strategize for longer races. An athlete cannot replace the amount of calories they are burning quickly enough to expect an outside fuel source to meet their race-day caloric demands. A person may be able to physically consume enough, but their body would simply not be able to process the fuel quickly enough to stay ahead.
This is why I strongly believe that the less you have to fuel during a race, the better. Not to mention that fueling can be a hassle, and if it can be minimized, the hassle lessens. There are a lot of other factors that come into play as well. Heat, for example, can greatly effect how the body accepts (or on super hot days, rejects) the calories you give it. This is why you see so many more stomachs turn at hot weather races. Less eating means your body can use its precious blood stores for cooling and muscle function, rather than for digestion.