Thursday, June 20, 2013

My Metabolic Efficiency status leading into IMCDA

In my work as a sport dietitian, I have assisted many triathletes of all experience levels with their daily and training nutrition leading up to Ironman, but now it’s my turn to feel the challenges of Ironman nutrition. I have to tell you I feel a great deal of excitement to see how the carb-controlled nutrition patterns I have been following will work for me during such a long and challenging event.  Sure, I’m looking forward to the event itself - absolutely. But as part of my (and Bob’s) work as sport dietitians, it is good to challenge the nutrition norms, especially as we are in the midst of an evolving field of sports nutrition for endurance athletes.  Now, don’t get me wrong.  I’m not foolish to think my nutrition plan is 100% bullet proof, given that there are always so many things we cannot predict in a race setting, but I do have a good level of confidence in my fueling needs based on my metabolic efficiency status and training nutrition trials to date.
As you can read in a previous post, I overhauled my nutrition patterns in November last year to a more carb-controlled daily pattern than previously. I started Ironman training essentially at the beginning of this year, so about 5.5 months have passed as part of this experiment. An assessment of my Metabolic Efficiency status in December, about 6 weeks after implementing a carb-controlled nutrition pattern, showed that I was fairly efficient at using my fat stores as a fuel source:

You can see the red line represents my percentage of expended calories coming from fat and the blue line is my percentage of calories coming from carbohydrate.  

I haven’t changed my daily nutrition patterns too much since this test, although amounts of foods have changed in bigger training blocks and I also have been experimenting more with nutrient timing to support my training sessions. By "nutrient timing", I am referring to the before, the during, and the after (training sessions)... which does roll into quite a bit of my “daily nutrition” time on long training days. I should clarify my use of the term “carb-controlled”. Please know this does not mean an absence of carbohydrates in my diet. Nor does it mean I am starving myself (I have a respectable appetite!). Rather, the amount of daily carbohydrates is about 50% less than what I would be eating (aside from training nutrition) if I had decided to train for an Ironman prior to last year. I can tell you it is much different than what the majority of sports nutritionists and sport nutrition companies say athletes must have in order to train, perform and recover well. Meals and snacks are focused on higher fat choices and a consistent and moderate amount of protein. I always have the goal of achieving stable blood sugar with my food combinations, but I do allow for some “misses” to occur.  

So, here are the results of my most recent Metabolic Efficiency Assessment:

Note that I opted to start the test at a higher level of watts for my first stage and not go as long as I did during the December test since I will not be biking at 180 watts and a perceived effort greater than 8 for this Ironman race.  Even though I did this test after completing a 70.3 race a few days prior and was in a high training block, the results show I am still efficient at using fat as a fuel source at the intensities and heart rates I plan for IMCDA. This is great news!

As I write this, I am waiting for my most recent round of blood work to show what has changed with my blood lipids since December. I will be sure to share the news. 

In my next post, I will share a few more notes about my Ironman training.


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