Watts Doc #10: Can Fat-Adaptive Diets Lead To Better Performance Through Glycogen Sparing?

7/21/2019

One of the theorized benefits of low carb or ketogenic diets for cyclists is that it spares glycogen so it can be used when needed most. Kolie and Kyle walk through a paper investigating this question. They then discuss the upsides and downsides and potential utility of fat-adaptive diets in daily training.

Show Notes
Fat adaptation followed by carbohydrate loading compromises high-intensity sprint performance
https://www.physiology.org/doi/full/10.1152/japplphysiol.00813.2005

2 Comments

David H

7/22/2019 06:08:46 pm

I've tried a low-carb diet for Randonneuring, thinking it would be a great fit. It has been... ok.

There is one really big negative, that O2/HR bottleneck. To produce Z2 power, my HR is in Z4 and RPE is also high. This makes sense, as fats require ~2x the oxygen per ATP when compared to carbs.

Regardless of how many carbs you have available, if you are burning more fats, your HR (O2 delivered) must be higher for the same power output!

This actually is an advantage if you want to specifically target the aerobic system over the muscular system - for example:

If you are recovering from injury, you could go on a low-carb diet and maintain your aerobic system with much lower stress on your skeletal muscles.

Nuno Prazeres

7/23/2019 04:43:20 am

No hate mail from me!
I totally agree with the conclusions except maybe stating that fat adaptation strategies only make sense for events much longer than IM.
In my case:
> 50 year old = body composition harder to optimize
> Very polarized training approach
> Reverse periodification
I timed the "fat adaptation" nutritional intervention to happen in the latter stages of preparation (but still strategically carbo fuelled higher intensity workouts) which allowed me to lose some more body weight and probably enhance my fat contribution at race target intensity: 0.70ish IF which I was able to get with a VI of 1.04.

I trained my gut a lot in the previous months and, maybe just for that and for genetic lottery, was able to eat and process more than 400kcal/hour gels+carbo drink without any GI distress during my bike leg.

My last 6k of the Marathon were the fastest of all and I was able to be very close to max HR sprinting for the finish line so I guess I still had a lot of glycogen availability even after almost 10 hours of effort .

But the drawbacks of this strategy were also there (but not in the race).

Because I think neuromuscular work in cycling translates to gained efficiency in the muscle fibers recruitment for all the intensities, I include short sprints in my program in a weekly basis. Prior to the "fat adaptation" I was reaching consistently around 1200w PMax. After the intervention I barely could get to a figure above 950w while Z2/Z3 efforts were unchanged in terms of watts per HR and RPE.

So this means that such an intervention would probably be a total disaster for regular road cycling or even time trialing.

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Watts Doc #10: Can Fat-Adaptive Diets Lead To Better Performance Through Glycogen Sparing?

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