Depriving yourself of sugar to raise efficiency?

[KWalker]

Horses for courses-

High fat utilization is great for long road races (generally 4 hours+), stage racing with longer races, or more endurance events (half ironmans, marathon MTB races, long grand fondos, etc.). You hear about Basso and Wiggins doing that kind of thing on low intensity LSD rides primarily because they care more about preserving glycogen stores because their glycolytic efforts come much later in their events than ours do and they rely much more on preserving stores.

Even a 60 mile road is often not more than 3 hours at race pace. Even then you might rack up a total of 2100-2300kj (at most, less if you sit in the pack protected from the wind). Lets say its a race with a final climb and you take in nothing but water then yes, you could arrive at the final climb having burned off a good chunk of your glycogen stores depending on what happened before, but the problem of trying to train yourself for fat metabolization is that your body is still going to rely on glycogen once the effort gets roughly over 90% of FTP so unless you can ride the entire first portion of the race never exceeding this power level then your body will derive energy from those pathways. Even pros still supplement with ample food during a race such as Milan San Remo, which is 7 hours long and has a really slow first half. Even though they've developed the ability to rely on fat stores for energy under a certain power output, the race is still going to bring other things into play and they still will need a lot of their stores for that last hour.

I have no direct knowledge of exactly how much eating whilst on the bike decreases the rate of depletion, but if you were to stick to the general eat after the first hour rule and take in 200-400 kcal after that, then you arrive at the end of your 3 hour race with 400-800 less calories burned from glycogen. I know that I would not want to push bonking at the end of a race because I had empty stores and can't synthesize glucose fast enough because I was limited by the digestion process. Even with gels, that's a relatively small amount of energy if you have little left in terms of natural stores.

If you primarily do crits, domestic road races, and amateur level road cycling events you do not need to worry as much about fat utilization since most of your energy will not come from that process. I remember a Hunter Allen talk where he noted that unless a cyclist is doing races over 4 hours it would make no sense for them to short change themselves by not taking in CHO like you're asking about.

Sure, I can do a 4 hour ride with nothing but water if its an LSD base ride, but it definitely slows down recovery and glycogen replenishment and doesn't benefit my goal. Moreover, if your ride is say 220w AP with a 300w FTP, your KJ turnover will be relatively low and you won't dip into your stores as much but then again you're not doing anything that would require that. I personally include lots of climbing in my base rides or might do a ride with SST/Temp/FTP or sprint work at the end, which ramps up my KJ turnover in that last hour to close to 800-900 kj/hour instead of the maybe 600 I'd burn in the middle of my L2 zone. I can say from experience that you tap out very fast if you attempt that and haven't been eating the entire ride and what's the point of letting your training quality and recovery suffer if its not going to benefit your racing? I've yet to hear a single person say that they lost a race from bonking in a 45m-60m crit because they used too many carbs and not enough fat. I also don't know anyone that rides an entire crit below tempo- for me its a very anaerobic bout almost right off the bat and often stays that way.