I'm looking at bumping up into the ultra racing distances. In doing so, I spent nearly the last 4 months (as can be observed in my log) doing low intensity workouts and curbing my reliance of carbs as fuel.

I had my Energy Systems (metabolism) tested two different times to see what combination of fat and carbs I was burning while running. The first test only had me on the treadmill for 12 mins (with increasing intensities every 4 mins) before I was at a 50/50 fat/carb mix. My second test yielded VERY different results. (I tried to attach a pic of my test result but couldn't figure it out . So, I made that image my profile pic if you would like to see the test details.) I spent a full 40 mins testing (with increasing intensities every 4 mins) and the energy I was burning was STILL a 59% Fat / 41% Carb mixture at the end of the test. The last testing segment was at 6:54 pace and while I was working (HR measured 183) I wasn't struggling with the pace.

Bully for me!    -   -   -   I think

So, now what do I do with this information? Diet and slow and easy training brought me to these test results so I do I keep plodding along? or since I know I would be burning 70-90 percent fats at 7-8 min/mile pace as measured by my test should I ratchet up the intensity to those levels? Any advice would help!

Thanks,

This was well said - Carbs can work fine ... But a bit of a balancing act that has more potential problems to solve.

The best I was ever at being a carb intake was when I was running so may miles (2300 in 3 months) that I could not keep up with glycogen stores, so I did not try to.  I would just fuel every run as I went ... always taking carbs, salt, H20 as if I was in the middle of an ultra.  I got to where I could intake 450 calories an hour.

I wish I had experimented with fat as fuel, mainly because of the fighting nausea between hour 16-24 of a 24 hour race.

Writing this from the standpoint of starting out 17 years ago by combining jogging with a protein-sparing modified fast for about 3 months, i.e. running on a highly ketogenic diet and gradually becoming a non-ketogenic ultrarunner.

 

Probably the one thing you don't want to do is run easy miles faster. The generally accepted wisdom around here: run often, mostly easy, sometimes hard, still applies. You still need to do several hard workouts a month across repeats, intervals, tempo, marathon pace, and long but not slow, to keep your speed up. Save the slow for easy days and back-to-back long run weekends. I have always been curious about was the recovery rate on a fat-adapted diet vs. the standard high-carb consumption during and after workouts to maintain glycogen stores. How many hard workouts do you do a week and how many days does it take in between the hard workouts to recover? One thing I noticed being in or near ketosis back in the day was that I tended to get a calf strain every few months, typically when I was running every day and trying to drop weight too fast.

 

Fat adaption gives you potentially a significant advantage for ultra-racing. Your ideal ultramarathon pace is determined by many things but one of those is your ability to maintain an equilibrium between fat metabolism (from body fat), carb metabolism and protein metabolism from food and drink consumed, and the energy expended to maintain a biomechanically efficient pace. Being fat adapted means, in theory, that you start at that equilibrium and can conceivably maintain it for many hours on perhaps half of the caloric consumption of a comparable non-fat-adapted runner. Being non-fat-adapted is a bit more of a balancing act, where too little calories eventually leads to a bonk, whereas too much causes nausea. This is a particular problem on a hot day and/or at high altitude, where there is not a lot of blood circulation to the gut and stomach emptying slows way down.

 

I think any ultrarunner would tell you that they would love to be able to consume less food, gels, and sports drink during a race without sacrificing pace. Dehydration in the absence of nausea can be resolved on the move, but nutrition failure leads to the death spiral. To the extent that nutrition is potentially "solved" for you, the focus during a race can be on other management issues, such as hydration (i.e. maintaining starting weight), pacing, blisters, chafing, sun protection, cold protection, etc. Thus, there is really only one thing to do: start training for and racing 50+ milers, with an eye towards a hundred or 24 hour.

I've been low-carb high-fat for a couple of years now, and it has worked very well for me.

However, the more races I do the less knowledgable I get. After this past race, I'm now working with a sports nutritionist to try to really figure it out. I would like to say that I'm able to do very long, mostly-flat races (e.g. 24-hour, or 153-mile Spartathlon) on 100 cal / hour, that I get mostly from Coke – taking nutrition completely off the table.

Sometimes that works, but other times, I bonk. It's taken a few of these experiences before I have finally acknowledged that it is indeed a bonk; I'm not getting enough fuel. The paradox is that I can bonk after 8-9 hours, walk a bunch, then come back and run out the 24 hours still on 100 cal / hour, finishing strongly.

As for what you do now, I second the above, but it really depends on what your racing goals are. E.g. for say 24-hour, I'd argue that you don't need any speedwork at all.