oh boy here we go again!

substrate utilization is dependent upon exercise intensity & diet. Want to burn more fat at all intensities? Eat a diet higher in fat. Want to burn more fat? Go slower. Fat burns in a carbohydrate flame, pretty sure that was the saying when I was in ex phys class last century.

Now you can workout fasted and burn more fat for that workout by waking up, ingesting zero calories and having some caffeine. Then go exercise at a low intensity, ~ 60%. You'll increase the amount of fat you burn for that workout. (you'll have to search on pubmed for this. iirc the author is Hawley)

What you should do first though is google Louise Burke Supernova I and Supernova II.

(Side note: If you're an endurance coach and you haven't read these shame on you.)

Read those studies. It's time to put the I can increase fat metabolism myth into the coffin and bury that bullshit 10 feet underground, sealed in a concrete tomb. Spoiler alert: the fad er fat adapted athletes got crushed....twice. The second paper is really good bc she addressed a lot of criticisms of the first paper, about 1.5 pages worth. These are seriously good reads.

Another good study to read is Havemann et al's paper on fat adaptation compromising performance. They did a crossover study with 8-10 cyclists doing 100k TT's on the bike. Worth the read. Spoiler alert the fat adapted athletes were slower

Your problem is not going to be fat adaptation or not. It's probably a combo of finding the correct mix of fuel, osmolality in the stomach, solids vs semi solids like blocks or chews vs liquids, and when to use each. Sugar type (fructose sucrose, glucose) may play a role for you as well. Nutrition is the 4th event in long course racing. Good luck with finding the right mix

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Brian Stover USAT LII
Accelerate3 Coaching
Insta

Thanks for the article - I read through the "supernova ii" article and I have a question. It seems to me that a key aspect to their negative finding is that they were dealing with elite athletes who are racing at a fairly high intensity (relative to their VO2 max). As I understand the article, for these elites, the ketogenic "gains" are negated by a decrease in economy at elite athlete race intensity and speed. I am nowhere near elite! I am trying to break 11 hours at IM Canada in August. Do you know if similar studies have been conducted on the non-elite crowd and, if so, did they also find decreases in economy at the lower intensities non-elites aim to maintain for IM?

Keep eating lots of carbs. All the time. Train hard. Recover well.

If your longer events are struggling, more carbs during the event is a possible fix. Check out https://forum.slowtwitch.com/...t=last-7417228#first

I also wrote this: Can Fat Adaptation Make You Faster? which might be informative.

PS. Louise Burke is a force to be reckoned with in research!

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Dr. Alex Harrison | Founder & CEO | Sport Physiology & Performance PhD
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📱 Check out our app → Saturday: Pro Fuel & Hydration, a performance nutrition coach in your pocket.
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Yes, many studies. In fact, I have yet to find a single well-designed study (calorie-matched, subject matched, optimal fueling allowed during test event, etc.) that indicates use of a low carb diet may be better than higher carb.

Primary reason I find most folks desire to stray from a higher carb diet: they're not eating enough carbs and are getting hypoglycemic at some point during their events.

Typical rationale for not eating enough carbs during long events: GI distress with additional carb consumption.
Typical cause of GI distress: dehydration.
Typical cause of dehydration, inadequate fluid or sodium intake or both.

When and How to Use High-Carb Fueling could be handy info, especially the bullet points.

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Dr. Alex Harrison | Founder & CEO | Sport Physiology & Performance PhD
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📱 Check out our app → Saturday: Pro Fuel & Hydration, a performance nutrition coach in your pocket.
Join us on YouTube → Saturday Morning | Ride & Run Faster and our growing Saturday User Hub

Alex hit the nail on the head.

We're not so different you and I compared to elite level athletes, we're just slower, although we may be better looking!

They may be operating at velocities that far exceed what we can produce. Yet if their 80% of max effort nets them an 8:30 and our 80% of max effort nets us an 11:50 we're operating at the same %. The 11;50 person just has a longer duration to deal with.

The reality is the 11:50 person is probably at 60-70%. As duration extends it's harder to hold a higher % of max effort. The 11:50 person may be utilizing a bit more fat as a substrate. Even a pro at 5.5% body fat has enough fat on them to do a double IM. They will be limited by CHO storage and replenishment rates.

I also can't think of a researcher than Burke who has spent more time trying to see if fat adaption for performance is a thing. I remember being in a fat adaptation study back in the 90's at ECU.

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Brian Stover USAT LII
Accelerate3 Coaching
Insta

Thanks for the links to those two articles, they really helped clarify some things for me.

Interesting to see your diagnosis above - in the IM where I experienced severe GI issues, I forgot my race belt in T2 and I had a container of salt tabs attached to that belt. So I didn't take any salt tabs during the run (I had been planning to pop one every couple of miles, like I had done in previous races). So when I think about my fuelling during the run, I had lots of carbs (gels and chews) but probably not enough sodium, so even though I tried to drink at every aid station I was probably dehydrated (especially given the liquid leaving my body at every portapottie) and not absorbing the carbs. It was a weird and troubling experience to feel as though I just couldn't get the energy to stay in my body - everything went straight through me and my marathon ended up being 1 hour 10 minutes slower than the open marathon I ran two months later.

You're welcome.

Bingo!

Carbs probably weren't going "through" you. Water was though, in absence of sodium. Which then limited ability/desire to consume carbs because of GI distress. (maybe a small amount of actual carb loss was present if lower GI distress was severe).

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Dr. Alex Harrison | Founder & CEO | Sport Physiology & Performance PhD
-------------------------------------------------------------------------------------------------------------------------------------------------
📱 Check out our app → Saturday: Pro Fuel & Hydration, a performance nutrition coach in your pocket.
Join us on YouTube → Saturday Morning | Ride & Run Faster and our growing Saturday User Hub