Glycogen is your main fuel source. Pretty much all of your energy for any effort above 70% vo2max will be predominantly derived from glycogen. You store 500g of carbs as glycogen typically, and only about 3-5g in the blood. Once glycogen depletes, you wont be able to perform intensity above 75% vo2max no matter how hard you try...thats the ‘bonk’, and the entire foundation behind race day nutrition

I would spend a week out consuming carbs to make sure your glycogen stores are full on race day, and consume ample carbs intra race to spare glycogen as much as possible.

Trainig on lower carbs to fuel aerobic efforts and strengthen the fat oxidation system is fine, but fats simply could never provide the energy needed for any reasonable degree of intensity. It is no secret that high carb diets lengthen the time to exhaustion dramatically

A high carb athlete with full glycogen stores will destroy a low carb athlete with no glycogen stores on race day, every time

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Strava

Not if they're fat adapted in full ketosis mode and fueling with bulletproof coffee and ketones.

OP, what do you mean that you have a hard time with carbs? Do you just get stomach issues? I'm by no means an expert at all, but I'm genuinely curious.

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@floathammerholdon | @partners_in_tri

No I am not doing ketosis or anything to that extreme I just find if I eat a lot of carbs particularly processed ones I feel lethargic and not well.

But there is the quandary is if I want to race on carbs and I think it is proven that that is optimal then I need to train with it. To train with it I don’t think I can not have it in my diet and every weekend or whenever I do a longer workout and slam the sugar and expect a good outcome.

Maybe I will just try that this weekend.

Have you tried using Skratch Labs? They are very strong on using “real” ingredients in their products. They don’t make gels, but they make powder and chews. They tend to be quite a bit easier on my stomach.

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@floathammerholdon | @partners_in_tri

Going high carb on race day only will not work
Saw a presentation of a sports dietitian on YT regarding this very topic (will try to find it for you), but the take away was that if you cut out carbs during training the body will also decrease the enzymes, etc to process and utilise those carbs meaning they wont be used come race day (as glycogen)

Edit Found it
https://www.youtube.com/watch?v=AJ1MFa2uvtA

The whole presentation is interesting but the section Im talking about starts at around the 1:22:30 mark

Yes I do not find anything really works. I can tolerate probably around 50g/ hr but then the absorption stops and the cramping and bloating starts.

I did read the study on this that basically said there are multiple ways to increase absorption including adding it to the diet. Need to find it and post it.

Now also what complicates this is I am a heavy sweater although I seem to have that figured out.

What carbohydrates are you eating, and how are they prepared, in which you feel lethargic? Many people eat ‘carbs’ but are not pure starches, like plain potatoes. They eat french fries, muffins, crackers for example...oil coated carbs essentially, which are quite different

You may very well simply not be used to carbohydrate consumption, and will need time to adapt. As another said, the body will adapt and shut off certain processes based on what it is receiving on a consistent basis. Gut flora plays a role here too, which is where bloating comes into play as bacteria ferment the sugars and release gas. The composition of flora changes with diet (if you dont eat beans, youll gtet a lot of gas when you do...)

A low carber will naturally have lower glycogen stores than a high carber, even when both fill their stores to full capacity. A high carber will be more tolerant and better absorb carbohydrates than someone who limits their exposure



Glycogen is a chain of glucose stored in the muscle and the first and dominant fuel source used in exercise as it is immediately available. Glucose in the blood must be transported into the cell where it can be used. Blood glucose can be used alongside glycogen to spare glycogen stores during exercise, and extend the duration of exercise.

This is why having full glycogen stores going into a race alongside a well tolerated carbohydrate consumption route intra race is vital for performance as it will extend the duration you can perform at higher intensities (and maintain rpe as glucose is needed for the central nervous sytem)

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Strava

Zach Bitter is an ultrarunner with a couple world records. He also eats mainly low carbohydrate. He has a great video series on how he periodizes his carbohydrate intake in parallel with his periodized training.

Phase 1: Rest and Low Intensity


Phase 2: Peak


Phase 3: Specified


Phase 4: Taper and Race


I followed his guidelines for a couple years while I ate low carb and was able to take in and digest high amounts of carb in races (100 g/hr or more).

Nowadays I'm eating all sorts of carbs (intermittent fasting with a couple of key supplements) and it's also been working really well for training. I feel as good as or better than during low carb, but now I get to eat homemade sourdough with my wife :)

One of my main takeaways is no matter what you do for nutrition, there's going to be a group of people who are totally on board and a group of people who think you're a total idiot. And there are scientific studies to support either side. Glad you've found a way to eat that works for you!

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Darren
https://www.strava.com/athletes/12385497

I'm low carb high fat diet and don't eat gels or energy drinks at all in training unless I am building to a race ultimately an Ironman. I have found the gels and energy drink powders that agree with me and I build them into my training the closer I get to a race. I like to use Vfuel gels which contain MCT oil and their energy drink mixed with Ucan as Tim O'donnell does. I have no real issue consuming high carb products but just prefer not to use them.

https://ucan.co/how-world-champion-triathlete-tim-odonnell-fuels-with-ucan/

Yes and no. I can see why one would think this though because it certainly does seem very mixed.

We should ask: studies to support either side doing what specifically?

There is absolutely a boatload of promising LCHF research.

But, regarding endurance sport performance enhancement, I think there is none.

I hope to be proven wrong with regard to my "no" here.

Here are some topics where I think there may be at least one study wherein LCHF diet has performed at least as well as other diet approaches:

1. Spare glycogen use during exercise.
2. Prevent hypoglycemia during exercise.
3. Improved blood sugar regulation among prediabetic and diabetic populations.
4. Performance enhancement in the forced absence of intra-workout carb-fueling.
5. Performance enhancement in the forced under-consumption of intra-workout carbs.
6. Reduced HR and RPE during long-duration submaximal exercise.
7. Weight loss.
8. Improved insulin sensitivity.
9. Hunger attenuation.
10. Diet adherence.
11. A dozen cellular and biochemical "mechanistic" changes that happen reliably during LCHF and point towards performance enhancement potential... but are not actually sport performance enhancement.

(Please note that I just took as "pro LCHF" of an approach as I can muster, in the above list. I am not advocating for LCHF diet approaches. In most cases I think the benefits, if any, are outweighed by the tradeoffs at play).

I have yet to see a single study that shows endurance sport performance enhancement via either Time To Exhaustion (TTE), Time Trial (TT), or any measurement of power output, is caused by chronic LCHF dieting, where the study has the following criteria:

1. Isocaloric HCLF & LCHF groups
2. A performance test that allows anywhere near optimal carb-centric intra-workout fueling during the warm-up, test effort, and any pre-fatiguing effort.

Please link the best studies you've seen in support of LCHF diets enhancing endurance performance. Help me out! I would love to review them. I don't think they exist. I'd love to be wrong. Mostly because if it works, I've got an ace in the hole that I haven't touched yet with my athletes and products. Help me be wrong.

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Dr. Alex Harrison | Founder & CEO | Sport Physiology & Performance PhD
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Maybe. I'm not sure. The research is so paltry at the higher end of carb consumption that it's non-existent with regard to a chronic LCHF diet paired with high carb race day fueling. Regardless of if answer is yes or no to first question, there appears some degree of certainty that there will be decreased ability to utilize exogenous carbs due to the chronic LCHF diet.

I'd start with more water + sodium alongside the 60+ g/hr carb intake if you're struggling with 50g/hr. I actually haven't found anyone who can't handle 60g/hr on the bike with sufficient water & sodium intake. On the run, GI tracts appear a bit more variable with regard to the lower end of tolerable limits.

By and large, the tolerable limit is almost always higher than people initially think. Some of that might be due to "gut training." I suspect most of it is due to poor strategy.

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Dr. Alex Harrison | Founder & CEO | Sport Physiology & Performance PhD
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First of all, I would say that there are many good answers already. Second, I can empathize with your troubles with carbs. I suffer from chronic IBS caused by "intolerance" to FODMAPs, which can cause me bloating and severe discomfort. Drastically reducing carbs from FODMAPs, and limiting carbs in general, relieves symptoms. To be honest, it also gives me a better feeling of well being and energy in my daily life.

However, applying this formula to endurance sport does bring challenges, especially for something like bike racing which inevitably involves high intensity efforts that ultimately require glycogen to support them... Your proposed solution of going high carb only for races probably won't work because your body loses the adaptations needed to utilise the carbs, as has already been stated. Somewhat related, this is why there has been increasing focus on the idea of periodised nutrition recently, where you try to combine benefits of low carb and high carb diets. I found this podcast with James Morton very good on this subject, where he explains that it is vital to keep regular medium carb and high carb days to maintain the ability to utilise them. The recent Fast Talk episode 150 with Asker Jeukendrup is also worth a listen.

On the flip side, if you can tolerate 50 g of carbs per hour when training or racing, from my perspective this is actually already pretty good. So, an alternative strategy to trying to push this higher is instead to leverage it as much as possible by improving capacity to perform on moderate carbs. For instance, threshold training before breakfast (a favourite of mine just should be done in moderation), or working on ways to stimulate/maximise glycogen storage pre-race.

thanks to all as this has been real helpful and confirms that I need to introduce some good carbs in race season which hopefully is now for me. BTW, here is the study I found discussing some of this. https://www.ncbi.nlm.nih.gov/...articles/PMC5371619/

I agree with this.

I've been extremely low carb (~50g day) for most of the last 8 years due to health (Type 1 diabetes), and having a 'carb up' day does little to nothing for me in terms of performance. I do however add some carbs, totalling 80-100g day during the specific training season (~12 weeks), I would do more if it wasnt the diabetes.

I do like abd recommend the approach of having a general low carb (say 80-100g), then from there you can either go even lower if the goal is weight loss or increased fat oxidation, or high higher ~150+ if the goal is performance

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--
Vinnie Santana, Multisport Coach
http://www.ironguides.net
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Search "Dr. Dan Plews"

You can argue with him, but you can't beat him.


-bobo

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"What's good for me ain't necessarily good for the weak-minded."

Ok spent roughly the last week with a higher carb diet that was mostly "healthy" carbs. Definitely not HCLF by any means but just adding in more carbs. I did not measure the amount as well life is just to short.

In any case I did a race simulation workout brick yesterday targeting around 100G/hr carb intake using a mix of Maurten gels and the Dr Harrison mix of Gatorade and kool-aid amounts of sugar.

I felt great during the bike with no stomach issues and the run which was warmer but only a few miles was great as well. We will see how this works in a real race and especially in the heat as I would probably adjust down a bit as I took in a lot of water and sodium in a 70 degree semi low humidity day.

But holy moly is that amount of sugar sweet!! I mixed 3/4 cup of sugar and 2 scoops of Gatorade endurance in a 24oz bottle and sipped on it every 10 mins or so.

It's been a while since I delved into the literature, but your post mostly matches what I found. Given that there weren't/aren't any trials assessing the way many serious endurance athletes actually implement LCHF (months of adaptation, not weeks; actual low carb, not reducing from 60% to 30%; strategic carb cycling; events upwards of 8 hours, not 20 minute high intensity cycling to failure, etc), the scientific evidence I alluded to is the laundry list of benefits you gave.
I don't think anyone is claiming that LC will increase power in a TT. But at the very least, points 1 and 6 from your list could be considered evidence in support for an ultra-distance runner or triathlete.

Tldr; no direct studies showing ironman performance improvements due to LCHF. In absence of such studies, many studies showing effects (such as glycogen sparing, increased fat oxidstion, lower HR) that could be extrapolated to improved ultra distance performance.

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Darren
https://www.strava.com/athletes/12385497

I would agree IF there was any evidence that 1 & 6 carried over to greater performance. But the glycogen sparing doesn't confer increased performance. Just reduced performance and slower use of glycogen to do it. And lower RPE and HR, while ironically not increasing performance.

There have been studies that do implement very low-carb approaches akin to what real endurance athletes do.

Louise Burke's 2020 paper is excellent. If you're not familiar she's been studying LCHF for the last 20 years and was at one time a proponent of it, or at least optimistic of its utility.

2020 paper TLDR: the cellular adaptations don't tend to increase further with longer-term use of LCHF and so the "chronologically longer studies needed" is incorrect. And they've examined diets that aren't just "reduced carbs" and have had folks fully ketogenic.

I think this may become one of the dead horses I beat to a pulp in my career: The "mechanism, therefore application" approach has gotten some of the best sport science researchers and practitioners of all time in lots of hot water. In fact, it's probably the most common way that otherwise trustworthy, well-read, and intelligent sport scientists find themselves making claims that are later proven erroneous.

I am guilty as charged. I have done the same.

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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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Funny you mention him. I recently got invited to debate him, and accepted. Smart guy. Super talented. I look forward to the discussion if it happens.

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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

Fair enough, I'm not a sport scientist, except in the loosest of terms (n=1 experiments on myself, beset on all sides by confounding variables). Actually did my undergrad in applied physics, where "mechanism, therefore application" is what the entire field rests upon, so it's where my brain defaults. But thanks for the reminder that that's not necessarily how physiology works.

I've stopped spending quite so much time thinking about nutrition and instead started spending a lot more time training. Maybe once I've gotten close to my potential I'll dive back into this. But for now, most of my additional speed is going to come from more SBR, not macro counting :)

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Darren
https://www.strava.com/athletes/12385497

The best kind!!


Likewise. Less time in office chair >> optimized nutrition (or even training methodology) for me.

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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

I can only speak for myself, but I struggle with high carbohydrate intake over an extended period of time (IM distance) in hot/humid conditions. Before my last hot/humid IM, I went keto (~90% calories from fat) for about 9 months. I wasn't very scientific about it, but the goal was to simply train my body to burn fat for fuel and require less calories on race day. Normally I would consume about 400 cal/hr for an IM once on the bike. For this latest IM, I consumed ~150cal/hr, which was even less than I planned due to a lost bottle on the bike. The run wasn't perfect, but I avoided the dreaded GI issues that hampered me in these long, hot, humid races. My point is that you may be able to train your body to not need the high carb intake on race day if it has historically been an issue for you. On 5 hour training rides that would normally call for 2000 calories, I was putting out equivalent effort with about 500 calories. Those rides would involve up to 90 minutes at 90%FTP. It was obvious to me that I had effectively trained my body to burn fat for fuel.

If improved performance in long course triathlons means more consistency and less GI issues for you, then an LCHF diet could get you there. Better race day nutritional options could also be an answer, but I just couldn't find anything that worked in the extreme conditions.

I feel like you are on the same path I was only this year I am hopeful will be my first Ironman but in multiple 70.3 most of which in hot weather i hear you. I had/have the same problem as I either get bloated or worse by historically my stomach shutting down so my solution was just go with out fuel. Like you i found this works and I can stay sub threshold and not bonk which i have proven to myself over multiple races. The thing that got me back on the carb/fuel journey is 2 things.
1) I cannot find a competitive athlete at the elite or sub elite level that follows not fueling during an event.
2) While i did not bonk in my races the RPE during the event did go up.....i thought it was just fatigue causing me to slow down but looking at data my HR goes down with Pace towards the end which tells me it is RPE and not fatigue on its own.

So back on the fuel train to try and figure this out. I get to practice this hopefully at Texas 70.3 but the plan is to drink-drink-drink with sodium and simple carbs split between the Maurten gels and Dr Alex's super fuel mix on the bike. The run I will take in less and undecided on strategy although Coke on the last loop just always seems to work. Will do another test this weekend in prep.