Interesting study. Points to 1:1 glucose:fructose ratio being pretty close to optimal. I suspect more will soon as well.

Fructose-Glucose Composite Carbohydrates and Endurance Performance: Critical Review and Future Perspectives

From that article:



Another interesting one:
Review: Glucose Plus Fructose Ingestion for Post-Exercise Recovery - Greater than the Sum of Its Parts?
From that article:


And another one pointing to utility of very high mixed sugar carbo oxidation rates as exercise exceeds 2 hrs:
Fructose and Sucrose Intake Increases Exogenous Carboydrate Oxidation During Exercise

From that article:

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https://www.semanticscholar.org/paper/Sports-Drink-Intake-Pattern-Affects-Exogenous-Mears-Boxer/42ffc8642ff5af57f2d047f363356fdcbb9efa9f
Key point to OP: Fueling every 5 or every 20 minutes appears okay while running, at least while only targeting only 100g carbs per hour and 1L of fluid per hour.

My comments here may be helpful too.

This forum is awesome and I feel like I'm finally with my people! Except... globally...please all start consuming more during training. You all might be faster. You'll almost certainly never have to feel like you "want a pepsi" during training.

If you are hungry or craving something specific during racing or training, you are WAY behind your intra-workout fueling and as far as your performance is concerned, it is an emergency.

Here is why it's an emergency:
Imagine being in a haunted house and having just been scared so much you jumped and your skin tingled. I doubt your next thought was, “I’m hungry.” Hunger was the last thing on your mind because the body has advanced cellular and hormone signaling that is designed to strongly inhibit hunger during times of “fight or flight.”
The strongest of which is epinephrine.

Epinephrine is also released during exercise because it is responsible for many of the cellular cascades resulting in energy availability.

If you sense hunger during prolonged exercise, it is because your hunger signals are so overwhelmingly strong that they have overpowered the extraordinarily strong hunger-inhibiting effect of epinephrine.

This only happens when you are lightyears behind on intra-workout fueling.

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Thanks for that, it's a truly super answer and one I appreciate you taking the time to post.

One of the responses I've read a lot is "it depend on my pace....if it's easy I'll go 2-3without fuelling, but pushing harder maybe a bit of food".

Is there any difference in the amount of fuel to take on board dependent on exertion? Or is it more a case of just load up because it takes a long time to get into the body?

I think the takeway from this for me is to fuel my runs for better activity and recovery.

My pleasure.


Short answer: Not necessarily, sometimes yes, but not as much of a difference between nutrition for hard vs. easy efforts as in the oft-cited all-or-nothing approach.

Longer Answer: If the run effort is easy, you can get away with not fueling better. Your HR and RPE will still be higher, per pace.

If the run is harder always fuel maximally for maximum performance.

You're just more likely to personally notice the consequences of not fueling adequately which is where this recommendation comes from.

Increased RPE is a lot more noticeable when moving from an 8 to a 9 RPE as compared to moving from a 4 to a 5 RPE.

The only good reasons not to fuel longer easy activities:

1. Efficiency. ie. your time is more valuable than your performance long-term.
2. Need for fat loss and you've already stripped out kcal from the rest of your day, so the easiest way to pull daily kcal lower is to short intra-workout fuel by 25-50%. Double-edge sword alert! Hypoglycemia is strongly hunger-promoting and strong hunger doesn't bode well for daily kcal deficit adherence!

The only good reasons not to fuel longer not-easy activities:

1. Efficiency. ie. time more valuable than performance.

Biggest negatives of not fueling easy long runs:

1. Lost opportunity to train gut to intake higher carb amounts in racing, which would otherwise be performance-enhancing.
2. Easy runs are no longer as easy on your body as they were supposed to be.
3. Decreased ability to utilize either endogenous or exogenous carbs in future. (ie. you get what you train for, carb burning, or fat burning in absence of carbs. Can't have both, and carb burning for performance wins.)
4. Muscle loss.

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Again many thanks, fascinating response, its great to have someone with passion and expertise talk about this.

If there is this science backing up constant fuelling, why aren't more people doing it? Is this new thinking or are people just stuck 20years ago with their sportscience? Somebody on another forum told me to read Noakes Lore of Running which is 35years old, is it just a case of it takes along time to filter into popular consciousness?

Agreed. Folks are just running calculated tradeoffs too. It takes some input of personal time and energy to fuel well. If you've got a spouse who wants to spend time with you or a job/business that is pulling at you, and you CAN run your long run with just a bit more fatigue without carbs... well, I do that all the time! Not optimal at all, but optimal for life happiness and financial well-being given the time-cost for sure. ;)

The performance improvement and RPE and HR reduction is quantifiable, even within-session. Just small effect within session. Almost certainly would be quantifiable in a more meaningful performance way if studied long-term. Feasibility of long-term study for something like this is.... challenging, to say the least, from a poor researcher's perspective.

NIH doesn't give grants to optimize the pointy end of endurance performance. They give grants to research prevent diabetes... which just exercising more is fine for! Sport nutrition research grants' dollar figures are <<1% of common NIH grants. I'll be impressed with the resolve of any researcher who chooses to study the even medium-term training adaptation effects of higher carb fueling.




You're very welcome. I'd love to spur some change.

There have been other areas where a certain piece of info becomes "common sense" before it's actually been well-tested. Low-rest hypertrophy training was touted as the gold standard in muscle building for a long time because of a (meaninglessly transient) bump in testosterone after performing such a lifting strategy. The testosterone bump does indeed exist. Just not sufficiently to merit low rest intervals in the weight room all the time for maximizing muscle growth. When weighing all thing tradeoffs it becomes infinitely clear that longer rest between weight room sets is better for strength and muscularity, long-term. But that took almost 15 years of a few sport scientists like me shouting from the rooftops to overcome because the low-rest recommendation had made it to the textbook level... primarily because the leader of the low-rest movement had written a book on it, and was also head of the NSCA at the time, the publisher of the main strength and conditioning textbook used in all college courses on the topic.

The current sticking points in exercise fueling nutrition dogma vs. science and press, as I see it:

1. A few leading researchers who first discovered that 90g carbs of multiple sugar sources was better than 60g/hr, got their work into every nutrition journal's position stand, subsequently into all the textbooks, and then amplified by every nutrition certifying agency and supplement company who seized the opportunity to sell more sugar when "90" became the new "60." Now 60 & 90g/hr are cited, rote, with no further thought.
   
   
2. Primary reasons researchers don't question the 90g/hr:


1. There was a single study that found that 30g/hr of fructose was the limit for fructose absorption during exercise. Turns out, fructose by itself is not absorbed well. When it's consumed with a glucose source, fructose absorption can far exceed 30g/hr, and I suspect may approach 80-90g/hr in a very well-trained gut.
2. 60g/hr glucose, in isolation also appears to be a bit of a hard limit before GI distress results. I think this may bump up closer to 70-75g/hr in well-trained guts, of regular exercisers, when consumed with fructose
3. The above two facts are probably recent to within the last 10 years or so, and most of my colleagues who I would consider experts in general sport nutrition, but not endurance nutrition, are surprised to learn of it when I point it out to them.
4. Most sport science researchers are young. They are within 10 yrs of having graduated with MS or PhD. Folks gravitate towards more complex and more clinical questions as they age as researchers. 60 & 90g/hr is the dogma taught in virtually all undergraduate and masters nutrition, dietetics, and exercise science programs, even some leading sport science programs. I don't blame them. Endurance nutrition is a bit of a niche and unless you've experienced suffering during long
5. Most studies only examine 1.0-2.5-hour exercise tests with maybe 3 hours being as long as any research has time to study. The difference between 90 and 130 grams of carbs per hour is likely amplified only beyond about 3 hours. It's very hard to carry out studies that involve 4-hr time or 5-hr time trials. No one has time or interest in killing themselves for 4 hrs multiple times for science because it interrupts their training process. Even fewer (none) researchers want to carry that out because of the time-cost involved!
   
   
3. Primary reasons lay-people and athletes don't question the 90g/hr:


1. Most folks can't even figure out how to do 90g/hr because they're messing up osmolality and hydration needs. Gotta have hydration, and with fluid you gotta have sodium. Miss out on sodium and you're going to get sweet aversion and performance-relevant hyponatremia and avoid the 90g/hr. Miss out on fluid and you're going to get gut cramps or worse downstream GI effects, from even 90g/hr. Lots of folks report "a gel doesn't sit well with me" because they don't drink water with it. Most folks could take 3 gels at a time with 16-20oz water on an empty stomach in the middle of a hard session and fair okay. They fail to do the water with it. When there are so many hurdles that are lost on the average person, it's easy to believe that 90 is the top when there appears to be mountainous social proof that corroborates.
2. The fat adaptation movement which I hope has been quashed has intensified any subconscious thought that maybe less carbs is better and so I don't always need to train with them because there may be a benefit. There is not. See my other recent posts for more there.
3. Most folks don't train more than 2-3-hr sessions where you CAN get by on less. If you're routinely doing 4-6-hr sessions or racing 4+ hrs, there will be noticeable difference in performance. This makes basically ultra-runners, P/1/2 cyclists, and 70.3 & 140.6 triathletes the only folks who are ever likely to investigate enough personally, to notice a difference.

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Here's my very niche n=1 story:
After doing tri for 11+ years and LD for 9 of them I was diagnosed with (late onset) Type I Diabetes last fall.

Since then I am wearing a continuous glucose monitoring device and have been able to monitor my current blood glucose level at all times. Obviously this has been very interesting, especially during workouts (I have a data-field on my garmin for that).
Knowing what I know, It is of no surprise to me that this very technology is beginning to get traction in performance application in elite athletes (e.g. jumbo-Visma).

Clearly my primary focus is managing my diabetes and still being able to do tri competitively.
Also my metabolic system is no longer fully comparable to that of somebody with a functioning pancreas.

That being said, I made a couple of observations:

• I usually have a sharp drop in blood sugar in the first ~30 minutes of exercise (probably diabetes related and not relevant to y'all)
• For Z1/2 endurance workouts like the long run, it then stabilizes usually just below the "normal" level of 100 mg/dL (5.6 mmol/L) without any fueling
• Then however it ever so slowly and steadily starts declining so that within an hour at the latest I am seeing and feeling low blood sugar
• That's why i started to always run with a 140ml gel-flask and fuel pretty much from the beginning (unless I had a snack just before the run).
  (In contrast: In the past I followed the boosting fat metabolism idea and would only have maybe one or two gels if I felt hungry/bonkish 2 hrs in.)
• As a consequence
  


• my long-runs feel much better,
  
• I can hold better technique for the full duration
  
• I am not as wasted afterwards.
• pace-to-heartrate ratio is getting better (see graph below)
  
  
  
• If I fuel till the end of the workout, my blood sugar starts rising pretty sharply after I stop running


• I need to be weary of this and correct with insulin,
  
• But I guess for the healthy person it means that your in-workout fuel will also "be there" for you for recovery after the workout.
  

In terms of what goes in my gel-flask i am still experimenting with various mixes of maltodextrin, fructose and dextrose with some citric acid and coke-flavour sirup for taste.
Going by the info in this thread I should apparently be looking into getting to a 1:1 Dextrose:Fructose ratio...

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if you can read this
YOU'RE DRAFTING!

This is a fantastic case study. Thank you for sharing. Most of it is highly relevant to folks without Type 1 diabetes.
The sharp drop in first 30min is relevant and probably common among folks with no diabetes. Probably related to GLUT4 translocation, but maybe other things too. https://journals.physiology.org/...2/ajpendo.00503.2020

This is actually all quite relevant and standard physiology for folks without Type 1 diabetes. I have suspected for a while, though I have no data on it other than yours, that during exercise is the time that folks with Type 1 diabetes metabolism tends to look most like the metabolism of folks without Type 1 diabetes. Just hasn't been a focus of my research yet. I may ask my wife who is an RD, triathlete/cyclist, and diabetes-interested.
100% correct. This is where your physiology starts to differ a bit from other folks who probably wouldn't have quite as steep of a rise or need to correct with insulin. My wife has often joked that there is a performance-enhancing opportunity for endurance athletes with Type 1 Diabetes if they're smart. (ie. pack in carbs for recovery faster.) Please take this as purely academic discussion and chat with your physician! I am not a medical doctor. :)

Yep, definitely closer to 1:1 than 2:1.


Sugar ratio change implications, during exercise: If you go to more optimal sugar ratios, absorption rate can be increased, which may elevate blood sugar marginally during training (a good thing), but also makes intaking the sugars at a higher rate per hour more optimal because there is less measured titration of the sugar from GI tract to bloodstream. For folks without Type 1 diabetes, and I suspect for you too, this means that if you were to NOT increase from your current consumption rate intra-workout, you may experience slight sugar crashes if there are 20-30min gaps between consumption. Recommendation: consume more. Consume steadily.

Sugar ratio change implications, after exercise: For you specifically, this may also merit closer monitoring of blood sugar rise post-workout until you have done further experimentation.

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Dr. Alex Harrison | Founder & CEO | Sport Physiology & Performance PhD
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Wow I have been doing a base training cycle and bumped up my mileage the past 12 weeks into the 60 mpw range which means (with all easy running) I've been doing multiple 2+ hour runs per week. The only intensity in them has been strides and/or some short fartleks. Right now I just take a few swigs of water every 30 minutes. After reading through this thread I guess I should start looking into taking in some carbs especially as I move toward 3 hour runs and begin working some longer periods of intensity in. I've never done this kind of mileage before and didn't really think about fueling at all (I do usually eat some carbs before I head out on my run though so maybe that has been enough). Thanks for sharing your knowledge!

Why does the g/hr recommendation reduce back to 90 for workouts greater than 6 hours? As an ironman athlete, how should that effect my nutrition plan. I thought the goal would be to take in as many grams of carbs as your gut can handle.

This is just anecdotal but I think there's a couple reasons runners in particular don't fuel their workouts as much as triathletes or endurance-oriented cyclists.


1. Distance- For non-ulta runners, a 90-120 min run is a "long run." Even if you run that hard, you can generally just consume some fluid and maybe a gel or some drink mix and be ok at the end. You may deplete your glycogen stores, but are less likely to bonk while actually running (and your glycogen will replenish before your next workout, so you may not know how far you've depleted your glycogen).

Now compare that to a 4+ hour triathlon or cycling event, and there's no way you can go that long without fueling unless you're fat adapted or performing at a very low intensity. Ultra runner get this- look at what they eat during 50-100 mile races. Candy, chips, pizza, literally anything and everything they can stomach. But someone running at most 2 hours will never be in the same boat as someone hour 4 into a long event.


2. Ability to fuel- It's a lot harder to fuel when running than cycling- harder to carry food/nutrition, and harder on the body to absorb. I can eat and drink pretty much anything at the bike, but once I start running at threshold, I can only tolerate little bits of liquid before I become prone to stitching (especially on hilly courses, running hard downhill really gets me if there's anything in my stomach).

To that tune, I would argue it's performance maximizing to not fuel short races. A 5k or 10k isn't going to be faster if you take a gel during, and if you're on the limit, you're more likely to risk gut distress than anything. Due to my issues with stitching above, I don't fuel any run <90 mins except with a couple sips of water/gatorade at aid stations (more water plus salt tabs if it's hot). I would actually prefer to be slightly hungry at the start of a really hard run because I know there's nothing in my stomach to cause issues (I know that's contrary to the science, but I've run my best races this year across every distance with this approach). Meanwhile I would rather start long cycling races slightly full because I don't have distress fueling on the bike.

Great question: hydration becomes so critically important for longer events that it trumps optimal fueling needs. Consuming 120g/hr sometimes marginally slows gastric emptying and ability to hydrate. If you know for sure that you're able to maintain 99% of your body weight during very long sessions via adequate fluid and sodium intake, then you can certainly continue to push the higher rates of consumption. Best way to find out. Try it. If you don't get gut cramps or GI issues doing >100g/hr in an 8-12hr event, then by all means increase carb consumption rate to 110 or 120g/hr and give it a go. Could also taper carb consumption rate throughout the event from something like 120-140g/hr at the outset down to 80-100g/hr when gut issues start to sneak up on you. The more practice the better, obviously.

In all honesty, I'll probably update that when I write v2 of the book. I think it can be pushed to 120 or 130 if in cooler temps or for a person who is a very limited sweater. Book was written a couple years ago. v2 is a couple years away. Other projects in the works first!

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Agreed on all.

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Good question, and a common one!

Once fitness is sufficient to burn 600+ kcal per hour, as you mention, I see very little reason to fall below recommended values. Gut tolerance should be your only determining factor. Fuel maximally, within that.

Gut tolerance is minimally related to bodyweight, fyi.

My wife weighs 63kg roughly, and frequently consumes 100-135g/hr on the bike, and 80-100g/hr on the run. For her, I'm not convinced there's much benefit over 80g/hr running, because of gut issues. On the bike though, we've yet to find a tolerance upper limit or utility upper limit. The more the better, in her case.

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Thank you- this is all very helpful. I have a couple months training left and I will experiment to see if I can increase my intake to at least the recommended amount without putting too much stress on my gut.

Kipchoge says you should only run for 1:59

OK all kidding aside lots of great advice on this thread. But I would say more people should be more worried about weekly aggregate mileage than with length of long run. 100km run with with a 2 hrs long run is likely going to be much better than 60km run week with a 3 hrs long run. Mileage is king, long run is less important if you have mileage to handle your race day.

in the 1980s, after the Leppin Squeezy came out as the first gel (based on Dr Tim Noakes research), I used to run with a chemist developing a competitor gel. His research showed a mix of glucose/fructose was more effectively absorbed than either alone. I'm not sure what happened to that product or if it even made it to market..

Arthur Newton was a great ultrarunner in the early 20th century. He developed the 'corpse reviver', a mixture of lemonade, bicarb, sugar and salt, for his long training runs for Comrades marathon (about 55 miles).
Turned out the mixture was isotonic and well absorbed..

--
We're forgetting-machines. Men are things that think a little but chiefly forget. That's what we are.
- Henri Barbusse

Gold quote.

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Completely agree,m winter and spring for me are all about metabolic efficiency and fat adaptation, plus high quality real food (and usually some fat loss). Close to race season, it's all about training the gut to absorb simple sugars under stress/duress/race intensity, so i definitely start to mimic race fueling strategy in training.