In this blog TrainerRoad copywriter @JesseFortson mentions that “For a long time, the standard advice has been 60-90g of carbs per hour using a 2:1 glucose to fructose ratio. However, research is emerging that shows that upwards of 140g/hr can be absorbed using a 1:1 ratio.”
Just out of curiosity, has anyone tried 140g per hour of a 1:1 ratio of gluco-fructo? Be interested to hear of any thoughts, experiences, etc.
Had 4 bananas and a drink mix within a hour workout, pretty sure that had me over the 140g of carbs. In mix form I don’t understand the fear (vs in food source it gets a lot)
Silly question is maltodextrin the same as glucose?
For the purpose of this discussion, yes (maltodextrin is a chain of glucose molecules, so is digested using the same pathway as glucose; because of its structure it can be absorbed more quickly than simple glucose).
Because it’s a chain, it’s absorbed slower than a single molecule of glucose. It has to be broken down first.
Here is a good article on the subject.
One of the greatest misconceptions is that simple sugars like glucose are absorbed into the blood too quickly, making it hard to balance energy needs for the duration of a marathon swim. Many athletes believe that since maltodextrin requires chemical modification before entering the blood it must be slower than glucose and provide more consistent long-term energy. This is actually not true.
I will ignore the marketing data provided by several companies and discuss the results of a Journal of Physiology article published in 1995 (Vist and Maughan). Here, the authors measured the rate at which food is emptied from the stomach to the intestines for a series of four liquid meals, all with the same volume (~20oz):
- 24g glucose feed;
- 24g maltodextrin feed;
- 113g glucose feed;
- 113 g maltodextrin feed.
The authors concluded that the more dilute feeds (24g) were emptied faster, and that maltodextrin was emptied faster than glucose at both concentrations (see chart)
Thanks for the reply. That doesn’t make sense to me if all is as it appears - would like read more about it. Where can I access the study?
The type of maltodextrin also plays a role.
Copied from Wikipedia:
Maltodextrins are classified by DE (dextrose equivalent) and have a DE between 3 and 20. The higher the DE value, the shorter the glucose chains, the higher the sweetness, the higher the solubility, and the lower heat resistance. Above DE 20, the European Union’s CN code calls it glucose syrup; at DE 10 or lower the customs CN code nomenclature classifies maltodextrins as dextrins
This is the study I guess? Only 9 pages long.
Here is the PubMed page. This Vist & Maughan study is cited often by other studies so I bet you can really dig in if you want.
Thanks - I’m interested to learn more about osmolality in here too, as I don’t have a great grasp of that at the moment. Concentration of solutions doesn’t seem to get discussed much. Will read it when I get a chance - thanks
@jwellford I had a read of the (PDF) review. So we can see that at high and low osmolality (concentrations of glucose/carbs in water) the glucose polymer solution, i.e. maltodextrin, emptied the stomach faster than the glucose solution.
So that’s the first half of the equation. Question is how fast are the two then absorbed into the blood stream once they reach the small intestine? (I’m assuming the process of ‘stomach clearance’ isn’t where the polymer is broken down, but I may be wrong). Have been looking for further studies on absorption to no avail so far.
Edit: found the sort of thing I was looking for:
…the enzymic digestion of MDs appears to take place at a high rate leading to an absorption rate not being different from absorption after ingestion of pure glucose, as reflected also by comparable post-ingestive insulin responses at rest and during exercise, as well as oxidation rates during exercise (Hawley et al., 1992; Wagenmakers et al., 1993; Jeukendrup, 2004). From https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4940893/
I still find it hard to understand that absorption speeds can be considered to be equivalent, considering more digestion is needed for a more complex polymer. And consider that’s a process that wouldn’t happen at all with pure glucose ingestion… although I haven’t had time to read the linked studies.
Surely a simpler sugar (or glucose) is a marginal gain in the small intestine, but that seems to be offset by increased stomach clearance (vs the polymer). Interesting!
I have 10kg of maltodextrin in the garage anyway, so the findings serve me well
Thanks for looking into that, I wondered about that half of the equation too. I figured that at the concentrations we’re aiming for (70g per bottle or so) gastric emptying would be the thing to optimize for, but I’m glad to hear that absorption into the blood stream isn’t negatively affected.
I’d assume for say 70g of malto in 600ml of water, the results for stomach clearance would be somewhere between the two concentrations shown on the graph in the review.
Next thing to think about, is ‘what’s the optimal concentration for stomach clearance’ with our usual CHO dosage. Should I further dilute my 60g glu/30g fru/750ml?
Obviously this has to be considered vs the capacity of a male bladder that at 34, already isn’t what it used to be
I just posted this on some other conversation and it applies here… I wake up early ass morning, drink some coffee, eat some Honey Nut Cheerios (dry) have a pouch of maple syrup and a bottle of fruit juice. That’s all for a 1-1.5 hour ride. It’s like 170g of carbs
Not sure glucose fructose ratio but it works and has been working so I don’t change it. My weight has been stable and I try to eat my most processed crap around or during my training on the bike.
That article is great thanks.
For the equivalency of absorption rate question, it’s all about the limiting step in getting glucose from the bottle to the muscles, and from my understanding that is the absorption step. The rate for MD breakdown by amylase (breaks down glucose polymers in your mouth and small intestines) and maltase (breaks maltose the product of amylase to glucose) is extremely fast relative to the absorption in the small intestine.
Overcoming the glucose absorption rate is the whole point of a glucose:fructose ratio, fructose uses a different absorption pathway circumventing the “traffic jam” at glucose absorption.
The use of MD just overcomes the problems with sweetness and osmolarity in your stomach. Drinking 90g of glucose is like suryp while MD is palatable.
I fuel with around 140g/hr of carbs for almost all of my workouts (I shoot to fuel with and replace every calorie burned at a 1:1 ratio -> 1000cal burned in a TR session? Eat 1000cal worth of carbs!). My recovery has improved by leaps and bounds. Keeps me from being hungry for the rest of the day. No weight gain associated with this for me (as long as the rest of my feeding throughout the day is in check, why would I gain weight??).
Anyways, +1 on my end, works for me!! Never felt better than I do now with this fueling strategy!
Yep. I usually do 120-150g per hour. My wife (63kg cyclist) typically targets 110-130g/hr.
I’m the author that @chad cited in this episode where >90g/hr fueling strategies were first brought up, I think.
Here’s the specific part of the discussion where they chat about my book and research.
Happy to answer questions here on the forum.
I’ve got a dozen other threads in my recent activity in my TR profile that you can review as well.
Thanks @Dr_Alex_Harrison, that’s really interesting. So, based on that, would you recommend 120g-150g of 1:1 malto-fructo for, say, a typical 60 minute sweet spot, tempo or threshold workout? Or would that be overkill?
Overkill for sure. Carb needs increase on a per hour basis, hourly. Confusing? This might help:
(table from my book below. I do make money on my book, in the fullest of disclosures)
Table of Intra-workout Carb Needs Per Hour of Training
Why does 6+ drop back down?