First for some context on why this rabbit hole has been the obsession of the last few weeks. If you want to go straight to the technical details, just skip down to the “glucose” title.

WHY CARE ABOUT CARBS, ENDURANCE SPORT EDITION

I’ve recently gone on a manhunt for the most ideal usage of carbohydrates, mostly thanks to Liam Messam #teamstrom beginning his training for the 2025 Iron Man. Being an intensive long duration endurance event, well managed glucose and glycogen levels, and hence carbohydrate intake, will be a high priority.

The considerations and stakes for endurance sporting is much higher than for our bodybuilding or powerlifting athletes, both of which only engage in short-medium periods of activity and can include plenty of rest time, and less stomach jiggling that makes liquid and whole food carb forms practical enough. However in the case of endurance events an athlete may carry multiple hours of fuel on them and only a limited water supply - then replenishing that at aid stations. Stating the obvious for those not yet immersed in that field. This unique condition is presumably how the market for gel carbohydrate products came about, being easily transportable and high carb yield per gram.

Liam initially received a care package of a good number of gels from a reputable brand who sponsors the in NZ Ironman, my first thoughts was “great that’s sorted! I’ll leave that to them!”… this foolishness was quickly crushed upon seeing the ingredient panel. There won’t be any call outs of product or brand here, but just know it’s a fairly standard formulation for the endurance carb gel market. The carbohydrate source was entirely maltodextrin, proudly touted to be a rapidly digesting carb to quickly replenish glucose levels. And while this is true, there’s clearly some lack of critical planning involved in this “replenish your glucose super fast!” narrative. And a gross oversight of the value of the fructose system.

For starters, if an endurance athlete is planning and executing their fueling right, they shouldn’t be planning for a low blood glucose state, but rather keeping a stable elevated level.

Planning to choke down rapid glucose sources for 12 hours or more, while running or cycling, is clearly a bad idea. Although apparently not so clear for the majority of persons doing the sports. Every dose would promote new rollercoaster spike of glucose and insulin for the body to attempt to manage. With such frequency of spiking, and then potential crashing being a short path to insulin insensitivity and inflamed gut conditions. With these two significant downsides, whatever fueling you do will be significantly less effective regardless of source. It will also increase risk of gut distress, of which is a significant and hopefully obvious compromise to performance.

Diagram below provides a visual example of the effect of rate of uptake of glucose on blood glucose and insulin level. Now of course the ethos encouraged by the manufacturers of fast acting carb gels will encourage you to use them every 20-30 minutes, therefore forcing off the glucose crash (below original levels) for later. The issue with this is if you miss time a dose for any reason, a greater risk of crashing will occur, as compared to the medium or low glycemic loading approach. It also directs most of the digestion and transporting stress to the upper section of the small intestine, increasing damage to that area and underutilising the full small intestine capacity. Faster is not inherently better if not sustainable, especially in a competition of endurance.

Mens Sana in Corpore Sano: Does the Glycemic Index Have a Role to Play? - Scientific Figure on ResearchGate. Available from: https://www.researchgate.net/figure/Schematic-diagram-of-the-influence-of-GI-or-GL-on-blood-glucose-left-axis-or-insulin_fig1_344584616 [accessed 10 Jul, 2024]

To propose an ideal: Keep blood sugar shifts steady with lower GI sources, and if a low glucose case arises then (perhaps) bring in the quick sources as a rapid recovery for performance reasons.

This is a concept well understood in the evidence based bodybuilding community for over a decade. With such outdated thinking as the mainstream endurance narrative, no wonder so many athletes are going to the opposite extreme of Keto. That’s a clear swing response and we won’t go there. Instead the goal being to utilise a slow release carb source that both keeps Liam in an ideal blood glucose, and glycogen range, as well as reducing insulin system stress. All while encouraging the highest amount of endogenous fat oxidation as possible while still fueling carbohydrates optimally.

Obviously we wouldn’t leave Liam to be fueling like every other sucker at the race, lured in to suboptimal product with a company sponsored “Iron Man Approved” care package. It was time for some serious R&D to make to ultimate Strom endurance athlete fuel.

In fact we’re a good way into that process at the time of writing this, with Shawn slaving away whipping up various combinations to my every whim. What a loyal slave, it’s a shame he’ll never be fully rewarded for his efforts. But that’s a conversation for another day. Below is my personal summaries and quick reference guide for the main sources of carbohydrates you’ll see in performance supplements today.

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POPULAR CARBOHYDRATE SOURCES

GI is a metric for rate of glucose uptake into circulation, using glucose itself as the reference at a GI of 100. Higher GI compounds will have faster glucose uptake, lower GI having slower.

Osmolality

Osmolality is the number of soluble particles per volume of solution.

This derives how much osmotic pressure the liquid has. Isotonic (300±10 % mOsmol/kg) means the same pressure as human blood, which allows for accelerated uptake of nutrients.

GLUCOSE

Glucose is the most common C6H12O6 simple sugar (monosaccharide) unit.

When ingesting glucose it has a high osmolarity yielding a 300±10 % mOsmol/kg at just 6 grams per 100ml. This means relatively low doses will delay gastric emptying (time in the stomach). However because it requires no digestion, when it reaches the small intestine will be taken up rapidly (GI: 100) by SGT1 and GLUT2 transporters (primarily), at rates between 1.2-1.7g/min, subject to individual variance.

Excessive intake will result in glucose passing into the large intestine which an cause various inflammatory effects, as well as compromised gut bacteria populations.

Glucose is a relatively cheap ingredient, generally derived from corn.

FRUCTOSE

Fructose is also a C6H12O6 simple sugar the same as glucose, but has a structurally different arrangement.

The functional group being a ketone, while glucose’s having an aldehyde. As such they are used by the body in different manners to obtain ATP, but both are useful to do so. Because fructose needs to be broken down by fructokinase, aldolase B, and triokinase in the liver first, the rate at which fructose will elevate blood glucose is relatively low compared to glucose, with a GI of 23.

Fructose is generally accepted to be well absorbed in the the range of up to 30g per hour, 0.5g per minute. But only 20% of individuals tolerating doses of 50g as a single bolus, in one trial. This lower limit can make it easier to overdose. Excessive intake will result in fructose passing into the large intestine which an cause various inflammatory effects, as well as compromised gut bacteria populations, much like glucose.

Primary fructose transporters are GLUT2 and GLUT5, however GLUT2 has stronger affinity for glucose and so in higher glucose to fructose ratios there may be compromised fructose uptake. There is some indication that the sucrase-isomaltase complex may facilitate uptake of fructose when in the presence of glucose, as demonstrated with increased fructose uptake when dosed alongside glucose, and decreases when sucrase-isomaltase is inhibited. Hence some glucose is good to pair with fructose for optimal absorption… just not too much.

Fructose is a relatively cheap ingredient, often extracted from corn.

SUCROSE

Sucrose, often known as table sugar, is a disaccharide with one glucose and one fructose bonded together at α-(1→2) [see the diagram below].

This means the bond must first be hydrolysed (broken) before the glucose and fructose is free for uptake into circulation. Because the bond is relatively weak, most individuals will rapidly digest sucrose into it’s glucose and fructose components as soon as reaches the small intestine. Hence it’s GI is mostly a reflection of an averaging between glucose and fructose, that being a GI of 65. Sucrose is hydrolysed by the sucrase-isomaltase intestinal membrane associated α-glucosidase, both cleaving the α-(1→2) bond and then transporting the glucose and fructose molecules across the the brush border membrane (ie. the gut wall). The current consensus is that sucrose is absorbable at up to 1g/minute, however I have yet to find the source of the claims origin.

Sucrose effect on osmolality is only marginally better than that of glucose, with just 9g per 100ml to reach 300±10 % mOsmol/kg.

Sucrose is a relatively cheap ingredient, often sourced from sugar cane or sugar beet.

DEXTRINS

Dextrin is a generic term for any series of glucose molecules linked together with α(1→4) bonds (in a line like a chain) and/or α-(1→6) bonds (branched between chains). These must then be broken by α-amylase and maltase to free the glucose for absorption through the small intestine. Those with weaker bonding points α(1→4) will absorb quickly, and hence raise blood glucose more quickly, stronger α(1→6) bonds less quickly. Hence within the dextrin family we can have both slowly digested (low GI) carbohydrates, as well as fast digesting (high GI) carbohydrates. As you will see below.

MALTODEXTRIN

Maltodextrin is a dextrin between 3 and 17 glucose units long, primarily linked with α(1→4) bonds, but also may contain some α(1→6) branching bonds. At one point maltodextrin was advertised to be a slower digesting carbohydrate than glucose due to it’s more complex structure. However due to the rapid rate at which α(1→4) bonds are digested by α-amylase and maltase in the upper small intestine, it tends to increase blood glucose at a similar rate to simple glucose delivered in monosaccharide form, using the same SGT1, GLUT2 transporters once free. As a homopolysaccharide of glucose that is rapidly broken to free form, the capacity for absorption is about equal to free glucose uptake between 1.2 - 1.7g/min.

Maltodextrin does have the product development advantage of lower sweetness than glucose, as well as properties that are useful for gel product applications. It also has a lower osmolality influence, allowing for approximately 18g/100ml simple maltodextrins to achieve isotonic 300±10 % mOsmol/kg, that’s three times the energy value of free glucose.

Maltodextrin is a relatively cheap ingredient, sourced from corn.

CLUSTER DEXTRIN™, OR HBCD

Cluster Dextrin™, or Highly Branched Cluster Dextrin’s (HBCD) are a new type of dextrin that is produced from cornstarch derived amylopectin. A “branching” enzyme is used on the amylopectin to break the α(1→4) glucose bonds, and create new α(1→6) bonds to create a branched cyclical structure. This slows rate of digestion, keeping in mind α(1→6) bonds take longer to break. This results in a 60-70 glucose unit branched cyclical structure - one which is now one of the most popular forms of “fancy” supplemented carbohydrates. The two main points going for it compared to other dextrins is the high number of glucose units, that are also highly branched making it slower digesting releasing the glucose for uptake into circulation slowly, hence the lower GI of 32. Like maltodextrin it also has a lower sweetness profile that makes it favorable for loading high doses into intraworkout products while maintaining favorable palatability.

HBCD has an extremely low osmolality contribution, with 10g/100ml contributing just 9 mOsm, much less than maltodextrin or the simple sugars.

Cluster Dextrin™ itself is just a Glico Nutrition Co. trademarked HBCD, meaning you can have greater assurance that the quality is according to what research has been demonstrated with Cluster Dextrin™ interventions. Quality variables would include the number of glucose units per molecule, and the ratio of α(1→4) to α(1→6) bonds.

HBCD is a relatively expensive ingredient due to the additional processing required compared to other corn sourced carbohydrates.

PALATINOSE™, OR ISOMALTULOSE

Palatinose™, or Isomaltulose, is a form of naturally occurring disaccharide made up of one glucose and one fructose, similar to sucrose. In fact, Palatinose™ is manufactured from sugar beets, first processing them down to sucrose, then re-arranging the glucose and fructose bond by an enzymic process. Sucrose is bonded with a α-(1→2) link which is relatively easy to break, isomaltulose is a restructured to be bonded with a α-(1→6) link, of which is broken by hydrolysis at approximately 20% of the rate of sucrose. This makes for a more sustained release of glucose and fructose, GI of 32, for uptake throughout the small intestine, rather than the quick release that occurs with sucrose (GI: 67).

Like HBCD, The flavour of isomaltulose is also altered, having a mild, natural sweetness approximately 50% of that of sucrose but similar in profile. Isomaltulose effect on osmolality is only marginally better than that of glucose, the same as sucrose at approximately 9g per 100ml to reach 300±10 % mOsmol/kg, hence rapid gastric emptying rate is not as easy to achieve as the dextrins.

Isomaltulose has been used within foods in Japan since 1985, primarily for it’s improved glycemic response, but also due to other food stability properties such as improved shelf life.

Palatinose™ itself is just a Beneo Gmbh trademarked isomaltulose, meaning you can have greater assurance that the quality is according to what research has been demonstrated with Palatinose™ interventions. Quality variables would include the purity of the Isomaltulose and whether any sucrose, free glucose, or free fructose is remaining.

Isomaltulose is a relatively expensive ingredient compared to other sucrose products, due to the additional processing. Unbranded isomaltulose is available on the market also, as well as in natural products such as honey - albeit in relatively small doses.

AN IDEAL ENDURANCE SPORT COMPOSITION?

A combination product of both HBCD and isomaltulose. In my opinion anyway.

With this pairing we can achieve a slow releasing combination of both glucose and fructose that will both serve to maintain steady glucose and stored glycogen levels, while maintaining high fat oxidation, as well as being easy on the guts and insulin system. Likely directing toward the 1:0.8 ratio glucose to fructose, recently demonstrated as ideal in the O’brien 2013 cycling trial which tested various ratios, of which also had a number of other investigations supporting that outcome. That said, anything between there and 1:1 and 2:1 would be a reasonable evidence based range, adjusting to individual tolerance is always optimal.

If a person needs a rapid acting source, the likes of maple syrup (high sucrose) or honey (high fructose, high glucose) are good options.

The main topic for this writeup is not dosing, of which is quite a lengthy discussion of caveats and circumstance.
Right now the most evidence based maximal dosing for mixed source (glucose and fructose) carbohydrate loading is around the 90g per hour mark, for multiple hours of high intensity activity as in the Iron Man Liam is training for. Dosing higher than 90g generally increasing gut distress, and reducing fat oxidation, sometimes even raising endogenous carbohydrate oxidation.

Considering isomaltulose has a lesser effect in reducing fat oxidation, and both isomaltulose and HBCD is slower releasing, and is more tolerable by the gut: there may be capacity to increase that dose… but that’s in the realm of speculation and not a substantiated approach as of now. There is some practice around increasing tolerance and capacity to high carbohydrate absorption, that would allow an even higher dosing, but this requires more research.

The yet unknown aspect of this combination is the feasibility of this as a stable and palatable fuel combination for the extended all day endurance applications.

But hey, we’re working on it, likely with the inclusion of other performance enhancing ingredients, for a particularly potent all-in-one solution. This is of course a relatively expensive solution, however still within practical range of supplement costing. It’s quite clear looking at the costing of the products currently on the endurance supplement market, the companies making them have a very low cost of goods sold, and a likely high marketing budget. Our philosophy is to do the opposite.

I hope you found value in this look through, it will be an ongoing project I’m sure.

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WHAT DO WE STOCK?

CarbMAX - Strom Sports Nutrition

Featuring 25g Palatinose™ per serve, alongside an electrolyte complex, 2g Citrulline Malate, and 500mg Glycerol monostearate.

PerforMAX - Strom Sports Nutrition

Featuring 15g Palatinose™ per serve, as well as 15g Fructose™, Taurine, PeakATP, Senactiv, as well as a full EAA and electrolyte blend.

CarbUp - HR Labs

Featuring 25g Cluster Dextrin™, Glycersize™ and Taurine.



11.07.2024 -This article was originally published at stromsports.co.nz, with additional media graphics.

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This content is for educational purposes only and does not intend to cure or diagnose disease, nor make any health claims. There is no intent to slander in any way, but rather produce an informed and accurate third party perspective on the product. Always consult your accredited medical professional before introducing a new supplement. This content is not to be copied or repurposed in any form without express permission from the author.