In training for a full-distance tri in 2022 (The Outlaw Nottingham, in July), I wanted to maximize my carb intake. Having dug around for the research behind the formulations for the latest and greatest for this (probably Maurten and SIS beta fuel), I discovered a few things: -
- Maltodextrin is better than glucose (e.g. from sucrose) because it has better osmolality - your body will cope with more carb for the same amount of water in your stomach.
- The optimal Glucose/MD:Fructose ratio of 1:0.8 does have some research behind it (TODO find ref), and does make quite a difference to max fuelling rate. Let’s say you’re maxing out on sucrose at 60g/hr, you should be able to tolerate 90g/hr of 2:1 glucose/MD : fructose mix (e.g. High5), and 108g/hr of 1:0.8 mix (e.g. Maurten, SIS beta fuel)1.
- The metabolic pathways for digesting fructose and glucose are independent. (From this, I conclude unless you’re taking as much as you can and maxing out one of those pathways there’s not much point worrying about that magic ratio too much).
- It’s important to train with high fuelling rates to both find and build your tolerance. Given the many, many hours of long rides and runs that go into a long event training plan, this can end up being expensive. I calculated that to fuel my Outlaw training fully on SIS beta fuel would cost me around £520.
I hate the plastic waste of gel wrappers, and used Active Root gel mix and drink mixes all last year. They’re great, made of natural ingredients (mainly cane sugar) and economical, but I wanted to move from a Sucrose-based fuel to a MaltoDextrin-based one for the reasons above.
Mix Maltodextrin powder with Fructose powder in a ratio of 1:0.8. I make it in large batches, and use a Kenwood Chef with the rubber paddle to do the mixing.
I find a concentration of 0.16 g(carb)/ml water is manageable for drinks mix, so a large 750ml bidon will take 120g of mixture. Add whatever electrolytes & nootropics you favour. My personal approach is to make the drinks at 0.1g / ml (75g per bottle). My max hydration rate has been 1l / hr, when it’s really hot and dry, which would give me 100g carbs / hr, which is my target for carbs. So that way if it’s hot I use drink for both fuel and hydration, and if it’s not I take gel as well. I add ~4g/l of (tri)sodium citrate (~3g per bottle) which gives me ~1g/l of sodium2.
Powdered maltodextrin does not dissolve very easily, I find the best way to make the drink is to add the powder to bottles that are 1/3 full, then shake hard, before topping up the rest of the way.
Multiplying this up to a larger batch:
- 400g Maltodextrin
- 320g Fructose
- 29g (Tri)sodium citrate.
- To the base recipe, add
- 4g high-methoxyl pectin (if you search for pectin and it doesn’t say it’s special, it’ll likely be high-methoxyl pectin) per 100g base mix
- 2g citric acid per 100g base mix.
- Again, whatever electrolytes and nootropics you favour. My preference is not to add any – I figure that electrolyte replacement should scale with hydration not fuelling. If you do add electrolytes, they might affect the pH of the mix, so you’ll need to reduce the amount of citric acid, or your gel might end up quite chunky.
- Mix well (another job for the Kenwood).
- Put your powder mixture in a pan containing 150ml near-boiling water per 100g base mix (the commercial gels with MD use a concentration of 0.67 g(carb)/ml(gel)).
- Bring to the boil and boil for 1 min. (Video)
- Cover, and let it cool for a few minutes, before transferring to a shaker bottle.
- Once it’s below 60C3 you can transfer it to gel bottles.
Multiplying this up to a larger batch: -
- 400g Maltodextrin
- 320g Fructose
- 27g Pectin
- 13g Citric acid
- 950ml water
Unflavoured, the gel tastes vaguely like a citrussy (thanks to the citric acid) version of whatever fruit your fructose supplier made the fructose from. Feel free to experiment with flavouring with whatever you like. I haven’t felt the need yet, but I have a low bar for gel acceptability4, and taste seems to be an important factor in all the gel reviews, so YMMV.
I don’t fool around with powdered caffeine in any of my DIY mixtures, because I don’t want to die from a units confusion. I’ve used caffeine bullets for my last couple of races, and they’ve worked fine.
Update: Although there’s research suggesting sodium alginate might promote carb uptake, the research wasn’t well controlled and the difference may well have been the sodium rather than the alginate (discussion). There’s also (possibly weak, possibly biased) research by a competitor of Maurten concluding that it doesn’t work / is deleterious.
I’d like to experiment using low-methoxyl pectin, which is also calcium-activated, but should work at room temperature, and potentially be a bit less acidic than my gel, which I suspect might help with absorption.
There is ongoing research and debate on the topic, and some experts maintain 1:1 is close to optimal, and that MD isn’t worth the hassle. Worth digging into this Slowtwitch thread for more. One of the key concepts is that the fructose pathway is more trainable than the glucose pathway, so that after a while of fuelling in training you end with an ideal ratio that’s 1:0.9 or even to 1. In the UK, the prices I get for MD and for sucrose are about the same, so I’ll stick with MD. ↩︎
Precision Hydration and Fuelling have been trying to get me to take more electrolytes and I’ve tried their products a couple of times, but I always blanched at the cost of using them regularly. Having done the maths they’re actually no more expensive per sodium than High5 zero tabs, they just recommend you take about 4x as much sodium. Then this amazing Slowtwitch thread led me to Alacrity Endurance, which has this video on the subject of sodium, which goes into the research evidence for higher sodium rates than people usually use. ↩︎
Do not pour near-boiling gel into the gel bottles, you’ll melt the heat welding holding the bottle together. If you do accidentally do this, you can repair small holes in the weld using an iron, covering with greaseproof paper or silicon paper to stop the plastic sticking to the iron. ↩︎
I tried powerbar gels years ago, and found that they tasted only marginally better the first time you swallow them. Everything since then has been an improvement. ↩︎