The science of carb gels has changed dramatically in the last five years. Old advice said 30 grams of carbs per hour was the upper limit. New research has pushed that to 90 grams or more for trained guts. Most SA runners are still fuelling with outdated information and wondering why they hit walls in long races. This guide explains what carb gels actually do, the difference between brands, and how to pick the right one for your distance.
What Is a Carb Gel and How Does It Work?
A carb gel is concentrated carbohydrate in a small sachet. Most contain between 20g and 50g of carbs in 30ml to 60ml of liquid. You tear it open, swallow it down, wash it with water, and within 10 to 15 minutes the carbs hit your bloodstream and start replacing glycogen as it burns.
Your body stores around 400g to 500g of glycogen in muscles and liver. At marathon pace, that lasts roughly 90 to 120 minutes before you bonk. Carb gels extend that window by topping up your fuel mid-run rather than relying on what your body stored before the race.
The difference between gels comes down to two things: how much carbohydrate they deliver per serving, and what type of carb sources they use. The latter matters more than most runners realise.
Single-Carb vs Dual-Carb: The Most Important Distinction
Old gels used a single carb source, usually maltodextrin or glucose. They worked, but the human gut has a maximum absorption rate of about 60g of glucose per hour. Push past that and you get the bloating, cramping and "runner's gut" so familiar to marathon and ultra athletes.
Modern dual-carb gels combine glucose-based carbs (maltodextrin or dextrose) with fructose. Glucose and fructose use different transport pathways in the gut. Layer them together and your absorption capacity climbs to roughly 90 to 120g of carbs per hour.
The optimal ratio according to current research sits between 1:0.8 and 2:1 glucose-to-fructose. The Gatorade Sports Science Institute has documented this dual-transport approach across multiple peer-reviewed studies. Brands like SIS, Maurten and Styrkr have built their premium products around exactly this ratio.
For SA runners targeting Comrades or Two Oceans, dual-carb gels are genuinely a different category of fuel. Not just a marketing upgrade.
How Many Carbs Per Hour Should You Aim For?
Modern guidance for endurance running:
Half-marathon: 30 to 60g of carbs per hour. Single-carb gels are fine.
Marathon at moderate effort: 45 to 60g per hour. Single-carb gels still work for most runners.
Marathon at competitive pace: 60 to 90g per hour. Dual-carb gels start mattering.
Ultra (Comrades, Two Oceans): 60 to 90g per hour for the first 6 hours, dropping to 40 to 60g per hour after as digestion slows.
Trail and ultra-trail: 50 to 80g per hour, varied with real food and liquid fuel for gut tolerance.
The catch: your gut has to be trained to handle high carb intake. A runner who has never taken more than 30g per hour cannot suddenly handle 90g on race day without a stomach revolt. Build up to higher carb intake gradually across your training block, not on race morning.
The Best Carb Gels Available in South Africa
What we stock and why. The honest version.
SIS Beta Fuel Gel: The Top Carb Delivery
The SIS Beta Fuel Gel is the strongest dual-carb option we stock. Each 60ml gel delivers 40g of carbohydrates using a 1:0.8 maltodextrin-to-fructose ratio.
This is the formula used by elite marathon and Ironman athletes at world-class events. At R75 per gel, it's the most expensive option in our range, but the carbs-per-rand ratio is actually excellent because each gel delivers roughly twice what a standard gel does.
Best for: marathon and ultra race day, runners pushing competitive paces, athletes targeting 60g+ of carbs per hour.
32Gi Sports Gel: The Gentle, Affordable Choice
The 32Gi Sports Gel takes a different approach. Brown rice syrup as the primary carb source, low glycemic index, single-carb formulation. Each gel delivers 20 to 22g of carbs at R32.
This isn't the gel for chasing a marathon PB on raw carb delivery. It is the gel for training runs, sensitive stomachs, and athletes who want clean ingredients without the high-fructose content of premium dual-carb gels.
Best for: training, half-marathon racing, runners with gut sensitivity, athletes who get queasy on sweeter formulations.
High5 Energy Gel: The Reliable All-Rounder
The High5 Energy Gel sits between the two. 23g of carbs per 40g sachet at R38, with a thinner texture that's easier to swallow than thicker gels mid-race.
Single-carb formulation, but pleasant to take and gentle enough for most stomachs. The mango flavour is genuinely good, which matters more than most runners admit when they're four gels into an ultra.
For runners who want to skip carrying water, the High5 Energy Gel Aqua is isotonic and goes down without needing a sip. Bigger sachet at 66g, but completely self-contained.
Best for: everyday training, half-marathon and marathon racing, runners who want one reliable gel without overthinking it.
32Gi Race Pro Gel 100g: The Big-Hitter for Ultras
The 32Gi Race Pro Gel is built differently. At 100g per serving and R98 each, it's a meal replacement in gel form rather than a quick top-up.
For Comrades and Two Oceans runners, taking one Race Pro at the 50km mark replaces two or three smaller gels. Less fumbling with packaging when your hands aren't cooperating, more sustained energy across the back half of an ultra.
Best for: ultra-marathon racing, three-hour-plus training runs, athletes wanting fewer feeding moments during long events.
What About Gels with Caffeine?
Caffeinated gels add 50 to 100mg of caffeine to the standard carb dose. Useful for the late stages of long races where mental fatigue is setting in.
The classic strategy: a caffeine-free gel every 30 to 45 minutes through the first half of a marathon, then a caffeinated gel at the two-thirds mark for the late-race lift. The combination works because caffeine reduces perceived effort and sharpens focus exactly when you need it most.
What not to do: drink three coffees, take five caffeinated gels, and then wonder why your heart's racing. Stack caffeine carefully. 200 to 400mg total across a race day for most runners is plenty.
How to Avoid Gut Trouble From Gels
The most common reason runners stop using gels: nausea, bloating or that special hell of needing a toilet at km 30 of a marathon.
Five rules that fix most of the problems:
Always take gels with water. 150ml to 200ml minimum. Pure concentrated carb without fluid sits like a brick in your stomach.
Train your gut. Use gels in training, not just on race day. Your gut adapts to higher carb intake the same way your legs adapt to longer mileage.
Don't mix multiple high-fructose gels. Stack two or three dual-carb gels in an hour and your fructose load can outrun your gut's capacity. Rotate brands.
Avoid trying new gels on race day. Test everything during long training runs first. The race entry isn't the day to discover you can't tolerate a brand.
Consider liquid fuel as a backup. When gels feel like too much, switching to Tailwind Endurance Fuel in your bottle gives you carbs and electrolytes in liquid form. 50g per serving without anything to chew.
Which Carb Gel Is Best for You?
Match the gel to your event:
Sub-90-minute racing: 32Gi Sports Gel or High5 Energy Gel. Affordable, simple, works.
Marathon at competitive pace: SIS Beta Fuel for the higher carb delivery. Mix in High5 if your stomach prefers something lighter.
Comrades, Two Oceans, ultra-trail: Mix it up. 32Gi Race Pro for sustained energy chunks, SIS Beta Fuel for high-carb hours, High5 Gummies when you need a chew, Tailwind in your bottle for steady fuelling.
Sensitive stomachs: 32Gi Sports Gel as the gentlest entry point.
We hand-select every gel in our store because we test it on ourselves first. Browse the carb gels we stock and pick the one that fits your distance.