Carbohydrate Supplements for Exercise

The VerdictMODERATE CONVICTION

Sports carbs genuinely work, but only for long endurance efforts.

Before you buy another box of sports gels, ask one question: is your workout longer than about 90 minutes of continuous effort? If yes, they genuinely help. If no — a normal gym session, a 5k, a HIIT class — you are paying for nothing.

Your body has two reasons it might want carbs mid-exercise, and they switch over at about the one-hour mark. For a short hard effort, carbs in your mouth just send a "fuel is coming" signal to your brain that pushes you a little harder — you could literally spit the drink out and still get it. Past two hours it becomes real fuel: your tank is running low and the carbs top it up.

That's the general answer. Your stack is different.

Check your whole stack

Before you buy another box of sports gels, ask one question: is your workout longer than about 90 minutes of continuous effort?

If yes, carbs genuinely help and they are cheap. If no — a normal gym session, a 5k, a HIIT class — you are paying for something the research says does nothing.

Takes less than 2 minutes. No equipment needed.

The Verdict

Sports carbs genuinely work, but only for long endurance efforts. For a normal gym session they do nothing.

Your body has two reasons it might want carbs mid-exercise, and they switch over at about the one-hour mark. For a short hard effort, carbs in your mouth just send a "fuel is coming" signal to your brain that pushes you a little harder. You could literally spit the drink out and still get the benefit. Past two hours it becomes real fuel: your tank is running low and the carbs top it up.

The verdict: carbs during exercise are one of the few sports supplements with genuinely strong evidence, but only for endurance efforts longer than about an hour.
What most people get wrong: using gels and sports drinks for short workouts or weight training, where the research shows zero benefit.
Start here: if your effort is longer than 90 minutes, take in about 30 grams of carbs an hour (roughly one banana or one gel) and build up from there.

Best for

Anyone doing continuous endurance exercise longer than about an hour — long runs, long rides, races. The longer you go, the more it helps.

Skip if

Your workout is under an hour, you mainly lift weights, or you are not exercising at all. Outside an endurance demand it is just sugar with a logo.

Want the full evidence? Keep scrolling

The Protocol

What to take depends entirely on how long you are exercising. The starred row is the everyday sweet spot for most recreational endurance sessions.

Context	Dose	Timing	Form
Endurance, 60-90 min	6-8% carb drink, ~30-60 g/h	During exercise	Sports drink (fluid + carb together)
Endurance, longer than 2-2.5 h	60-90 g/h, build up with practice	During exercise, start early	Glucose-fructose drink, gel, or food
Pre-event top-up (events over 60 min)	1-4 g per kg body weight	1-4 h before exercise	Mixed carb meal or snack
Short hard effort (under 1 h)	Mouth rinse (~6% solution)	Periodically through the effort	Rinse and spit, or any palatable carb
Resistance training, fed, up to 10 sets/muscle	No effective dose — does not help	—	—
Non-exercising adults	No use case	—	—

Forms — They All Work, Pick on Cost and Stomach Comfort

Maltodextrin powder

up to ~60 g/h

Cheapest option that works. Efforts up to ~2 h.

Pennies per serving

Glucose-fructose blend

up to ~90 g/h

The one form that is a different tool. For long events needing high carb rates.

~£15-25 / kg

Sports drink

6-8% solution

Carb plus fluid plus electrolytes in one. 60-120 min efforts.

~£1-2 per serving

Gel

concentrated

Convenient to carry on long events. Take with water.

~£1.50-2.50 each

Whole food

matched carb dose

Banana, dates, dried fruit, honey. Performance-equal to a gel.

Pennies

Mouth rinse

not swallowed

Short efforts under 1 h, or when your stomach is the limit.

Negligible

Getting It In Without the Stomach Trouble

Match the carb rate to your gut, not your ambition. Start at about 30 g per hour and build tolerance over weeks of training.
For more than ~60 g per hour, use a glucose-fructose blend. A single carb type cannot be absorbed faster than that, and the excess just causes stomach upset.
Take gels with water. A concentrated gel with no fluid sits in your stomach and turns into cramps.
Rehearse your exact race-day fuelling in training. Your gut is trainable, and a high dose attempted cold on race day produces distress, not a personal best.

Safety & Interactions

Carbohydrate is food, not a drug, so there is no toxicology in the usual sense and no upper intake limit. The real cautions are your stomach, your teeth, and calories you do not need.

Stomach distress — the main side effect

Bloating, cramps, nausea and diarrhoea, common past 2 hours and worse with high intake rates or solid food. Manage it: lower the rate, switch to a glucose-fructose blend, choose drinks or gels over solid food.

Dental erosion with frequent sugary products

Repeated sugar and acid exposure from gels, chews and sports drinks raises tooth decay and erosion risk. A known issue in endurance athletes. Rinse with water and do not use them when there is no training reason to.

Rebound low blood sugar before exercise

A large carb dose taken 30-60 minutes before exercise can cause a transient dip in blood sugar at the start of the effort in some people. It usually self-corrects. Avoid it by timing the dose, or by fuelling during exercise instead.

Over-drinking sports drinks

Sports drinks do not contain enough sodium to prevent dangerously low blood sodium (hyponatraemia). The risk comes from over-drinking volume during very long events, not from the carbohydrate. Drink to thirst.

Drug Interactions and Cautions

No pharmacological drug interactions of significance. Carbohydrate pairs additively with caffeine (a genuine performance combination), so manage your total caffeine dose and timing separately. If you have type 2 diabetes or impaired glucose tolerance, routine sports-drink and gel use outside a genuine endurance need adds glycaemic load and should be individualised. Carbohydrate fuelling during real endurance exercise remains appropriate.

Conviction

MODERATE

The core finding — carbohydrate improves prolonged endurance performance — is settled and rated HIGH on its own. The overall conviction is MODERATE because the verdict splits sharply by context: strong for long endurance, near-zero for lifting and short workouts.

What would change this verdict

The settled core will not be overturned. Two trials would move the stratified verdicts:

For resistance training: an adequately powered, double-blind trial in trained lifters using a sensory-matched, equal-calorie placebo and measuring muscle glycogen directly, testing carbohydrate across both moderate and high training volumes. A clear benefit at high volume only would upgrade that verdict.

For the dose question: a head-to-head trial in recreational endurance athletes comparing roughly 15-30 g/h against 60-90 g/h over a long (more than 2.5 h) effort, which would settle whether low doses make high carb rates unnecessary for non-elite athletes.

Worth Your Money?

Weekly costAbout £1-£3 a week using plain maltodextrin powder. £8-£15+ a week if you buy branded gels for regular long sessions.

Worth it ifYou regularly do endurance exercise longer than an hour and want a cheap, genuinely well-evidenced performance edge. Maltodextrin is one of the best-value sports supplements there is.

Lower priority ifYour training is mostly weights or short sessions. Your next £10 is better spent on protein, or on fixing your sleep, than on sports carbs you will not benefit from.

Conditional Value

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Sources

Carbohydrate Supplementation on Exercise Performance or Capacity of Varying Durations (2014). Appl Physiol Nutr Metab. Systematic review, 61 studies (n=679). 82% showed significant benefit; gain correlated with exercise duration. (PMID 24951297)
A Systematic Review and Meta-analysis of Carbohydrate Benefits in Competition-Based Performance Trials (2016). J Int Soc Sports Nutr. 24 RCTs. Benefit specific to 6-8% concentration and exercise over 90 min in trained cyclists. (PMID 27408608)
The Ergogenic Effects of Acute Carbohydrate Feeding on Endurance Performance (2024). Crit Rev Food Sci Nutr. 136 studies. Benefit grows with event duration, larger in less-trained participants. (PMID 37449467)
The Effect of Carbohydrate Intake on Strength and Resistance Training Performance (2022). Nutrients. Systematic review, 49 studies. No improvement in fed-state resistance-training performance at typical volumes. (PMID 35215506)
Effect of Carbohydrate Mouth Rinse on Muscle Strength and Muscular Endurance (2023). Crit Rev Food Sci Nutr. 13 RCTs. No effect on maximal strength; +1.24 reps muscular endurance. (PMID 35373671)
Synergy of Carbohydrate and Caffeine Ingestion on Physical Performance (2024). Crit Rev Food Sci Nutr. 13 RCTs (n=128). Additive ergogenic effect. (PMID 36178302)
A Food First Approach to Carbohydrate Supplementation in Endurance Exercise (2022). Int J Sport Nutr Exerc Metab. 15 studies (n=151). Food and supplements performance-equal; food caused more GI symptoms. (PMID 35231883)
Thomas DT, Erdman KA, Burke LM (2016). Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and ACSM: Nutrition and Athletic Performance. J Acad Nutr Diet. Canonical carbohydrate intake and timing guidance.