SiS Beta Fuel vs GO Isotonic: the quick answer
- GO Isotonic is the smaller, everyday gel: 22g of carbs from maltodextrin in a 60ml gel. It suits shorter sessions and lower hourly targets.
- Beta Fuel is the high-carb gel: SiS lists 40g of carbs from maltodextrin and fructose at 1:0.8. It suits 60 to 90g an hour.
- Per gel, GO Isotonic is cheaper (£1.33 against £2.20). Per 30g of carbs, Beta Fuel is cheaper (£1.65 against £1.82).
- You need about 2 and a half GO gels an hour to reach 60g, or 1 and a half Beta Fuel gels.
| Product | Format | Carbs per serving | Pack and price | Per serving | Per 30g of carbs |
|---|---|---|---|---|---|
| SiS GO Isotonic Energy Gel | Gel | 22g | 30 pack, £40.00 | £1.33 | £1.82 |
| SiS Beta Fuel Gel | Gel | 40g | 30 pack, £66.00 | £2.20 | £1.65 |
What is SiS GO Isotonic?
GO Isotonic is the gel most people picture when they think of SiS: 22g of carbohydrate in a 60ml gel, made with maltodextrin. SiS sells it as an isotonic gel. A 30 pack is £40.00 for single flavours (£44.00 for the mixed pack), so about £1.33 a gel.
What is SiS Beta Fuel?
Beta Fuel is SiS's higher-carb range. SiS lists 40g of carbohydrate per gel from maltodextrin and fructose at a 1:0.8 ratio. A 30 pack is £66.00, about £2.20 a gel. The range also includes Beta Fuel +Nootropics and +Electrolyte gels, and Beta Fuel Energy Chews (SiS lists 46g of carbs per serving).
Which is better for running?
For a half marathon or a steady long run, GO Isotonic does the job: three or four gels covers most needs. For a marathon at 60g an hour or more, Beta Fuel cuts the number of gels you carry roughly in half. A 4 hour marathon from the 30 minute mark needs about 210g: 10 GO Isotonic gels, or 6 Beta Fuel.
Which is better for cycling?
Long rides are where Beta Fuel earns its place. At 80 to 90g an hour over four or five hours, you would need about four GO gels an hour, which is a lot of sachets. Beta Fuel gets you there with two. GO Isotonic is still useful for shorter rides or as a top-up.
How many SiS gels for a marathon?
| Race and finish time | Carbs needed | SiS GO Isotonic Energy Gel | SiS Beta Fuel Gel | FTP Tart Cherry Energy Pastilles |
|---|---|---|---|---|
| Half marathon, 1:45 | 75g | 4 gels, £5.33 | 2 gels, £4.40 | 3 servings (6 pastilles), £4.30 |
| Marathon, 3:00 | 150g | 7 gels, £9.33 | 4 gels, £8.80 | 5 servings (10 pastilles), £7.17 |
| Marathon, 4:00 | 210g | 10 gels, £13.33 | 6 gels, £13.20 | 7 servings (14 pastilles), £10.03 |
| Marathon, 5:00 | 270g | 13 gels, £17.33 | 7 gels, £15.40 | 9 servings (18 pastilles), £12.90 |
Why the fructose matters
Above about 60g an hour, a mix of glucose and fructose lets you absorb more carbohydrate than glucose sources alone, because the two use different routes through the gut. GO Isotonic lists maltodextrin only, so it suits targets at or under 60g an hour. Beta Fuel adds fructose for the higher targets. Either way, build your hourly amount up in training. Our gut training guide covers how.
Can you mix them?
Yes. A common plan is Beta Fuel as the main fuel and a GO Isotonic when you want something smaller or runnier. Count the carbs, not the gels: 40g and 22g are very different servings.
The cheaper way to get 30g of carbs
Full disclosure: we make energy pastilles, so read this part knowing that. Two FTP pastilles give you 30g of carbohydrate (34g serving, sugar, which is 50% glucose and 50% fructose). That is the same carb hit as a 30g gel, and you can take one pastille at a time if you prefer smaller, more frequent feeds.
- Tart Cherry Energy Pastilles 1kg: about 30 servings, £1.43 per 30g of carbs.
- Mixed Fruit Energy Pastilles 1kg: about 30 servings, £1.50 per 30g.
- The Rotation Pack (1kg of each flavour): about 60 servings, £1.13 per 30g.
4.8 stars from 500+ reviews, and Awarded Best Energy Chew in the Runner's World Sports Nutrition Awards 2026. If you would rather test them on a long run first, the Taster Pack is £5.49 for two servings.
See also our page on alternatives to SiS Beta Fuel.
Our verdict
Choose GO Isotonic for shorter sessions, lower hourly targets and the lowest price per gel. Choose Beta Fuel for marathons, long rides and 60 to 90g an hour, where it is also the better value per 30g of carbs. In our UK energy gel price comparison, Beta Fuel was the cheapest gel per 30g of carbs that we found.
Questions people ask
How many carbs are in an SiS GO Isotonic gel?
22g of carbohydrate per 60ml gel.
How many carbs are in an SiS Beta Fuel gel?
SiS lists 40g of carbohydrate per Beta Fuel gel.
Is SiS Beta Fuel worth the extra cost?
Per gel it costs more, but per 30g of carbs it was cheaper than GO Isotonic in our check: £1.65 against £1.82.
How we worked out these numbers
Prices were checked on 20 October 2026. They are full one-off prices for the multipack named, not subscription or member prices. Carbs per serving come from each brand's product page. Price per 30g of carbs = pack price, divided by servings in the pack, divided by carbs per serving, times 30. Race-day counts assume 60g of carbs an hour from the 30 minute mark and are rounded up to whole servings. Prices change, so check before you buy.
- SiS GO Isotonic Energy Gel: 30 pack, £40.00
- SiS Beta Fuel Gel: 30 pack, £66.00
