SiS Go Review: What is Isotonic Energy Gel? Hype or Real Deal?

SiS Go review summary: SiS Go Isotonic Energy Gel is a 60 ml energy gel with 87 calories and 22 g of carbohydrates. Its primary sugar source is maltodextrin. The brand’s isotonic formula allows the gel to empty from the stomach quickly as no fluid needs to be drawn into your stomach to dilute the gel. You can take the gel without a fluid chaser, reducing the risk of stomach bloating from over-drinking.


Not gonna lie. I had to look up “isotonic” (SAT verbal wasn’t my forte).

Here’s the definition:

Isotonic solution: A solution that has the same salt concentration as cells and blood. It’s used as intravenously infused fluids in medical patients.

Okay, so its a kind of IV drip, but what does that mean for us endurance athletes?

UK-based Science in Sport (SiS) is a pioneer in applying isotonic solutions to sports fueling, and claims that its signature GO series is the world’s first isotonic energy gel. Today, let’s have a look at the science behind it, followed by some thoughts of a 36km long run fueled by SiS GO Isotonic Energy Gels.



Company claims – water not necessary

SiS has been in the sports nutrition game for three decades and the GO Isotonic Energy Gel series was launched in 2002.

An Isotonic gel, in chemistry terms, means that it has the same concentration as cells inside your body, and therefore no osmotic movement of water. According to SiS, its isotonic formula “allows the gels to empty from the stomach quickly as no fluid needs to be drawn into your stomach to dilute the gel, providing fast energy.”

You can take the gels without a fluid chaser, reducing the risk of stomach bloating from over-drinking, claims the company.

What are the Ingredients of SiS Go – maltodextrin as fuel

  • Water
  • Maltodextrin (from Maize) (33%),
  • Gelling Agents (Gellan Gum, Xanthan Gum)
  • Natural Flavoring, Acidity Regulators (Citric Acid, Sodium Citrate)
  • Preservatives (Sodium Benzoate, Potassium Sorbate)
  • Sweetener (Acesulfame K)
  • Sodium Chloride
  • Antioxidant (Ascorbic Acid)


The majority of the carbohydrates comes from maltodextrin. Compared with other carbohydrates, It requires less water to digest, and it’s a good way to get quick calories without becoming dehydrated.


Nutritional facts

Each SiS Go energy gel comes in a 60 ml sachet and provides the following. Not a big bang for the volume.

  • 87 calories
  • 22g carbohydrates
  • 0g protein
  • 0g fat
  • 0.01g salt.
Next up, taste and consistency.

What are the taste and consistency of SiS Go?

The main ingredient maltodextrin is almost tasteless, only about 0-5% of the sweetness of sucrose (table sugar). Combined with the relatively watery texture, the energy gel is very palatable (like thickened, fruit-flavored water).

However, a negative is that each pack of gel comes in a robust 60 ml, meaning you have to ingest more gel to get the same amount of carbohydrates and calories.

Packaging – it’s big

The SiS sachet is noticeably bigger than the more standard packages of GU and Hammer. I get it. Higher water content requires more sachet volume. But a pack of SIS energy gel takes up quite a bit of space, especially for runners using only a running belt. Its longer shape also doesn’t fit well in the pockets of some hydration vests.

In terms of tearing open and consuming the energy gel on the move, it’s very well designed. Despite the watery consistency, it wasn’t messy and no accidental spillage occurred.


Performance – 36km long slow distance

The hilly route was an 18km out and back, which I ran twice. It was just under 1000m in elevation and took just over 4 hours. I maintained an easy-to-moderate pace and brought 4 SiS GO Isotonic Energy Gels (flavors: 2 x Pink Grapefruit and 2 x Tropical).

I had my usual pre-long distance breakfast of overnight oats with honey. I ate my first gel 40 minutes into the run and took a gel every hour afterward.

Some takeaways:

  • The flavor really wasn’t bad. One of the better-tasting gels I’ve had. The temperature was a scorching 34 degrees, so a lighter, less syrupy gel was nice.
  • For the first two energy gels, I ate them without water as the company suggested. However, I still wanted a little water to wash down the aftertaste (which is already much milder than other brands). This is obviously a very subjective opinion.
  • In terms of fast absorption, there was no noticeable difference compared with other gels that had worked for me in the past. But it did what it’s supposed to, providing an energy boost (about 5-10 minutes mouth-to-muscle in my case) without stomach issues. But of course, when it comes to training and nutrition, everyone responds differently.
  • At 60 ml, it provides only 87 calories and 22g of carbohydrates, meaning you have to eat more for the same amount of energy.
  • It takes more “effort” to gulp the entire 60 ml. Not necessarily good or bad, but I think it’s worth noting.


So hype or the real deal? It lies somewhere in between.

It’s an effective gel that fueled my long training run and caused zero stomach issues. However, due to the larger packaging, I would reserve SiS for longer-distance challenges when I will have a hydration pack or vest.

For marathons, when I only wear a compression running belt, carrying 6 to 7 SiS energy gels feels bulky.

I also found that eating a full 60 ml gel at a higher intensity (running at marathon pace) is a bit of a chore. But at a slower ultramarathon pace or moderate-effort cycling, SiS is an excellent option.

SiS is lighter and more watery, making it a refreshing fuel for hot summer adventures and workouts.

Overall, I’m a fan of the isotonic energy gels. Most gels taste bad to me, but this is very palatable and contains all the body needs. Using maltodextrin as its primary source of carbohydrates certainly helped soften the sweetness.

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