ProView – Gnarly Nutrition Fuel2O

I used Gnarly Fuel2O throughout the month of August – both at work and play. I was especially excited to test Fuel2O as a runner who is always adding and subtracting nutrition to see what works best for me. Though training this time of year is always a challenge with work, I often manage 30-40 mile weeks and have been experimenting with calories and hydration for several years now.

Gnarly Nutrition Fuel2O

Product Name: Gnarly Nutrition Fuel2O

Product Description: Gnarly Nutrition’s Fuel2O is the all-in-one, vegan-friendly solution for long days on the trails, in the mountains, at the gym or the crag. Fuel2O was created with fueling, replenishment and recovery in mind. Calories come from the easy-to-digest carbohydrates sucrose and dextrose, providing quick energy without causing an upset stomach.

Offer price: MSRP: $28.95 - $34.95

  • Palatability
  • Quality
  • Content
  • Digestibility


Gnarly Fuel2O was an excellent way for me to supplement calories during longer endurance efforts. I found it to work best in a slightly more dilute form, so I sacrificed a few drinkable calories in an effort to keep my gut happy. The flavors are delicious!



  • Carbohydrates from two different sugars (sucrose and dextrose) 
  • Added sodium and potassium to supplement electrolytes 
  • Easy mixing and palatable flavors


  • Recommended serving is very concentrated
  • Mixes for 12oz instead of 16oz size of most hydration bottles
  • Very similar to tailwind, though without the variety of flavors and higher cost per serving

I work for the Forest Service as a wildland firefighter, so I am often on my feet outside in the woods dressed in pants and long sleeves. The caloric requirements of the harder days on the fireline are quite difficult to meet at times, so something drinkable I can mix into one of my nalgenes while working is incredibly helpful. Given the dynamic nature of the job, it was highly convenient for me to have a stash of liquid calories I could tap into if the intensity suddenly increased and I needed quick sugar. That being said, eating while firefighting isn’t nearly as difficult as eating while running – that extra 30-40 pounds of gear keeps you moving much slower, though effort levels may be the same or even higher. I also find myself drinking much more water during work. While Fuel2O was delicious, drinkable, and effective on the fireline, the real test was how it would sit in my small intestine over miles of ups and downs in the heat… 


Fuel2O is designed primarily as a source of calories. While it may seem intuitive that drinking a mixture of carbohydrates and water can satisfy hydration and caloric needs simultaneously, things are actually much more complicated. Studies have shown that a certain concentration of glucose (generally 3-4%) aids in the transport of fluid and electrolytes across the intestinal boundary. This is due to a similar osmolality of both the solution consumed and the blood circulating around your digestive tract. Generally, carbohydrate solutions are considered easier to digest due to the minimal amount of chemical breakdown necessary. However, when drinking fluids with higher concentrations of carbohydrates, you employ transporters for water, electrolytes, and glucose – both hydration and digestion. GI issues often arise when competition for transporters leaves an unabsorbed solution in your small intestine. Your ability to hydrate will therefore likely be affected by the increased concentration of glucose in your gut (the same thing happens with gels, which are packets of hyper-concentrated glucose), and uncomfortable symptoms may occur. Because the ability to absorb and digest glucose can vary greatly from person to person, old fashion trial and error is often your best bet when it comes to endurance nutrition. (1,2) 


I found for myself that I needed to add plain water to Fuel2O to supplement absorption – usually in the form of one bottle of Fuel2O to one bottle of plain H2O. Without added plain water I got the all-too-familiar sloshy-bloated stomach and sugary-mouth feeling. I also supplemented calories with other sources of ‘real food’ to taste and tolerance. With the mix of plain water and some additional salty snacks, Fuel2O went down smooth, felt clean, and kept my digestive tract functioning well throughout runs up to 7.5 hours in summer temps. For shorter runs in the 2-3 hour range, Fuel2O and plain water were adequate. 

The nutritional content of Fuel2O is most similar to Tailwind (another liquid fuel source), using sucrose and dextrose sugars. I found this to be a positive for myself personally, as I have had issues in the past with maltodextrin – a processed form of corn sugar that can have negative impacts on overall gut health (3,4). I also found the higher potassium content to agree well with me – something I actually look for in hydration/fuel mixes. As sodium needs are highly individual, I needed a little more than the 250mg per serving. Some general nutrition facts of popular liquid fuel products are listed below for easy comparison**: 

Gnarly Fuel2OSucrose/Dextrose33.3333132
Skratch SuperfuelDextrin/Fructose1004000
Hammer Heed*Maltodextrin27+6031
Gu RoctaneMaltodextrin/Fructose4624438

*contains Xylitol 

**approximate values taken from commonly available marketing materials

Final Word

Fuel2O is an excellent source of drinkable calories for endurance efforts. While I didn’t find the product to work best as a single source of hydration and nutrition, Fuel2O is a great way to take in carbohydrates and definitely my preferred alternative to gels. I found Fuel2O easy to incorporate into a nutrition plan, clean, and highly palatable.

1. Jeukendrup, A.E., Currell, K., Clarke, J. et al. Effect of beverage glucose and sodium content on fluid delivery. Nutr Metab (Lond) 6, 9 (2009). 
2. Sims, S., & Yeager, S. (2016). ROAR. Harmony/Rodale.
3. Arnold, A. R., & Chassaing, B. (2019). Maltodextrin, Modern Stressor of the Intestinal Environment. Cellular and molecular gastroenterology and hepatology, 7(2), 475–476. 
4.  Nickerson, K. P., Chanin, R., & McDonald, C. (2015). Deregulation of intestinal anti-microbial defense by the dietary additive, maltodextrin. Gut microbes, 6(1), 78–83. 

Shop the Gnarly Nutrition Fuel₂O on Outdoor Prolink. Not a member? Apply today!

About the Gear Tester

Outdoor Prolink Pro
Sarah Jakober
Firefighter :: USDA Forest Service

Sarah is a firefighter for the USDA Forest Service, an avid backcountry skier, trail runner, climber, and a grad student. She is also a contributor to and an RMU brand ambassador. 

Leave a Reply

Your email address will not be published. Required fields are marked *