Hello Runner,
Welcome back to your weekly moment of endurance nutrition!
Happy Weekend!
How are you?
I'm fine. I've been feeling much better this week. I found out that I slightly sprained my ankle while running last week, and that's what caused the pain in my lower calf. Actually, my ankle swelled up from the sprain, and the pain radiated upward. It wasn’t the first time this happened, and I’m almost 100% sure it was because of the poor stability of the running shoes.
I’ve been running in the Adidas Evo SL for quite a while, but I’ve always found them to be very unstable. After these two sprains and more than 700 km run in them, I decided to “retire” them.
I bought another pair of running shoes with more stability that arrived this week, and I’ll probably break them in tomorrow.
I have to admit that these past two weeks of spin classes have been wonderful for escaping the hellish heat we’re having in Barcelona.
Other than that, I worked hard this week and kept up with my studies as usual.
Today’s topic is based on a client I had recently who came to me with fructose intolerance. I’d heard of people, including runners, with this intolerance before, but I’d never treated anyone with it.
For runners, it’s more complicated, since fructose is present in many supplements used during races. So, how do you handle this situation if you have it?
Most runners who say they are "fructose intolerant" actually have dietary fructose malabsorption, a condition where the small intestine struggles to absorb fructose efficiently. The unabsorbed fructose travels to the large intestine, where it's fermented by gut bacteria, causing bloating, gas, abdominal pain, diarrhea, and nausea.
Running can make these symptoms even worse. During exercise, blood flow is redirected from your digestive system to your muscles, slowing digestion and reducing carbohydrate absorption. That's why foods you tolerate during the day may suddenly become a problem during a long run or race.
(Note: This is different from Hereditary Fructose Intolerance, a rare genetic disorder that requires lifelong medical management and complete avoidance of fructose, sucrose, and sorbitol.)
Foods to limit in case of fructose intolerance
Everyone's tolerance is different, but many runners benefit from reducing foods that are naturally high in fructose, including:
Apples, pears, mangoes, watermelon, cherries, peaches, and dried fruits
Honey and agave syrup
Soft drinks or processed foods containing high-fructose corn syrup (HFCS)
Fruit juices and smoothies made with apple or pear juice
Sugar-free products containing sorbitol
Large servings of onions, garlic, and wheat-based products (high in FODMAPs)
Instead, build your meals around foods that are generally better tolerated, such as rice, potatoes, oats, quinoa, bananas, berries, citrus fruits (in moderation), lean proteins, eggs, and dairy products if tolerated.
What if you accidentally eat too much fructose?
Unfortunately, there's no supplement or medication that instantly "fixes" fructose malabsorption.
If you accidentally* eat foods high in fructose and experience symptoms, follow these recommendations:
Stop eating the trigger food.
Drink water to stay hydrated.
Choose simple, low-FODMAP foods for the rest of the day, such as white rice, potatoes, eggs, or plain chicken.
Avoid running until symptoms settle, as exercise often worsens gastrointestinal distress.
Seek medical advice if symptoms are severe, persistent, or accompanied by dehydration, vomiting, or blood in the stool.
*This happens more often when you buy processed foods in a hurry, without reading the ingredients.
Choosing the right running fuel
Many modern sports nutrition products combine glucose and fructose because this combination allows healthy athletes to absorb more carbs during longer runs and rides. However, if you have fructose malabsorption, these products may trigger gastrointestinal symptoms.
Instead, look for products that use carbohydrate sources such as:
Maltodextrin
Dextrose (glucose)
Glucose polymers
Highly Branched Cyclic Dextrin® (Cluster Dextrin®)
→ Always check the ingredient list and avoid products containing fructose, honey, agave syrup, fruit juice concentrates, or high-fructose corn syrup.
RECOMENDATIONS
Fructose-free supplement options
Formulations can change, so always read the label before purchasing. Some brands offer suitable products because they are carbohydrate-free or rely primarily on glucose-based carbohydrates. Good options are:
Science in Sport (SiS): Some GO Isotonic Energy Gel formulations have historically been based primarily on maltodextrin (check current labels).
226ers: High Energy Gel 76g, High Energy Gel XS 45g, Energy Drink are fructose-free.
Overstim-s: Gel Coup de Fouet and gummies Ultra (Lemon and Blueberry flavours).
Decathlon: Energy Gel -3H
ESN: Perfect NRGY Gel Hydro Energy
→ Cluster Dextrin®-based products: Available from several sports nutrition manufacturers.
⚠️ Be aware that many popular gels and drinks → including numerous products from Maurten, GU, Tailwind, High5, Powerbar, Puresport, and many others contain fructose, sucrose, or mixed carbohydrate sources and may not be suitable if you have fructose intolerance.
→ All products that are labeled on the packaging as “ratio 2:1,” “ratio 1:1,” or “ratio 1:0.8” contain fructose.
By understanding your personal tolerance, choosing everyday foods carefully, and selecting glucose-based sports nutrition, you can significantly reduce gastrointestinal symptoms and perform with confidence.
As with any nutrition strategy, test your race-day fueling during training, not on race day, and consider working with a registered sports dietitian to develop a plan tailored to your needs.
After getting to know my client well and conducting a thorough assessment, I created a personalized plan for him that minimizes the symptoms of his intolerance. He is still undergoing treatment, and over time we’ll make adjustments to anything that isn’t working (if that happens).
→ If you're unsure whether your current fueling strategy is helping or hurting your performance, I can help you identify trigger foods, optimize your daily diet, and find the right fructose-free supplements for your training and racing goals.
Schedule a 20-minute call with me. We'll talk, I'll assess your current situation, and I'll explain how I can help you.
Product of the Week
This week's Product of the Week is the SIS Go Isotonic Energy Gel Pink Grapefruit.
It’s been a while since I tried this flavor, and I forgot to mention it here in the newsletter.
I’d already tried the lemon one and liked it.
I’m a fan of grapefruit, so I decided to give it a try. And it gets my full approval.
This is one of my favorite gels. I find the flavor mild, and it doesn’t cause me any stomach issues.
This option doesn’t contain fructose, which is good for those who are intolerant.
Scientific References
Burke LM, et al. (2019). IOC Consensus Statement: Dietary Supplements and the High-Performance Athlete. British Journal of Sports Medicine, 53(12), 731–746. https://doi.org/10.1136/bjsports-2018-099027
Costa RJS, et al. (2017). Systematic review: Exercise-induced gastrointestinal syndrome. Sports Medicine, 47, 111–124.
Gibson PR, Shepherd SJ. (2010). Evidence-based dietary management of functional gastrointestinal symptoms: The FODMAP approach. Journal of Gastroenterology and Hepatology, 25(2), 252–258.
Jeukendrup AE. (2017). Training the gut for athletes. Sports Medicine, 47(Suppl 1), 101–110.
Jeukendrup AE. (2004). Carbohydrate intake during exercise and performance. Nutrition, 20(7–8), 669–677.
Reynolds KM, et al. (2022). Apple Puree as a Natural Fructose Source Provides an Effective Alternative to Artificial Fructose Sources for Fuelling Endurance Cycling Performance in Males. Nutraceuticals, 2(3), 15. https://doi.org/10.3390/nutraceuticals2030015
Stellingwerff T, Cox GR. (2014). Systematic review: Carbohydrate supplementation in endurance sport. Sports Medicine, 44(Suppl 1), S25–S33.
Thomas DT, Erdman KA, Burke LM. (2016). Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. Journal of the Academy of Nutrition and Dietetics, 116(3), 501–528.
Track of the Week 🎧️
This week's Track of the Week is a song I discovered this week, and I thought it would be good for a casual run outside of my regular training routine, one of those laid-back ones.
I’ve chosen Moments - Ben Bohmer & Nils Hoffmann Remix by Kidnap, Leo Stannard, Ben Bohmer, Nils Hoffmann.
Any questions or something you would like to share? Drop me an email
Wishing you a great weekend and week ahead!
Here’s to health and good runs⚡️
Ana Paula Alonso