Intra Training Nutrition: What and When to Eat During Training

Written By Anna Estes

In this post, we’ll continue on with our nutrient timing theme, this time focusing on what and when to eat during training. For a review of what to eat before training, check out the previous blog post, Pre-Training Nutrition: What and When to Eat Before a Workout. 


How to eat during training depends on a variety of factors, including training activity, duration, intensity, goals, and personal tolerance. Regardless of variation across those factors, the main focus should be on carbohydrate consumption. If you spend much time looking into sports nutrition recommendations, you’re likely to come across the phrase “carbs are king” at some point. This is for good reason. Decades of sports nutrition research highlight carbohydrates as the most efficient substrate to provide energy for physical activity, especially high intensity aerobic activity (1,2). There is ample data showing that appropriate carbohydrate supplementation enhances performance and delays fatigue (3,4,5). The physiological mechanisms behind this are thought to be due to maintenance of plasma glucose concentrations, the high rate of carbohydrate use for energy production, the sparing of glycogen use, and some effect on the central nervous system (5).

Carbohydrate Recommendations by Activity Duration

Carbohydrate supplementation recommendations depend largely on training duration and intensity. As a general rule of thumb, carbohydrate intake should increase with training duration (2,6,7). 

  • For activity less than 1 hour - Provided that you are starting the activity properly fueled, carbohydrate supplementation is not required for activities under 60 minutes. However, there is some research indicating benefits from consuming small amounts of carbohydrate or even just rinsing the mouth with a carbohydrate drink for short duration activity (2). Multiple studies have shown that simply using a carbohydrate mouth rinse (without swallowing) contributes to performance improvements and reduced perceived effort (8). This is thought to occur due to a neural mechanism with oral carbohydrate receptors rather than a metabolic mechanism. Of note, the performance benefits seen with mouth rinse are fairly similar to those seen with ingesting carbohydrate drink and there does not appear to be a disadvantage to actually swallowing the carbohydrate drink unless gastrointestinal tolerance issues arise (2). In most settings, many people will find it more practical to simply swallow the carbohydrate drink instead of swish and spit. 

  • For activity 1-2.5 hours - Consume 30-60 grams of carbohydrate per hour. 

  • For activity greater than 2.5 hours - Consume 60-90+ grams of carbohydrate per hour. In recent years, elite athletes have started pushing the boundary to 120+ grams of carbohydrate/hour. This is likely not feasible (or necessary) for many recreational athletes, but nevertheless it is fascinating to see just how far athletes can push the limit when well fueled. 

Note that the recommendations above are given in grams of carbohydrates per hour rather than the total recommended carbohydrate intake for the entire duration of activity. Let’s say you go on a 2 hour run. The recommended intake is 30-60 grams of carbohydrate per hour, meaning that your total carbohydrate intake on the run might be anywhere between 60-120 grams of carbohydrate, depending on your hourly rate. 

Using Multiple Transportable Carbohydrates

If your goal is to take in at least 60 grams of carbohydrates per hour or more, you’ll benefit from the use of “multiple transportable carbohydrates” to help maximize gut absorption and carbohydrate use. This means that you should try to combine different types of carbohydrates, typically glucose (or its polymer, maltodextrin, which is just a long chain of glucose molecules) and fructose. 

Carbohydrates are absorbed in the small intestine using specific intestinal transporter proteins. Glucose and maltodextrin rely on a sodium-dependent glucose transporter called SGLT1. This is a very efficient pathway, however, the SGLT1 transporter becomes saturated once glucose ingestion exceeds approximately 60 grams of glucose per hour. In other words, if you are taking in more than 60 grams of glucose per hour, you will have some excess glucose that remains unabsorbed in the gut, increasing your risk of gastrointestinal distress. Fructose, a different type of simple carbohydrate, uses a separate pathway that involves the GLUT5 transporter. By adding fructose, we can “bypass” the intestinal saturation limit that occurs around ingestion of 60 grams of glucose/hour and take in a greater amount of total carbohydrate per hour to better support performance (9,10). 

The “optimal” ratio of glucose to fructose depends primarily on your hourly carbohydrate intake target and your personal tolerance. A simple approach is to aim for 60-70 grams of glucose per hour to max out the glucose transporter SGLT1, then add fructose on top of that to provide the remaining carbohydrate needed to meet the hourly target (11). The following ratios are discussed in sports nutrition research: 

  • For moderate to high intakes, e.g. ~60-90 grams of carbohydrate per hour - A 2:1 ratio of glucose to fructose is the established standard. 

  • For very high intake, e.g. 90-120+ grams of carbohydrate per hour - A ratio of ~1:1 or ~1:0.8 glucose to fructose may be better for higher carbohydrate intake goals because the increased amount of fructose may support higher oxidation rates and improve gastrointestinal tolerance (11,12,13).

In reality, there is no one true optimal carbohydrate ratio. Most commercially available sports nutrition products will utilize either a ~2:1 or ~1:0.8 ratio of glucose to fructose, as this is what is consistently supported by scientific literature. If you are mixing a variety of fuel sources, you are likely already employing the concept of multiple transportable carbohydrates without knowing it.

Ways to Consume Carbohydrates During Training

In general, intra training carbohydrate intake should come from easily digestible, simple carbohydrates like sports nutrition gels, chews, sports drinks, and low fiber whole foods if tolerated. When we exercise, blood flow is diverted away from the gut toward working muscles. This happens to a larger extent with higher intensity activity, meaning that it becomes even more important to prioritize easily digestible carbohydrates during high intensity training. We see this play out in real world performance situations regularly - most people running a half marathon or marathon will rely exclusively on sports nutrition gels, drink mix, and maybe chews, whereas people running an ultra distance event are much more likely to mix in whole foods like ramen, salted boiled potatoes, chips, and other delicious aid station offerings. This happens for a few reasons. With the exception of elite athletes, most people competing in ultra distance events are moving at a slower pace and lower intensity, meaning they have greater gut tolerance and can incorporate whole foods. Additionally, ultra distance events often occur over a much longer time frame, meaning that participants are more likely to experience flavor fatigue with just sweet gels/chews/sports drinks and their overall caloric requirement is higher due to the event duration, so they need to supplement with real food every once in a while. 

Training the Gut

When putting this all into practice, the most important thing to consider is your gut tolerance. Ninety plus grams of carbohydrates hourly to improve performance and reduce perceived exertion? Sounds great in theory, but you need to practice first before you try it on race day. 


You may have heard of a concept called “training the gut.” The idea behind this is that the gut is an adaptable organ and with practice, you can gradually tolerate and use more fuel during activity. Remember the SGLT1 transporter that helps absorb glucose in the small intestine? Evidence shows that a high carbohydrate diet increases the density and activity of intestinal SGLT1 transporters, leading to greater carbohydrate absorption and use during activity. Additionally, gut training can increase gastric emptying and reduce perception of fullness/bloat, leading to lower risk of GI distress (14). There are a variety of methods that you can use to train your gut. For example, you could train immediately after a meal. The most practical method for training the gut is to 1) eat enough carbohydrates in your daily diet and 2) progressively increase your hourly fueling rate during activity until you reach your goal, then practice your fueling plan repeatedly in a wide variety of conditions.

The exact process and timeline for gut training will depend on your existing fueling practices and current level of tolerance. If you’re consistently taking in 30 grams of carbohydrate per hour, you can likely incrementally work your way up to 60 grams of carbohydrates per hour with fairly limited issues. If you aren’t currently fueling your activity at all, you might need or want to start really small (e.g. 10 grams of carbohydrate, or roughly half a sports gel, per hour) and then gradually increase as tolerated. Ideally, you’d practice your fueling strategy in a variety of conditions, like higher intensity training sessions (e.g. run with speed work), hotter conditions, and on technical terrain if that’s relevant to your sport, etc. This will not only help you test your tolerance across conditions, but also learn how to make adjustments as needed come race/event day.  

Hydration During Activity

While “carbohydrates are king,” we certainly can’t forget about fluids. Since hydration needs vary widely across individuals, your hydration strategy should be personalized, and should ideally include some planning for both fluid and electrolyte intake. There are generally two different schools of thought regarding fluid replacement during exercise. One school of thought is to drink ad libitum, i.e., simply drink when you feel thirsty. The other school of thought is to engage in scheduled or programmed drinking, which is a more structured approach. Scheduled drinking may be helpful if you struggle to notice thirst sensation, which is more common during exercise than at rest. Scheduled drinking may also be helpful during prolonged events (e.g. ultra distance events), as well as during hot and humid conditions. If you’re not sure where to start, some general starting points for endurance activities are 450-750 milliliters of fluid per hour and 500-700 milligrams of sodium per liter of fluid (15).

Ideally, you’d have a personalized hydration plan based on your sweat rate and perhaps even sweat composition. Measuring your sweat rate, or the amount of fluid lost during a given training session, is actually quite simple to do at home if you have access to a scale and can weigh yourself. Measuring sweat composition, or the concentration of electrolytes in your sweat, can be a bit more involved depending on the methodology. There are several companies that ship patches for you to wear during activity and help measure sodium losses. Once you know your sweat rate and perhaps sweat composition, you can aim to replace a certain percentage of your fluid and electrolyte losses and have a more precise plan. Note: it is not recommended to replace 100% of fluid or electrolyte losses. We’ll dive into the specifics of personalized hydration strategies in another post, but for now, the takeaway is that carbohydrates, fluid, and sodium are the three critical components of your intra activity fuel plan. 

Putting It All Together

All of this might sound complex, but it doesn’t have to be. The best thing that you can do to level up your intra activity fueling is to first assess what you’re already doing. If you currently don’t eat or drink anything during activity >60 minutes, you have a lot of potential to improve your fueling practices. Consider this an exciting opportunity! If you already take in some carbohydrates, fluid, and sodium during activity, try to tally up your hourly totals, then make adjustments to better meet the goals outlined above. Remember that repeatedly practicing your fueling strategy helps to increase your tolerance and familiarity so that you have your plan dialed in prior to a big event. If you need help putting all of the pieces together, book an appointment for 1:1 sports nutrition counseling or reach out with questions.

References

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  2. Jeukendrup A. A step towards personalized sports nutrition: carbohydrate intake during exercise. Sports Med. 2014;44 Suppl 1(Suppl 1):S25-S33. doi:10.1007/s40279-014-0148-z https://pmc.ncbi.nlm.nih.gov/articles/PMC4008807/ 

  3. Sánchez-Oliver AJ, et al. Carbohydrate and electrolyte supplementation strategies to enhance sports performance: a systematic review and meta-analysis. Appl Sci. 2026;16(6):2967. doi:10.3390/app16062967

  4. Bourdas DI, Souglis A, Zacharakis ED, Geladas ND, Travlos AK. Meta-analysis of carbohydrate solution intake during prolonged exercise in adults: from the last 45+ years’ perspective. Nutrients. 2021;13(12):4223. doi:10.3390/nu13124223

  5. Rollo I, Gonzalez JT, Fuchs CJ, van Loon LJC, Williams C. Primary, Secondary, and Tertiary Effects of Carbohydrate Ingestion During Exercise. Sports Med. 2020;50(11):1863-1871. doi:10.1007/s40279-020-01343-3 

  6. Cermak NM, van Loon LJ. The use of carbohydrates during exercise as an ergogenic aid. Sports Med. 2013;43(11):1139-1155. doi:10.1007/s40279-013-0079-0

  7. Thomas DT, Erdman KA, Burke LM. American College of Sports Medicine Joint Position Statement. Nutrition and Athletic Performance. Med Sci Sports Exerc. 2016;48(3):543-568. doi:10.1249/MSS.0000000000000852

  8. de Ataide e Silva T, Di Cavalcanti Alves de Souza ME, de Amorim JF, Stathis CG, Leandro CG, Lima-Silva AE. Can carbohydrate mouth rinse improve performance during exercise? A systematic review. Nutrients. 2013;6(1):1-10. Published 2013 Dec 19. doi:10.3390/nu6010001

  9. Currell K, Jeukendrup AE. Superior endurance performance with ingestion of multiple transportable carbohydrates. Med Sci Sports Exerc. 2008;40(2):275-281. doi:10.1249/mss.0b013e31815adf19

  10. Wilson PB. Multiple Transportable Carbohydrates During Exercise: Current Limitations and Directions for Future Research. J Strength Cond Res. 2015;29(7):2056-2070. doi:10.1519/JSC.0000000000000835

  11. Jeukendrup A. The optimal ratio of carbohydrates. MySportScience. Published March 24, 2024. Accessed April 30, 2026. https://www.mysportscience.com/post/the-optimal-ratio-of-carbohydrates

  12. Rowlands DS, Houltham S, Musa-Veloso K, Brown F, Paulionis L, Bailey D. Fructose-Glucose Composite Carbohydrates and Endurance Performance: Critical Review and Future Perspectives. Sports Med. 2015;45(11):1561-1576. doi:10.1007/s40279-015-0381-0 

  13. Podlogar T, Wallis GA. New Horizons in Carbohydrate Research and Application for Endurance Athletes. Sports Med. 2022;52(Suppl 1):5-23. doi:10.1007/s40279-022-01757-1

  14. Costa RJS, Gaskell SK, McCubbin AJ, Snipe RMJ. Systematic review: exercise-induced gastrointestinal syndrome—implications for health and disease. Aliment Pharmacol Ther. 2017;46(3):246-265. doi:10.1111/apt.14157

  15. Tiller NB, Roberts JD, Beasley L, et al. International Society of Sports Nutrition Position Stand: nutritional considerations for single-stage ultra-marathon training and racing. J Int Soc Sports Nutr. 2019;16(1):50. Published 2019 Nov 7. doi:10.1186/s12970-019-0312-9

Anna Estes
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Pre-Training Nutrition: What and When to Eat Before a Workout