Most of us know the basic advice when it comes to nutrition: eat more carbohydrates when training is harder, eat a little less when training is easier, and fuel the work that matters most. That sounds simple. But nobody is perfect.
A new observational study tried to answer a practical question:1Rothschild, J. A., Morton, J. P., Stewart, T., Kilding, A. E., & Plews, D. J. (2026). Dietary Intake of Endurance Athletes During 12 Weeks of Self-Selected Training: An Observational Study. International Journal of Sport Nutrition and Exercise Metabolism, 1–10. https://doi.org/10.1123/ijsnem.2026-0032 Are endurance athletes actually adjusting carbohydrate intake based on training load in the real world?
Researchers followed 46 endurance athletes for 12 weeks as they self-selected their training and logged both dietary intake and exercise using a smartphone app. That gave the researchers a large day-to-day dataset: 3,718 days of dietary assessments and 3,160 days of training. The main focus was on carbohydrate intake and its relationship to training volume, exercise duration, and fasted-state training.
Higher weekly training volume was associated with higher average daily carbohydrate intake, and longer exercise sessions tended to come with more carbohydrate. So the broad picture was not that endurance athletes are completely ignoring fueling demands.
But the individual-level data were much more variable. Average carbohydrate intake ranged widely, from 1.2 to 7.2 g/kg/day, with a group average of 3.9 g/kg/day. That is not very high for endurance athletes, especially during heavier training. Fasted training was also common: 65% of athletes did it regularly, and it was more common among men than women. Athletes who trained fasted more often tended to have lower overall carbohydrate intake.
The most interesting part of the study is that some athletes adjusted carbohydrate intake closely with training load, while others barely did. Individual correlations between daily training load and carbohydrate intake ranged from negative to strongly positive. In other words, some athletes were fueling more on bigger days, some were not changing much at all, and some appeared to eat less carbohydrate when training more.
This is where the study becomes useful. The average athlete may understand carbohydrate periodization in theory, but applying it day after day is a different skill. The study does not tell us whether the lower-carb or fasted-training athletes performed worse, recovered worse, or had more health issues. It simply shows that “fuel for the work required” is not yet how many endurance athletes actually behave.
What this means for runners
Carbohydrate intake should probably move more intentionally with your training. Easy short run? You may not need much beyond normal meals. Long run, workout, race-specific session, or a big-volume day? That is when carbohydrate availability becomes performance nutrition, not just calories. I’d especially pay attention to whether your hardest sessions are being accidentally under-fueled because they happen early, because you’re busy, or because you’re trying to keep daily intake artificially low.
The overall goal is not to micromanage every gram, but to avoid treating a 30-minute jog and a 2-hour run as having the same fueling demands. Just be a bit more intentional about fueling.
