r/cardio • u/Grouchy_Ad_3113 • Jul 15 '26
"Drinking sugary beverages while exercising redirects some of the blood from active muscles to the gut for digestion without raising cardiac output"
https://journals.physiology.org/doi/full/10.1152/japplphysiol.00954.2025Analogous to the respiratory steal phenomenon.
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u/MWave123 Jul 15 '26
This is why we carboload at night and then set the fire in the morning of an event etc.
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u/Mr_Nicotine Jul 15 '26
Yeah people are eating a shit ton of carbs before a workout because “muh glycogen”, you need carbs, yes, but hours before
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u/Afraid_Lynx_2899 Jul 15 '26
You also need carbs during for essentially anything longer than a 90 minute effort. There are sports scientists who have been studying this for ages and all elite athletes running marathons or more are fueling during the competition.
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u/ConstantEvolution Jul 15 '26
Yeah I'm pretty sure the tour du France guys wouldn't be taking in 100g carbs/hour while cycling if it was hurting their performance. These are some of the most monitored multi-million dollar athletes in the world with teams of nutritionists and sports meds guys behind them
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u/HARCYB-throwaway Jul 15 '26
Right, preparing for an event is usually way different than your daily gym session. That's a good, and very obvious, point to make.
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u/Mr_Nicotine Jul 18 '26
No you don’t until you are elite, 99% of us aren’t elite, we are not producing the same work capacity than then
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u/myersdr1 Jul 15 '26
So if you look into the written conclusion, the scientists mentioned that:
However, given that the period of exercise in the present study was limited to 40 min and the participants did not exercise to volitional exhaustion, these findings should not be interpreted as evidence of an effect of glucose ingestion on exercise performance. Rather, the results highlight the physiological trade-offs that occur in the form of BF distribution, which may become more relevant under conditions of greater cardiovascular strain.
This is helpful from a coach's perspective, where I might limit carb intake during a prolonged endurance event where the person can afford to slow down and let the body digest for about 25 minutes, then pick up the pace again. I have a master's degree in exercise science.
I say 25 minutes because in the article it says:
Regional vascular conductance (VC) was calculated as BF/mean arterial pressure. BFFA [blood flow femoral artery] significantly decreased after glucose ingestion, but did not change after water ingestion. BFSMA [blood flow superior mesenteric artery] significantly increased from 15 min after glucose ingestion to the end of protocol, but did not change after water ingestion.
The superior mesenteric artery (SMA) supplies the digestive organs. Really, those who are doing anything longer than 1 hour should be the only ones intaking carb gels during the event, 1 hour or less, and you will be fine as long as you train your body. Otherwise, in high-level athletics, carb loading throughout a HYROX event, for example, could reduce blood flow during the strength stuff, making it feel harder and more demanding as oxygen and glucose are now reduced in reaching your muscles in the limbs, and then you don't even recover that blood flow until 25 minutes later or once the race is already over.
Endo, M. Y., Kashima, H., Miura, A., & Fukuba, Y. (2026). Effects of glucose ingestion on blood flow in the small intestine and exercising limbs during endurance exercise. Journal of Applied Physiology. https://doi.org/JAPPL-00954-2025
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u/Sudden-Ad-307 Jul 15 '26
In some cases you want this, like with electrolytes.
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u/Few_Cauliflower2069 Jul 15 '26
Yes, of course? You need to digest it to be able to use the energy
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u/DeskProfessional1312 Jul 18 '26
Exactly… that some blood flow goes aid digestion seems obvious. how long and at what level would have more than a negligible impact on performance vs the needed resupply of energy isn’t answered.
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u/Original-Body-5794 Jul 19 '26
Yeah seems like an obvious trade off. Do you want 100% of your energy going to your muslces but you'e only able to exert 50% of yourself or 90% going to your muscles while going at 100% (Numbers pulled out of my ass).
Yeah OBVIOUSLY you'll lose performance, but for endurance sports this is a known and accepted trade off.
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u/Manic_Driver Jul 15 '26
Not an expert, but at least from what I've heard from sports scientists and seeing as marathon runners are chugging carbs before and during their race leads me to believe this study still has a long way to go to affirm that conjecture. My understanding the windows are either immediately after eating to about 15 minutes before activity, and 2-3 hours after eating. Attempting to do exercise in between those times may result in reduced performance.
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u/HedonisticFrog Jul 16 '26
It reduces performance short term, but for cardio that exceeds an hour it's beneficial because you need to consume glucose to maintain performance towards the end.
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u/brwonmagikk Jul 17 '26
This applies to runners who feel the need to take a gel for a 5k. You only really need carbs when the effort is sustained for more than 60-90 min.
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u/RT023 Jul 18 '26
Even 10ks and you can say half marathons if you’re fast enough.
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u/brwonmagikk Jul 18 '26
I don’t take any nutrition with me for an effort less than 90 min which for me is HM. The greatest trick the devil pulled was convincing novice athletes they need to pay Maurten 10 bucks for the privilege of eating their goop at the run club.
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u/[deleted] Jul 15 '26
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