One gram of carbs is 4 calories., so more like 400 calories per hour.

It was confusing when the running industry switched from calories to grams of carbs, but that's all anyone talks about now.

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mbesto 8 hours ago | parent | next [-]

Because calories simply do not matter. At high intensities of working out, it's the amount of carbohydrates you can consume that allow more fuel to be burnt.

"In the aerobic exercise domain up to ~100% of maximal oxygen uptake (VO2max), CHO is the dominant fuel, as CHO-based oxidative metabolism can be activated quickly, provide all of the fuel at high aerobic power outputs (> 85-90% VO2max) and is a more efficient fuel (kcal/L O2 used) when compared to fat."

https://www.gssiweb.org/sports-science-exchange/article/regu...

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teiferer 6 minutes ago | parent | next [-]

Then why replace one imprecise term with another? Fiber is a carbohydrate. Humans use close to nothing from its energy. (Though it plays another important role in the digesive system.)

Try eating 100g of grass per hour during a marathon and you will see. That's the metabolic edge horses have over humans.

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fc417fc802 7 hours ago | parent | prev | next [-]

Calories do matter (obviously, as energy intake is the entire point) but as you note the specific form that the fuel takes matters. However "carbs" is a catch all that includes plenty of things that (I assume) would be of similarly minimal use in this scenario. The calories need to take a very specific chemical form for this to work.

	▲	mathgeek 6 hours ago \| parent [-]
		The wording is certainly confusing here, but yes the calories don’t matter as much as the form. Eating protein and fats simply give you minimal useful calories during the race. Even most carbs won’t be useful if they are more complex.

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loeg 7 hours ago | parent | prev [-]

They're equivalent modulo some multiple. It doesn't matter which one we talk about, as long as we're consistent.

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whycome 8 hours ago | parent | prev | next [-]

It’s also confusing that most nutritional labels say “calories” (Cal) when they really mean kilocalories (kcal). And those are different from regular (‘small’) calories (a measure of energy needed to heat 1g water 1c).

1 food calorie as listed on a food label is enough to heat 1kg of water by 1c

	▲	schoen 3 hours ago \| parent [-]
		This was the explanation for why the scotch and soda diet doesn't work: https://www.futilitycloset.com/2008/11/16/the-mensa-diet/ (If the nutritional calories in the drink had been only the same number of thermodynamic calories, the drink would have been energetically negative for the body because of its low temperature.)

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justinwp 8 hours ago | parent | prev | next [-]

It's deliberate, because you generally do not want calories from fat or protein during a marathon or other running race.

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7 hours ago | parent | prev [-]

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