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I was curious about this. I'm on a diet now and I often weight like 0.5-0.8 kg less in the morning. And when I go on a 20km walk on the weekend I lose about 1k

by ajuc 6y ago

I was curious about this. I'm on a diet now and I often weight like 0.5-0.8 kg less in the morning. And when I go on a 20km walk on the weekend I lose about 1kg in 5 hours. Is it mostly water? Cause I drink a lot during the walk and I don't go fast enough to get sweaty.

breischl 6y ago
It pretty much has to be. 1kg would be 1L of water, which is not that much to lose over 5 hours. But 1kg of fat is 7700 kcal, which would be a massive amount of energy to expend in 5 hours. Unless your "walks" involve running uphill with a 25kg pack or something like that. :)
- PeterisP 6y ago
  Short-term energy consumption on a 5 hour hike would be from stored glucose, fat breakdown IMHO would happen slower. A 20km hike can consume 1000-2000kcal depending on how hard it is (climb, terrain, weight of hiker, weight of pack matter) so that would be 0.25-0.5kg of carbs - so potentially that loss could be 50/50 carbs and water. But hydration definitely is a big aspect of mass simply because of how much you add and lose. I once did a ~90km hike in 24 hours or so, and I believe I drank something like 15+ litres of liquids during that.
  - ashtonkem 6y ago
    Depends on what you’ve eaten recently. It’s pretty easy to burn fat on a hike if you go while fasting.
pjc50 6y ago
Yes. A lot of fad diets and supplements work on this principle; dehydrating you appears to lose weight really quickly initially. It's not sustainable.
k__ 6y ago
The human body is darn efficient. You would probably have to run 50-70km to lose 1kg fat. It's easier to not eat calories than to burn them after eating.
ashtonkem 6y ago
Humans lose moisture for a variety of reasons normally, you don’t need to be sweating in order to lose it, although that obviously drives the loss rate up. You lose a ton of water through just breathing. On your walks you’re probably burning glycogen, the carbohydrate we store in our liver and muscles for easy access energy, and exhaling a lot of water. We store about half a kilo of glycogen which is then bound up with 3-4x as much water still. While you’re not likely to consume all your glycogen in a 20km walk (you need a marathon to do it), burning a decent chunk of it on top of normal water loss isn’t an unreasonable hypothesis.

by ajuc 6y ago

breischl 6y ago

It pretty much has to be. 1kg would be 1L of water, which is not that much to lose over 5 hours. But 1kg of fat is 7700 kcal, which would be a massive amount of energy to expend in 5 hours. Unless your "walks" involve running uphill with a 25kg pack or something like that. :)

PeterisP 6y ago
Short-term energy consumption on a 5 hour hike would be from stored glucose, fat breakdown IMHO would happen slower. A 20km hike can consume 1000-2000kcal depending on how hard it is (climb, terrain, weight of hiker, weight of pack matter) so that would be 0.25-0.5kg of carbs - so potentially that loss could be 50/50 carbs and water. But hydration definitely is a big aspect of mass simply because of how much you add and lose. I once did a ~90km hike in 24 hours or so, and I believe I drank something like 15+ litres of liquids during that.
- ashtonkem 6y ago
  Depends on what you’ve eaten recently. It’s pretty easy to burn fat on a hike if you go while fasting.

pjc50 6y ago

Yes. A lot of fad diets and supplements work on this principle; dehydrating you appears to lose weight really quickly initially. It's not sustainable.

k__ 6y ago

The human body is darn efficient. You would probably have to run 50-70km to lose 1kg fat. It's easier to not eat calories than to burn them after eating.

ashtonkem 6y ago

Humans lose moisture for a variety of reasons normally, you don’t need to be sweating in order to lose it, although that obviously drives the loss rate up. You lose a ton of water through just breathing. On your walks you’re probably burning glycogen, the carbohydrate we store in our liver and muscles for easy access energy, and exhaling a lot of water. We store about half a kilo of glycogen which is then bound up with 3-4x as much water still. While you’re not likely to consume all your glycogen in a 20km walk (you need a marathon to do it), burning a decent chunk of it on top of normal water loss isn’t an unreasonable hypothesis.