Adaptive Responses to Dehydration


#1

According to ISBN 978-3-642-29056-5 (eBook), the inevitable proteolysis that occurs during fasting might contribute to restoring euhydration in migratory birds during their uninterrupted days long flights. Does anybody have scientific evidence/sources that the 16 moles of H2O produced by the oxidation of fatty acids contributes as well?


(Bacon by any other name would taste just as great.) #2

No, but it’s entirely plausible. Not sure how you’d look for studies on PubMed, though.


(Michael - When reality fails to meet expectations, the problem is not reality.) #3

A quick search for ‘lipolysis aids hydration’ produces studies that support the contention that hydration aids lipolysis but not that lipolysis aids hydration. I might have time for more rigorous search later after I get home from work.


#4

See, I ask because it seems paradoxical and against the basic principles of LeChatelier and homeostasis that a reaction that produces so much water (fatty acid B-oxidation) would be accelerated by more water ?!?
Indeed, according to [doi: 10.3389/fnut.2016.00018], AngII (released in dehydration) induces UCP1. Insulin resistance, a hormone that induces lipogenesis, is a consequence of dehydration according to the paper as well.
Seems to me like dehydration promotes lipolysis and hydration might be counterproductive.
I believe the lipolysis associated with overhydration is the temporary increase in renal metabolism processing the excess water.


(Bacon by any other name would taste just as great.) #5

I have to confess that I’m not clear what you are talking about. Lipolysis is the the chemical reaction that reduces triglycerides to their component fatty acids plus the glycerol backbone. It is inhibited by insulin and facilitated by hormone-sensitive lipase.

Fatty-acid metabolism, on the other hand, is the term for metabolising fats into energy. It occurs in the mitochodondria, in particular of muscle cells.

Not the best chosen terms, perhaps, but we’re stuck with them. So which are we talking about?


#6

Lipolysis is ultimately the oxidation of a fatty acid into CO2 and water, lots of water :slight_smile:
It is indeed inhibited by insulin and induced by glucagon amongst other things.

I was just wondering whether drinking water would accelerate lipolysis or slow it down.

“Casual” websites recommend drinking more water. However, what I gather from scientific principles and publications [doi: 10.3389/fnut.2016.00018] seems to indicate the contrary.


(Michael - When reality fails to meet expectations, the problem is not reality.) #7

Abstract

Drinking lots of water is commonly espoused in weight loss regimens and is regarded as healthy; however, few systematic studies address this notion. In 14 healthy, normal-weight subjects (seven men and seven women), we assessed the effect of drinking 500 ml of water on energy expenditure and substrate oxidation rates by using whole-room indirect calorimetry. The effect of water drinking on adipose tissue metabolism was assessed with the microdialysis technique. Drinking 500 ml of water increased metabolic rate by 30%. The increase occurred within 10 min and reached a maximum after 30–40 min. The total thermogenic response was about 100 kJ. About 40% of the thermogenic effect originated from warming the water from 22 to 37 C. In men, lipids mainly fueled the increase in metabolic rate. In contrast, in women carbohydrates were mainly used as the energy source. The increase in energy expenditure with water was diminished with systemic β-adrenoreceptor blockade. Thus, drinking 2 liters of water per day would augment energy expenditure by approximately 400 kJ. Therefore, the thermogenic effect of water should be considered when estimating energy expenditure, particularly during weight loss programs.


(Ben ) #8

And I’ll have a dry fast to that thought.