How does the body speed up metabolism?

[Darkmisc]

TL;DR Summary

Could someone explain what happens in the body when metabolism speeds up? For example, does it produce more stomach acid? Or does it produce more concentrated stomach acid?

Hi everyone

Could someone explain what happens in the body when metabolism speeds up? For example, does it produce more stomach acid? Or does it produce more concentrated stomach acid? Thanks

 

[jedishrfu]

Here's a description of how your metabolism works:

https://www.vox.com/2016/5/18/11685254/metabolism-definition-booster-weight-loss

 

[jim mcnamara]

The thyroid gland produces hormones that control the basic metabolic rate - BMR. Is that what you are asking?
It is usually measured in units called METS. It is a major measurement in exercise physiology. It tells us how fast a person is burning fuel - glucose - by tracking oxygen consumed or carbon dioxide given off.

One MET is ~3.5 milliliters of $O_2$ consumed per kilogram of body weight per minute.
By definition, one met is what a human uses sitting at rest. If you have a BMR related disease like hyperthyroidism - too much thyroid hormone - your MET measure will be elevated because how fast you burn oxygen just sitting still changed. It went up. Exercise raises METs, too. But it goes back to normal when you rest.

See: https://www.healthline.com/health/what-are-mets

FWIW - your question is hard to answer, for me it sounds more related diet thinking. But metabolic rate is NOT controlled by a normal diet necessarily. Stomach acid secretion is not part of a BMR measurement.

 

[russ_watters]

FWIW - your question is hard to answer, for me it sounds more related diet thinking. But metabolic rate is NOT controlled by a normal diet necessarily. Stomach acid secretion is not part of a BMR measurement.

I think that's what the OP is asking/confused about...or maybe is just looking at it from the wrong direction. Correct me if I'm wrong, but rate of food digestion(input) is not directly related to metabolism(output), is it? The body doesn't digest food faster once you start exercising, does it?

 

[jim mcnamara]

@russ_watters
Not really - food intake and digestion diverts energy. There are a variety of studies that show the metabolic cost of ingestion and digestion. They vary, a lot, big surprise. There are no foods - celery is exemplar, wrongly attributed often - that require more calories to process than they contain. Water is not considered a food stuff in this context.

When you exercise, energy usually comes either
- from small amounts of simple sugars you recently ingested ( mouth & stomach) - these have low access overhead.
or
- from breakdown of stored sugar "polymers" like glycogen - higher access overhead. Ketones work as well. Parts of the brain (some cerebellum tissues) create ketones from glucose before they can be used. So it is a done deal biochemically.

And AFAIK digestion takes a hit and slows down when you exercise strenuously, mostly because of diversion of blood flow to muscles and pulmonary areas. Ever try to run a couple of miles after a Thanksgiving meal? Suggestion: don't.

[opinion]
Nutrition studies have a pollution factor --- per Robert Ludwig - UCSF
A significant number of studies have been funded by agencies/entities with a strong financial interest. And it is not declared in the paper.

Please take that into consideration.

Robert H. Lustig, M.D., M.S.L. is Professor emeritus of Pediatrics, Division of Endocrinology at the University of California, San Francisco (UCSF). You can see his pediatric sucrose research presented on youtube.
[/opinion]

 

[Darkmisc]

The thyroid gland produces hormones that control the basic metabolic rate - BMR. Is that what you are asking?

Sort of. I'm wondering why it feels like I digest food faster after exercise. I'd guess that I get hungry 30 - 60 mins sooner than on days I don't exercise.

What does the body do in response to the hormones from the thyroid gland?

 

[jim mcnamara]

Exercise burns more calories than sitting. Your hunger is a response to lowered blood sugar levels induced by exercise using more calories than sitting.

Thyroid - short answer: it controls how fast or slow the cells in your body take up and burn glucose.
Actually there are several hormones, the primary one is thyroxin, named for the thyroid gland where it is created. And there is a broad range of effects. Too much for this post.

There is also a circadian 24 hour "clock" that raises and lowers body temperature from a low at ~3:00am to a high 12 hours later. Artificial lighting can "mess this up". Thyroid and pituitary gland hormones are involved in this cycle.

 

[EmpireJones]

It's interesting how we can estimate energy expenditure based on how hard we're breathing! And indirectly, we could estimate how hungry we'll be, based on how hard we're breathing. Perhaps I could automate a notification for when to start cooking, based on when I work out, and how many MET-minutes are logged from the workout!

For anyone interested, here's an elementary explanation of what MET-Minutes are, which also lists how many METs various exercises consume.

 

[jrmichler]

The topic of nutrition, digestion, and energy systems is of considerable interest to endurance athletes, so has been extensively studied. For example, The Lore of Running, 4th Edition, by Dr. Tim Noakes has over 190 pages on the subject.