Ok, I know when you burn 3500 calories it equates to one pound of weight loss. My question is when does that weight loss occur? Are you losing the weight immediately? Does you body have to dispose of the burnt calories over a few hours?
For the sake of this question lets say I started an exercise routine weighing 200 lbs. I burn exactly 3500 calories (no more and no less) during my workout. After I am done I replenish all the water lost through sweat (no more no less).
Well, an exercise routine to burn 3500 calories would be something larger than a marathon, so I would fully expect a pound to be lost, and be measurable, even after replenishing the exact amount of fluid lost.
Why is what hard to believe? I understand that burning 3500 calories takes a hell of a workout. What I want to know is when the weight loss happens. Is it immediate? Or can you burn calories faster than your body can lose the weight? Meaning your body has to play catch up to your workout.
I only used 3500 calories as an example because it equates to one pound of fat. I figured it would be easier to explain using 3500 cal. per pound ratio instead of talking about 218.75 calories per ounce.
If you prefer, I just burnt 218.75 calories sitting at my computer. Am I exactly one ounce lighter than when I started?
In order for your body to use energy, it has to have it first. So no, you can’t burn calories faster than your body can drop weight.
No offense, but your question suggests that you don’t know much about physiology and energy production. You should go over to http://www.howstuffworks.com and poke around the body stuff. Something there should be useful.
I’ll admit doubt with regards to whether exhausting a pound of body fat means burning it all as heat, or whether part of the body fat cell is actually support material that is flushed out as waste once the energy (heat) portion of a fat cell is exhausted.
So, if a fat cell is 80% energy and 20% support material, then the body needs to play ‘catch up’…i.e. the body needs to flush out the remaining support material later before the cycle of fat loss is complete.
No offense either, Ultrafilter, but if I understood physiology and energy production really well I wouldn’t be asking the question. No need to sound condensending while trying to help. Thanks for the link though.
NYR407, I think your question is a good one. Let me see if I can rephrase it. (BTW, I’m a marthon runner). Despite what ultrafilter says, I’d say you have to burn calories “faster” than your body loses weight. The fat mass would have to be converted into waste materials, to be excreted later. If this were not the case, then the only way to lose weight would be according to E=mc^2. I don’t thnk anybody’s metabolism works quite that way.
So, the question is- how much later?
I suppose we’re neglecting sweat, so how does the mass actually leave? Urine? Bowels? Resparation?
I know I’ve dropped 5 lbs or more running marathons, but that data point’s no good due to hydration, snacks along the way, etc.
Race Bannon, thanks for the input. Yes I am negating sweat because that needs to be replenished. Which I believe is why you have lost more than 5 lbs during a marathon when you have not burned enough calories to equate to that loss. You will eventualy put some or most of that weight back on when you refuel.
sailor if what you are saying is correct then is the carbon dioxide expelled through breathing? Pores?
To go back to my earlier hypothetical question: Lets say I burn 218.75 calories (1/16th of 3500 in case anyone was wondering) in 30 mins in a completly rested state. I do not eat, drink or sweat. Will I be exactly one ounce lighter at the end of those thirty mins?
If sailor is corect than I must be, right? If not, then we have to excrete them some time after we burn them. Or at least at a slower rate than when we burn them.
The fuel you are burning is mostly glucose, not carbon. Some fat is burned, too. (Protein, too, but rarely.) In order to use fat as a fuel, your body must have sufficient oxygen. Glucose can be burned without oxygen, but that is not very efficient, especially insofar as re-synthesizing ATP (adenine triphosphate) which is the source of your ability to convert fuel into work. ATP stores chemical energy which is used when it breaks down into other phosphate chemicals.
If you don’t get enough oxygen (you get anaerobic), the end product of the glucose metabolism is lactic acid which accumulates in the blood before the liver can convert it into glucose. If you get enough oxygen, the end product is pyruvic acid and you don’t get the lactic acid build-up. The pyruvic acid is synthesized into glucose again.
No matter what the fuel, glucose, fat, or protein (which can be used in an emergency), it must be converted into glucose before it can be used. That is why fat requires more oxygen.
All other factors being equal (such as the state of hydration), you will lose as much weight as you expend over and above your intake.
Nope. The fuel you are burning is a mixture of carbon, hydrogen, and oxygen (and sometimes nitrogen). In the case of a carbohydrate such as glucose or glycogen it is only about 40% carbon by weight.
So only about 40% of weight lost in catabolism is expelled in the breath as the carbon in CO2. 60% shows up initially as water in the tissues, and is expelled rather more slowly in sweat and urine.
Since the level of hydration also varies with exercise, diet, and a diurnal rhythm, weight loss is not only delayed until urination, but rather hard to detect against a background of varying levels of hydration.
This isn’t quite right. Urine and sweat aren’t the only means of water loss. Your lungs are very wet, and a significant part of the body’s cooling takes place via water evaporation in the lungs.
We agree, though, that weight loss consequent upon exercise is spread out in time by delays in some of the paths involved in the excretion of metabolically-produced water, and that it is hard to measure against a background of changing levels of hydration. Is that right?
Do you know roughly what proportion of water excreted leaves the body as the humidity of exhalations, under typical circumstances?
It depends on what you’re doing, and what the ambient conditions are, but roughly speaking, you lose 1/3 through urine, 1/3 through sweat and 1/3 through respiration.
My eldest brother, who is a medical doctor now, but was a research biochemist for twenty years, tells me that vertebrate physiology is able to convert protein to glucose and glucose to fat, but cannot convert fat to glucose or protein, and cannot convert glucose to protein. And he tells me that nerve cells and red blood cells need glucose, though other cells can run on fat. Which is why, he says, you cannot survive in health burning your fat: if you don’t eat either carbohydrate or protein, your body will be forced to break down proteinaceous tissue to power the nervous system, and you will get sick.
Now, metabolism wasn’t his speciality (his field was the design of low-toxicity dyes that bind temporarily to specific tissues for use in non-invasive organ imaging). So he was remembering classes he took in 1969, and it is entirely possible that he is wrong. But if so, I’d like to see some quality citations.
I have read the section of the article on metabolism in Encyclopaedia Britannica that discusses the catabolism of fats. According to it fatty are broken down stepwise into acetyl groups (each attached to attached to a molecule of coenzyme A), not converted into sugars at any stage. But encyclopaedias have been known to contain errors.
So:
What is the primary evidence that human muscle cells (or instance) cannot run on fat?
What is the primary evidence that human physiology can convert fat to glucose?
If you still have the EB handy, check on the Krebs Cycle entry, or check the Krebs Cycle on the Web. Only glucose (not fat or protein) enters this Cycle, which is the process wherein the stored energy in ATP is used to provide for all work performed, including metabolism, running, etc.
I may be wrong - again - but if I am, please inform me through what process fat is used for energy. I’d be most grateful for enlightening me.
Using basic figures (from the EB!) for respiration, such as volume of lungs, volume of normal breath, percentage of oxygen in air, percentage of carbon dioxide exhaled, breathing rate, mass of carbon in carbon dioxide, etc., you can show that it’s possible to lose a pound or more of carbon while sleeping. That surprised me, but there it is.
And, while you’re losing that weight, you’re also sweating, and losing water weight in respiration. That’s why non-strenuous activities such as sleeping or typing have a weight loss figure associated with them. However, during the normal course of the day, you also drink water (one pint, two cupfuls, adds a pound), shit and urinate, and eat breakfast, lunch, dinner, snacks–a varying background, which is why it is often recommended that you weigh yourself once per day at a regular time (before breakfast, if you want to use the lowest possible value), or even less often than that.
Actually the muscles do not burn glucose directly but transform it into ATP first. ATP can be got from fat and protein too but it is much more inefficient. Glucose is the best fuel.
The body does use glucose as fuel, but it is transformed into pyruvate and then Acety CoA as it enters the Krebs cycle. Glucose is also used to resynthesize ATP, but neither ATP or glucose actually enters the Cycle. ATP provides the energy (kick-start) for metabolic reactions which use Acety CoA. http://www.people.virginia.edu/~rjh9u/krebsum.html
