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Where does the weight go?

aggle-rithm

Ardent Formulist
aggle-rithm
Joined
Jun 9, 2005
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As I've been trying to lose weight recently, it occurred to me that losing weight is a perfect example of Einstein's equation showing that mass is the equivalent of energy. You expend more energy, you take in less mass, and you lose weight.

Then it occured to me that the amount of mass I've lost so far (about ten pounds), if converted into pure energy, would come out to somewhat more than what I have exerted being awake for 16 hours a day and occasionally riding an exercise bike. In fact, it would probably be enough energy to vaporize a city.

So probably only a very small fraction of the lost ten pounds was actually converted into energy. Perhaps just the amount of energy released by a run-of-the-mill exothermic reaction.

So where does the rest of the weight go? I assume it must break down and be eliminated by the body. Is anyone familiar with the process?
 
Your body stores excess energy as fat. This fat contains chemical bonds that, when broken release some energy that can be captured by the body (though both converting energy to fat and the reverse are not 100% efficient).
This energy is used by the body to maintain itself. The remnants of the fat are shunted into the metabolic cycle of the body and either used to build new cells or discarded trough your intestines.
But the only energy created is what is contained in the chemical bonds in the fat, not the potential energy of the atoms making up the fat. Releasing that would require some form of nuclear reactions.
The energy you released is roughly equivalent to taking the weight you lost, draining it of water and then burning it. The heat the flames produce is the energy released by using up the fat.

Taking 1 kg weightloss, that means 300 grams of dry weight, so the heat of burning a small pan of olive oil would be a good indication of the amount of energy used. Which would be barely enough to raise an average room 1 degree in temperature.
Still impressive, but nowhere near as much.
 
Lukraak_Sisser said:
Your body stores excess energy as fat. This fat contains chemical bonds that, when broken release some energy that can be captured by the body (though both converting energy to fat and the reverse are not 100% efficient).
This energy is used by the body to maintain itself. The remnants of the fat are shunted into the metabolic cycle of the body and either used to build new cells or discarded trough your intestines.
But the only energy created is what is contained in the chemical bonds in the fat, not the potential energy of the atoms making up the fat. Releasing that would require some form of nuclear reactions.
The energy you released is roughly equivalent to taking the weight you lost, draining it of water and then burning it. The heat the flames produce is the energy released by using up the fat.

Taking 1 kg weightloss, that means 300 grams of dry weight, so the heat of burning a small pan of olive oil would be a good indication of the amount of energy used. Which would be barely enough to raise an average room 1 degree in temperature.
Still impressive, but nowhere near as much.
Click to expand...

I hadn't considered that most of the weight is actually water trapped in fat cells. That makes sense.
 
A related mystery (to me anyway) is why I can't put on weight no matter how much I eat, unless I exercise damn hard and long-term and add muscle. Does my body refuse to digest that 'spare' food? That seems unikely. Or does the liver keep tabs on what food is actually required and/or can be stored and discard the 'spare' via the kidneys or some other route?
 
Lukraak_Sisser said:
Your body stores excess energy as fat. This fat contains chemical bonds that, when broken release some energy that can be captured by the body (though both converting energy to fat and the reverse are not 100% efficient).
This energy is used by the body to maintain itself. The remnants of the fat are shunted into the metabolic cycle of the body and either used to build new cells or discarded trough your intestines.
But the only energy created is what is contained in the chemical bonds in the fat, not the potential energy of the atoms making up the fat. Releasing that would require some form of nuclear reactions.
The energy you released is roughly equivalent to taking the weight you lost, draining it of water and then burning it. The heat the flames produce is the energy released by using up the fat.

Taking 1 kg weightloss, that means 300 grams of dry weight, so the heat of burning a small pan of olive oil would be a good indication of the amount of energy used. Which would be barely enough to raise an average room 1 degree in temperature.
Still impressive, but nowhere near as much.
Click to expand...

You're spot on. Another way of putting it is that the 300g of light oil would keep a modern high economy diesel car running for about 6 kilometres.

Hans
 
Fat is considered to have about 9kcal of energy per gram. 10lb is 4536g, so that's about 41,000 kcal, or about 172MJ/48kWh, which is roughly the energy requirement for the human body over 16 days (i.e. 2500kcal per day).

If you lost 10lb in 16 days that would be about the same amount of energy as consumed by a 3kW electric heater left on for the same period of time.

IIRC, the human body is about 15% efficient at converting chemical energy into mechanical energy (the rest being converted to heat), so even quite modest exercise can require large amounts of energy to be consumed.
 
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GlennB said:
A related mystery (to me anyway) is why I can't put on weight no matter how much I eat, unless I exercise damn hard and long-term and add muscle. Does my body refuse to digest that 'spare' food? That seems unikely. Or does the liver keep tabs on what food is actually required and/or can be stored and discard the 'spare' via the kidneys or some other route?
Click to expand...

Well, you are one of the lucky ones. In fact, all people do that; if you ad up everything an obese person has eaten in his/her life, and deduct their exercise, you will find that they should weigh a couple of tons. Fortunately, the body has ways of discarding excess food. Some is simply not absorbed, but discarded as faeces. Some is burnt off as excess heat.

Your 'weight-stat' is simply set low, so your body keeps lean. If you are male and below 25 or so (20 for females), beware, though: It may not last, so don't adapt any overeating life-style.

Also, these lean people, who 'can eat anything' if you sum up what they actually eat, over a period of time, you will often find that it isn't that much after all. They can binge unpunished at times, but then there are all those skipped lunches, and the fast ham sandwiches for dinner.

Hans
 
You all probably aren't speaking literally, but all the mention of heat inspires me to ask a stupid question. Feel free to laugh at and otherwise mock me.

I feel hot all the time, especially when I have gained a lot of weight (or when I am in the process of gaining it). Is the feeling of radiating heat related to the weight? If so, when you burn calories, does the heat dissipate? (I warned you it was a stupid question.)
 
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Twice in recent years I've lost 50 pounds in six months or less. Low card diet helped with the appetite, but mostly the bust ass labor of restoring old trucks:
http://imageevent.com/bigchriscase/53powerwagon?n=0

Water loss during the day was replaced in the evenings, but noticed the real losses occurred overnight. Maybe two pounds. I figured that the fat was being metabolised into 'fuel' with in the cells. Fat -> ATP gives off water and CO2, both of which are exhaled. Think of the ATP as gunpowder. Then the next day the ATP is set off while working. Repeat daily, 10 pounds per week some weeks.

I'm down nearly 20%, yet my body fat percent has only dropped 3%. So it must have been mostly water.

And, as an aside, there was a Kaiser study done a couple years ago that showed that a BMI range of 17-34 was PERFECT. 17 no better than 34, and 24 no better either. I believe it was the first large study on weight vs health. Previous goals were based on Metropolitan Life Ins Co. chart that equaled "at five feet tall, for women, start at 100#, for men 125#, add 5# per inch". WAAAAY to pat to have been scientific.

My MD gave me the target of 251, BMI 34. I went on past to 239 before re-gaining 5.
 
GlennB said:
A related mystery (to me anyway) is why I can't put on weight no matter how much I eat, unless I exercise damn hard and long-term and add muscle. Does my body refuse to digest that 'spare' food? That seems unikely. Or does the liver keep tabs on what food is actually required and/or can be stored and discard the 'spare' via the kidneys or some other route?
Click to expand...

Body builders need the capacity to digest 10,000 calories per day. Pumping iron, plus excess to ensure they don't burn muscles for energy. Plus some excess to build mass.

So, with pancreatitis in the family, I suspect that there are genetic variations in digestive capacity. Can you even eat 3,000 calories at a meal?
 
FattyCatty said:
You all probably aren't speaking literally, but all the mention of heat inspires me to ask a stupid question. Feel free to laugh at and otherwise mock me.

I feel hot all the time, especially when I have gained a lot of weight (or when I am in the process of gaining it). Is the feeling of radiating heat related to the weight? If so, when you burn calories, does the heat dissipate? (I warned you it was a stupid question.)
Click to expand...

The chemical reaction of breaking ATP bonds gives off heat if its not used for anything else. It is possible for the body to 'short circuit' this reaction to generate heat and nothing else. Its how we keep our bodies a constant temperature.
However by excercising you use the excess energy to move your body around as well.
Feeling hotter when you've gained weight might be due to a slightly more active metabolism, but fat is also a good insulator, thus allowing your body to get less cold.
If you burn calories the heat does dissipate, trough sweating ed, but a significant part will also be used to do whatever excersize you do.
 
aggle-rithm said:
So where does the rest of the weight go? I assume it must break down and be eliminated by the body. Is anyone familiar with the process?
Click to expand...
Since 'most' of it is carbon & hydrogen, most of it is exhaled in the form of CO2 and H2O (with liquid water in sweat and urine also contributing a lot).
 
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