If you lose 1000 grams: What mechanisms?

Discussion in 'Human Science' started by Dinosaur, May 10, 2011.

  1. Dinosaur Rational Skeptic Valued Senior Member

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    Suppose an ex-athlete was a kilogram overweight & lost it via diet & exercise over a period of 4-6 weeks.

    Does anyone here have a clue about how much would be lost via the following?
    I would not expect much, if any, to be lost by perspiration.

    I think quite a bit would be lost by respiration: The carbon in CO[sub]2[/sub] & perhaps some oxygen & water vapor.

    I think some would be lost via urination.

    I think some, but not much would be lost by defecation.​
    The above are guesses on my part. I have no clue relating to percentages due to each possibility.

    I would expect the percentages to be much different for somebody 50 or more kilograms overweight. For example: Consider loss of water weight. I would expect an athlete one Kg overweight to maintain the same percentage of water in his body. I think an obese person would lose a lot of water weight.

    Does anyone have some pertinent knowledge or know of an article at some Web site?
     
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  3. Read-Only Valued Senior Member

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    I used to quite a bit about this but due to not needing it often, knowledge of specific numbers ten to slip away. However, I *can* tell you a few of them.

    First and foremost, water loss depends on the environmental conditions and diet (such as a lot of salt eaten/not eaten). In a hot, dry climate, sweat alone can easily use 2.5 L /hr. Typical respiration loss under temperate (mild) conditions is about 50 mL/hr.

    Hopefully you see just from those two alone that a Kg can be lost in almost no time at all if not replaced.
     
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  5. chimpkin C'mon, get happy! Registered Senior Member

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    My experience only? excreta-urine and feces.

    Either that or I'm just usually full of crap.

    Obesity isn't much water weight-it's fat. The "water weight" loss is usually the result of diets often including less sodium and more sweating via exercise.
     
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  7. Stoniphi obscurely fossiliferous Valued Senior Member

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    If it was indeed an athlete and the weight loss was for real (not transient like water loss) than it would be a combination of fat and lean muscle that was lost. The athlete would needs burn more kcals exercising than he/she took in eating to accomplish this.

    If the weight loss was merely a change in weight before and after exercise, than it would be mostly water loss through sweating, respiration and urination. I drop about 3 - 4 pounds every day during my 10 mile run. I gradually replace that over the next 24 hours, only to re-lose it during the next days run. This is obviously water - weight loss.

    Many diets cause you to lose a lot of water the first week in order to hook you on their effectiveness so you stay with the program.
     
  8. DRZion Theoretical Experimentalist Valued Senior Member

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    I actually covered this in my biochemistry class. Its mostly respiration. When fatty acids burn they are basically converted into CO2 as consecutive carbons are knocked off the fatty acid chain. Its called beta oxidation.

    Fatty acid chains are composed of anywhere between 14-32 saturated or unsaturated carbons. These are chomped off by some enzyme in twos as acetyl CoA. There are several enzymes and they form a complex.. but I don't remember their names!

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    some of the enzymes phosphorylate, others chomp, others pass the acid around. The acetyl CoA is fed directly into the citric acid cycle, which produces CO2.
     
  9. Fraggle Rocker Staff Member

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    If you lose any significant amount of weight and keep it off permanently, the only way your body can do that is by "burning" fat, a colloquial term for the biochemical reaction that extracts energy from the fat molecules by breaking down their complex chemical bonds (which store energy) and turning them into simpler molecules. (If you don't have any fat you can burn muscle, but people who are that much underweight aren't usually the ones asking questions like this.) In other words, you're exercising and your body, almost literally, "burns" the fat as fuel.

    As in any reduction process for organic molecules, the vast majority of the simpler molecules produced will be carbon dioxide and water. (Muscle tissue is largely protein, whose molecules contain nitrogen atoms, so if you burn muscle mass you will also produce some nitrogen compounds.)

    Most of these waste molecules will be exhaled in gaseous form. Matter that passes into your intestine and is excreted in solid form is primarily the indigestible portion of your food, i.e., fiber or "roughage." Metabolizing fat (or protein, sugar, starch, or any other digestible substance) will not generate a lot of feces, although it may generate some because our digestion is not 100% efficient.

    I think most of the water molecules produced by the metabolization of fat are exhaled in our breath, which has a very high moisture content. I don't think many of them go through the kidneys and bladder and come out as urine--that process would be too complicated. Urine is generally nothing more than the water you drink (in any form including milk, beer, tea, soda pop, etc.), which is used as a medium for carrying away various waste molecules that can't be exhaled, including things you shouldn't have ingested in the first place. We generally take in somewhat more water than we excrete as urine; we need it to soften our stool and secrete as tears, perspiration, etc.

    So in summary, if you lose ten kilograms of body weight and keep it off--which therefore had to be fat--probably 9.99 kg are exhaled as water and carbon dioxide, and the other ten grams may take one of the various other exit routes.

    The reason I increased the mass in the example is that people store and release water in their metabolic cycle. It's possible to reduce your weight by a kilo by simply not drinking enough water to replenish what you lose in urine, sweat, feces, saliva, etc. This is a common "dieting" trick: Oh look everybody, I lost five pounds last week! Sure ya did honey, and four and a half pounds of that was from going jogging in San Diego in the summer without a canteen and then heading for the sauna. Check back in next week, if you're still alive.
     
  10. Dinosaur Rational Skeptic Valued Senior Member

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    DR Zion & Fraggle Rocker: Thanx for the replies. I suspected that respiration was a major factor in permanent weight loss, but do not know enough about body chemistry to consider it more than a not bad guess.

    BTW: Recently, I have been able to post replies but an attempt to start a new Thread results in an error message suggesting that the site is undergoing maintenance or has a problem.
     
  11. Fraggle Rocker Staff Member

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    24,690
    Well I suppose that's one way of looking at it, but I don't think it's a very useful way. People who want to lose a great deal of weight are looking for ways to decrease their caloric intake or to increase their energy consumption, or (hopefully) both. Knowing how respiration works isn't a very useful bit of knowledge for them.

    Of course, we all really do know how it works. If you want to lose a pound of fat, you have to burn off 3,500 calories more than you take in. Few of us have the discipline to withstand constant hunger--especially if we're the kind of people who eat for solace and end up fat in the first place--so most people can't reduce their daily intake by more than about 500 calories, which means a maximum weight loss of one pound per week.

    Unfortunately what most people don't understand is that since the technology of agriculture is only 12,000 years old, we still have the bodies of cavemen. If we reduce that body's food supply by a very large percentage, the Inner Caveman says, "Ohmigod, it's a famine!" Our metabolism becomes very efficient in order to survive on short rations. Sleep more, sit more, lose nervous tics, digest what little food there is much more efficiently. This is why reducing our calorie intake by 500 per day does not necessarily result in losing a pound a week.

    What's better in the long run is to reduce it by 200-300 calories a day and try to lose no more than 25 pounds in a year. (Ten would be even better but people stop reading when I tell them that.) This will not trigger the famine response, but it will put you on the maintenance diet for your new weight, so you're developing eating habits that you can continue forever.
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  12. Absane Rocket Surgeon Valued Senior Member

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    If you are losing only fat mass and nothing else, the only byproducts of fat metabolism (fat + O2) are water, CO2, and energy. I imagine that well over 90% of the water is lost through urination.

    However, this reaction does not take into account the protein and micronutrient requirements that are metabolized and processed to make this happen. After all, fats are LONG chains of carbon, hydrogen, and oxygen that are not easy to break down.

    As for losing water weight... this will be made up when the dieting is over. The body will not metabolize body fat at any appreciable rate until the glycogen stores are depleted (the body's easiest source of stored energy). For every 1 gram of glycogen, the body requires 3-4 grams of water. When glycogen is used, the water associated with it is released, used if necessary, and then excreted via the usual methods. Once depletion occurs, the body will try to use the next available source, muscle tissue. This is why exercise is very important in any weight loss program. Muscle is the metabolism powerhouse of the body and it will burn fat for energy, but only when the muscle is there to do the job. Muscles will be burned for energy BEFORE fat if the muscles aren't perceived as being necessary for the survival of the body. So, assuming that the athlete is successful in sparing his muscles, normal eating patterns will resume after the diet and glycogen stores will be replenished along with the water required with the storage.
     
  13. S.A.M. uniquely dreadful Valued Senior Member

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    Think of weight in terms of energy

    There are three ways to address the difference between energy intake and energy output such that the overall effect is net loss of energy

    1. Decrease intake
    : If you eat less without simultaneously changing your output, you will have a net loss of energy

    This involves cutting down on your total calorie intake, however, this has the "side effect" of alerting your body that it is in starvation mode and the body will respond by reducing your basal metabolic rate which can drop as much as 5% thus making you susceptible to weight gain. The only way to counter this is to simultaneously increase your heart rate alerting your body's fight or flight mechanism, thus preventing a drop in metabolic rate


    2. Store less: If your energy intake and energy output is balanced such that output > intake, you will have net energy loss.

    This can also be achieved by eating foods that are less energy dense and more indigestible [i.e. high in water and fiber, low in calories]. A diet which includes small meals before exercise combined with adequate fluid intake and a largely low fat, low sugar, high fiber, high fruit and vegetable [not juices, but whole foods] diet will aid in decreasing the calorie intake of your diet while maintaining the bulk required for satiety.


    3. Lose more: If you workout more such that energy output > energy intake, you will have net energy loss.

    The biggest contributor to energy output is muscle because every additional gram of muscle gained and maintained through regular consistent exercise will lead to energy losses [this may not translate to weight loss since muscle is heavier than fat]

    In any exercise program initial weight losses are water, hence the necessity for adequate fluid intake. Next is the glycogen stores, in muscle and liver, which can be easily replaced in 18 hours and only after that, fat stores, beginning with fat droplets in the muscle and later long term fat stores in the abdominal and gluteal and peripheral regions [there are individual differences in how abdominal and gluteal fat is handled and gender is a major consideration]

    It takes time for the hormonal systems to adjust to changes in energy intake and output - this involves changes in gene expression at the cellular level so it requires consistent effort on the part of the subject since gene expression only changes when the body senses a long term demand made on its energy stores - and hence lower intensity exercise performed on a daily basis is more effective than high intensity exercise performed sporadically

    Note that the body is highly resistant to loss of energy stores and at some point your diet/exercise regimen will no longer work and will need to be stepped up [there is something called set point body weight and unless stressed the body tends to defend it. You can gradually reset your set point with increasing step wise stresses so don't be discouraged if you reach a "plateau"]
     
    Last edited: May 25, 2011
  14. Absane Rocket Surgeon Valued Senior Member

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    There is a strategy to deal with the hunger, but I don't imagine that the average American (or perhaps Westerner in general) is going to follow it.

    Point 1: Eat 1 gram of lean protein for every pound of bodyweight every day.
    Point 2: Except for fruits and vegetables, limit your intake of carbohydrates to about 1-2 grams per pound of bodyweight.
    Point 3: Consume at least 30 grams of fiber a day.
    Point 4: Satisfy the rest of your hunger needs with fruits and vegetables (mostly vegetables).

    Following points 1 and 2, only about half of the calorie requirements will be covered. The rest you try to fill with fruits and vegetables... which isn't an easy feat because the calorie density isn't there. However, given the bulk of the food and the fiber content of the food, you're unlikely to feel hungry.

    On the point of the famine instinct... this can be trumped to a large degree by exercise. Dieting alone will cause the body to slow down its metabolism in order to preserve energy stores.
     
  15. Enmos Valued Senior Member

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    I thought you already had your poop-talk..

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