Suppose one is in the process of losing weight. Via what route or mechanism does the fat leave your body?
In the past year I’ve lost about 25 pounds. Think about the volume of that. That’s like losing three newborns. So where did the triplets go? Down my toilet? Vanished into thin air? Hidden in a box in my closet?
It was released into your bloodstream and burned for energy; the ‘ashes’ were mostly exhaled and excreted in urine.
(Obviously, the full story gets complicated, but that’s the core.)
I too have thought the same question… I also have a very weird, irrational, and probabilistically incorrect fear that if after I work out and don’t remove my sweaty clothes ASAP, the sweat will somehow be soaked back into my skin and I won’t lose any weight.
Interesting. I once heard that it left in the urine stream, but then I wondered why there were no oily blobs floating in my toilet bowl. So I’m guessing that the “ashes” are water soluable.
Actually, the metabolic breakdown products of fat are mainly carbon dioxide and water. Most of the fat by weight is converted into carbon dioxide and exhaled. Some water may be excreted in the urine (some is exhaled or perspired). If you are breaking down protein, the amino acids will be excreted in the urine. But by far the greatest portion of the weight you lost left your body via your lungs.
I should say rather that the nitrogen from the breakdown of the amino acids will be excreted as water-soluble urea in the urine.
Really? Wow. I always assumed that it left your body the same way that food waste does.
While we’re on the subject, may I add a question of my own? My grandmother (not exactly a credible source of medical information) claims that the fat cells never “leave.” They decrease when a person loses weight, but they’re always lurking there, waiting to swell again if the person over-eats. Anecdotally, I’ve always heard women say, “That’ll go straight to my thighs!”
Is there some sort of “body memory” for fat? Does the fat from that eclaire really go to the location most prone to previous weight gain?
So when I say that “You’re shitting more then you’re eating” I’d be wrong? I like saying that.
AFAIK, your grandmother is correct. Fat cells can swell on their own, or increase in number by some mechanism I confess to not understanding. But, again AFAIK, losing fat really means shrinking down the fat cells you’ve already got.
Memory? I don’t think so. It’s just that women tend to collect fat on their butts and thighs. Men collect it on their guts. As overweight as I still am, I’ve always had an excellent butt.
bordelond got this one. You can lose fat, but you can’t lose fat cells.
Yes, but it has nothing to do with memory. If a particular part of your body is more prone to gaining fat than others, it’ll get fatter faster whether it’s the first time or the tenth.
No, feces consists mostly of undigestible food remnants that were never incorporated into your body, plus bacteria from your digestive tract. There are some remnants of red blood cells, plus other cells shed from your digestive tract. But little material that was ever part of your body ends up in your feces.
I’d like to add that there is one way to lose fat cells and that is to have them sucked out via liposuction.
This is not meant in a nasty way, but some of the misunderstandings on this thread about how food is metabolised and/or excreted say a lot about why people find it hard to lose weight.
As Colibri says, when fat (or glucose, for that matter) is used for energy, much of the “bulk” is converted into carbon dioxide which is exhaled. So it goes the same place that the petrol in your car “goes”.
So, if I lose 40 lbs, it will make a huge difference in appearance (well, huge is a relative term, but work with me here). Assume that after this loss, I look fit ‘n trim – or do I? Is grandma saying that no matter what I do, weight loss and a bazillion crunches, I will always have a thin (even if barely perceptible) layer of fat on ye ol’ gut?
What about getting liposuction after getting into shape – would the procedure be easier and less risky? Would it have benefits?
Another thing I don’t get – what’s inside an enlarged fat cell? Just more protoplasm or water? If so, then why is the blood and whatnot needs of a big cell any (or significantly) different from a smaller cell? Doesn’t the body need to maintain the same mileage of blood transport as it used to when tubby? Do deflated fat cells ‘breath’ less?
In light of that, I find it mildly surprising that dieters don’t have really bad breath.
Sometimes they do, actually. I know when I was trying the Atkins diet, I had a nasty taste in my mouth all the time, and made constant use of mints and mouthwash.
I’ve heard fasting can cause it as well.
Colibri is correct that most of the byproducts of lypolysis are water, carbon dioxide, and (under healthy conditions) a modest amount of nitrogen; however, lipids stored in adipose tissue (what people generally mean when they talk about body fat) are also excreted via the sebaceous glands as oils that protect skin and hair from the environment. In polite society we wash these oils off in order to be “clean”. Certain fats are also required for various organ regulartory functions and to provide materials for endocrine production (like natural steorids). Admittedly, the latter doesn’t use up much fat, and most of the lipids we consume are not required for this, but the essential fats are required for proper metabolic function.
Fats from adipose tissue are only metabolized in quantity when blood glucose (sugar) levels are low. Fat is also converted to glucose via gluconeogenesis; the evolutionary value of this is being able to store chemical energy as fat which is then used when a ready source of carbohydrates (which cannot be stored and don’t typically last long in nature) is not at hand, hence the popularity of low-carb diets like Atkins, although this has other problems when done regularly. However, in modern diets, we generally consume far too many calories in all forms, and too high a proportion of nonessential lipids, leading to excess fat storage.
It is true that once adipose cells are manufactured that they don’t generally disappear spontaneously; however, they have a remarkable ability to expand and contract, and having more or less cells has little impact upon how much fat you store. The greater effects on weight gain come from dietary habits (voluntary and unconscious) and glucose regulation; if you regularly consume large amounts of simple carbohydrates (refined sugar, high fructose corn syrup, honey) that are quickly broken down without immediatley using that energy then your insulin levels will bounce up and down, stressing the pancreas and kidneys. As a result, your body will do two things; one is that it will try to store away dietary lipids rather than use them (which results in secondary dysfunctions by “diluting” essential fats necessary for body regulation), and second is that it will attempt to convert excess carbohydrates into more lipids via lipogenesis. The best way to prevent this is to moderate your overall calorie intake, maintain a carb/protein/fat balance somewhere around 50%/30%/20%, and make the bulk of your carbohydrates complex and preferably fiberous carbs that take longer to break down and are therefore self-regulating, saving the simple sugars for pre- or post-exercise periods when the body needs a ready source of glucose for energy.
Actually, people on reducing diets that do not maintain an appropriate carbohydrate balance do typically have bad breath. In fact, during intentionally induced ketosis dieters tend to have breath that smells like spoiled milk or dilute ammonia.
You will always have a thin layer of fat on your belly, although if you exercise enough and/or reduce your calorie intake you’ll see the “definition” of muscles beneath it. Again, the quantity of adipose tissue is essentially irrelevent to this. Liposuction is a way of quickly removing fat, but it does nothing for either the dietary habits or metabolic conditions which resulting in gaining fat, and therefore is generally of little effect in the long run, other than subjecting the patient to invasive surgery and the likelyhood of serious bacterial infection.
Stranger
As Stranger said, the cells are still there, but this isn’t necessarily a bad thing. We’re, for lack of a better term, supposed to have fat cells. They act as long-term storage for the energy we gain from food in the form of chemicals like triglycerides, which get packed into compartments within the fat cells.
Here’s a picture of what fat cells look like.
The large white areas are where the triglycerides are stored, called liposomes–essentially bags of oil. When you burn more energy than you get from food the liposomes shrink because you’re “burning” their contents to get the energy you need, but the cells are still there to “fill up” again if needed.
That’s what basically happens when you lose weight from exercise. One could argue that liposuction isn’t a good idea because getting rid of those cells means that, if you gain weight again, it’ll just get stored in another area where you still have fat cells. I’m of the opinion that liposuction is an option best reserved for people who need to lose fat for more imminent health concerns, but I’ll leave that for someone with more education and training in that area.
Not sure if I’m being whooshed, but carbon dioxide is pretty much odourless at the concentrations you’d find in your breath.
On the other hand, if you want an excuse for not losing weight, you could always say you’re doing your bit to stop global warming 
