When you lose weight, what do you lose and what happens to it? I doubt that there is an atomic reaction going on (if there was, I have a few hundred million more miles to run), so the weight must be lost through chemical or mechanical means. Now Ihave heard that fat cells are real cells, just like skin or brain cells, and that they grow or shrink with weight. What is growing or shrinking? What is the thing that adds weight? How is it broken down? There must be some “ash” left over. What is it and how is it used or gotten rid of? When does the body start “burning” fat? I doubt that you are actively using that stored energy during exercise, it seems like something that needs to be triggered into use, like some long-term solution.
Fat is essentially just a set of big molecules made from Carbon, hydrogen and oxygen - when your body breaks it down, the waste products are ultimately exhaled (carbon dioxide) or excreted in urine (water).
Ooops, and water can be exhaled as vapour too.
Yes, it’s a chemical reaction that coonverts fats into CO[sub]2[/sub] and water as Mangetout said.
It’s pretty accurate to simply think of fat cells as little bags filled with oil. When the body needs energy it sucks some of the fat out of those bags and uses it elsewhere. The fact that the cell has physically less fat inside it is what causes it to shrink.
Fat. When you eat more food than you need the body doesn’t bother digesting the fat, it just shunts it straight through the gut lining, into the bloodstream and deposits in the fat cells. The body can also convert starch and sugar into fat but it takes a bit more work. The fat still ends up in the fat cells, which is what adds weight.
That’s a biochemistry lecture all by itself. At this point I think we will just say that it leaves the fat cells and is taken into the cells that need energy such as the muscles and nerves. There it is broken down in a complex series of steps by a number of enzymes.
There is no solid residue. The breakdown of fat is essentially a reversal of the process used to construct it in the first place. Since fat is ultimately derived from water and CO[sub]2[/sub] it is returned to that form. It is then breathed out th ewater is excreted in the faeces or urine.
No, it pretty much starts burning as soon as you deplete you carbohydrate reserves. The body will burn carbohydrates first, and these come from either food in the gut or in the form of glycogen which the body stores in the muscles and liver primarily. However those reserves are rapidly depleted with exercise, and as soon as they are then you start using fat. That could mean that you start burning fat within a few minutes of heavy exercise or within a few hours of more sedenatry work if you don’t eat anything. There’s no special trigger at play, it’s basically as simple as your body neeeds energy, there’s no food in your gut, it starts to mobilise your fat reserves.
There are some caveats in there about the effects of anaerobic vs aerobic exercise but at this stage we’ll keep it general and simple.
quote - When does the body start “burning” fat? I doubt that you are actively using that stored energy during exercise, it seems like something that needs to be triggered into use, like some long-term solution.
quote - No, it pretty much starts burning as soon as you deplete you carbohydrate reserves. The body will burn carbohydrates first, and these come from either food in the gut or in the form of glycogen which the body stores in the muscles and liver primarily. However those reserves are rapidly depleted with exercise, and as soon as they are then you start using fat. That could mean that you start burning fat within a few minutes of heavy exercise or within a few hours of more sedenatry work if you don’t eat anything. There’s no special trigger at play, it’s basically as simple as your body neeeds energy, there’s no food in your gut, it starts to mobilise your fat reserves.
Atkins and other low carb type regimins use dietary ketosis as the ‘trigger’ By reducing your bodies dependance on glycogen for fuel, forcing you to burn off your fat and proteins as fuels [ketones] you run less risk of depositing unburned glycogen into fat… however you do need to maintain a minimum amount of protein coming in, and limit stricktly the amount of fat coming in…
<one of the things I hate the most about people who jump into fad diets without researching them is they get things WRONG! Real low carb is not a license to pig out on higly fatty meats…you reduce the number of carbs coming in by eliminating processed grains and sugars, and eating more fresh veggies like spinach, broccoli, artichokes - not things like potatoes, corn, beans, and eating low sugar fruits like strawberries, rasperries, blueberries and avoiding heavily sugard fruits like melons and stonefruit. sigh>
Do keep in mind, any weight loss effort does mean a change in eating patterns…and also there are websites out there that will help you calculate the number of calories your body actually needs…dont just blindly drop the calories you eat to as small as possible because you will trigger the famine response that slows down your metabolism to conserve energy =\ under 1200 - 1400 kcal is generally the trigger point for many people.
How general is this?
I’m a pretty heavy carb-eater. Granola for breakfast, sandwich and chips for lunch, meat and rice/pasta/potatoes for supper.
Could I work out for 45 minutes and not “get to” my fat?
Your body cannot burn fat during heavy exercise, since oxygen is a prerequisite for using fat for energy. If you are in oxygen debt, you continue to use carbs for energy, since you can do so without oxygen; however, the production of ATP is much reduced. The carbs can sustain energy for quite a while, not just a few minutes. When you first start out in a sprint, creatine is the source, but after about 10 seconds, the glucose kicks in. How long it can last depends upon your carb storage. The blood glucose is rapidly used up, but muscles contain glucose and the liver can produce glucose. During normal exercise, both carbs and fats are used for energy, the proportion of which is dependent upon your exercise intensity. If you completely run out of glucose, you “hit the wall,” and any exercise you would be capable of doing would be very slow, needing to rely on fats, and then protein as a last resort.
I know your said you’d keep it simple and neglect the aerobic vs. anaerobic, but the above is not complicated.
In my experience, the weight of the world remains constant, which has always meant that I gain all weight that’s otherwise lost :rolleyes:
Not easily. Even moderate exercise like walking extended for 45 minutes will mobilise fat reserves in most people.
There’s an upper limit to how fast the body can absorb carbohydrate fom the gut, as well as how much it can store. So long as the exercise is intense enough and long enough to burn off the carbohydrate reserves in the body and is intense enough to burn calories faster than they can be absorbed form the gut then the body will have to find the needed calories elsewhere. The first way it is going to make up that energy deficit is by mobilising fat reserves.
The body has an absolute limit in how much food it can store as carbohydrate, and it’s pretty small. Once all the possible carbohydrate stores are full any more food pulled form the gut will be burned immediately or else laid down as fat. Because of that it doesn’t really matter how much carbohydrate you eat so long as it more than the amount that your body is burning at any point in time. The difference between you and a person who only eats a few dozen grams of carbohydrate in each meal and replaces the rest of the calories with fat and protein is nil in terms of carbohydrate storage. The only difference is that you will be converting your excess carbohydrates to fat or burbing them, while the other person will be burning fats and proteins for energy and laying down fat directly as fat. Once exercise begins all differences will evaporate because in both cases the body will be unable to meet its energy requiremenst with what is coming from the gut and what is already stores as carbohydrate.
aruvqan I’m not going to get into a debate on the Atkins diet in GQ, however I will point out that there is absolutely no scientific evidence that the Atkins diet uses ketosis to trigger mobilisation of fat reserves. The Atkins diet works by reducing the intake of available calories, it’s that simple. There’s no scientific mystery behind it and there’s no special trigger for fat utilisation. People on the Atkins diet eat less and the food they do eat is lower in energy value. As a result they can’t meet energy requirements from the food coming from the gut and the body starts to mobilise fat reserves just as I said. That will occur with or without ketosis.
I diasgree. Some fat can be used, and the amount used increases as the duration of exercise increases, irrespective of exercise intensity.
In normal individuals, blood glucose levels do NOT drop by much during exercise, and certainly no more than 30%. If they did, we’d all be dropping like flies from hypoglycemia whenever we exercised. That is one of the beautiful things about the body and its metabolism. Just think, you could be a near-starving caveman and then have to run for your life from a sabre-toothed tiger - even so, your blood glucose would be maintained.
Regulation of glucose levels, muscle fuel utilization, etc. during exercise is a wonderfully complex balancing act between substrate use/production (locally in the muscles and systemically), hormonal and neural regulation, and blood flow itself. It is one of those things that may be impossible to summarize succintly.
Here is a nice set of notes which do a good job of discussing the salient features. I haven’t read them in any detail, but a quick skim leads me to believe that they’re accurate (and well presented).
That may be so, but the latter link had the subjects exercise to only 30% of max VO2, which is a very low level of activity, altho the activity lasted 4 hours:
I could not access the last link, which uses Acrobat Reader. (I have AR, but the link contained only incomprehensible charts.)
Right. And the opposite of what happens when you gain weight!