What is “metabolism” exactly?

http://www.mayoclinic.org/healthy-lifestyle/weight-loss/in-depth/metabolism/art-20046508

Perhaps you would be better off taking a college biology course rather than asking your questions on a forum. But let me give you the Reader's Digest version: If you move more you burn more.

Having more muscle means you will burn more even while sitting still, but to get more muscle requires you to move more. Fat people burn more than skinny people, but again, they are moving more because they have more fat to push around. Eating too little causes your metabolism to slow down because you aren't giving your body enough to fuel your activities. Without enough fuel you'll tend to lie around on the couch, or stay in bed longer, or just sit in a chair rather than doing activities that require fuel.

Your metabolism is measured by how much oxygen you use. If you want a super fast metabolism, maximize your effort in activities that cause you to get out of breath. Don't go to hard or you'll have to stop and give your muscles a rest. Don't go too light or you won't need much oxygen. Cardio exercise seems to work very well because you can go for a long time without stopping.

myszka0611 wrote: »

I mean, I know it’s the chemical processes that occur within a living organism in order to maintain life, but how is it regulated? What constitutes a fast metabolism? And WHAT regulates it? Brain? Thyroid? Pituitary? Sadistic aliens? Why, if I eat too little, does my metabolism slow down? Why then, in the reverse scenario, doesn’t it speed up if I eat too much?

I can't give you a scientist's answer. The following has useful insights about why, if you eat too little, your 'metabolism may slow down'.

Reduced metabolism/TDEE beyond expected from weight loss

And, under some circumstances, if you eat more, your metabolism may, in fact, 'speed up" (primarily through impact on NEAT, is the assumption).

If, as I age, I can eat so much less and so easily gain weight on fewer calories, doesn’t that mean my metabolism is operating at peak performance (from the perspective of making sure I maintain my vitals on fewer and fewer calories)?

Let me first take on your assumption: Research is suggesting that the majority of the "slowing with age" phenomenon is loss of muscle mass and reduced daily activity. People who counter those two factors, don't necessarily see that happen.

As far as your question about efficiency: In common conversation, efficiency at something is often defined with respect to goals. Hard gainers may be more interested in 'slowing down their metabolisms' - that would be efficient for them. For the obese, it's the reverse.

If you think of a metabolism as being like a furnace, thus use 'efficiency' in a more technical sense, I guess that reduced input for the same output is 'efficient'. But in the case of aging metabolism, the problem is probably more about the necessity of reduced input because of (optional) reduced output, than about efficiency in the technical sense.

(BTW, I keep putting things about speed of metabolism in quotes because I find those concepts so imprecise and unhelpful for me, as a nonscientist - more like a metaphor than a real thing.)

I understand the concept of CICO causing weight loss/maintenance/gain, but what can I do to rev my metabolism? I know muscle burns more calories than flab, but I’m relatively slender, (want to lose 10 pounds), and have (genetically) muscular legs, although I do walk a lot. Really, the only muscle mass I could gain would be in my torso area if I lifted weights, and I have to wonder what significance, if any, a rock hard abdomen would be in upping my metabolism.

You would be surprised what kind of muscle mass you could gain over many parts of your body, as a woman, at any age, and without looking "bulky", if you adopt a progressive lifting program.

Females only - lifting/weight training results?
HALP! Heavy Lifting Made Me SUPAH Bulky!!!

I wish there was some sort of knob on my metabolism tuner, like a volume switch, or a faucet where I could regulate the flow.

You can certainly improve the situation. Regulate exactly? No, of course not.

Metabolism is just fuel consumption for the body, and slowing down metabolism is something the body can do if it thinks it is necessary, but it doesn't like to do it because it requires shutting down useful services, much in the way that you could save fuel when driving by shutting off the air conditioning, switching off the radio, headlights etc. Your body is much happier when it has plenty of fuel and can run everything optimally. However, if fuel is scarce it will make savings, for example:

- Making you feel lethargic so you are less inclined to move around
- Making you feel cold so you will put on a jumper or turn up the heating rather than burning energy to heat yourself
- Making you feel tired so you will go to bed rather than burn energy being awake

If these savings aren't enough and starvation becomes serious (eg in anorexia) your body will make deeper cuts, eg:

- reducing cognitive function
- reducing function in the reproductive system
- growing hair to conserve heat
- serious lethargy/sleepiness

And at the same time will start desperate attempts to get more calories by making you obsessive about food.

Metabolism slowing is not an increase in real efficiency, which means getting more for less - it's "efficiency" as governments or irresponsible corporations see it, put less in and get less out. It's a survival adaptation, not an ideal state.

For weight loss, you're trying to keep your body to a minimum of savings and as close as possible to full fuel consumption. This can be done by keeping your deficit small and eating as much as possible while still losing weight. But you'll notice from the above that mild metabolic changes are not outside your control. You can still exercise despite feeling lazy; you can still do without a jumper and warm yourself up by moving rather than wrapping up and shutting down. Metabolism is not a mysterious process that's beyond your control. It's just your body trying to burn less fuel, and you always have the choice to burn more.

(note: I'm not talking about thyroid conditions, which need specific treatment).

myszka0611 wrote: »

CattOfTheGarage wrote: »

Metabolism is just fuel consumption for the body, and slowing down metabolism is something the body can do if it thinks it is necessary, but it doesn't like to do it because it requires shutting down useful services, much in the way that you could save fuel when driving by shutting off the air conditioning, switching off the radio, headlights etc. Your body is much happier when it has plenty of fuel and can run everything optimally.

I guess (without taking a biology course) I was wondering what part of "the body" was unilaterally making this decision for me. I can't regulate it, 'cause I don't know "who" (in my body) is making the decision for me that I can subsist on 1500+/- calories per day. If I overfill my car with gas, it just spills out the full tank. My car doesn't gain weight if I give IT too much fuel. What mechanism makes me want to overeat? It seems like my metabolism tells "my body" I can make do on 1500 calories per day, but my body ALSO wants to eat 3 slices of pizza, rather than one (or whatever I'm eating to keep me at my calorie goal). My body seems to be fighting me. I want to be comfortable at 1500 calories (or whatever maintenance will be when I lose this ten pounds). I want my metabolism (or whatever) to say, "this is all you need, so quit eyeballing that hot fudge sundae" and have me really truly NOT want to overeat. Am I making any sense?

Yes, but that's not how it works. You are adapted to eat food (especially high calorie food) whenever the opportunity comes up because that's how you survive in an environment where you can't be sure of the next meal. It doesn't work in our current environment, but that's the fault of a set of freakish circumstances (free access to all kinds of food in any quantity) not the fault of your body, which is reacting in a reasonable way when you consider the survival pressures that got us where we are. Your body, because of your evolutionary background, does not react to excess fat as a threat but as a boon, a nest-egg, worthy of protection and preservation for a rainy day. It makes sense.

I'm personifying "your body" to simplify things. There's not some secret evil mind that's planning all this, it's just a complex system with a complex set of reactions honed for survival. As for which part of your body regulates this, I imagine several different parts of the brain plus your thyroid and probably various hormone pathways that are beyond the layman. I'm not a biologist.

But the fact you can't pin down which part of your body is driving metabolic adaptations does not mean you have no control over it. As I said, most metabolic savings are made by feeling lethargic and cold. If you exercise and eschew the blanket, you've overridden that adaptation - it can't happen. And if you make sure your deficit is small and your rate of loss is moderate, you'll avoid the more extreme adaptations that come with crash dieting.

It's not this big looming thing that you need to find a way to hack. It's just a change to the way you feel and you can generally power through it by choosing to move more. In any case, the calorie savings made by metabolic adaptation are small and I think you may be focusing on them too much. Just eat less and move more. If you feel like sitting on the sofa under a blanket, don't, get up and move instead. Barring thyroid dysfunction, that will take care of it.

myszka0611 wrote: »

I mean, I know it’s the chemical processes that occur within a living organism in order to maintain life, but how is it regulated? What constitutes a fast metabolism? And WHAT regulates it? Brain? Thyroid? Pituitary? Sadistic aliens?

It's not one chemical process, but rather ALL the chemical processes that occur in our body throughout our normal everyday lives. More accurately, it's simply a measurement of the amount of energy our bodies use each day to do ALL the things our body does. What regulates it? Depends on which process your talking about. Ultimately, the brain regulates the organs that regulate the processes. Different organs regulate different processes. So ultimately, the answer is your body regulates metabolism. Not one specific thing, but rather the entire collection does. Fast Metabolism? That's simply a very unscientific way of saying your resting metabolism rate is above the general average of the population.

Also.. our metabolisms aren't static things. When we sleep, our metabolism drops to it's lowest point of the day. It increases when we wake up. It increases as we move. It increases when we eat. Our metabolism is higher when you read a book then it is when watching TV.

myszka0611 wrote: »

Why, if I eat too little, does my metabolism slow down? Why then, in the reverse scenario, doesn’t it speed up if I eat too much?

Actually it does go higher if you eat too much.. it's just not a direct correlation. If you eat 3000 calories in a day, your body needs to work a little harder to digest it then if you eat 2000 calories in a day. But that doesn't mean it raises up enough to actually burn off all those extra calories. Also.. a 250lb person will have a higher metabolism then a 200lb person

myszka0611 wrote: »

If, as I age, I can eat so much less and so easily gain weight on fewer calories, doesn’t that mean my metabolism is operating at peak performance (from the perspective of making sure I maintain my vitals on fewer and fewer calories)?

No. We burn less as we age because certain chemical processes stop or slow down as we get older. Around age 25, most of our growth processes stop and our body goes more in to maintenance mode. Our brains are no longer growing, our bones are no longer growing and most of our organs have settled into their adult sizes. Short of getting fat or building muscle, there's not much growth processes left (Hair and nails are about it). Then around age 35-40, our maintenance processes begin to slow down (Why we start to see signs of aging about this time). This slow down, slows down our metabolism again. This slow down is a continual and gradual process right up until we die. So even a healthy, in shape adult will burn less calories at age 80 then he did at age 60.

myszka0611 wrote: »

what can I do to rev my metabolism? I know muscle burns more calories than flab, but I’m relatively slender, (want to lose 10 pounds), and have (genetically) muscular legs, although I do walk a lot. Really, the only muscle mass I could gain would be in my torso area if I lifted weights, and I have to wonder what significance, if any, a rock hard abdomen would be in upping my metabolism.

Ultimately, the best way to rev your metabolism is to essentially move your body more and eat a cleaner, more healthier diet. A pound of muscle burns six calories a day at rest and a pound of fat burns about two calories a day. So yes... while adding muscle mass will boost your RMR (Resting metabolism rate), it's a small bump. But a bump is still a bump. Doesn't mean it's still not a great way to lose weight, as the process of "building" muscles burns a lot more calories by adding a temporary metabolism boosting building process. This means you can create a daily calorie deficit without actually cutting down on the amount of food you eat.

But eating a healthier diet means you give the body the fuel it needs to burn energy better. It takes the formula beyond the simple CICO and even more then just tracking macros, but paying attention to getting the vitamins and minerals you need through food (as opposed to a pill). This is what leads to the body working more efficiently, but it still helps slightly raise the RMR as there are more processes involved in dealing with vitamins and minerals then there is in dealing with simple sugars. Though the most important effect is the boost in energy available for consumption (The more energetic feeling you feel).

Though if you don't use this energy, it's still not helpful. This is the move the body more part of the equation. Beyond just going to the gym and working out for an hour a day, rather, finding ways to make our entire day more active then it is. Modern living has left us far more sedentary then we were just 50 years ago, so it takes some thinking outside the modern box to make our days more active. Staying home and cooking your own meal burns more calories then going to the restaurant and being served by a waiter. Going to a library and finding books to look up research burns more calories then simply googling from your home PC. Like I stated above, we burn more calories simply reading a book rather then watching TV. Most are just small upticks (some may be only 5-10 cals more then the alternative), but readjusting your daily life, these daily upticks can add up to a couple hundred extra calories a day.

myszka0611 wrote: »

CattOfTheGarage wrote: »

Metabolism is just fuel consumption for the body, and slowing down metabolism is something the body can do if it thinks it is necessary, but it doesn't like to do it because it requires shutting down useful services, much in the way that you could save fuel when driving by shutting off the air conditioning, switching off the radio, headlights etc. Your body is much happier when it has plenty of fuel and can run everything optimally.

I guess (without taking a biology course) I was wondering what part of "the body" was unilaterally making this decision for me. I can't regulate it, 'cause I don't know "who" (in my body) is making the decision for me that I can subsist on 1500+/- calories per day. If I overfill my car with gas, it just spills out the full tank. My car doesn't gain weight if I give IT too much fuel. What mechanism makes me want to overeat? It seems like my metabolism tells "my body" I can make do on 1500 calories per day, but my body ALSO wants to eat 3 slices of pizza, rather than one (or whatever I'm eating to keep me at my calorie goal). My body seems to be fighting me. I want to be comfortable at 1500 calories (or whatever maintenance will be when I lose this ten pounds). I want my metabolism (or whatever) to say, "this is all you need, so quit eyeballing that hot fudge sundae" and have me really truly NOT want to overeat. Am I making any sense?

There are approximately 37.2 trillion cells in the human body and each one is making decisions independently while at the same time working in coordination with the other cells. A lot of the communication involved is through the blood stream. The bloodstream carries both the "fuel" and the oxygen your body needs. When the concentration of fuel is high cells in your body convert it to fat and store it away. When the fuel in the blood stream is low there are cells that begin releasing stored fuel into the blood stream to bring the level back up. When oxygen is high your breathing slows along with your heart rate. When oxygen in the blood stream is low then your heart speeds up to compensate and you begin breathing more quickly to draw in more air. But this was caused by cells that were triggered to contract, which causes them to use various forms of stored fuel along with oxygen. The spent fuel is dumped into the blood stream and sent to the lungs from where it exits the body. After this is released, the blood can take on oxygen and fuel. If there is insufficient oxygen and fuel then the extremities will begin to shut down first because the blood has to travel farthest to them. Internal organs are the first place the blood goes, so they will be the last to shut down.

myszka0611 wrote: »

..........I understand the concept of CICO causing weight loss/maintenance/gain, but what can I do to rev my metabolism? .......

I wish there was some sort of knob on my metabolism tuner, like a volume switch, or a faucet where I could regulate the flow.

It's not a mystery. You increase your metabolism by simply being more active.

CattOfTheGarage wrote: »

I have to pull you up on this. Eating a healthy diet does not mean there is more energy available - if it does, it will make you fat. The amount of energy in food is the amount of calories, and that is completely different from the feeling of being energetic. Being energetic is a measure of how keen your body is to spend energy. It's not a measure of how much energy it has available. If it were, fat people would never get tired.

And you never escape from "simple CICO".Cars, ships, stars, planets, they're all governed by energy conservation, it's the closest thing to an absolute in this crazy quantum universe. The CI and CO can change but the CICO never goes away.

Maybe I should have used the term "readily available"... meaning that instead of the calories being stored in fat cells, it's actually processed and pushed to the places that need and want to use it. I'm talking about the difference between two people.. one who eats 2000 calories of low nutrient dense, high simple sugars foods versus the 2000 calorie diet rich in nutrient dense foods made up of proteins, complex carbs and healthier fats. While CICO is that basic formula, our bodies are actually more complex then that. So when asking questions about how to change ones metabolism, you must dive deeper then the simple CICO.

fbchick51 wrote: »

CattOfTheGarage wrote: »

I have to pull you up on this. Eating a healthy diet does not mean there is more energy available - if it does, it will make you fat. The amount of energy in food is the amount of calories, and that is completely different from the feeling of being energetic. Being energetic is a measure of how keen your body is to spend energy. It's not a measure of how much energy it has available. If it were, fat people would never get tired.

And you never escape from "simple CICO".Cars, ships, stars, planets, they're all governed by energy conservation, it's the closest thing to an absolute in this crazy quantum universe. The CI and CO can change but the CICO never goes away.

Maybe I should have used the term "readily available"... meaning that instead of the calories being stored in fat cells, it's actually processed and pushed to the places that need and want to use it. I'm talking about the difference between two people.. one who eats 2000 calories of low nutrient dense, high simple sugars foods versus the 2000 calorie diet rich in nutrient dense foods made up of proteins, complex carbs and healthier fats. While CICO is that basic formula, our bodies are actually more complex then that. So when asking questions about how to change ones metabolism, you must dive deeper then the simple CICO.

I think we have to consider what people mean when they ask about metabolism. What many people on weight loss forums are actually asking is "What can I do so I can eat more without having to exercise?" Telling these people what it takes for a more efficient metabolism doesn't really answer their question because a more efficient metabolism means that we require less food to do the same amount of effort. That's great for an athlete, but people trying to lose weight would classify that as a "slow metabolism." For an athlete, food choices and timing can make a huge difference because you want your body to be processing the right type of food for ready access when you are active and you want protein available when your body is repairing cells. You don't want the body to have already processed the food and stored it away and you don't want to run out of the food you need. If weight loss is the main concern, it might make sense to try to make one's metabolism as inefficient as possible, though diets that do that are only marginally better at weight loss than others. For that reason, it seems like sticking with simple CICO is the way to go.

myszka0611 wrote: »

TimothyFish wrote: »

What many people on weight loss forums are actually asking is "What can I do so I can eat more without having to exercise?" Telling these people what it takes for a more efficient metabolism doesn't really answer their question because a more efficient metabolism means that we require less food to do the same amount of effort.

I don't particularly "want to eat more without having to exercise", I was simply asking what mechanism in the body...this amorphous "metabolism"... creates, IMHO, a contradiction. Why it seems to be at odds with what is best for the body it is supposed to be working to protect. I have to consciously fight my urge to eat more. One part of "me" says "eat more!!!" Another part of "me" says, "You're eating too much! Just for that, I'll make this nice plop of fat for you right here on your belly.".

This was my line of thinking in my original query...not necessarily "how to circumvent my metabolism", but just "what the heck is a metabolism in the first place?" Why does my "metabolism" cause me to crave more than my body needs? I wondered what constitutes a "metabolism"? What makes it work/not work? How to fine tune it?

(You guys have since provided a plethora of great responses! Thanks for that!)

We tend to think about "best" in terms of how fat we are. We should instead think in terms of what we need to fuel our bodies. We know about how long it will be before we can eat again. Our bodies don't. As intelligent beings we can and should either decide to eat less than we can now because we'll be eating again in a few hours or maybe we should decide to eat more because we know we are going to be burning more calories than normal between meals. All our bodies can do is react to the current situation. It would be a bad thing if we ate more in preparation for going for a few days without food and our bodies refused to store the food.

myszka0611 wrote: »

Why, if I eat too little, does my metabolism slow down? Why then, in the reverse scenario, doesn’t it speed up if I eat too much?

Because, for the vast majority of human history, the most important thing was to prevent you from starving to death when food became scarce. Food availability wasn't reliable, as it is today in our culture. The body reacts to dieting like you are at risk for starving. The best thing for your survival is to be able to survive the worse case scenario. So if your body thinks food is scarce, it will make your metabolism slow down and become efficient at using what little food you have. When calories increase, your body doesn't respond right away because it wants to protect you against that food shortage happening again. It will stay efficient for a while so that you store fat. The stored fat will protect you against future food shortages.

Eventually, if you maintain your weight loss, your metabolism does go back to normal. If things are stable, your body eventually stops freaking out. For some people this takes months, for others it takes years. You can't really speed up metabolism past it's "normal" point. And I don't know of a way to hasten going back to normal either. "Normal" is genetically determined.

The slowing down of the metabolism in response to food shortages is called "adaptive thermogenesis". There are a few things your can do to PREVENT this while losing weight. One is to maintain your lean body mass (namely muscle). You can do this by eating sufficient protein and lifting weights. The other is to lose weight slowly and take diet breaks. This tricks your body into thinking that there is no real food shortage, or at least not one that is lasting for long and is of any danger.