Human Biochemistry, the basics as relating to dieting.

[thorfinn]

Some of you have probably seen this before in other fora, and I've mean to post it up here for a while, but hadn't summoned enough round tuits. A reasonable chunk of my audience here are quite aware of this stuff already, but there's also plenty who aren't. If you're one of the former, feel free to drop corrections in if any are spotted. And if you're one of the latter, feel free to ask for clarifications on anything that seems complicated or confusing or wrong. The idea is that even if you know absolutely nothing about this, you should hopefully be able to understand a bit more about it after this post.

"Calorie Counting" Is Bogus (ETA: in the sense of not useful on its own).

"Calorie counting" doesn't take into account 90% of what's going on in the body when food is processed and used. This is biochemistry. It's not that simple. Calorie counts don't work on their own. It's the wrong thing to be measuring. It's like comparing different brands of computer by measuring their CPU speeds in MHz and claiming that's all that matters. It's not the only factor that matters, and there are plenty that matter more.

What Are We Made Of?

Humans (indeed most animals) are composed basically (leaving out micronutrients) of water, proteins (composed of amino acids joined together into twisted up chains), fats/lipids (fatty acids - long, flat chainlike molecules), and carbohydrates/polysaccharides (simple sugars/monosaccharides stuck together like globs of multi-angled lego).

All cells are composed of proteins, lipids, and carbohydrates. What varies is the types of stuff and the proportions based on what the cell's job is. Muscle cells have more proteins than any other types, because they build long protein chains that allow them to contract when triggered. Fat cells have more lipids, because their job is to store lipids for times of hunger.

What's Going On Under The Hood?

The primary biochemical cycle that our cells use to do any sort of work is known as the "Krebs" cycle, named after the main discoverer of it. Mostly known as the "Citric Acid" cycle, these days, since that's a molecule that features heavily in the cycle.

Basically, the Krebs cycle is a long chain of sequential chemical reactions which break down stuff, resulting in the conversion of ADP (Adenosine Di-Phosphate) to ATP (Adenosine Tri-Phosphate) at several points along the chain. The conversion of ATP to ADP is then used to fuel most other reactions in the cell (eg, muscular contraction, etc). Think of ATP as a little charged battery, and the Krebs cycle as a process that churns out these little charged batteries, which then float around and get used up elsewhere inside the cell.

The Krebs cycle when fully used is designed for breaking down glucose (the simple sugar molecule/monosaccharide that we use) by adding Oxygen, and turning it into Carbon Dioxide plus water. However, because it's a multi-step process, there are plenty of extra points where things can get inserted.

Fatty acid metabolism happens quite close to the end of the Krebs cycle. Basically small bits get chopped off the end of the fatty acid, and they get inserted into the Krebs cycle, and generate a small amount of ATP each.

Amino acid metabolism is more complicated than I want to know about, but basically it also results in a shortcut of the Krebs cycle, and generates ATP. The insertion point is usually earlier than that for fatty acids, and is easier.

So, there are three basic sources of energy for cells. Amino acids, glucose, and fatty acids. Glucose is floating around in the bloodstream, and same for amino acids and fatty acids, although in much lower proportion. Muscles have amino acids on site, which they are made of.

Food Processing.

Food is digested (at various points for different substances, ranging from starting at the mouth for carbohydrates through the various intestines) into it's basic components before being absorbed into the body. The more "complex" the thingy, the longer it takes to digest into its absorptible bits (ie, amino acids for proteins, fatty acids for fats, monosaccharides for carbohydrates).

Once those bits are absorbed, they travel from the intestines and stomach, via the only vein in the body not to go directly back to the heart (the hepatic portal vein), straight to the liver.

The liver usually then grabs as much of the monosaccharides as it can, and turns them into glycogen, which is the body's main store of carbohydrate. Glycogen is stored mostly in liver cells, but also it's stored in muscle cells, which pull glucose out of the bloodstream, and convert it to glycogen.

If blood sugar is low, body cells convert glycogen to glucose, and vice versa for high.

Fatty acids are collected by fat cells, and bundled together, if there is a lot of fatty acids in the bloodstream, and vice versa... but this process is slower than the process for glycogen/glucose conversions.

Amino acids are used everywhere, but the biggest store is in the muscles. Again, muscle cells build up proteins more when there is high amino acid blood content, but a bigger factor in this process is whether the muscles have been used recently.

I'm Running I'm Running I'm Running!

Now, when one exercises, the muscles start to burn glucose, run out of glucose, and start converting glycogen to glucose (well, continue to - this is a dynamic equilibrium - since they always do some conversion, the rate just goes way up). Also the liver starts dumping glycogen into glucose also, to maintain blood-sugar levels.

Eventually, the entire glycogen store runs out, at which point the only energy sources are fatty acids and amino acids.

Muscles, if they run out of glucose during exercise, don't have fatty acids to burn. Or not much, anyway. So, they generally eat amino acids, plus whatever fatty acids are in the bloodstream at the time.

In fact, exercise burns fatty acids, amino acids and glucose, all at the same time, sucking them out of the bloodstream as you exercise.

As they come out of the bloodstream, they are replenished into the bloodstream from storage sources (the liver, for glucose, fat cells for fatty acids, muscles for amino acids).

So - longer, slower exercise has more time to suck fat out of the fat cells than short fast exercise, since you spend longer with "low" levels of fatty acids in the bloodstream.

It's got nothing to do with the calorie count. You can burn more "calories" by running fast for 10 minutes instead of walking slow for an hour, but most of those calories will come from glycogen storage and amino acids, and hardly any of them will be from fatty acids.

Other Tidbits.

Your brain can detect the levels of various substances in your bloodstream, and if you practice, you can learn to tell what state your body is in, to distinguish between false hunger and real hunger, and what your body is actually hungry for.

Aerobic exercise is exercise which burns sugars "properly", meaning that your bloodstream is carrying enough oxygen to actually complete the Krebs cycle fully. Anaerobic exercise is exercise which occurs too fast for full burning to occur, resulting in the byproduct "lactic acid" being produced. Fast and heavy exercise (e.g. sprinting) is anaerobic, gentle exercise (e.g. walking) is aerobic.

The way to tell the difference? Listen to your muscles... if they're feeling "crunchy" during exercise, that's bad. "Crunchy" means that you have lactic acid buildup, and lactic acid is the direct byproduct of anaerobic metabolism. (ETA updated info)

Doing fifteen minutes of aerobic exercise will raise your metabolic rate for quite some hours afterwards. This overall raise in metabolic rate is likely to burn more energy than doing fifteen minutes of fast running, after which your body collapses and reduces your metabolic rate for hours afterwards.

Executive Summary.

Basically, fat metabolism occurs last. Your body burns protein (i.e., muscle tissue) in preference to fats! Thus, over-exercising whilst hungry does nothing for reducing fat. All it does is burn off muscle tissue. You should eat a balanced diet, doing so by learning to tell whether your body is hungry or not, and you should do 15 to 30 minutes of gentle aerobic exercise daily. That will reshape your body much better than counting every calorie.

Comments

[wildilocks.livejournal.com]

Interesting. I've found the most effective wieght loss to come from eating a low-carbhoydrate diet, because your body usually will send you "false" hunger pangs after eating too many carbohydrates, resulting in a very bad cycle of eat crap, feel hungry, eat more crap, gain weight!

I also have in the last 6 months achieved an excellent level of fitness from 2-3 sessions of 1 1/2 hours per week of high intensity cardio workout, and I'm pretty sure I've been mostly eating more, but not putting on extra weight in that time. While you say that anaerobic exercise reduces your metabolic rate for hours afterward, I was always udner the impression that regular higher-intensity workouts raised you BMR overall. Yes or no?

[thorfinn]

"High-intensity" does not necessarily mean "anaerobic". The term literally means "without air" - i.e. your body is burning glucose without using oxygen. Sprinting is so energy intensive that after the first second or so, more energy is needed than there is oxygen to burn, resulting in anaerobic exercise. "Aerobics" is about the level of exercise where almost all the exercise is "aerobic", hence the name. It does teeter a bit on the border between - but that's the idea. The point of "aerobics" is to maximise the amount of exercise that you're doing without getting into anaerobic metabolism. That's not necessarily a point that your particular instructor actually understands, but it's certainly the original reason for the name.

The way to tell the difference? Listen to your muscles... if they're feeling "crunchy" afterwards, that's bad. "Crunchy" means that you have lactic acid buildup, and lactic acid is the direct byproduct of anaerobic metabolism.

The other thing is, your muscle "tiredness" is fairly strongly correlated with muscle glycogen content... the more "tired" your muscle feels, the less glycogen is left in that muscle, and thus the more likely that muscle is to have had to burn proteins. Overall tiredness is a summation of overall body glycogen content.

Running completely out of glycogen is likely to lower your metabolic rate, as is doing anaerobic exercise.

[australian-joe.livejournal.com]

Useful to have it all collected in one place like that, and in places you've extended my knowledge.


I have a question, if this is something you know about :

Your body burns protein (i.e., muscle tissue) in preference to fats!

I've always thought that the amino acids L-Carnitine (and the related Acetyl-L-Carnitine) altered that balance, to the point where stored fats were promoted in terms of at which point they were used. Used in combination with CoQ10, I've been told the effect is that muscles are spared and that further energy demands would be fueled preferentially from fat rather than muscle? Have I misunderstood?

[thorfinn]

I suspect there are things that can change that balance (presumably by messing with the concentrations of co-factors that promote the different steps)... But, bear in mind that the body has further regulatory mechanisms to bring those things back into balance. Biochemistry is a very complicated dance of multi-way dynamic equilibria, and a swing in one direction typically results in swings elsewhere.

So - what you're describing is possible, but I don't know off hand without doing plenty more research. Personally, I'd go with relying on my body's actual mechanisms, and keeping the gentle exercise on, the protein intake up, and reducing the amount of carbs I eat, as well as keeping fats down to a non-crazy level.

[elindal.livejournal.com]

Thank you for that.

Now all I need is someone to tell me how to override the hunger urge. The medication I am on makes me constantly hungry, even when I know I don't need to eat (like when I have just gorged myself at Squire's Loft). The brain can tell the status of the bloodstream, but certain things can screw it up. :(

I will walk more - I promise.

[thorfinn]

Glerk! You're probably in a situation where you do need to calorie count. If your brain mechanism in control of that is screwed, then you've got no option apart from actually doing the numbers. I'm told that you do get quite adept at estimations and suchlike once you've been doing it for a while... just remember that you need to track fat, protein, and carbs separately.

[thorfinn]

Further to my previous reply, simonb has mentioned http://www.fitday.com which looks like a good way to get started with counting.

[halloranelder.livejournal.com]

Thank you. It even makes sense!

[thorfinn]

That's what I was aiming for. Good o.

The first diet that is actually working for me...

[domesticmouse.livejournal.com]

After many years of trying to lose weight, I finally had one shoved in my face - Potatoes not Prozac (http://www.amazon.com/exec/obidos/tg/detail/-/0684850141?v=glance). What the book basically covers is that some of us are actually hyper sensitive to sugar, i.e. everything from sucrose, fine milled white flour (think french bread), to beer. She found this sensitivity was particularly prevalent in alcoholics and children thereof.

I know I'm sounding like a salesman, but if anyone here is having trouble with food, go grab that book. It's on the shelves at about $20. It has made me a lot happier... (Being sugar low induces grumpiness in a major way... ;-)

Re: The first diet that is actually working for me...

[thorfinn]

Yeps. The biggest irony with "diet" foods, is that they are generally zero fat, but 50% sugar, and the rest is relatively simple carbohydrate. That's the worst thing you can eat if you're trying to diet... because excess glucose in the bloodstream is used to make glycogen, but there's only so much glycogen the body can store... and the rest is used to make fat!

[simonb.livejournal.com]

This is interesting to me given the amount of training at the gym I do, along with wanting to cut that last little bit of body fat away.

Recently with a change in my fitness programme - a switch to endurance training - I got a heart rate monitor to help monitor the kcal I burn during training as it was next to impossible for me to work out how I was doing without one (lots of circuit training). One of the useful features is that it will work out how long you spend within your aerobic heart rate zone; along with that it will also do things like count the kcal you've burned off, along with a guess at how much of that was fat.

I'm also monitoring the food I eat to ensure that I eat enough protein (I aim for 120g on the days I'm training, 60g on the ones I'm not) and not too much fat.

[thorfinn]

No need to cut out all body fat - arguably, the human body is designed to have some, and expects that there is some to call on, and removing it entirely may not be good for your health. Keeping to "trim and firm shape", fine, but zero body fat seems like a dangerous idea, to me.

But yes, that heart monitor sounds like an improvement, but it's important to bear in mind that the guess is just that... a guess. And definitely more protein on exercise days is crucial - without it, you would lose muscle mass. But you know that, which is why you're doing it.

Well explained

[my-ichiban.livejournal.com]

Cool. You give a nice explanation of energy use by the body. ( was feeling the cobwebs being removed when you talked about the sytems)

I will say that anyone who does make changes need to make sure that they drink plenty of WATER.
LACTIC acid can also build up in the muscles after exercise if a person is dehydrated.
It is important that people drink small amounts during exercise.
"Hunger pains" can sometimes be dehydration.

actually there is a lot that can be said about the benefits of water after my brief ramble.

Re: Well explained

[thorfinn]

Yay, yes, water good. That's one of the most likely issues to be struck by people increasing the amount of exercise they do... Water balance gets thrown out, for a variety of reasons. Breathing causes water-loss (dry air into lungs, water laden air comes out), as does sweating. Also note - salt balance is important. Your kidneys control whether they let out salts or keep them in based on bloodstream concentrations, but sweat always has salts in it. This is the "electrolytes" that they talk about in "sports drinks". A bit of salt (whether in food or drink or whatever) is good after sweating, because you need to make up the salt from somewhere.

[fizit.livejournal.com]

Thank you, you've just backed up my desire to do gentle weight training rather than aerobics classes (when I finally get to the gym, that is :)

[thorfinn]

Aerobics is a cool idea, but especially when just starting, it's very likely that a "standard aerobics routine" is going to dive well into anaerobic activity. Build up slowly.

Wow

[longi.livejournal.com]

Congrats on avoiding the inevitible "Use LJ-cut!" comment from kitling :)

Re: Wow

[thorfinn]

Heh. I think she's away down the beach. But even so, my journal, my rules. I generally won't cut pure text if it's an informative post. I will cut stuff that could be construed as uninteresting by a reasonable proportion of readers, or if it contains inline images.

[vatine]

As an aside, muscle mass (in general) aids in increasing the metabolism, so gentle muscle-building activity (and protein intake while training and possibly he day after) can be quite beneficial.

[thorfinn]

Yes, most definitely. Muscle burns energy just being there, and more "conditioned"/fit muscle burns more energy, since "conditioning" is training the muscle to keep itself at a basic level of activity so that it's "ready to go" whenever.

wayhey

[gudriba.livejournal.com]

You are by far one of the most informative people I know! Please keep posting your very interesting posts.

I always knew there was more to the calories in/calories out thing than a simple equation, but could never adequately explain why (never studied much biology and such). Now I understand it.

Walking two Border Collies seems to be good exercise. Woof. :)

Re: wayhey

[thorfinn]

No problems. *grin* I like informing people, and informing smart people is a helluva lot easier than trying to write popular science articles. The stuff I post is "concised" but not dumbed down, which makes it impossible to sell as popular science. But people I know generally like it...

[aaangyl.livejournal.com]

Seeing the recent round of nice, sensible posts about nutrition and biochemistry has made me very heppy. Thanks for contributing to it! Hopefully if people read stuff like this enough places, they'll start trying out methods other than fad diets and 'magic pills'.

[thorfinn]

That's what I'm hoping. And it was seeing your post touted in anthologie's journal that reminded me that I meant to post this article... I loaded it into Semagic when I read the pointer to your post and the draft sat there until the other day...

[drwally.livejournal.com]

You should post this to pro_ana or something. It is remarkably inoffensive, yet I can already anticipate the flutter it would cause...

[thorfinn]

You're an evil man, drwally. I shall have to sic my aphrodisiac bone dart firing snail army upon you...

[simonb.livejournal.com]

Something I've been pondering for a little bit which you may be able to answer - is it best to eat lots of protein before you hit the gym or after ?

[thorfinn]

Err... Depends. You want the digested results (amino acids in the bloodstream) to be available immediately after you complete exercising, which is when the "increase muscle mass" hormones are at their peak. So, for meat eaters, eating meat a few hours before is probably good, along with some low glycemic index carbs so that there's plenty of glycogen available for the exercise itself. IIRC, you're vegetarian, though? Protein digestion is faster from vegetables, I think, so eating closer to gym is fine. But either way, not for an hour or so before exercising... Digestion draws a lot of blood into the intestines, and you do not want that happening whilst you're trying to exercise. I believe that eating some protein after exercising as well is a good idea, that way there's a slow trickle into the bloodstream for a number of hours afterwards, whilst the hormones are all still going.

[g-na.livejournal.com]

Hello. I know I'm writing this months after your post, but someone just pointed me to it. You have a lot of good information here; the kind of stuff you rarely see all in one place. Thanks for putting it together.

I had one question I was hoping you could answer. You state, "Doing fifteen minutes of aerobic exercise will raise your metabolic rate for quite some hours afterwards. This overall raise in metabolic rate is likely to burn more energy than doing fifteen minutes of fast running, after which your body collapses and reduces your metabolic rate for hours afterwards." I had never heard this before. Could you tell me the physiology behind why your metabolic rate would drop? (I've been trying to determine the exact reasons why aerobic exercise is better for weight loss than anaerobic, but nowhere can I find an actual scientific reason.)

Thank you.

[thorfinn]

No problems on the months afterward reply... That's one of the beauties of LJ, that these posts sit here for people to continue to find.

On to your question... The relatively simple answer is that when you do anaerobic exercise it burns glucose, but in a short-cut fashion, not using oxygen (anaerobic literally means "non air using"). The product of this is lactic acid. Lactic acid is pretty much the thing that makes muscles "tired". When they're full of lactic acid, they can't continue to operate at any kind of reasonable rate, because they have to sit there and wait for the bloodstream to carry the lactic acid away.

That overall signal to your body when your blood goes "hey, I'm full of lactic acid" contributes to a general slowdown of your metabolism all over, as well as just in the "tired" muscles.

The biggest factor, though, is simply that as a result of production of lactic acid, you cannot do anaerobic exercise for any lengthy period of time. Even if you wanted to, your muscles would eventually fill up with actual crystals of lactic acid, and physically seize up, no matter what you want to do with them. Properly aerobic exercise doesn't generate lactic acid, because it burns the glucose molecule "fully", making carbon dioxide and water.

Note that the amount of exercise that is "aerobic" vs "anaerobic" is directly related to how "fit" a person is. "Fitness" means that your blood circulatory systems are in better shape, your lungs are in better shape, your muscles are in better shape to absorb oxygen and glucose from the blood and push CO2 back out to the blood, etc, etc. The whole point of "fitness" is to improve the ability of your body to burn glucose "properly", rather than having to short-cut to lactic acid.

The corollary to that is that depending on how fit you are, you should do a rate of exercise that is in proportion. Your theoretical obese TV couch potato would find walking to the kitchen and back a partially anaerobic exercise, whilst your olympic athletics competitor would find that several laps around a football field at top speed would still be almost entirely aerobic.

The key for any individual is learning where that rate-point is, and exercising at that rate and no faster. If you're unfit or unsure, start with slow walks around the block. Your body will tell you when it's capable of going faster - your muscles will feel bored, and so will your brain. If you push the rate too fast, your muscles will get tired very quickly. That's "the wall" that runners talk about - the point where lactic acid production starts to outstrip the rate at which it can be pulled out from your muscles by your bloodstream.

Erm... that's lots of digression. :-) Anyway. The main point is that the metabolic crash is due to lactic acid production.