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

Comments

wayhey

[gudriba]

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...

[velvet_wood]

_Oh_ yes. Concise is good, as the ol' attention span isn't what it used to be. However, I _loathe_ dumbed down scientific/technical articles of any sort. The whole idea behind current publications seems to be that if the lowest common denominator can't grasp it, it's unacceptable. The reader isn't held responsible for anything. I don't know about everyone else, but I was raised to understand that if you don't know what something means, you go look it up. I find it irritating beyond belief to be trying to acquire actual information and half of what I'm reading seems to be definitions for imbeciles and the other half is so simplified as to be nearly incorrect.

V

[aaangyl]

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...

[thorfinn]

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

[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.

[thorfinn]

That's okay, there should still be plenty of amino acids kicking around unmetabolised, and quite likely still some being digested. I'd have a boiled egg or two (and free range, definitely) when you got home, just to top up the amino acid levels a little bit. Pull the yolk out of every second one if you're very concerned about cholesterol. I wouldn't be unless you have evidence that you need to worry, or you eat a lot of eggs already.

[g_na]

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