About Dieting

[gusl]

HowStuffWorks on Calories

What they didn't explain:

How do people measure the energy content of food? Can they measure it by using it as fuel?

How do they estimate how much energy you spend on a physical activity?

One reflection: while warming food makes it more energetic, burning it invariably makes it less energetic (or browning bread).

I would very much like a machine that keep track of my energy intake & spending, but such technology still seems far away.

I calculated my Basal Metabolic Rate (BMR) to be 1825.5 Calories / day, but does this mean my energy expenditure if I do nothing but breathe? Should I simply add exercise expenditures on top of this amount?

Comments

[mathemajician.livejournal.com]

Last time I read about it the way they worked out the energy content of food was by blowing it up with a bomb.

They get some quantity of explosives that are very precisely measured out and then stick it around some food and the put it in a special chamber and then blow it up. They then measure the exact amount of light and sound and heat generated to compute the energy released. Then they subtract from this the amount of energy that is released when this quantity of explosives is detonated without any food present. That gives the energy content of the food.

Of course this method isn't so useful if you want to work out the energy content of something you are about to eat!! ;-)

[gustavolacerda.livejournal.com]

So the assumption is that the bomb can consume food as fully as our digestive chemicals. Are both processes close to 100% efficient? (of course, an efficiency measure assumes there is a state of absolute null chemical potential energy)

[mathemajician.livejournal.com]

This part I don't understand. Perhaps the bomb is really good at consuming the energy with all that heat?

As for what percentage of the energy in the food the body actually makes use of? I don't know. Perhaps it depends on the person, their age etc?? I vaguely remember that they also measure a person's energy output by putting them in a special room making them exercise there. They then measure the amount of heat and sound generated. If you did this for a long enough period of time, for example by having a person live in one of these rooms for a couple of days, you might be able to work out how much energy the body actually got from the food.

Heh, the other possibility would be to blow up their shit! The difference between the food and the shit would let you know how well the body was extracting the energy.

[jbouwens.livejournal.com]

Calculating your energy needs/expenditure to one decimal place is completely useless, as are diets based on calculating how many joules you eat and fitness equipment that tells you how much energy you "burned".

If you want to loose weight, you only need to do two things:

1) Eat less and/or healthier. Don't try and quantify this too much, it's mainly common sense: Eating fruit and vegetables every day is good, paying a visit to the Mac every day is bad. Pretty obvious.

2) Work out. And I don't mean going to the gym once a week, leaving at 18.00 and returning at 19.00 claiming you did an hour of excercise, but at least 2-3 hours a week of actual, intensive excercise.

Your body is quite capable of taking care of itself. It decides what to keep and what to reject based on its needs. Working out doesn't just let you loose weight because you burn energy, it also means your body starts optimizing for a more active life-style. This means less fat so your body has to carry around less weight when you're excercising.