How Calories are Counted?

Anyone know how they figure the calories in food?

The naive way would be to notionally "burn" the food, and calculate what the energy output of the combustion equation is (this could be done very accurately), and I wouldn't be surprised to discover that this is exactly how the number of calories advertised in food items is calculated. If so, I think you'd find that this massively overstates "effective calories", because our bodies don't burn things all that efficiently. From a "calorie counting" point of view, this needn't be a problem if there's a simple relationship between actual "calories in" to "calories available", because the studies the counting was based on would accidentally take the ratio into account (I think?). I would actually guess that there is something like this, just because calorie counting seems to work, even if the figures may be overstated.

What's interesting to me is more to do with how calories spent on effort would match up to calories consumed as fuel. What I've heard is that we don't have a tremendous peak power output. We don't "burn calories" terribly well. And yet you keep hearing of people's waistlines starting to reduce quite rapidly with exercise. If we're not burning more than the estimates suggest, how's that possible?

And for what it's worth, here's what I think: When it comes to the amount of energy we convert while doing exercise ("output"), we actually do burn what it says on the container. For instance, if I'm on my spinny thing and it says I'm putting out 150 Watts, it means that at the generator out there, the power output is exactly that. That's where the reading is done, and it can be done very accurately (I suspect they've managed to wangle things so that it flatters the user quite a lot, but that's another issue).

So when you say you burned 500 calories on a run, you're physically correct. That's exactly what the external measurements would say; however, when you say you "ate 3500 calories", you're probably skipping out the detail that you threw 2000 of that away. Maybe. It would be interesting to know.

14 Replies

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  • It's a great question Gary but I can't answer it except to say the highest calorie foods are the tastiest! This is interesting.

    todayifoundout.com/index.ph...

  • Taste has something to do when calories were not so abundantly available. So the best way to get the body to consume more calories was to make food rich in calories tastier. Evolution!

  • Thanks. It also confirms what I suspected. The number of Calories given in the food's label is the total available, rather than the total that eventually is converted to valuable fuel reserves conveniently stored round our middles.

  • As I understand it after 3 billion years of evolution, the body is amazingly efficient at extracting calories from food. Some does go to waste, but not much. Exercise is lousy at consuming calories, You have to run an hour to use up 1000 Calories, mostly as a result of the heat generated and our bodies efforts to dissipate it.

    Reduced waistlines without weight loss is a bit baffling. The obvious answer is muscle gain, but muscle is almost never gained when you are dieting apparently. You do build up other tissues, but probably not nearly enough. Water balance is probably the answer. I've used fitday to record everything I eat etc, and there doesn't seem to be much in the way of unexplained calories, either way. I tend to lose a little bit more than fitday expects, which suggests I run a bit hot maybe. Or I could be totally wrong.

  • I have very vague memories of long cascades of reactions to "burn" fuel for whatever it's used for. At the very end of the line, like a kind of "magnet", is Oxygen, which is "the ultimate fuel" (just to keep this as non-technical as possible). If we went straight to the Oxygen, we literally would just burn up, but because there are all these intermediate steps, the last one to Oxygen is not so hot that we boil. Each of those intermediate reactions has heat losses, and what's lost to heat is lost to fat assembly or motion or whatever the respiration is supporting. I seem to recall that the losses were quite large, but the memories truly are far too vague for me to say so for sure. It could well be that we are indeed extremely efficient - complexity of our chemistry notwithstanding. Us humans certainly generate quite a lot of heat, respiring, but plants don't, and nor do lizards, so I suppose it's not an inevitable consequence of "fuel burning".

    And yes, we don't have such a great rate of energy conversion. Even elite athletes would struggle to supply the energy needs of a small vacuum cleaner for any length of time, and most of us would only manage to keep a few lights burning if we tried to treadmill our own energy supplies. It's just that if you find a way of measuring that small output, you are not left in any doubt that you were burning something at that rate, and you used that total amount of energy after some time. The readings are directly of what your muscular effort actually did, and not of the potential your fuels provided for effects like expanding a waistline.

    Interesting, the mystery of the reduced waistline. I think maybe there is sometimes muscle gain in dieting people who are exercising. Definitely, it seems to happen to a lot of people here. I've also heard of muscle loss with dieting and exercise, though. Maybe it's necessary to also do strength training? That might be what distinguishes those losing muscle from those gaining it.

  • On the first part of your query, yes energy content is measured by, essentially, burning it.

  • I'd forgotten how it was done, but that bomb calorimeter contraption definitely rings some bells. Isn't it strange that we're like a bunch of slow burning fires (literally), in some sense?

  • Calories are one of life's great mysteries. So many in so little amount of food. So few needed to do so much.

    They once used an equivalent of 100 calories for an explosion. And that was quite an explosion!

    Given what we call 1 calorie is actually 1 Kilo Calorie = 1000 calories, it is even more mysterious.

    I have given up counting. I now just run and do crossfit. And eat as healthy as possible.

    Results:

    1. Smaller double chin

    2. Smaller waist

    3. Better cardio capacity

    Calories and how women's minds work are 2 of life's greatest mysteries.

  • I think a few lines back I went and tripped up over calories and Calories and ... mysteries, yes. People do measure, though, and in spite of what looks like a deficiency in some of the assumptions behind the measurements, it seems to work. I suppose the act of measuring is just something that supports a self-disciplined attitude. Maybe.

    Maybe, perhaps, and mayhap. :-)

  • Well, they say that a 4000 calorie (KCal) defecit equates 1 pound of weight loss.

    I had been to a weekend's residential bootcamp where I had a defecit of about 4000 calories or so over the weekend. However, I lost a total of 8 pounds!

    What did we do? About 6 classes a day from 7:00 AM until 6:00 PM. Lots of walking. Lots of activities. And very limited food.

    Since that is not sustainable, that weight has gradually crept back.

    Folk should count...just not let it drive their lives though.

  • Well there's why it's so much harder to lose weight than to get running, then. That's a big deficit required. They must have starved you at the bootcamp. I've heard that if you make rapid losses like that, most of it is in water, too.

    Agreed that it's not something anyone should allow to rule them. Life is to be enjoyed. Break that rule, and it's not sustainable.

  • You will get to the weight you desire. I am sure of it.

    I hope you enjoy the journey too.

    We had something like:

    1. Porridge / bran flakes for breakfast

    2. Fruits / Teas / Coffees mid-morning

    3. Soup for lunch with salad for lunch

    4. Fruits / Teas / Coffees mid-afternoon

    5. Chilli with rice for dinner

    6. Some more fruits / teas / coffees after dinner

    Portion sizes were about one ladel (or ladle?).

    Hope this helps.

  • I'm probably at my target already. My cholestrol is on the lower end of elevated, but everything else came back fine in my last medical. So everything else is just a bonus.

    I took up exercise round about the beginning of the year, because the Blood Bank wouldn't take my blood. My resting pulse rate had crept up slowly to too high, and I got a fright and joined a gym. From there it's been a process of great discoveries like c25k (which I was amazed to find I enjoyed so much).

    When it comes to calories, I just try not to snack too much, not to dish too much up, not to go back for seconds too soon ... etc. What got me thinking about this whole matter was more the calorie count the spinning cycle at the gym gives (so output rather than input). I should probably count a bit more, though.

  • If snacking is an issue, I would recommend keeping some seeds like sunflower seeds and pumpkin seeds handy. They are natural, low of the bad stuff and full of good stuff.

    Best of all, they are reasonably priced too.

    Well done on getting all the numbers in check!

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