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Thread: Energy question

  1. #1
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    Default Energy question

    This is really a question for UK/European posters...

    On the nutritional labels on your foodstuffs, is the energy content marked in Calories or kjoules? I have plenty of UK imports but I guess they're labelled for the US market as, for instance, my Mr Patak's garlic relish has calories.

    I've been asked recently why "workout" calories are different from "food" calories.....and asked in a way that makes me think that the difference they were talking about isn't just a factor of 1000 (as I tried to explain the cals., kcals.,Cals. thing) The only thing I can come up with is maybe the difference is they've seen something pertaining to kjoules minus the adjustment that, say, the power meters make to account for the 20-25% biochemical to mechanical efficiency.....

    ....if that makes sense??

    Vivienne

  2. #2
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    Question answered already.

    Had the gumption to e-mail SIL and ask her to check her pantry and, lo, her Sainsbury's Raspberry Conserve boasts that, for each 100gm of the stuff, there's 1050kJ/240cal

  3. #3
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    Yup. It's pure math.

    1 kilojoule = 0.238 845 896 63 Calorie [nutritional] (This is always true and has nothing to do with efficiency - it's like converting inches to centimeters.)

    It's important not to confuse kilojoules of work (what you read off of your power meter) and kilojoules of chemical energy (what you read on a food label). By coincidence, your body's about 24% efficient in converting chemical energy into mechanical energy. Therefore, the rule of thumb that kilojoules of work equals dietary Calories (capital C) is only true because of dumb luck.

  4. #4
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    Quote Originally Posted by Todd S View Post
    Yup. It's pure math.

    1 kilojoule = 0.238 845 896 63 Calorie [nutritional] (This is always true and has nothing to do with efficiency - it's like converting inches to centimeters.)

    It's important not to confuse kilojoules of work (what you read off of your power meter) and kilojoules of chemical energy (what you read on a food label).
    By coincidence, your body's about 24% efficient in converting chemical energy into mechanical energy. Therefore, the rule of thumb that kilojoules of work equals dietary Calories (capital C) is only true because of dumb luck.
    Ooops, I think I was tending down that path. Thanks Todd.

    See, if only the rest of the world would be like us there'd be no problem......wouldn't need these fancy joules and celsiuses etc.

    Vivienne

  5. #5

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    We had an extensive discussion on food energy vs. energy output a while back:
    http://www.pedal-on.com/showthread.p...New-To-Keiser/

    On a side note, it's a little strange we ask "how many calories are in that food" rather than "how much energy" is in it. Maybe it's the engineer in me, but it's as if we asked "how many pounds do you have" rather than "how much do you weigh". And I'm sure Vivienne is joking...
    Quote Originally Posted by Vivienne View Post
    ...See, if only the rest of the world would be like us there'd be no problem......wouldn't need these fancy joules and celsiuses etc....
    ...but it really is time we in the US fully adopt the metric system. We already run in 5K's, buy soda and wine in liter-sized bottles, we should finish the job.

  6. #6
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    Quote Originally Posted by Paul S. View Post
    On a side note, it's a little strange we ask "how many calories are in that food" rather than "how much energy" is in it. Maybe it's the engineer in me, but it's as if we asked "how many pounds do you have" rather than "how much do you weigh". And I'm sure Vivienne is joking...

    ...but it really is time we in the US fully adopt the metric system. We already run in 5K's, buy soda and wine in liter-sized bottles, we should finish the job.
    I've had a strange experience with the metric system.

    The UK started with decimal currency in 1971 and I got used to that.

    Then temperatures.....and for ages, the weather forecasters used fahrenheit and celcius. By the time the fahrnehiet was dropped, I was used to thinking in C. Now I have to convert to tell my family and pals the temp (unless it's bang on freezing) Oddly enough, my parents who complained about changes when they happened as much as the next person, passed a similar comment the first time they visited us here.......you'd think the US'd catch up with the civilised world (or maybe that was our septic tank)!

    When weights and measurements started to change for real it was shortly before we moved to the US. I can remember one garden center close to us with an honkin' big sign reading "This is ENGLAND. All our measurements wil remain in ENGLISH" Never did get used to thinking in kilograms......but also I thought of weights in "stones" and "pounds".

    Litres instead of gallons came in after our move here.......I'm fine with the booze (get plenty of practise, I guess) but have trouble working out how much petrol's costing us when we visit.

  7. #7
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    001cy2-300x300
    And believe it or not, the question I was originally asked turned out to be nothing more than the difference between cals and kcals.....the "k" and the "000" not being a big enough give away, I guess.

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