Calculating food Carb %

Discussion in 'Health Links / FAQs about Feline Diabetes' started by Seattlebrian, Aug 11, 2010.

Thread Status:
Not open for further replies.
  1. Seattlebrian

    Seattlebrian Member

    Joined:
    Jun 18, 2010
  2. Janet & Binky (GA)

    Janet & Binky (GA) Senior Member Staff Member Moderator

    Joined:
    Dec 28, 2009
    Well, I disagree with the assertion that you'll get reliable results using the guaranteed minimum values. But if it's used with the actual values, the calculations seem to be reasonably correct. (They seem to be using 8.7 kcals/g for fat rather than the standard 8.5, but that's not a big deal.)

    I have an Excel sheet which calculates percent of calories from each of the components at http://binkyspage.tripod.com/foodfaq.html.

    -- Janet
     
  3. Seattlebrian

    Seattlebrian Member

    Joined:
    Jun 18, 2010
    I was thinking that since it uses the min values from the can, that it would yield a "Max" carb %. Not the actual carb %.

    Might be useful for companies that absolutely refuse to give real numbers.

    I was also thinking, I could look at the javascript "guts" of it and rewrite a different version that would be more useful to people here. I could see people getting % of carbs confused with % of calories from carbs.
     
  4. Monique & Spooky

    Monique & Spooky Well-Known Member

    Joined:
    Dec 29, 2009
    Here is the "formula"

    When we talk about "less than 10% carbs" we are reffering to the fact that the food has say 8% of it's calories from carbohydrates. The actual carbohydrate amount (scientifically Nitrogen free extract=NfE) in the orginal or dry substance is calculated as follows using as fed values (not the Minimum and maximim given on most labels)

    Subtract the as fed values of protien, fat, ash, fiber, and moisure from 100%

    100% - crude protien% - crude fat% - ash% - crude fiber% - moisture% = NfE (carbohydrate)%

    example canned food: 100% - 10% - 5,5% - 2,5% - 1,0% - 79% = 2% NfE
    example dry food: 100% - 30% - 10% - 6,5% - 2,5% - 9% = 42% NfE



    To calculate the carbohydrate content in the dry substance



    canned food: 100% - 79% moisture = 21% dry matter (DM) = 0,21
    dry food: 100% - 9% moisture = 91% dry matter (DM) = 0,91


    Then divide the carbohydrate procent by the DM

    canned food: 2% NfE / 0,21 = 9,52% carbs in the dry substance
    dry food: 42% NfE / 0,91 = 46,15% carbs in the dry substance


    To calculate calories each component has a differnt calorie value (depending on digestability typically the modified Atwater-Factor is used:
    Protein: 3,5 kcal/g, Fat: 8,5 kcal/g, NfE (carbohydrates): 3,5 kcal/g

    The Energy in kcal / 100 g Food is calculated as follows:

    (%Protein * 3,5 kcal/g) + (%Fat * 8,5 kcal/g) + (%NfE * 3,5 kcal/g)
     
    Jessica1995 likes this.
  5. Janet & Binky (GA)

    Janet & Binky (GA) Senior Member Staff Member Moderator

    Joined:
    Dec 28, 2009
    Correct, it would give you a max carbohydrate value, unless water, ash, and fiber (which are maximum values) were vastly overstated.

    The real problem, I think, is that companies tend to seriously understate the fat value of the food. This has led to some really bad estimates -- for example, one food where the GA values indicated that the carbohydrate content was over 25% of calories, whereas in fact it was around 10%.

    -- Janet
     
  6. dodgingwrenches

    dodgingwrenches Member

    Joined:
    Jun 12, 2010
    I have a spreadsheet calculator as well in my signature if anyone would find it useful. This document can be edited btw, so be careful what you do! I made it that way in case anyone wanted to add to it :) Call it "open source"!
     
  7. KristenP&Sam

    KristenP&Sam Member

    Joined:
    Dec 11, 2010
    I just used your spreadsheet and I'm surprised by some of the carb counts on food that was supposed to be lower carb! They don't match up with Binky's list, which is what I've been using. Interesting.
     
  8. dodgingwrenches

    dodgingwrenches Member

    Joined:
    Jun 12, 2010
    That spreadsheet is just for estimates using the formulae I found. Real content info received from the manufacturer (which is where most of Binky's chart values come from) could be different and more accurate. I just created that spreadsheet since in Canada, many flavours are different than what is on Binky's chart - even if it's the same brand (eg. Wal-Mart's Special Kitty) so we can't really follow Binky's chart up North unfortunately :(.
     
    Brashworks likes this.
  9. Bump per request.
     
Thread Status:
Not open for further replies.

Share This Page