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kai-man 05-25-2012 11:01 AM

Vitamin A calculation in custom foods is demonstrably wrong
This will be somewhat complicated, but I hope I manage to explain it well enough.

This is about the creation of a custom food from a recipe and the resulting Vitamin A values.

To add a recipe I go to an empty day, enter all the ingredients and look at the total values in both the Calories tab as well as the Nutrition tab.

Taking into account that entry has to be done as DV and will be expressed by FitDay as RDA, I now want to create a custom food for "recipe" that contains all the same amounts of macro and micro nutrients.

<Short digression>

The value I use is the actual weight of the substance in question, based on the assumption that if my recipe contains 100 mcg of something per serving, then I can calculate how much of a DV that is and create the appropriate value for data entry for the custom food such that the custom food will also contain 100 mcg.

I have created a spreadsheet that will do all the calculations.
In the end, my Total Nutrition of the custom food = the values of the recipe.

<End digression>

These calculations work out for all nutrients, except for Vitamin A.
There are 2 independet errors involving Vitamin A.

Using data for a seafood salad I have created:

1) In the Nutrition tab a value of 69.90 mcg Vitamin A is shown.
In the line below this is converted to 256.40 IU.

This is incorrect.
In fact, using 69.90/0.3 (the conversion between mcg and IU for Vitamin A) I get 233 IU.

2) This error is indpendent of Error 1, even though it might not seem so.

My spread sheet works for all nutrients equally, except for Vitamin A.
I have to multiply the DV Vitamin A by a fudge factor or 3.45176470588235 in order to get the correct weight in the custom food.

Calculation I use:

My recipe for Seafood Salad contains 69.90 mcg Vitamin A
I want my custom food of "Seafood Salad" to contain 69.90 mcg Vitamin A as well.
The DV for Vitamin A is 5000 IU = 1500 mcg
Therefore (69.90/1500)*100 = 4.66% DV

This works for all other nutrients, except for Vitamin A.

If I now enter 4.66% as my input for Vitamin A in the creation of custom food "Seafood Salad" I get a value of 20.3 mcg Vitamin A and not the expected 69.90 mcg.

Applying the fudge factor to the formula making it
(69.90/1500)*100*3.45176470588235 = 16.09% DV

If I enter this DV value I get the appropriate 69.90 mcg in Vitamin A.

This error is probably related to error 1)
Again, using Seafood Salad as an example.
Vitamin A is 69.90 mcg in the sum total for a day that has nothing but seafood salad ingredients.

Having correctly created a custom food with 69.90g of Vitamin A, the IU calculation shows 804.5 IU in the custom food.
This is neither the incorrect 256.40 IU nor the correct value of 233 IU, but yet again completely off.

So, something is screwy with your Vitamin A calculation.
I hope this makes sense.

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