Why Doesn't Cronometer adjust for bioavailability?

UpRiverMatt

Hi,

I like this application quite a lot, but the major problem I have is that the micronutrients do not adjust for bioavailability. For example, beta-carotene from plant foods has a 12:1 conversion to the usable form retinol, yet that is not reflected into the RDI listed. This means if I consume 100% RDI from plant foods for Vitamin A, it is actually only about 8% of my RDI. If I consume 100% from animal foods, that would actually be 100% of my RDI.

Thanks!

Karen_Cronometer

Hi there,

Beta-carotene, and other carotenoids, are converted to Retinol Activity Equivalents RAE to take into account the fact that they are converted to active vitamin A at different rates.

When foods list the total Vitamin A value in RAE or IU, these conversions have already been done.:)

UpRiverMatt

Thanks for the answer! When I calculate it I get a different answer than cronometer.

1 oz of beef liver is showing on cronometer as 8991 IU, whereas 1 oz of carrots is showing 4736 IU.

1 oz of beef liver has 2643 micrograms of retinol = 2643 mcg RAE / 0.3 = 8810 IU so that makes sense. However, 1 oz of carrots has 2320 micrograms of beta-carotene / 12 = 193 mcg RAE / 0.3 = 643 IU, which is much less than cronometer reports. It seems the beta carotene conversion cronometer uses is about 7x too high.

Does this seem correct?

Karen_Cronometer

The USDA uses a different method to calculate IU from the carotenoids, rather than converting them to RAE first.

First, they calculate the beta-carotene equivalents to include vitamin A activity from the provitamin A carotenoids: beta-carotene, alpha-carotene, and beta-cryptoxanthin.

Beta-carotene equivalents are calculated from the following:
mcg beta-carotene equivalents = mcg beta-carotene + ½(mcg alpha-carotene + mcg beta-cryptoxanthin)

Values are expressed in micrograms.
6 mcg beta-carotene equivalents provide 0.5 RAE vitamin A, 1 RE (retinol equivalent) vitamin A, or 10 I.U. vitamin A.

To convert Vitamin A as beta-carotene:
From mcg to IU: mcg * 1.66 = IU

For 1 oz (28 g) of raw carrots we can calculate:

beta-carotene equivalents = 2320 mcg beta carotene + 1/2 (974 mcg alpha-carotene + 0 mcg beta-cryptoxanthin)
= 2807 mcg

2807 mcg beta-carotene equivalents * 1.66 IU/mcg = 4660 IU

They are moving the American nutrition labels to reporting vitamin A in mcg RAE instead of IU and the DRIs have already changed over to using these units. We will be free from the confusion around IU some day!

UpRiverMatt

Very interesting, thanks! I didn't realize there was so much discrepancy between conversion methods. It seems the USDA method will reflect bioavailability much better when using mcg RAE.

Will Cronometer switch to using mcg RAE instead of IU as well?

Karen_Cronometer

You can view RAE already! Check out the Nutrient Target settings, where you can add it to your nutrient targets. Vitamin A in RAE is listed in the Vitamins tab.