At 4:10 PM -0500 26/1/02, Keith Thomas wrote:

>1.  Does the USDA data base report on n-3 and n-6 fats?

I have just checked out the latest version of the USDA database (SR14).
The nutrient descriptions list n-3 and n-6 fats as well as trans fats.
However when you dig a little deeper you find that there are actually
only two foods with data for those new fats. Pretty misleading, but
hopefully these extra fields will be populated in future versions of
the database.

The polyunsaturated fats listed in the database are:

n-6 fats:
18:2 linoleic
20:4 arachidonic

n-3 fats:
18:3 linolenic
18:4 stearidonic
20:5 timnodonic (EPA)
22:5 clupanodonic (DPA)
22:6 docosahexaenoic (DHA)

There is also listed:
20:3 eicosatrienoic
I don't know whether this is n-3 or n-6. One reference I found
suggested this fat even comes in n-3, n-6 and n-9 varieties! In any
case it is only found in the tiniest quantities (0.017 grams per 100
gram portion is the highest).


>2.  If it does, how do I derive that ratio from its analyses?

Add up all the n-3 fats and the n-6 fats and divide one by the other :)

You have already seen my old chart listing ratios of linolenic:linoleic
fats. I have updated that page with data from the USDA database version
SR14 (there are only a few very small differences). This old chart has
a new URL: http://www.juggernaut.com.au/food/linolenic-linoleic.html

As an exercise in SQL programming, I have also compiled a similar chart
for all n-3 and n-6 fats, including DHA, DPA, EPA, 18:4 n-3 and 20:4
n-6.

This chart is much more meaningful than the previous one since it
considers all EFA's including EPA, DPA and DHA. It's not surprising
that fish feature prominently in this new chart. I have also improved
the layout somewhat, so that the file is shorter than 76 pages :)
This new page is at: http://www.juggernaut.com.au/food/omega3ratio.html

Any improvements/suggestions welcome.

 ...Richard.