Sunday, June 22, 2014

Nutrient Database

Download the nutrient database here.  Don't try and read it in the Google drive viewer, just download it.
All of the data I used was sourced from the USDA database and the RDIs and AIs are from Australian NRVs.

Purpose

When I came around to looking at nutrients I had no way of knowing for sure if a particular food was high or low in it.  It’s easy to say a particular food is high or low in a given nutrient, but very rarely are these claims justified.  I wanted to find an objective way to know what nutrients are in food.

I also wanted to put the quantity of nutrients in context.  Rather than listing nutrients for every 100 grams of food, it’s more relevant to discuss nutrient density per calorie, as we are limited by the calories we can consume, rather than by weight.

Finally I wanted to compare foods on many nutrients.  When we list positive qualities of food, we often limit ourselves to a few nutrients at the most.  Functional foods add some nutrients and are then marketed as healthy.   There are many nutrients; nutrient dense foods are those that have at least sufficient quantities of most of them.  At this point I found one website that got as far as measuring nutrient density by calories and comparing it to the RDI.  What they didn’t do, which I think is important, is to list as many nutrients as possible for each food, to compare many foods, group like foods together and then compare those food groups.

The Process

I got all the data directly from the USDA nutrient database.  After I got enough I arranged the rows by nutrient.  Initially the foods were measured by 100g so I made a new sheet and changed the quantity of food to equal 2,000 calories.  I picked those nutrients that had an RDI, made a new sheet, and divided the quantity of nutrients (in 2,000 calories of food) by the RDI for each nutrient and each food.  I separated the foods into food groups, got the medians for the nutrient/RDI values for each nutrient, and then compared the food groups on this basis.

(The RDI is the amount of a nutrient so 97.5% of the population aren’t deficient in it.)

No measurement is perfect.  I used median rather than mean (average) because there were some foods with ridiculously huge nutrient/RDI values.  Liver for instance has 81 times the RDI for vitamin A.  Liver is grouped with other organ meats and shellfish, both of which don’t have very much vitamin A.  If I used the mean, the number would have suggested that the average organ meat and shellfish group has 9 times the RDI for vitamin A, which is true, but misrepresents that group.  Although in appropriately representing the group, I have misrepresented liver as the highest vitamin A containing food.  It’s a trade-off.  I suppose the knowledge of any foods that are extraordinarily high in a nutrient is fairly well known.  There’s nothing to stop you looking within the food groups themselves.

I made some assumptions and manipulated the data a little:-

·         I took all fibre to yield 2 calories
·         I often used higher alternatives of the RDI and those for 70kg adult men
·         For vitamin A I took the vitamin A RAE (retinol activity equivalent), converted it to IU by multiplying by 3.33 and used that measurement for the vitamin A row
·         Short chain omega 6/3 refers to 18 carbon long fatty acids
·         Short chain omega 6 came from 18:2 undifferentiated minus other 18:2 isomers, such as trans LA and rumenic acid, to approximate the amount of LA (18:2) and then I added GLA (18:3).  The approximation of LA is slightly high because there usually wasn’t data from the other isomers to subtract, but because GLA was often 0 because it was rarely measured directly it sort of balances out
·         Short chain omega 3 came from 18:3 undifferentiated minus other 18:3 isomers such as GLA or conjugated linolenic acids, to approximate the amount of ALA (18:3) and then I added stearidonic acid (18:4).  The approximation of ALA is slightly high because there usually wasn’t data from the other isomers to subtract
·         Long chain omega 6/3 refers to 20+ carbon long fatty acids
·         Long chain omega 6 came from 20:3 and 20:4 undifferentiated.  In each of these there is an omega 3 isomer, but they weren’t as common as DGLA and AA.  I also added adrenic acid (22:4).
·         Long chain omega 3 is simply the addition of EPA (20:5), DPA (22:5) and DHA (22:6)
·         Milk was measured for rumenic acid (18:2 i), but not for CLAs, so I used the rumenic acid for milk instead of the CLAs
·         Methionine and cysteine, and phenylalanine and tyrosine were added together for the RDI measurements because the RDI was for each group.  This is because in each group the essential amino acid can be synthesised into the non-essential amino acid, which is more commonly used by the body
·         Histidine is an essential amino acid, but we don’t need much of it and so the RDI is low.  The very low RDI caused histidine/RDI ratios of 100+ to be the norm.  I thought it was useless information and removed it

Limitations

I remember reading that to measure each food cost the USDA $2,000.  Getting that data wasn’t easy and therein lies the problem.  Even although the data was the best I found it was still incomplete.  Most of the incompleteness came from the more difficult tasks such as the isomers of fats.  So the following were missing to a degree:-

·         Biotin (vitamin B7) was missing from all the foods.  The RDI for biotin is 30 µg, which is a really small amount.  Biotin is found in roughly the same foods as vitamin B6, which could act as a proxy for biotin on the spread sheet.
·         Vitamin K2 (menaquinoe-4) was missing from almost all foods.  Vitamin K1 is also measured in µg and we eat much less K2 than K1 (about 10 times) so the K2 presence in food may have been difficult to measure.  Also vitamin K, especially K2, is a very under researched and not a well-known vitamin
·         Fats such as CLA (rumenic acid), EPA, DPA, DHA and fat soluble vitamins such as A, D and E often were measured as 0 in animals that must obviously contain some.  EPA and DHA are essential fats and the fat soluble vitamins are essential nutrients that would both be incorporated into the animal’s tissues.  Even grain feeding in feedlots doesn’t entirely deplete these fats
·         Isomers of 18:2, 18:3, 20:3 and 20:4 were rarely measured individually

What this also doesn’t measure or account for is:-
·         The bioavailability of nutrients
·         Other nutrients that don’t have an RDI
·         The variation of nutrients in plants that depends on soil (minerals) and health (vitamins)
·         The variation of nutrients in animals that depends on what they eat
·         Just meeting the RDI doesn’t necessarily mean healthy, the amount of a nutrient so that 97.5 of the population have optimal blood levels may be considerably higher

3 comments:

  1. sounds good - how do I actually get the file? - when i click on them - and clikc around that file sharing site - I just keep getting commercials for illvid and different browsers - I can't seem to get access to either file?

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