Date: 20 Aug 1994 07:44:59 -0700
From: taltar@vertigo.helix.net (Ted Altar)
Subject: What are RDAs? (repost)
Newsgroups: rec.food.veg
Organization: Helix Internet
Lines: 156

WHAT ARE RDA'S?
                            Ted Altar
Topics briefly covered:
     A.  General Preamble
     B.  The American Rda's
     C.  Toxic Effects Of Vitamins
     D.  The Example Of How A Rda For Protein Is Obtained.


A.  GENERAL PREAMBLE

   Let us remember that a public health official recommendation like
that of a country's RDAs, actually only represents:

      "optimal values for a population often FAR above the simple
     and strict average of the basic biological needs"
          (Millet et al, AM. J. CLIN. NUTR. 50:718-727, 1989)

   Margins of safety are built in to not only protect healthy
adults but some of those with unique needs or absorption
problems.

   For example, Victor Herbert, who is probably the leading
authority on B12, puts the actual requirements to be round .1
microgram/day (hence, even the recently reduced NRC
recommendation of 3mcg is still some 6-30 times greater than the
actual requirement of healthy adults who suffer from no unusual
absorption problems other than the general inefficiency of not
being able to absorb all dietary nutrients consumed (remember,
over 95% of B12 deficiency cases are a result of absorption
problems).  Hence, the American RDA levels of 3mcg for B12 is
somewhat ethnocentrically based upon the American population,
whose meat-eating diet incurs a greater loss bodily stores of B12
through the excretion of more bile.

The WHO recommended daily allowance of B12 for adults is only
1mcg.  Personally, I think the WHO recommendations are more
useful, especially for vegetarians, since they are less
ethnocentrically biased upon a gluttonously high fat, meat-eating
diet.

In general, the RDAs are NOT requirements for an individual but
are simply recommendations for the daily amounts of nutrients
that *POPULATIONS* should consume over a period of time to
protect almost all members of that population.

While single numbers have been employed (for simplicity to help
inform a nutritionally naive public), sometimes ranges are used,
as in the case of the 1980 RECOMMENDED DIETARY ALLOWANCES (9th
edition) of vitamin K, pantothenic acid and biotin.


B.  THE AMERICAN RDA'S
The American RDA are standards developed by the FDA for use in
the nutrition labelling of the general food supply and for
labelling dietary supplements and special dietary foods.  They
are based mainly on the 1968 RDA as formed but the then
judgements of the COMMITTEE ON DIETARY ALLOWANCES of the then
constituted FOOD AND NUTRITION BOARD.

In the USA, RDAs are set 2 standard deviations above the mean
requirements of subpopulations (as categorized by age, weight,
sex and pregnancy or lactation) so as to encompass the needs of
97.5% of the population.

For simplicity, the Amer. RDA uses only 4 pop. groups (compared
with 26 groups listed in the 1968 RDA and 17 in the 1980 RDA
editions).  Too bad nobody has seen fit to devise tables for
lacto-ovo vegetarians and vegans :-(

Generally the HIGHEST values for the all ages combined are used
in the US RDA.


C.  TOXIC EFFECTS OF VITAMINS

Undesirable effects ranging from trivial to lethal have been
reported in the literature in association with use of
inappropriately high does of vitamins.  For instance, serve
illness has resulted from the excessive use of vitamin A, and
death has occurred from large doses of vitamin D.  Even an
intravenous does of 80 g of good old vitamin C caused the death
of one patient with a glucose-6-phosphate dehydrogenase
deficiency.

Excessive doses of vitamins are conventionally defined as around
10 or more times the RDA, but toxic effects from long-term
ingestion of, say, vitamin A has been well documented with
supplements ranging in only 5 times U.S. RDA.  [see "Council
Report: Vitamin Preparations as Dietary Supplements and as
Therapeutic Agents", JAMA, 1987, 257(14, April 10):1929]


D.  THE EXAMPLE OF HOW A RDA FOR PROTEIN IS OBTAINED.

To help make more concrete the above, I thought it might be
helpful to here give a more concrete example of how a RDA is
actually obtained.  The RDA for protein is fairly precise, unlike
that of the vitamins which due to lack of information on base
allowances, upper limits are often chosen.

The following RDA by the COMMITTEE ON DIETARY ALLOWANCES of the
NATIONAL ACADEMY OF SCIENCES, FOOD AND NUTRITION BOARD, comes
from Frances More Lappe, in her recent edition of "DIET FOR A
SMALL PLANET" 1991:.

     step 1.  Estimating average need.
     Since nitrogen is a characteristic and relatively constant
     component of protein. . . experimenters put subjects on a
     protein-free diet. . . measure how much nitrogen is lost in
     urine and feces.  They add to this an amount to cover the
     small losses through the skin, sweat, and internal body
     structure.  For children additional nitrogen for growth is
     added.  The total of these nitrogen losses is the amount you
     have to replace by eating protein. . .

     step 2.  Adjusting for individual differences
     To allow for individual differences and to cover 97.5% of
     the population, the committee sets this protein requirement
     30% above the average, arriving at 30 grams per day of
     protein for a 154-lb man, or .45 gram per kilogram of body
     weight per day.  This assumption that 30% above the average
     requirement will cover 97.5% of the population is one of the
     issues in dispute by nutritionists.

     step 3.  Adjusting for normal eating compared to
     experimental conditions.
     Scientists have discovered that protein is used less
     efficiently when people are eating a normal diet containing
     some extra protein than when they are eating at or near
     their protein requirement, as they do under experimental
     conditions.  Apparently, when people are deprived of protein
     their bodies compensate by more fully using what's there and
     excreting less.  So to account for the less efficient use of
     protein in ordinary eating patterns, the committee adds
     another 30%  This brings the allowance up to 42 grams for a
     154-pound "average" American, .57 gram per kilogram of body
     weight per day.

     step 4.  Adjusting for protein usability
     The protein in our food is not fully used by the body.  The
     above estimates are all based on ideal "reference protein".
     Scientists estimate the average usability of protein in the
     U. S. diet at 75%  Therefore, the allowance of 42 grams of
     protein for a 154-lb man is pushed up to 56 grams because it
     is assumed that only 75% of what is eaten is actually used.

Note that by setting the intake 30% above average right at the
beginning, already we have a RDA that is in excess of what most
people really need.  Still, even a vegan diet will easily meet
this RDA of protein and more.


                                     ted