From: altar@beaufort.sfu.ca (Ted Wayn Altar)
Subject: Re: Milk and calcium (here we go again)
Organization: Simon Fraser University, Burnaby, B.C., Canada
Date: Sun, 24 Jan 1993 04:57:40 GMT

In rec.food.veg you write:

>    I'm not sure why I'm posting, because I've seen this topic discussed
>before, without any good resolution.  There seems to be a lot of
>conflicting opinion.
. . .

Depends on the specific issue and of course, who is better
informed and more reliable.  Now, you should never uncritically
trust anyone's word here on the net, but always check things out
for yourself.  That is why I think it is important that we make
the extra effort to cite our sources and try to provide
*relevant* references.

To help sort things out, it is always good idea to remember that
the best data is usually going to be that which is most direct
with respect to the question at hand.

In general, human data is going to be more immediate and relevant
than animal studies, especially with respect to questions at the
practical level about what whole foods humans should eat.

As a general guide, put more trust in human studies and among
those studies place more confidence in those studies higher up in
the following table than compared to those studies at a lower
level.


                  IN ORDER OF DEPENDABILITY

I. experimental studies     1) volunteers randomly assigned to
                            different dietary regimens for a
                            "long" period of time (> 2 wks).

                            2) volunteers randomly assigned to
                            different dietary regimens for a
                            short period of time (< 2 wks).

II. epidemiological studies 3) prospective cohort studies

                            4) cross-sectional studies attempting
                            to use matched samples

                            5) cross-sectional studies with no
                            matching on potential confounds

III. case studies           6) individual case studies


Human experimental data is best as it most readily permits
inferences of causality, but such data is difficult to obtain due
to the practical constraints of feeding people specific diets for
long periods of time.  Yet, there do exist many such studies,
but only a very few that were carried out for a month, let alone
for years.
.
For long terms results, we thus rely on what has loosely been 
referred to as a "natural experiment" (not a "true"
experiment) of humans choosing on their own a specific dietary
practice, like that of vegetarianism.  We are now at the level
of epidemiological evidence, which is founded upon such "natural
experiments".  Epidemiological studies provide good indications
and early warnings of potential problems due to diet, life-style
and environmental circumstances.  They can be used to even infer 
causal relationships but not as readily as we can with a true
experiment.

A prospective cohort study is one where, say, a group of
vegetarians and omnivores are followed for a certain number of
years in order to observe which group later incurs the greater
incidence of a specific problem.  Such studies are much superior
to simple cross-sectional studies since they control for interactions
of a disease with eating patterns, and, will permit inferences of
causality.  They also tend in practice to better match the two groups (
(viz., "cohorts") so as to control for individual  differences 
between the two groups (e.g., genetic, life-style, and potential 
well-known confounds on diet and health like for example smoking,
etc.)

Cross-sectional studies, when matching on relevant confounds are
undertaken, can also provide good information, but unlike the
prospective cohort studies, disease interactions with dietary
patterns cannot be ruled out.  For instance, with the development
of diabetes a person might start consuming more fat.  Did the fat
cause the diabetes or did the diabetes cause the appetite for
fat?  While maybe this latter event is not likely, it is a 
realistic possibility.  A prospective cohort study, however,
rules out this possibility by starting off at the beginning with
non-diabetic vegetarians and omnivores and then seeing which of
the two groups *later* incurs the greater incidence of
its members actually developing diabetes.  Also, causal relationships 
here can only be "suggested" informally or through causal modelling
as predicated upon some assumptions and lots of correlational data.
Predictive relationships, however, can be readily obtained, but
such relationships are less dependable at a practical level for
the individual who wants to know what they as an individual 
should or shouldn't eat.

Case studies is really at the level of anecdotal evidence.  When
assessed by experts using objective diagnostic criteria, then the
information is going to be better than simply what the
individuals themselves report on their own or according to what
what their great auntie professed.  Still, we don't have enough
information from case studies to warrant general conclusions,
only possible warnings of potential problems, warnings that
should be researched further via experimental studies, or at
least good epidemiological studies.

It is always the case that we must work with limited information.
Science does not give us absolute truth, but only probable
knowledge rationally obtained but always open to possible
correction.  The rational and practical approach is of
course use what is available, even if that means case
studies.  But what confidence we place in the information given
should be commensurate with how rigorous that information was
obtained and generally according to where it ranks in the above
table.

If this seems too overwhelming, than settle for good reviews by
informed sources. Gill Langley's book is an excellent place to
begin (see below).



>    Basically, I stopped drinking milk for awhile, then I went back to it
>this week because I was feeling very poor and it costs 1/3 to 1/4 what
>Rice Dream does.  But then I discovered that I prefer the taste of Rice Dream
>So if I go back to Rice Dream, I'll be eating mostly vegan food.
>But after all those years of agribusiness propaganda :-) I guess I've
>been brainwashed enough that I'm at least a bit worried about, yep,
>calcium.

For a good review about how vegans fare with respect to calcium,
take a look at:

         Gill Langley's (PhD), VEGAN NUTRITION: A SURVEY OF THE
            RESEARCH, 1988.

I think every vegan and vegetarian should have a copy!

You may, however, have to order it from Britain, as it is not
easy to find, but it is the single best review on this topic I've
seen and was highly recommended by Dr. Barrie Margetts, Medical
Research Council Environmental Epidemiology Unit, University of
Southamptom.  Vegans have been more prominent in Britain and
there is a good body of research from British researchers.

Another very good source are the papers presented at the First
International Congress on Vegetarian Nutrition published in:

        AMERICAN JOURNAL OF CLINICAL NUTRITION, 1988, 48:703-927.

This reference is well worth xeroxing.  What we have here, along
with some research reports, are some very comprehensive review
papers by some of the leading researchers in this area, like
Victor Herbert, TAB Sanders, T. Dwyer, D.A. Snowdon, etc.  There
are 3 papers on this topic "Vegetarian dietary practices and bone
density".



>    I've wondered about a few things when I've considered this
whole
>question of whether milk is essential for good health, so in no
particular
>order:

You've asked quite a few questions, many of which are not easily
answered.  To help with some of your questions, I've posted some
notes on this issue, under the thread "calcium:"  that I had
posted earlier.  I hope that will be of some help.


. . .
>a)  Conventional wisdom from the medical establishment or diary 
>industry.  Don't just say that old women don't have enough calcium
>in their bones so young women should eat more cheese.  If you have data
>showing that the old women with brittle bones actually did eat less
>cheese in their youth than the women with strong bones, _that_would
>be worth posting.

See:

    Ellis et al. (1974).  Osteoporosis in British vegetarians
        omniovres. AM. J. CLIN. NUTR., 27:769

    Sanchez et al. ((1980).  Bone mineral mass in elderaly
        vegetarian and omnivorous females.  In R. B.
        Mazess (Ed.), PROCEEDINGS OF THE 4TH INTERNATIONAL
        CONFERENCE ON BONE MINERAL MEASUREMENT, p94-98.

These studies included vegans as part of their subject pool.

                        Cheers
                           ted


Newsgroups: rec.food.veg