IUBio Biosequences .. Software .. Molbio soft .. Network News .. FTP

Soy Neurotoxicity?

Thomas Carter tcarter2 at elp.rr.com
Sat Aug 9 21:40:57 EST 2003

Hi Ian,
      Your well researched recent additions to this question of soy
consumption add to the slowly growing picture. I look forward to your
future updates. While in vitro and animal studies may suggest caution,
human studies must dominate the question when available. The HAAS
study which you posted has been widely misinterpreted by the popular
press, peer reviewers, and the authors themselves. I'm disappointed at
the lack of competency shown by the authors and their peer reviewers,
but take heart in the many good studies being done at an ever
increasing rate. Here is my critique.
      As of late it seems to have fallen my lot to criticize several
large observational and randomized trials. IMO the discrepancies I've
seen in the papers are due to a marked bias on the part of the
investigators against natural dietary supplements. The HAAS study that
Ian posted doesn't seem to follow the pattern, never the less the
rudimentary nature of the mistakes suggests to me some psychological
pressure rather than plain incompetency, perhaps the desire to be
published or to splash louder with the publication is the cause of the
large number of serious mistakes.
      I first read the paper with a sense of doubt that the long
standing custom of tofu consumption could display enough negative
power to stand out against such a cacophony of variables. Table 1
first caught my eye because of the small size of the low tofu
consumption group and the astounding fact that the authors had ignored
the second dietary survey, basing the table on the results of only the
first. In the absence of an explanation this surely smacks of
"doctoring" data. At the very bottom of the table they give scores of
the intelligence test. (CASI) It turns out that the failures of the
low consumption group are only 2.0%. This is an impossible number
since the denominator of the calculation is 38, the group size. If
unadjusted it must clearly be zero, or some multiple of 2.6%,
corresponding to failures of 1,2, 3 individuals etc. divided by 38.
The paper says these values were adjusted for age, and education, (why
only these factors among the many available?) but such an adjustment
would leave the values at zero or raise them to some value higher than
2.6%, probably, judging from similar adjustments in the study to about
four or five, which would take away almost all of the impact of tofu
consumption. "Mistakes" like this are almost always indicative of data
doctoring IMO.
       The hypothesis of the authors is not that the tofu consumption
in the cohort is associated with lifelong lower intelligence, but with
"accelerated brain aging". Figure two clearly shows them wrong on both
counts. The median age at testing was 80, putting the first two bar
graphs below the medium, and the last three above. A quick glance
shows that the younger members of the hi-hi tofu group failed at about
four times the rate of the low-low tofu group. As the members get
older this failure rate is gradually reduced to near equality.
Comparisons of the other two groups show the same trend but not as
BETWEEN AGE 71 AND 93. Why were the hi tofu eaters so much less
intelligent at age 71-75 than the low group? They went to grade school
in Japan. People always (groups, not individuals) demonstrate a
relative lack of intelligence when dealing with written or oral tests
in a second language. A most pertinent example of this is the wives of
the cohort. Those who went to grade school in Japan failed the CASI
test at a rate of 2.7 times those who didn't (table 4). THIS HUGE
have eliminated the difference in the CASI scores of the husbands at
age 71, and would have destroyed the thesis of the paper. A much
milder factor of 1.04 based on childhood years in Japan was applied to
them. Why was such a different factor used? All I know is there would
not have been a story without it. Why were the hi tofu eaters of about
equal intelligence at near age 90? Perhaps, because they ate tofu. No
other reason is apparent to me. This was the dependent variable after
adjusting for all others in the study. The stratification of the group
into two smaller groups (over 80 and under 80) would have reduced the
P values by about half leaving results only of marginal significance,
but still indicating with a probability of about ten to one that tofu
consumption attenuates brain aging from ages 71 to 93.
    Table 2 gives the heart of the papers results, the OR for the
failure rate in the CASI test of 1.0 (reference), 1.42, 1.74, and 1.62
for the low-low, the low, the hi, and the hi-hi groups respectively.
The difference for these rates is miniscule and totally insignificant
for all groups except the low-low one. The difference for the failure
rate between the low-low group and the low group is significant, but
the difference in tofu consumption is little more than answering once
last week instead of zero times last week in the second dietary survey
ALONE. That one serving per week of tofu can increase your failure
rate in a test by 42% is just not believable especially in the face of
such a small dose response and the many errors made by the authors.
Speaking of which they have more of the wives going to school in Japan
than were born there. (table 3), and they put the OR for going to
grade school in Japan at an unbelievably low 1.04, they may have meant
to add per year. These mistakes led to the apparent failure to adjust
properly for the all important lack of schooling in English. The data
are especially unconvincing since we are asked to believe that tofu
consumption until age 71 accelerates brain aging and then begins to
attenuate it after that age.
      Apart from the fatal mathematical and procedural mistakes listed
above. The authors made two fundamental mistakes in logic. First they
did not use the average CASI score, but rather the percentage of
failures. This would have been the appropriate dependent variable only
if their hypothesis were "tofu accelerates brain aging of those who
are of low mentality, but not those of normal or hi mentality." And
second their assumption that they had listed all the reasons for a
lower apparent intelligence of the hi tofu groups at age 71 was based
only on the logic that since that's all we can think of, there are no
more. I can easily think of several quite probable ones.
      Contrary to the CASI data the relationship with brain size was
most pronounced in the hi-hi group, being totally insignificant
between the other three groups. I would guess that this was caused by
lower growth due to the fact that soy protein is lacking in
methionine, a deficiency of which is known to slow growth rates, but
only at hi levels of deficiency.  The high-high group, which show
lowered growth would have been deficient to at least some extent in
this amino acid, the restriction of which is also shown to extend
       Buried in the small print is the important datum that tofu was
related to a lifespan extension of the autopsied members of about a
year and a half.
       In summary the data of the experiment, in contradiction to the
author's claims indicate that tofu consumption in men extends life
span and protects the aging brain from dementia, and further that the
vaunted peer reviewing of world class medical journals has room for


More information about the Neur-sci mailing list

Send comments to us at biosci-help [At] net.bio.net