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Discussion in 'The Lighter Side' started by -, Aug 7, 2003.

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    FINDINGS MAY SUPPORT SOY-DEMENTIA CORRELATION IN MALES

    (c) 08/06/03 - Ian Williams Goddard

    In April 2000, Lon White and others reported a dose-dependent positive
    correlation between tofu consumption and brain atrophy in a large
    sample of men over several decades. [1] While correlation does not
    prove causation, study size and duration along with the robust
    dose-dependent relationship caused me, even as a vegetarian, to avoid
    tofu and other soy products.

    Correlation-based hypotheses should be tested against the availability
    of possible causal mechanisms. In addition to possible causal
    mechanisms previously cited by this author, [2] recent findings
    significantly increase the case for a causal mechanism of soy-induced
    brain atrophy.

    Pro-Atrophy Pharmacology Indicated

    Brain-derived neurotrophic factor (BDNF) facilitates the survival and
    genesis of brain cells. [3-4] The neuroprotective effects of caloric
    restriction are attributed in part to increased BDNF. [5] On the other
    hand, reduced BDNF is known to cause brain-cell atrophy and is
    associated with Alzheimer's disease. [6-7] Now, a study in
    "Neuroscience Letters" reports that soy significantly reduced BDNF in
    the hippocampus and cerebral cortex of male rats. [8] Since reduced
    BDNF can cause neural atrophy, these findings appear to provide
    compelling evidence for a causal mechanism that might explain the
    positive correlation between tofu (soy) consumption and brain atrophy
    demonstrated by White et al. [1]

    Bad For Boys, Good For Girls?

    While soy appears to reduce BDNF in male rats, it has also been shown
    to increase BDNF in female rats. [9] In fact, soy appears to affect
    neurological parameters in a sex-defined fashion wherein females
    benefit and males suffer. [10-13] There is little doubt among
    researchers that this is because soy is high in phytoestrogens, which
    are plant-derived substances that act like the female hormone
    estrogen.

    However, that sex-defined difference fails to explain the findings
    regarding the wives of male subjects in White et al, who reported: "A
    similar association of midlife tofu intake with poor late life
    cognitive test scores was also observed among wives of cohort members,
    using the husband's answers to food frequency questions as proxy for
    the wife's consumption." [1] White et al proposed that long-term
    consumption of weaker soy estrogens may displace the body's own
    stronger estrogen along with its benefits.

    Evidence Against Soy-Dementia Hypothesis?

    A possible signal contrary to a soy-dementia link is the low
    prevalence of dementia [14] and high consumption of soy in Okinawa,
    Japan. [15] However, that negative correlation, like any correlation,
    does not prove causation. For example, perhaps soy does cause dementia
    but other factors in Okinawa offset the effect.

    Also, White et al explored correlations of a range of foods to
    neurological parameters, whereas this Okinawa analysis is a sweeping
    generalization of only tofu to all of Okinawa. In other words, it
    stands to reason that the study by White et al finding a positive
    tofu-dementia correlation has the greater likelihood of providing the
    more accurate picture. Nevertheless, in my view this Okinawa data
    warrants further examination as a possible route to falsifying the
    soy-dementia hypotheses.

    In closing, the findings of soy-induced BDNF reduction in male rat
    brain regions that are central to the onset of dementia, in addition
    to previous findings, [2] appear to provide compelling evidence of a
    possible causal mechanism that might explain the soy-dementia
    correlation reported by White et al. [1] Obviously further research is
    necessary before a clear picture emerges regarding the effects of
    long-term soy consumption on the brain. But in the meantime, my
    inclination is to play it safe and avoid soy.

    _______________________________________________________________________
    [1] White et al: "In this population, higher midlife tofu consumption
    was independently associated with indicators of cognitive impairment
    and brain atrophy in late life."
    http://www.ncbi.nlm.nih.gov/entrez/...ve&db=PubMed&list_uids=10763906&dopt=Abstract

    [2] Goddard (scroll to): "Is There Reason to Believe Tofu May Cause
    Brain Atrophy?" http://iangoddard.net/soy.htm

    [3] Exp Neurol (Sep 2002): "Neurotrophic factors have long been known
    to promote neuronal survival and differentiation."
    http://www.neuro.mpg.de/research/csn/bdnf_ltp

    [4] J Neurochem (Sep 2002): "These findings suggest that BDNF plays an
    important role in the regulation of the basal level of neurogenesis in
    dentate gyrus of adult mice [...]."
    http://www.ncbi.nlm.nih.gov/entrez/...ve&db=PubMed&list_uids=12354284&dopt=Abstract

    [5] Endocrinology (Jun 2003): "Recent studies have shown that DR
    [dietary restriction] stimulates the production of brain-derived
    neurotrophic factor (BDNF) in brain cells, which may mediate
    neuroprotective and neurogenic actions of DR."
    http://www.ncbi.nlm.nih.gov/entrez/...ve&db=PubMed&list_uids=12746306&dopt=Abstract

    [6] Arch Gen Psychiatry (Jul 1997): "stress can decrease the
    expression of brain-derived neurotrophic factor and lead to atrophy of
    these same populations of stress-vulnerable hippocampal neurons."
    http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9236543&dopt=Abstract

    [7] Brain Res Mol Brain Res (Oct 3, 1997): "a reduction in BDNF mRNA
    expression has been observed in human post-mortem Alzheimer's disease
    hippocampi. [...] These results support and extend previous findings
    that BDNF mRNA is reduced in the human Alzheimer's disease hippocampus
    and temporal cortex, and suggest that loss of BDNF may contribute to
    the progressive atrophy of neurons in Alzheimer's disease."
    http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9387865&dopt=Abstract

    [8] Neurosci Lett (Feb 27, 2003): "significant reductions were found
    in brain-derived neurotrophic factor (BDNF) mRNA expression in the CA3
    and CA4 region of the hippocampus and in the cerebral cortex in the
    [male] rats fed the diet containing phytoestrogens, compared with
    those on the soya-free diet."
    http://www.ncbi.nlm.nih.gov/entrez/...ve&db=PubMed&list_uids=12566171&dopt=Abstract

    [9] Neurosci Lett (Feb 1999): "soy phytoestrogens significantly
    increased the mRNA levels of BDNF [...in] female rats."
    http://www.ncbi.nlm.nih.gov/entrez/...ve&db=PubMed&list_uids=10081916&dopt=Abstract

    [10] Neurotoxicol Teratol (Jan-Feb 2002): "when learning and memory
    parameters were examined in a radial arm maze testing visual-spatial
    memory (VSM), the diet treatments significantly changed the typical
    sexually dimorphic pattern of VSM. Specifically, adult Phyto-rich fed
    females outperformed Phyto-free fed females, while in males on the
    same diets, the opposite pattern of maze performance was observed."
    http://www.ncbi.nlm.nih.gov/entrez/...ve&db=PubMed&list_uids=11836067&dopt=Abstract

    [11] BMC Neurosci (2001 2(1):20): "Female rats receiving lifelong
    exposure to a high-phytoestrogen containing diet (Phyto-600) acquired
    the maze faster than females fed a phytoestrogen-free diet
    (Phyto-free); in males the opposite diet effect was identified. [...]
    These findings suggest that dietary soy derived phytoestrogens can
    influence learning and memory and alter the expression of proteins
    involved in neural protection and inflammation in rats."
    http://www.ncbi.nlm.nih.gov/entrez/...ve&db=PubMed&list_uids=11801187&dopt=Abstract

    [12] BMC Neurosis (2001 2(1):21): "When a diet change was initiated in
    adulthood, control phytoestrogen-rich fed females outperformed control
    females switched to a phytoestrogen-free diet. Whereas, in control
    males the opposite diet effect was identified. "
    http://www.ncbi.nlm.nih.gov/entrez/...ve&db=PubMed&list_uids=11801188&dopt=Abstract

    [13] Neurosci Lett (May 15, 2003): "This study is the first to show
    that lifelong consumption of dietary phytoestrogens alters the HPA
    stress response in male rats."
    http://www.ncbi.nlm.nih.gov/entrez/...ve&db=PubMed&list_uids=12727319&dopt=Abstract

    [14] Dementia: http://okinawaprogram.com/images/dem.gif

    [15] Soy intake: http://okinawaprogram.com/images/ment.gif

    Some alternative views on soy:
    http://www.soyonlineservice.co.nz
    http://www.healingcrow.com/soy/soy.html