Day 269 - 25 Jun 96 - Page 54


     
     1        availability of fat in a diet and variations in breast
     2        cancer mortality rate.  A voluminous amount of information
     3        is also available in literature linking increased fat
     4        consumption particularly polyunsaturated fat and
     5        stimulation of the mammary tumour genesis in animal
     6        models.  In the past few years our reporters have been
     7        studying the impact of several confounding factors that
     8        could modulate the enhancing effect of fat on neoplastic
     9        development of the mammary gland in female rats treated
    10        with a carcinogenic.  It is our conclusion that fat
    11        promotes mammary carcinogenesis only under a very strict
    12        set of conditions which might not be duplicated in the area
    13        of fat intake and human breast cancer risk.  Previous
    14        studies on fat and mammary cancer in experimental models
    15        have used young virgin rats which are given doses of
    16        carcinogens at a particular age.  The question arises as to
    17        whether the promoting effect of fat might be a consequence
    18        of the characteristics of the model.  We have supportive
    19        evidence showing that the following criteria must be
    20        satisfied in order that fat enhancement of mammary
    21        carcinogenesis to be manifested,
    22        (a) carcinogen administered at a time when the mammary
    23        gland is exquisitely susceptible to tumour induction.
    24        (b) animals maintained on a semi-purified diet.
    25        (c) ad libitum feeding necessary.
    26        (d) unusually high requirement of linolenic acid for tumour
    27        development.
    28        On the other hand, the stimulator effect of fat is
    29        attenuated or sometimes even negated by (a) feeding of a
    30        natural ingredient diet; (b) sub maximum calorie intake;
    31        and (c) previous history of pregnancy and lactation.  Given
    32        the spectrum of confounders that are inherent in
    33        epidemiological studies linking fat intake in breast
    34        cancer, including differences in lifestyle, reproductive
    35        history, eating habit, as well as complexity of the total
    36        diet, our findings suggest that there may be need to
    37        re-evaluate the validity of extrapolating animal data that
    38        are obtained under a highly defined set of conditions to
    39        the etiological significance of dietary fat in human breast
    40        cancer."
    41
    42        Now, as a caveat against over-reliance on the results of
    43        animal studies, at any rate in relation to breast cancer,
    44        this is pretty powerful, is it not?
    45        A.   Yes, this paper was discussed actually in Rome at the
    46        conjoint expert consultation with FAO and WHO, and it has
    47        been discussed and indeed it has presented further evidence
    48        to several conferences that I have attended, and I think
    49        the point that needs to be made here is that their
    50        understanding in that research group of the role that
    51        essential fatty acids played in biology was somewhat
    52        inadequate.
    53
    54        They, Carol was really the person who first started
    55        studying the effect of dietary fat on mammary cancer and he
    56        showed that there was an effect of linolenic acid which
    57        appeared to promote mammary cancer and Ip has then, I
    58        think, produced data, and I cannot remember exactly when
    59        and where he produced it, but I know he has produced data
    60        which shows that you can titrate the level of linolenic

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