Day 035 - 12 Oct 94 - Page 15


     
     1   Q.   Certain -- if I may put it this way so you are sure and
     2        I am sure that I have understood it -- certain substances
     3        observed to have been produced in the cooking of meat,
     4        particularly at high temperatures, have been observed to
     5        have carcinogenic effects on laboratory animals.  That is
     6        right, is it not?
     7        A.  That is correct.
     8
     9   Q.   Those are, broadly speaking, called mutagens?
    10        A.  They are, yes; they are mutagens and carcinogens.
    11
    12   Q.   In a class of substances called mutagens?
    13        A.  They are mutagens, yes.
    14
    15   Q.   In relation to the promotion of tumours in animals in the
    16        laboratory one thesis has been (and again you will correct
    17        me if I am wrong), has it not, that in some way a diet
    18        high in fat is apt to promote the translation of the fecal
    19        or, sorry, the bile acids into secondary bile acids; is
    20        that right?
    21        A.  Yes, that is right.
    22
    23   Q.   And it is demonstrated that secondary bile acids have
    24        carcinogenic effects on animals?
    25        A.  That is correct.
    26
    27   Q.   It is, however, only one theory of the mechanism by which
    28        diet may be related to the promotion of colon cancer, is
    29        it not?
    30        A.  That is one aspect, yes.
    31
    32   Q.   The second question I was going to ask you about this
    33        passage in this publication by the National Cancer
    34        Institute in 1991 is this:  Do you or do you not believe
    35        that it may be that dietary fibre and particularly,
    36        perhaps, now resistance starch has a role to play in the
    37        inhibition of tumour genesis independently of the amount
    38        of fat in the diet?
    39        A.  That is probably true.
    40
    41   Q.   Yes, thank you.  May I read on?  We got to the words, six
    42        or seven lines down:  "... fibre has a protective effect.
    43        Fibre, often referred to as 'roughage' or 'bulk', is the
    44        indigestible part of plants.  Scientists do not yet
    45        understand exactly how dietary fibre reduces the risk of
    46        colorectal cancer, but several possible mechanisms have
    47        been suggested.  We know that increased fibre results in
    48        greater stool bulk and more rapid movement through the
    49        colon.  Thus, a high-fibre diet may reduce both the
    50        concentration of carcinogens in the stool and the amount 
    51        of time during which these substances are in contact with 
    52        the bowel wall.  In addition, increased fibre may change 
    53        the chemical composition of the stool by altering the
    54        nature and behaviour of the bacteria in the colon.
    55
    56        Colon cancer risk also appears to be related to the amount
    57        of fat in the diet.  Considerable evidence links a
    58        high-fat diet to a high incidence of colon cancer.
    59        Scientists theorize that dietary fat increases the amount
    60        of bile acids (needed for digestion) in the colon.  These

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