Day 036 - 13 Oct 94 - Page 21


     
     1   Q.   "Two limitations in the ability to detect associations of
     2        dietary fat and breast cancer in analytic epidemiologic
     3        studies have been the narrow range of fat intake in the
     4        study population and the substantial measurement error
     5        associated with dietary assessment methods.  Several
     6        authors note that the range of fat intake in most analytic
     7        studies, in which the magnitude of the dietary fat-breast
     8        cancer association has tended to be small, is
     9        substantially narrower than in ecologic studies, where a
    10        strong association has been observed.  The effect of a
    11        narrower range of fat intake would be to decrease the
    12        relative risk between extreme categories of fat intake in
    13        the study population.  If it is assumed that the relative
    14        risks observed in ecologic studies represent 'truth', then
    15        the underlying relative risk between high and low
    16        quintiles of fat intake in a cohort study such as the
    17        Nurses Health Study" -- that I will tell you is (you will
    18        know it is by Willett, but it is important which one it
    19        is) the one that was reported in 1987 in the New England
    20        Journal of Medicine -- "in which fat intake according to
    21        four 7-day food records ranged from about 32% to 44% of
    22        energy, is about 1.4.  In our study, mean fat intake in
    23        the extreme quartiles according to the food-frequency
    24        questionnaire was 26.8% and 41.2% of energy, indicative of
    25        a fat intake range that is essentially comparable to that
    26        in the Nurses Health Study.  This suggests that the Iowa
    27        study population was also not ideally suited for
    28        investigating the dietary fat-breast cancer
    29        association."
    30        A.  Yes.  Perhaps what Dr. Kushi is referring to is the
    31        fact that Iowa is a state underneath Minnesota, just south
    32        of Minnesota, where Dr. Kushi's office is, where pork
    33        production and cattle production is a principal industry
    34        where a high-fat diet is particularly common, and there
    35        are obviously other problems with the study that Dr. Kushi
    36        is citing as well.
    37
    38   Q.   He is telling us anyway, is he not, that his mean extremes
    39        were 26.8 and 41.2 per cent?
    40        A.  Yes, that is what it says there.
    41
    42   Q.   The lowest extreme, the mean lowest extreme was 26.8 per
    43        cent; he did not go any lower than that?
    44        A.  This was very similar to Willett's study, as he says.
    45
    46   Q.   He gives the figure for Willett's study as 32 per cent to
    47        44 per cent, does he not?
    48        A.  Although in Willett's follow-up study he ended up at
    49        27, I believe was the lowest, but, yes, you are quite
    50        right. 
    51 
    52   Q.   In fairness to Willett -- we are going to look at him in 
    53        1992 in just a moment after the short break -- "Willett
    54        et al. (38)" -- we had better just see which one that is;
    55        that is 1990 -- "pointed out that this argument may not be
    56        valid because the same dietary assessment methods were
    57        adequate to detect positive associations of fat intake
    58        with colon cancer in the Nurses Health Study."   Is that a
    59        fair point made by Dr. Willett and his colleagues, do you
    60        think, Dr. Barnard?

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