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
