Dissent: Response to wynder et al.'s paper on dietary fat and breast cancer

Comparison of dietary assessment methods in a low-fat dietary intervention program

The food frequency questionnaire (FFQ) is commonly utilized for assessment of dietary fat intake, but its validity among individuals following a low-fat diet is unclear. We evaluated the agreement of nutrient estimates derived from FFQ, 24-h recall, and 3-day food records obtained from 104 participants in a randomized trial of a low-fat dietary intervention for women at elevated breast cancer risk. Comparisons were made for total calories, percent calories from fat, and total fat after 1 yr. Correlation was assessed using standard methods based on a null hypothesis of no agreement between instruments as well as by a methodology based on a null hypothesis that the instruments should be in agreement. With the use of standard methods, FFQ estimates for women on the low-fat diet were significantly correlated to records only for percent calories from fat (r = 0.39), whereas recall and record estimates were significantly correlated for all three dietary variables. Using the new method, we found no significant correlation between FFQ and either recalls or records for women following a low-fat diet but significant correlation between recall and record estimates for total calories (r = 0.67). Traditional correlation testing may overestimate the extent of agreement in dietary instruments among women on a low-fat diet. We found empirical support for the nontraditional method.

Breast cancer risk factors in two distinct ethnic groups: Indian and Pakistani vs. American premenopausal women

Asian Indians from the Indian subcontinent have low rates of breast cancer, but studies on breast cancer risk factors in Indian and Pakistani women living in the United States are lacking. This study contrasted breast cancer risk factors [serum total 17 beta-estradiol (E2), sex hormone-binding globulin-bound E2, available E2, estrone (E1), and dehydroepiandrosterone sulfate, reproductive history, family history of cancer, body composition/size, dietary intake, physical activity, and excretion of isoflavones] between two distinct ethnic groups of premenopausal women residing in the United States. We also determined the contribution of these and other factors to the variability of each sex hormone. Distributions of values for serum total E2, available E2, and sex hormone-binding globulin-bound E2 (%) were greater (p < 0.005) in American (n = 47) than in Indian and Pakistani (n = 47) women. Multiple regression analysis indicated that 26% of the variability (p < or = 0.0001) in serum E2 was accounted for by the ratio of total cholesterol to high-density-lipoprotein cholesterol, length of time in the United States, and saturated fat intake, whereas less (17%) variability was accounted for by available E2 (representing free E2 + albumin-bound E2), contributed by the ratio of total cholesterol to high-density-lipoprotein cholesterol and saturated fat intake. Five variables accounted for 31% of the variability (p < or = 0.0001) in E1. The major finding of this study was that circulating sex hormone concentrations were determined more by environmental factors than by ethnicity, which was not a significant contributor to any of the serum hormones.

ras may mediate mammary cancer promotion by high fat

High fat consumption has been implicated as a risk factor for breast cancer. Experimental mammary carcinogenesis studies have demonstrated that the effect of high fat consumption is mainly exerted on the postinitiation stage of the disease process. We report data that have recalled in the formulation of a new hypothesis about the effect of dietary fat on mammary carcinogenesis, namely, that it promotes the development of a subpopulation of cells lacking a specific pathogenetic characteristic. In comparison with animals fed a low-fat diet, female Sprague-Dawley rats fed high-fat diets during the promotional stage developed significantly more (number and proportion) 1-methyl-1-nitrosourea-induced mammary adenocarcinomas that did not contain a codon 12 GGA-->GAA mutation in the c-Ha-ras protooncogene. The effect was independent of the types of fat fed, i.e., corn oil vs. fish oil. A model is presented to account for the preferential promotional effect of high fat consumption on 1-methyl-1-nitrosourea-initiated mammary epithelial cells. The hypothesis that the level of dietary fat consumed affects the proportion of mammary carcinomas that occur with a particular pathogenetic characteristic, in this case, the presence or absence of a Ha-ras point mutation, has important implications on the direction of future investigations concerning fat and cancer risk.

Diet and breast cancer: trial and error?

The risk of developing breast cancer in females is determined by characteristics of hormone- and pregnancy-related tissue growth and development and mechanistic interactions between carcinogens and molecular targets and clonal selection of cell lines. Animal models have substantiated the idea that breast tissue may have periods of increased sensitivity to carcinogens and that dietary fat, and particularly energy intake, affect cancer risk. In epidemiological research, ecological studies clearly demonstrated positive associations between dietary fat and breast cancer risk, but individual-based case-control studies and cohort studies did not support a causal interpretation. The debate is now whether the ecological fallacy or biases in analytical epidemiology account for the apparent discrepancy, and the character of the debate is mainly of a methodological nature. Ecological and analytical studies, however, are fundamentally different with respect to the time- and age-axes considered. The lack of association in analytical studies addressing late-stage carcinogenesis may be attributed to exposures being relevant earlier in life. Analytical studies that integrate insights relating to periods of increased tissue susceptibility and mechanistic models of carcinogenic action may be fruitful in producing new outlooks for breast cancer prevention.