The team from the University of Malmo in Sweden measured prospectively the associations between intakes of plant foods, fibre and relative fat, in comparison to risk of breast cancer in more than 11,700 postmenopausal women.
Those in the highest quintile of fibre intake had a 40 per cent lower risk of breast cancer, they report in the British Journal of Cancer 90, 122-127. But combining high fibre with a low fat diet had the lowest risk they add, noting an interaction between fibre- and fat-tertiles.
The data were obtained by an interview-based diet history method, a structured questionnaire, anthropometrical measurements and national and regional cancer registries.
There was no significant association between breast cancer risk and intakes of any of the plant food subgroups.
"These findings support the hypothesis that a dietary pattern characterised by high fibre and low fat intakes is associated with a lower risk of postmenopausal breast cancer," write the researchers.
Last year a study found that girls with a lower fat intake during puberty may lower the risk of breast cancer later on. This group also tended to have a higher fibre intake.