Food choice and phytoestrogen consumption in women previously treated for postmenopausal breast cancer

Background

Phytoestrogens are plant-derived, bioactive substances with a chemical structure similar to that of 17β-oestradiol. Women previously treated for breast cancer may increase their phytoestrogen intake to avoid conventional hormone replacement therapy or because of a belief that they may help avoid recurrence [1,2]. There is no recommended daily intake and there are some concerns about phytoestrogen safety in this group, although the evidence is conflicting and more research is needed [3,4].

Methods

Three hundred and sixteen women each completed a 4-day food and drink diary (14 of whom also completed a 7-day weighed intake diary 6 weeks previously). The 55 most recently recruited women collected their urine for 24 hours whilst completing their diaries and were interviewed by telephone regarding their food choices since diagnosis.

Results

A new dietary analysis database was created using peer-reviewed published data and analysing 34 additional foods and beverages for which there were no published results. The urinanalysis results contributed validation data. A summary of the dietary intake data is shown in Table 1. There was a lack of primary analytical data on the phytoestrogen profile of many foods and beverages routinely consumed by this study population. However, food frequency data from the highest quartile show the important contribution of nonsoya foods to high intakes (Table 2). Telephone interviews were completed by 39 subjects. For most women, having breast cancer had not changed their diet. Health concerns unrelated to cancer, the needs of other family members, cooking on a budget and physical appearance all seemed more important than the impact of the cancer diagnosis.

Table 1.

Summary of intake data by receptor status and antioestrogenic drug prescription

Total phytoestrogen intake (μg/1,000 kcal) (n = 316)			n	First quartile	Second quartile	Third quartile	Fourth quartile
		Receptor status
Mean	8,388	ER-negative	42	11 (14%)	11 (14%)	13 (16%)	7 (9%)
Range	126 to 77,703	ER-positive	182	40 (51%)	42 (53%)	48 (61%)	52 (66%)
Quartile ranges		Not available	92	28 (35%)	26 (33%)	18 (23%)	20 (25%)
First quartile	<3,817	Antioestrogenic drugs
Second quartile	3,817 to 6,798	No prescription	109	30 (38%)	30 (38%)	25(32%)	24 (30%)
Third quartile	6,799 to 10,255	Tamoxifen or arimidexa	200	47 (59%)	47 (59%)	52 (65%)	54 (68%)
Fourth quartile	>10,255	Other/missing	7	2 (3%)	2 (3%)	2 (3%)	1 (2%)

^aAstraZeneca, London, UK.

Table 2.

Main food sources of phytoestrogens

From highest quartile	Daidzein	Genistein	Glycitein	Formononetina	Biochanin Aa	Coumestrola	Matairesinola	Secoisolariciresinola
Main food group source	Cereal foods	Cereal foods	Soya products	Fruit, vegetables	Legumes, blackcurrants	Fruit, vegetables	Tea (black leaves), cereal foods	Tea (black leaves), fruit, vegetables

^aLimited data available on content in some foods.

Discussion

Variation in phytoestrogen intakes and metabolite excretion reflect food preferences, dietary analysis database limitations and likely variations in existing knowledge combined with a lack of routine access to dietary information. In the absence of definitive advice, more immediate health and social concerns influence food choice rather than past breast cancer diagnosis.

Conclusion

No data previously existed on intake in this potentially vulnerable group and these data will help evaluate the health implications related to such phytoestrogen consumption patterns.

Acknowledgements

Funded by the Food Standards Agency, UK.