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Investigation of the Phytoestrogen Intake of a Group of Postmenopausal Women Previously Treated for Breast Cancer

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Plant foods are nutritionally important, contributing many essential nutrients to the diet. Some are familiar, such as vitamins and minerals, others like phytoestrogens are less so and their role in promoting health is beginning to be broadly understood through experimental and clinical research. Phytoestrogens are naturally occurring, bioactive substances, found in plants and they have a chemical structure similar to that of the hormone, 17â-oestrodiol. Little is known about actual consumption by specific subgroups in the UK population, however some ingest relatively large amounts due to food preference or ethnic origin.

Women who have been treated for breast cancer may, as a result of their diagnosis, increase their phytoestrogen intake because of a desire to avoid conventional hormone replacement therapy or because of a belief that phytoestrogens may help avoid a recurrence of the disease [1]. At this stage, there is no recommended intake for phytoestrogens and there are some concerns about the safety of high intakes. This study was designed to:

  1. Determine the dietary intakes of specific phytoestrogens in a group of women previously diagnosed (and treated) for postmenopausal breast cancer
  2. Assess which food groups (including beverages) and supplements provide the greatest source of phytoestrogens in this population
  3. Measure phytoestrogen urinary metabolites in a representative subset of women from the WINS population
  4. Identify the numbers of women prescribed anti-oestrogenic drugs (such as Tamoxifen) within each quartile of phytoestrogen intake
  5. Identify the oestrogen receptor status of women within each quartile of phytoestrogen intake
  6. Investigate the effect of breast cancer diagnosis on women’s decisions to consume or avoid phytoestrogens
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Outcome – key results obtained:
In order to analyse the diaries for specific phytoestrogens (daidzein, genistein, glycitein, formononetin, biochanin A, coumestrol, matairesinol and secoisolariciresinol), a new computer database for dietary analysis was created by using peer-reviewed published data from other researchers, checked against 20 quality criteria, and by analysing 34 additional foods and beverages for which there were no published results.

Comparison of the results obtained from the 7-day and the corresponding 4-day diaries showed the 4-day diary method to be appropriate for assessing the women’s intakes of the phytoestrogens (Spearman’s rho [for total phytoestrogen intake as ug/1000kcal] = .749, p<0.01). The urinanalysis results also contributed validation data to confirm the appropriateness of the 4-day food and drink diary as a measurement tool for phytoestrogen intake (Spearman’s rho was calculated to compare quantified intakes with urinary excretion and, for all but the lignans, significant correlations were observed, p <0.01).

Women ate a variety of foods which contributed to their phytoestrogen intake and, for each 1000 kilocalories eaten, total phytoestrogen intake ranged between 126 and 77,706 micrograms daily. Some variation (as yet unquantified) may be explained by missing figures in the computer analysis database and this initial work, which aimed to create such a database, may underestimate true intake. It is also possible, however, that some variation in total intake is explained by differences in food preferences and individual dietary intake patterns.

No differences were seen in the frequency of reported anti-oestrogenic drug prescription when the women’s results were divided into quartiles of consumption. However, the average phytoestrogen intake of women taking such drugs tended to be higher than for those not prescribed these drugs (an observed trend in the data). No differences were seen between quartiles of intake when the oestrogen receptor status of the breast cancer was explored.

The use of dietary supplements was self-reported by subjects at the time of their food and drink diary completion. While 99 subjects (31% of the study population) reported taking at least one dietary supplement, only 3 (less than 1%) reported taking a supplement which contained phytoestrogens. (These 3 women listed black cohosh, red clover blossoms and soy isoflavones respectively).

The food choices of the women with the highest intake of phytoestrogens (n=79) were used to draft a food frequency guide as a tool for use by health care professionals wishing to quantify phytoestrogen intake in women who have been treated for breast cancer. Although the role of phytoestrogens in the management of breast cancer is still to be fully understood, the guide will give an indication of intake, recognizing that the available analysis information on phytoestrogens in foods and beverages is incomplete.

Telephone interviews explored how a small subgroup of women who have been diagnosed with breast cancer (n=39) make decisions about their diet and what those decisions are. It also explored levels of information and awareness about phytoestrogens and specifically whether attempts have been made to include or exclude phytoestrogen-rich foods or beverages in the diet and the reasons why.

For most women, having breast cancer had not changed their diet. There were a few exceptions to this – women who had undergone a “lifestyle revolution” since their diagnosis. However, in general it seemed that other issues were more important. Health concerns unrelated to cancer, the needs of other family members, cooking on a budget and physical appearance all seemed more important that the impact of the cancer diagnosis.

In part, this was because the women had received little or no information or advice at the point of diagnosis on any possible connection between diet or nutrition and cancer. This lack of information meant that they relied on their own existing knowledge about healthy food and common-sense. Emotionally, they experienced food-induced guilt in the same way that is often reported for healthy women: for example, chocolate and biscuits were often described as naughty. Such similarities with the general female population are interesting to note.

What it means and why it’s important?
The creation of a more complete dietary analysis database for determining the intake of phytoestrogens (given its limitations) is important as it has prompted the primary analysis on additional food items for which the phytoestrogen content had not been determined. It also provides a yardstick against which further work can be planned, moving the Agency closer to identifying usual intake levels for this and other groups within the population and towards possible recommended intake levels in the future. Progressing this work and ensuring it links appropriately with other database creation work (for example, the EuroFIR* project) should be a future priority.

There was considerable variation in phytoestrogen intakes between the 316 women’s diaries analysed, reflecting individual food preferences, the limitations of the dietary analysis database and, quite possibly, variations in the women’s existing knowledge combined with a lack of routine access to dietary information both generally and specifically. The variations observed in phytoestrogen excretion also reflect individual food intake variations in the absence of a comprehensive dietary analysis database.

Currently there seems to be a lack of advice and education for women with breast cancer from health care professionals and associated with this limited information is awareness about the role of nutrition in breast cancer. There are no definitive answers on issues such as soya and dairy and this means that more immediate health concerns are addressed in preference to breast cancer.

Those women who had made changes to their diet and lifestyle had paid privately for nutritional advice. The only advice offered to women interviewed addressed issues faced while in active treatment, for example how to cope with nausea or lack of appetite while on chemotherapy. A gap has been identified in the routine availability of evidence-based dietary information for breast cancer patients. Importantly, however, it is not possible to generalise from these interviews to women with breast cancer from a different age group, background or location. Any further research in this area might fruitfully look at a different group of breast cancer survivors.

This project assessed the intake of and systemic exposure to dietary phytoestrogens in a potentially hyper-exposed sub-population of the UK population. No data previously existed on intake and/or exposure in this group and these data will help evaluate the health implications related to such phytoestrogen consumption patterns.

Find more about this project and other FSA food safety-related projects at the Food Standards Agency Research webpage.

Funding Source
Food Standards Agency
Project number