The Pharmaceutical Journal Vol 267 No 7169 p510-525
13 October 2001

BPC 2001 summary

Superbroccoli and other foods in cancer prevention

There is huge interest from the public, and from medical and pharmaceutical scientists, about ways to prevent cancer through diet and lifestyle, according to Professor Peter Houghton, school of pharmacy, King’s College London. This is an area where those involved with educating pharmacy undergraduates need to consider including this subject in the pharmacy curriculum, he said.

Phytoestrogens

Dr Aedin Cassidy, head of molecular nutrition, Unilever Research, discussed whether dietary phytoestrogens have a role in cancer prevention. Phytoestrogens comprise several groups of non-steroidal oestrogens widely distributed within the plant kingdom including, for example, isoflavones (found in soya beans as well as chick peas and other legumes) and lignans (which are ubiquitous in fibre-rich foods). Other groups included resorcylic acid lactones (found in rye and wheat) and coumestans. There are many phytoestrogen products on the market, but according to Dr Cassidy, phytoestrogen content varies and may be much less than is claimed on the label.

The metabolic fate of phytoestrogens, such as daidzein and genistein, may be important in terms of their clinical efficacy. There is wide interindividual variation in metabolism. Also, antibiotic administration may prevent further metabolism of daidzein and genistein. The pharmacokinetic profile of the compounds also vary depending on the source, eg, soya milk or textured vegetable protein.

There is structural similarity between phytoestrogens, eg, genistein, and oestradiol, therefore phytoestrogens have the potential to bind to the oestrogen receptor (ER). Biological effects documented for phytoestrogens include both ER-mediated and ER-independent effects, such as effects on steroid metabolism, and antioxidant, antiproliferative and antiandrogenic effects.

Summing up, Dr Cassidy said: “We have a high mountain to climb ... consumers believe that just because compounds come from plants and that they are natural, they are healthy.”

In healthy women, phytoestrogens have a weak oestrogenic effect on the hypothalamic-pituitary-gonadal axis. However, the optimum dose for potential health effects is unknown. There is an array of products on the market, but no standardisation of dose, and some data suggest that there is a lack of quality assurance. If these were novel compounds, they would need to be tested in strict controlled clinical trials, but much of the evidence is based on epidemiological studies and there is currently a distinct absence of controlled trials.

Superbroccoli

Following on, Professor Gary Williamson, head of phytochemicals team, Institute of Food Research, Norwich, described his group’s work in developing “superbroccoli”, obtained by crossing Marathon broccoli (available from supermarkets) with a wild broccoli from Sicily. Superbroccoli contains enhanced concentrations of the isothiocyanate compound sulforophane, which has multiple activities against early stages of cancer progression, for example, protecting against the formation of DNA adducts.

The action of isothiocyanates, such as sulforophane may be enhanced by interactions with other food components, such as selenium, although this requires further investigation. Also, there is limited information on the bioavailability of sulforophane and other isothiocyanates in humans. A range of biological effects has been documented, but there has been no concerted efforts with clinical studies.

Dietary flavonoids

Professor Catherine Rice-Evans, Wolfson Centre, King’s College London, discussed the antioxidant properties of dietary flavonoids and the implications for cardio- and neuroprotection.

There is epidemiological evidence to support the effects of flavonoid-rich dietary components (such as red wine, tea, apples or onions) in reducing the risk of coronary heart disease. Also, anthocyanin-rich fruits are associated with protection against the age-related declines in cognitive function.

There are five major families of flavonoids:

1. Flavanols, eg, epicatechin
2. Flavanones, found in citrus fruits
3. Flavones/flavonols, eg, quercetin
4. Anthocyanidins, eg, cyanidin, found in berries
5. Hydroxycinnamates, eg, caffeic acid

Biological effects for flavonoids documented in vitro included antioxidant activity, inhibition of DNA damage, and modulation of cell signalling.

Back to Top