I have a prostate problem with a high prostate specific antigen (PSA) reading of 11.5. I just had a biopsy, but fortunately it was negative. I have been a lacto-ova vegetarian for the past 30 years (no eggs, meat or milk), so I rely on soya products to supply my protein requirements. I have lately read on the Internet articles condemning the use of soy and also stating that soy can exacerbate prostate cancer. I am now in a quandary as to whether to continue to eat soya or to desist. I.Y., Tel Aviv Prof. Amnon Brzezinski, director of the Women's Health Center at Hadassah University Medical Center in Jerusalem's Ein Kerem and a leading expert in the use of phytoestrogens, comments: There has been speculation that phytoestrogens such as soya, being estrogenic compounds, may exert inhibitory effects on the prostate and protect from prostate cancer. Experimental studies in rodents show that diets supplemented with soya or isoflavones may inhibit the development of tumors of the prostate, perhaps by down-regulation of androgen receptors. However, human studies are contradictory and too few to draw any conclusions regarding this point. Four studies have evaluated the effects of phytoestrogens on PSA. Three did not observe any effects while the fourth observed a 50 percent to 70% reduction.Therefore, it seems that eating "normal" amounts of soya products does not have any deleterious effect for increasing the risk of prostate cancer, it might even have a beneficial effect. I am a 24-year-old man about to be married. I spend most of my free time bike riding over long distances. I have heard that this can cause erectile dysfunction. Is there any way I can avoid this problem and still ride my bike as I have been? B.V., Rosh Ha'ayin Judy Siegel-Itzkovich comments: The Harvard Medical School recently issued a report about this subject. The research suggests that riding a bike for long periods can cause temporary erectile difficulties, with the risk highest among men who cycle more than three hours a week. The researchers explained that sitting on a bicycle for a long time puts pressure on the perineum, the area between the genitals and anus. This pressure can harm nerves and temporarily impede blood flow, causing tingling or numbness in the penis and, eventually, erectile dysfunction. However, one study showed that while a conventional bicycle caused a dramatic (though temporary) drop in oxygen supply to the penis, a recumbent bicycle did not. If you don't want to switch to a recumbent bike, these precautions may help you prevent cycling-related erectile problems: Wear padded biking shorts. Raise the handlebars so that you're sitting relatively upright; this shifts pressure from the perineum to the buttocks. Use a wide, well-padded or gel-filled seat instead a narrow seat, which places more pressure on the perineum. Position the seat to reduce pressure; make sure it is not so high that your legs are fully extended at the bottom of your pedal stroke, and don't tilt the seat up. Change your position and take breaks during long rides. If you feel tingling or numbness in the penis, stop riding for a week or two. A reader, Shmuel Shimshoni, comments on the reply of Dr. David Lipschitz about proper aid to combat constipation. Lipschitz suggested a combination of three seeds, including flax seed, that should aid the sufferer. Flax seed, says Shimshoni, has been a part of his daily diet for a couple of years and has helped keep his gastrenterological system working properly. However, he says, unless the flax seed is ground it is of no value. Ground flax seed does not keep well however, and should be kept refrigerated. One important point though - the grinder should not be metallic, or else the ground flax seed spoils quickly. He says he uses a ceramic grinder and freshly grinds a tablespoonful each day. Rx For Readers welcomes queries from readers about medical problems. Experts will answer those we find most interesting. Write Rx For Readers, the Jerusalem Post, POB 81, Jerusalem 91000, fax your question to Judy Siegel-Itzkovich at (02) 538-9527, or e-mail it to firstname.lastname@example.org, giving your initials, age and residence.