If you turn your nose up at the thought of tofu, you might want to reconsider and add this food to your
diet - especially if you're male. According to a study published in the April issue of the Journal of Clinical
Nutrition, men who eat plenty of soy foods - versus little or none - are less likely to
be diagnosed with prostate cancer.
Prostate cancer is the most common cancer among Canadian men. It's also considered a diet-related cancer, meaning the foods you eat - or don't eat - can influence your risk.
It's long been thought that soy might protect from prostate cancer. In Asia, where soy consumption is high, rates of prostate cancer are lower than in North America. However, the incidence of the cancer is much higher among Asians living in Western countries, an observation that has sparked much research into the link between diet, especially soy, and prostate-cancer risk.
In the current study, researchers from the U.S. Department of Agriculture pooled the results of 24 studies on soy and prostate cancer conducted with Asian, European and North American men. Over all, men who reported the highest intake of soy foods were 26 per cent less likely to develop prostate cancer compared with those with the lowest intakes.
When specific types of soy foods were analyzed, non-fermented soy foods such as tofu, soybeans and soy bever- ages were linked with a 30-per-cent lower risk. Traditional fermented soy foods, including miso, tempeh and natto, had no effect - consuming these foods did not decrease or increase prostate-cancer risk. It's thought that the non-protective effect of fermented soy has to do with its high salt content.
Soybeans contain natural compounds called isoflavones, substances thought to have cancer-fighting properties. Clinical trials suggest that isoflavones can increase certain sex hormones, which results in a slower production of prostate-cancer cells.
How much soy you need to eat to help reduce prostate-cancer risk remains unclear. Protective effects were observed in men who ate soy foods at least twice a week and also for those who consumed it almost daily.
The vast majority of men I see in my private nutrition practice rarely or never eat soy. To increase your intake, start by adding non-fermented soy products to your diet twice per week. Replace meat with firm tofu in stir-fries, use an unflavoured soy beverage on cereal and in smoothies, add soybeans to soups and chili, and snack on edamame (young green soybeans).
Of course, there are other dietary modifications that may offset your risk. Studies suggest that the following nutrition strategies may lower the risk of prostate cancer.
Reduce saturated fat
Higher intakes of fatty foods, especially meat and dairy products, have been linked with a greater risk of prostate cancer and with more advanced forms of the disease. Saturated fat may increase production of testosterone, which may promote prostate cancer.
Cooking meat at high temperatures produces heterocyclic amines, compounds shown to promote cancer. Researchers have identified at least 20 different heterocyclic amines formed during cooking meat that may up cancer risk.
Eat fish and poultry
breast more often
In a study of 47,882 men, those who ate fish at least three times a week were much less likely to develop prostate cancer compared with infrequent fish eaters. Omega-3 fats in fish are thought to have an anti-tumour effect on prostate cells.
If you do eat meat, choose lean cuts such as sirloin, inside round and tenderloin. Research shows that marinating meat before grilling can reduce the formation of heterocyclic amines by as much as 99 per cent.
Heat-processed tomato products such as tomato paste, tomato juice and tomato sauce are excellent sources of lycopene, an antioxidant that helps protect cells from damage. Many studies, but not all, have found that eating at least two servings of tomato sauce per week - compared with less than once monthly - reduced the risk of prostate cancer by 23 per cent.
Don't overdo multivitamins
While a daily multivitamin can help meet nutrient needs, more is not better. A 2007 study published in the Journal of the National Cancer Institute found that excessive multivitamin use - more than seven times per week - was linked with a greater risk of advanced prostate cancer and risk of death from the disease.
The link was strongest in men with a family history of prostate cancer and in men who also took zinc, selenium or beta-carotene supplements. Regular multivitamin use (no more than once daily) did not boost prostate-cancer risk.
A study published last year linked long-term zinc supplementation with a doubling in the risk of prostate cancer.
that won't help
Despite earlier hints that selenium and vitamin-E supplements could ward off prostate cancer, a recent study of 35,000 men found that, taken alone or in combination, these nutrients did not prevent it.
Take vitamin D
Although research doesn't support the notion that vitamin D reduces prostate-cancer risk, it is a supplement worth taking. To help guard against other cancers, the Canadian Cancer Society recommends taking 1,000 IU of vitamin D in the fall and winter, and all year round if you're over 50, have dark skin, don't go outdoors often, or wear clothing that covers most of your skin.
Evidence also suggests that vitamin D helps prevent osteoporosis, heart attack, stroke and heart failure.
The link between obesity and the risk of prostate cancer is unclear, but carrying excess weight can have a negative effect on disease outcome. That's because a common test used to screen for the disease can produce falsely reassuring results in men who are obese. The prostate-specific antigen test results can be lower in obese men despite the presence of disease, potentially leading to a delay in diagnosis and treatment. (PSA, a protein produced by the prostate gland, is often, but not always, linked with prostate cancer. In general, the higher the PSA level, the more likely that cancer is present.)
Leslie Beck, a Toronto-based dietitian at the Medcan Clinic, is on CTV's Canada AM every Wednesday. Her website is lesliebeck.com.