Over the past decade, more and more people have become aware of and use supplements and alternative medicine (CAM). Population surveys have shown that this is largely due to the desire to prescribe their own nutritional status and the belief that what is natural is always safe. The most common dietary supplements used by patients with prostate cancer are those who have been diagnosed and treated, and progressive patients are more likely to use CAM than stable patients.
Legumes
The function of legumes and the preventive effect of the phytoestrogens they contain on prostate cancer has been a hot topic of research in recent years. Most studies have focused on two classes of isoflavones, specifically 5,7,45-trihydroxyisoflavones and isoflavone glycosides.
Epidemiological studies
Epidemiological studies have found a low incidence of prostate cancer in populations whose diets are rich in soy products. The incidence of prostate cancer has been reported to be lower in Chinese and Japanese men than in American-born men, and the incidence of prostate cancer among Asian immigrants in the United States is consistent with that of Americans. Dietary intake of soy products may be responsible for these differences, as surveys have found that the average Asian diet contains 10 times more soy products than the standard American diet, and that Asian isoflavone intake is 50 mg/d compared to only 2-3 mg/d for Americans. in a survey of the dietary habits of 12,395 explorers in the United States, it was found that men who consumed soy milk more than once a day had a lower prostate cancer incidence was 70% lower than that of non-drinkers.
Laboratory studies
5,7,45-trihydroxyisoflavones and isoflavone glycosides and their metabolites have weak estrogenic effects, inhibit the growth of benign and malignant prostate epithelial cells, down-regulate the expression of androgen receptor genes, and have been found to inhibit tumor growth in animal models. In addition, 5,7,45-trihydroxyisoflavone also inhibited the growth of androgen-dependent and androgen-independent prostate cancer cells in vitro. At present, large-scale clinical studies on the application of beans and soy products for the prevention and treatment of prostate cancer have not been reported. Therefore, some current conclusions can only be drawn based on epidemiological studies and ex vivo experiments in animal models.
Although increased intake of legumes may reduce the risk of prostate cancer, the reality is more complex as indicated by a recent study in which equol, a metabolite of isoflavone glycosides, was found to have an inhibitory effect on prostate cancer. However, not all people who ingest isoflavone glycosides produce equol in their bodies. long-term habitual diet causes some flora to form in the gastrointestinal tract. Although this study focused on only one metabolite, there is still the difficulty of applying the findings from one population to another because individual gut flora and diet can influence the production of biologically active metabolites.
Consumption of soy products is generally not dangerous, although animal studies have confirmed that feeding rats a diet rich in soy protein isolate accelerates the growth of androgen-independent tumors in vivo.
Clinical studies
The clinical information available to date has been limited and controversial, with most studies being either too few participants or too short in duration. Some studies have shown no effect of beans on PSA levels or PSA rates in healthy men and prostate cancer patients, while others have reached opposite conclusions in prostate cancer patients. Large-scale human studies in this area are necessary to assess the clinical effects of legumes, but are currently lacking.
Pomegranate juice
Pomegranate juice is a strong oxidant that has attracted increasing attention in recent years. Pomegranate juice contains high levels of polyphenol flavonoids, which are the active components of pomegranate juice that exert antioxidant and antiatherosclerotic effects.
Epidemiological studies
Epidemiological studies have shown that the intake of fruits and vegetables rich in phenolic compounds is associated with lower cancer mortality. Pomegranate juice has been marketed as an antioxidant-rich product, and laboratories have been working on its potential to prevent prostate cancer. Because of the industrial processing that extracts certain tannins from the peel, commercial pomegranate juice is rich in flavanols. Therefore, consumption of pomegranate juice, especially processed pomegranate juice that includes the peel, is beneficial.
Clinical studies
In a recently completed 2-year single-center clinical trial, 48 patients with elevated PSA levels after surgery or radiation therapy were selected to take 8 ounces of pomegranate juice daily, and it was found that the mean 1-fold increase in PSA in patients after supplementation with pomegranate juice was significantly longer, from a mean of 14 months to 26 months. It is suggested that a multicenter randomized clinical controlled trial is needed to further confirm this finding.
Green tea
Tea is the second most widely consumed beverage in the world after water. Green tea, oolong tea and black tea are all made from the leaves of the same plant, because the fermentation process is different resulting in their chemical composition and flavor varying greatly. Green tea contains a number of polyphenolic compounds, including several polyphenols and gallocatechin pentaerythate (EGCG), and is safe to drink. A study of 49 patients with solid tumors found that 3.5-4 cups of green tea per serving, three times daily, was easily tolerated and safe to consume for at least 6 months.
Epidemiological studies
Epidemiological studies have found a lower incidence of prostate cancer in men who consume green tea regularly. Another study found that Asian men who consumed high doses of green tea had a lower incidence of prostate cancer than Western men.
Laboratory Studies
Laboratory studies have focused on the effects of the polyphenols contained in green tea, but their mechanism of action is still uncertain. Known antitumor effects include: inhibition of protein hydrolases thereby preventing metastasis, alteration of cellular information, and inhibition of angiogenesis. These antitumor effects require prolonged exposure to green tea [10].EGCG induces apoptosis and inhibits cell growth in both animal experiments and in vitro studies. The administration of polyphenols isolated from green tea (green tea polyphenols or GTP) to TRAMP mice at a dose equivalent to six cups of green tea per day in humans significantly inhibited the development of prostate cancer and improved survival, and GTP also inhibited distant metastasis of tumors.
Clinical studies
Several clinical studies have shown no effect of green tea on androgen-independent prostate cancer, possibly because the patients in those studies had advanced cancer, making the green tea intervention ineffective.
Fish oil (omega-3 fatty acids)
Omega-3 fatty acids are found in fish oils from deep-water fish such as mackerel, salmon, sardines, anchovies and tuna. In addition, some vegetable oils also contain some content, such as flaxseed and soybean, etc. EPA and DHA are mainly found in fatty fish, which usually refers to fatty acids from marine fish. They can be synthesized in the human body from their precursor α-linoleic acid, however, the conversion from α-linoleic acid to EPA or DHA is inefficient, and direct intake from the diet is a more efficient way to elevate serum fatty acids. Levels of omega-3 fatty acids in blood or adipose tissue are associated with intake of fatty fish and not with intake of alpha-linoleic acid. the FDA-recommended intake of fish oil should be limited to 3 g per day, as high intake can increase the risk of bleeding.
Epidemiological studies
The role of deep-sea fish oil in reducing the risk of prostate cancer is not known. One study analyzing the diets of 47,882 men found that those who consumed fish >3 times/week had a 7% lower incidence of prostate cancer, 17% lower advanced prostate cancer, and 44% lower metastatic cancer compared to those who consumed fish <2 times/week, with no significant difference. A similar study also found that fish oil supplementation was not associated with the risk of prostate cancer. In an article published in The Lancet, Teny et al. analyzed the relationship between fish intake and prostate cancer risk in 6272 Swiss men over 30 years and found that the incidence of prostate cancer was 3-4 times higher in those who did not eat fish than in those who consumed medium or high doses of fatty fish. Another study concluded that the low incidence of prostate cancer was mainly associated with high selenium and high omega-3 fatty acid levels in the body.
Laboratory studies
In vitro studies have confirmed that ω-3 fatty acids inhibit cell growth and PSA protein expression. In animal studies, human prostate cancer cells were transplanted into mice and dietary fish oil was found to have an inhibitory effect on the transplanted tumors. It was also found that both EPA and DHA inhibited the biological activity of prostaglandins and androgens, which have a promotive effect on the growth of prostate cancer cells.
Clinical Studies
A large number of clinical studies have been conducted on the preventive and therapeutic effects of fish oil on cardiovascular diseases, but clinical studies on the relationship between fish oil and prostate cancer are lacking.
Conclusion
There are many, often conflicting, recommendations on nutritional supplementation for patients with prostate cancer and those at risk for the disease. Different epidemiological studies and experimental studies have come to different conclusions, and further studies need to be conducted with more rigorous clinical trials to verify the efficacy of these dietary supplements.