Nutrition

Meta-analysis of soy food and risk of prostate cancer in men

International Journal of Cancer June 8 2005 [E-pub ahead of print]
L Yan, E L Spitznagel

Study purpose: Many claims have been made about the ability of soy foods to protect against cancer. This meta-analysis evaluates studies that link a lowered risk of prostate cancer in men to the consumption of food products made from soybeans. Soy foods are traditionally eaten in Korea, China and Japan but have been more recently introduced to Western countries. Types of soy products used by Western consumers include: soy sauce and tamari sauce, tofu, tempah, miso, soymilk, packaged meat or grain substitutes, and soy protein powders and drinks

Study description: A meta-analysis is a statistical method combining results from published studies in order to re-examine the overall evidence together. To begin, the authors carried out a search of the English-language literature on soy food and prostate cancer risk with the use of computerized databases. Two cohort and six case-control studies providing risk estimates were identified. Cohort studies compare an outcome in groups who are very alike but differ by a certain characteristic; case-control studies compare an ill group against a similar, healthy group and analyze medical records and lifestyles to explain the differences. A meta-analysis was then done on pooled data from the studies using a specific statistical method. Studies on fermented soy food, such as the Japanese staple, miso, were not included.

Findings & Conclusions: Results from data pooled from the studies showed an inverse overall risk estimate (0.70). The overall study results show that eating soy foods and products is linked to a lower risk of prostate cancer in men.

Diet, anthropometric measures and prostate cancer risk:
A review of prospective cohort and intervention studies

British Journal of Urology 93(8):1139-1150, May 2004
P C Dagnelie, A G Schuurman, R A Goldbohm, P A Van den Brandt

Study purpose: This study from Holland reviews the medical literature in order to look at diet as a potential risk factor for prostate cancer.

Study description: The literature review evaluates results from 37 studies on foodstuffs and supplements as potential risk factors for prostate cancer, all published between 1966 and 2003.

Findings: The authors discuss the studies’ support of a protective role against prostate cancer for selenium, a non-metallic trace substance similar to a mineral. Vitamin E, legumes (peas, lentils and beans), and tomatoes may also help protect against prostate cancer. Tomato products contain lycopene, a type of beta-carotene and anti-oxidant that prevents cell damage and may help ward off cancer. Overall consumption of meat, eggs, vegetables, fruit, coffee, tea, carrots and vitamins A, C and D was not consistently linked in the studies to prostate cancer risk. Some studies indicated that taking beta-carotene does not lower prostate cancer risk, except possibly in men who lack beta-carotene to begin with. When it came to specific types of meat, fat, alcohol and dairy products, the studies suggested either an increased risk or no link to prostate cancer at all. Two studies suggest an increased prostate cancer risk when taking very large amounts of calcium (more than 2000 milligrams per day).

Conclusions: The studies analyzed consistently show that selenium, possibly along with legumes, tomatoes and vitamin E, can help to prevent prostate cancer. However, regularly taking very large amounts of calcium seems to be linked to an increased prostate cancer risk.

Note: The studies looked at were inconclusive on the role of meat, dairy products, fat, vegetables, fruits, alcohol, and body weight in increasing prostate cancer risk.

Dietary Fat and Prostate Cancer

Journal of Urology 171(2, part 2 of 2): S19-S24, February 2004
Neil Fleshner, Scott P Bagnell, Laurence Klotz, Vasundra Venkateswaran

Study purpose: Data from studies as different as laboratory research and epidemiological overviews of disease in large populations suggest that dietary fat may play a role in the development of prostate cancer. However, other studies show no such evidence. This review from the University of Toronto looks at the evidence for a link between dietary fat and prostate cancer. It also describes ideas about biologically possible relationships that would explain such a link, including total energy consumption, altered androgen (male hormone) metabolism, specific fatty acid consumption, pesticide intake, and oxidative stress. Oxidative stress is a term used to describe damage levels in a cell, tissue or organ caused by reactive oxygen species like free radicals that result from the metabolism of oxygen.

Study description: The authors reviewed 33 published case-control and cohort studies examining the links between prostate cancer and dietary fat or specific fatty food types. Case-control studies (or “retrospective” studies) compare a group with disease against a similar but healthy group, and study their medical records and lifestyles to learn what factors may be linked to the disease. Cohort studies compare disease in groups of individuals who are alike in many ways but differ by a certain characteristic.

Findings: Eight of the studies suggested a statistically significant link between dietary fat and prostate cancer. Many studies noted links with prostate cancer for types of fatty foods such as milk or meat. The review’s authors do not favour any one biological explanation for a link between dietary fat and prostate cancer.

Conclusions: The authors conclude that while the evidence showing a link between prostate cancer and dietary fat is consistent, more studies are needed. They feel studies involving changes in diet should be encouraged.

Tomato lycopene and its role in human health and chronic diseases

Canadian Medical Association Journal (CMAJ) 163(6) September 19 2000
Sanjiv Agarwal and Akkinappally Venketeshwer Rao

Diabetes mellitus and risk of prostate cancer: a meta-analysis

Diabetologia 47(6):1071-1078, June 2004
S Bonovas, K Filioussi and A Tsantes

Study purpose: The idea of a link between diabetes and prostate cancer is controversial. Some researchers argue that men with diabetes have been shown to be at lower risk for prostate cancer. This meta-analysis from Athens, Greece pools 14 studies on the subject from 1971 to 2002. A meta-analysis is a statistical method that combines results from similar published studies in order to re-interpret all the evidence.

Study description: Five case-control studies and nine cohort studies were looked at. Case-control or retrospective studies compare a group with a disease against a similar but healthy group, and analyze their medical records and lifestyles to learn what factors may be linked with the disease. Cohort studies compare a specific outcome in groups of individuals who are alike in many ways, but differ by a certain characteristic.

Findings: Statistical calculations were used to devise an overall “pooled relative prostate cancer risk” derived from the data of the 14 studies. A slight though statistically significant link between prostate cancer and diabetes was found, but the studies’ overall “pooled relative risk” was negligible. When researchers broke down the results further, the link between prostate cancer and diabetes was shown to be inversed in the cohort and case-control studies, indicating a low and potentially lessened prostate cancer risk. However, this was statistically significant only in the cohort studies.

Conclusions: The authors assert that the findings of their meta-analysis provide strong evidence that people with diabetes experience a significant drop in risk for prostate cancer. There is biological evidence to support this view.