Food, Nutrients, and Prostate Cancer Risk

Food, Nutrients, and Prostate Cancer Risk

Review of Cancer Causes Control 2004;15(1):11-20

A study published in the journal Cancer Causes and Control looked at foods and nutrients in the diet and risk of prostate cancer. The results of this study tell us that eating a diet that contains plenty of vegetables in general, allium vegetables in particular, and tomato-based foods may reduce prostate cancer risk. Eating more margarine appeared to increase the risk of prostate cancer in this study. This article review discusses the findings of this study. We provide PRACTICAL information on what these findings mean. We discuss which foods are in the allium vegetable category, what tomato-based foods appear to protect best against prostate cancer, and how you can get these foods into your diet. Factors such as age, gender, and genetics cannot be changed, but diet and nutrition can. This type of information will allow men to take concrete and practical steps that may decrease their risk of prostate cancer.

Note: Numbers appearing at the end of sentences indicate research references. References are listed at the end of each article.

Background

Dozens of studies have been published on nutrition and prostate cancer risk, but results of different studies don't always agree. Some factors that may increase prostate cancer risk include eating more total fat, saturated fat, dairy foods, and calcium, while factors that may protect against prostate cancer include more vitamin D (from diet and sunlight) and eating fish, brassica vegetables, soy foods, tomato products, and plant foods (1-15). To better understand how diet may affect risk of prostate cancer researchers continue to study specific foods, groups of foods, and nutrients in relation to this disease. A recent study published in the journal Cancer Causes and Control looked at the possible connections between foods, nutrients, and prostate cancer risk (16). It is hoped that this type of research will identify specific dietary factors that increase or decrease prostate cancer risk. Factors such as gender, age, and genetics cannot be changed, but diet and nutrition can! This type of information can help men take concrete and practical steps to decrease their risk of prostate cancer, which is one of the most common cancers occurring in men today (17).

What The Researchers Studied

For this study, researchers looked at the diets of 858 men with prostate cancer and 905 men without prostate cancer (16). The researchers were interested in studying prostate cancer that occurs in younger men and included only men who were less than 70 years old when diagnosed. Information on other important factors including age, year of prostate cancer diagnosis, family history of prostate cancer, country of birth and socioeconomic status was collected and accounted for in the study. The researchers used all of this information to examine which specific dietary factors, foods, or nutrients might be related to being diagnosed with prostate cancer. Some useful results came out of this study.

What The Study Found

First, men who ate margarine 7 or more times per week, on average, had 30% higher likelihood of being diagnosed with prostate cancer (1.3 times the risk) when compared to men who ate margarine less than 7 times per week on average. In other words, eating margarine more often, on average about once daily, appeared to increase the likelihood of being diagnosed with prostate cancer in this study.

Second, men who ate allium vegetables five and a half times or more per week had 30% lower likelihood of being diagnosed with prostate cancer (0.7 times the risk) when compared to men who ate these foods less than five and a half times per week. In other words, eating allium vegetables more often appeared to decrease the likelihood of being diagnosed with prostate cancer in this study.

In this study, allium vegetables included onions, leeks, and garlic.

Third, men who ate tomato-based foods six and a half times or more per week had 20% lower likelihood of being diagnosed with prostate cancer (0.8 times the risk) when compared to men who ate these foods less than six and a half times per week. In other words, eating tomato foods more often, on average almost once daily, appeared to decrease the likelihood of being diagnosed with prostate cancer in this study.  

In this study, tomato foods included tomatoes, pasta, and pizza.

Fourth, men who got more of their dietary fat from certain types of fat appeared to have lower likelihood of being diagnosed with prostate cancer. In particular, men eating more of two types of fat (fatty acids), known as palmitoleic and oleic acid, had roughly 20% lower likelihood of being diagnosed with prostate cancer (0.8 times the risk) when compared to men who did not eat much of these types of fat.

Olive oil is a good source of both oleic and palmitoleic fatty acids. These are two types of fat that appeared to decrease prostate cancer risk in this study.

What do these results mean?

If the men in this study are like most men, this study suggests that eating more margarine may increase prostate cancer risk while eating more allium vegetables, tomato foods, and olive oil (a good source of two fats that may be protective against prostate cancer) may decrease prostate cancer risk (16).

This study does have a several weak points.

First, this type of study cannot prove cause and effect; it only tells us that there is an association between certain dietary factors and risk of prostate cancer. It is important to remember that an association is not causation (cause and effect).

As well, this study asked people about their diet after they were diagnosed with prostate cancer. This can create problems with the research because sometimes people remember their diet differently if they already have a disease. This is called recall bias and it can be a problem with this type of research.

Finally, this study was conducted in Australia. This means that the overall diet and lifestyle patterns may be different from men in other countries and therefore these results may not apply to men living outside of Australia. However, these results may be important for men living in the United States because researchers have found that several important health factors may be similar among people living in Australia and people living in the United States (18).

On a positive note, the results of this study (16) do agree with other research on diet and prostate cancer. Several studies have come to the conclusion that tomato foods, allium vegetables, and olive oil may protect against prostate cancer (19-34).

In summary, despite some weaknesses of the study reviewed (16), it fits well with what we know about diet and prostate cancer risk. It adds another useful piece of information to the puzzle.  

More importantly, there are NO downsides to improving diet and eating healthy! In addition to lowering risk of prostate cancer, these same foods (allium vegetables, tomato foods, olive oil) may reduce risk of other cancers as well (27,29,32,35-47).

How can I change my diet to lower my risk of prostate cancer?

According to this study, eating more allium vegetables (garlic, onions, leeks, and chives), more tomato foods, and trying to eat more of your dietary fat from olive oil may help decrease risk of prostate cancer (16). Remember, to keep disease risk low, do not simply add olive oil to your diet. This will result in a higher fat diet with excess calories. Instead, begin to replace the other sources of fat in your diet, such as margarine, butter, and other cooking oils, with olive oil. Use the tips below to get started on a "lower prostate cancer risk diet"!

Use Olive Oil As A Healthy Fat In Your Diet

• Try substituting olive oil for other oils in your diet.
• Do not simply add olive oil to your regular diet. This will add extra calories and fat. Instead, try replacing other oils, such as corn oil and soy oil, with olive oil.
• Olive oil is suitable for cooking with temperatures up to, but not above, 400º F.
• Instead of butter or margarine on your whole grain bread, try dipping the bread in a little olive oil.
• Olive will oxidize (break down) over time so store it in a cool, dry place. You can store olive oil in the refrigerator. It will become cloudy, but this is ok. It does not hurt the quality of the oil.
• To learn more about olive oil, try visiting the website for the North American Olive Oil Association.

Eat More Tomato Foods

• For an easy dinner, pour 1/2 cup marinara (tomato based or 'spaghetti sauce') sauce over whole grain pasta. Drizzle a small amount of olive oil over pasta, then toss the pasta with marinara sauce. Serve with a side of steamed vegetables or a dark green leafy salad.
• Keep small 6 oz cans of low sodium V8® juice handy in the refrigerator or in your desk at work. Enjoy one of these each day.
• If you have a choice, always chose tomato soup or soup made with a tomato based broth.

Eat More Allium Vegetables

• Learn to enjoy Italian food! Italian food has all three of the foods that were found to be protective against prostate cancer in the study reviewed here (16). Italian food contains olive oil, tomato foods and plenty of allium vegetables too!
• Instead of butter or margarine on your whole grain bread, try roasted garlic! It's easy to make and enjoyable to eat!
• To roast garlic, simply take several garlic bulbs, wrap each bulb individually, in aluminum foil. Place the wrapped bulbs on the oven wrack and bake at 350ºF for 30 to 40 minutes (longer for softer garlic). Unwrap and let garlic cool for a few minutes. Squeeze soft garlic directly onto whole grain bread and enjoy.

NOTE: If you are in cancer treatment, these diet changes may not be right for you.

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Publish Date: 06/2004