June 2012 Issue
Can Tomatoes Slice Prostate Cancer Risk?
By Sharon Palmer, RD
Today’s Dietitian
Vol. 14 No. 6 P. 20
Evidence suggests a tomato-rich diet benefits men.
Armed with a $400,000 grant from the National Institutes of Health (NIH), scientists from the University of Illinois and Ohio State University are tracing how tomato compounds help reduce the risk of prostate cancer in humans. Using isotopic labeling of the three tomato carotenoids—lycopene, phytoene, and phytofluene—they’re tracking the absorption and metabolism of these substances in the body, hoping to unlock the mysteries of how tomatoes seem to protect against prostate cancer.1
The prospect that something as simple as eating tomatoes can help fend off prostate cancer is exciting. After all, the National Cancer Institute estimates there will be more than 217,000 new cases of prostate cancer in the United States this year, resulting in more than 32,000 deaths.1
“Most men are going to get prostate cancer if they live long enough,” says John Erdman, PhD, professor emeritus of the department of food science and human nutrition at the University of Illinois who’s been studying the effects of tomatoes on prostate cancer since the mid-1990s and is the co-lead researcher on the NIH-funded study. “Many men between 40 and 50 develop early-stage prostate cancer, and it may continue to develop over 20 years. It’s important to reduce the growth of the tumor. If you can control this by diet so that the tumor doesn’t get large enough to cause problems, you’ve saved a lot of lives.”
Tomato Lovers
What’s so special about tomatoes? For one, they hold an intriguing place in the history of the human diet. While tomatoes are a fruit, botanically speaking, the USDA classifies them as a vegetable. The tomato (Lycopersicon esculentum) likely originated in South America, where the Spanish explorers fell in love with it and introduced it to the world. It traveled to the Caribbean, Asia, the Middle East, and Europe, where it was especially embraced in Italy. Yet it’s only in the past two centuries that tomatoes caught on in the United States. The tomato was generally considered poisonous before that, given that it was a member of the nightshade family. The tomato gets its name from tomati, the word used by Mexico natives who’ve consumed them since prehistoric times.2
As tomatoes were cultivated in countries spanning the world, they became an important element in many traditional dishes—from Mexican salsas to South Asian curries to Italian red sauces. And in the United States, the tomato is the second most popular vegetable, behind only the potato.3
While we love tomatoes sliced fresh in sandwiches and salads, we’re also consuming plenty of them in their processed forms in soups, ketchup, canned tomatoes, paste, and tomato or pasta sauce. With the advent of preservation, canning tomatoes became an important, economical way to rely on them all year long. Today, about 75% of the total tomato crop is processed into juice, canned tomatoes, sauces, paste, and ketchup.4
Nutrient Buzz
Tomatoes contain a symphony of nutrients that may be responsible for their cancer-protective properties, including vitamins A and C,, fiber, and potassium, as well as carotenoids, which give tomatoes their red, yellow, and orange colors.4 The most abundant carotenoid is lycopene, followed by phytoene, phytofluene, zeta-carotene, gamma-carotene, beta-carotene, neurosporene, and lutein.5
Several studies have linked lycopene with cancer protection. While lycopene is present in other fruits such as watermelon and guava, tomatoes account for 80% of the lycopene in the American diet. Research shows that single daily servings of processed tomato products produce significant increases of lycopene concentrations in blood and buccal mucosal cells in healthy adults.6 And evidence indicates that the lycopene from processed tomatoes is more bioavailable than that of fresh tomatoes. Processing breaks down the tomato cell matrix and promotes isomerization of lycopene from all-trans isomers to the more bioavailable form of cis-isomers.7
Erdman believes the cancer protection seen in tomatoes isn’t a mere result of lycopene. More effective benefits have been linked with the whole tomato, which contains a full range of carotenoids and nutrients. “The work we’ve done so far with tomato powder is positive. We strongly feel that there are lots of goodies in tomatoes well beyond lycopene—for example, other carotenoids,” he says.
According to Nancy Engelmann Moran, PhD, a postdoctoral researcher from Ohio State University who worked with Erdman and produced the isotopically labeled carotenoids for the study, tomato products are more effective than isolated lycopene due to other carotenoids, such as phytoene and phytofluene, the colorless precursors to lycopene.
Science on Tomatoes and Prostate Cancer
The tomato-prostate cancer connection is rooted in a body of observational studies of populations. “There’s very good, strong, epidemiological support for increased consumption of tomato products and lower incidence of prostate cancer,” Erdman says. “Animal models are fairly conclusive. We can’t make a direct correlation to humans, but a number of animal models have shown strong results.”
A small number of intervention trials focusing on tomato products have been performed with positive results measuring improvements in prostate-specific antigen (PSA) concentrations8-11 and increased cell death in carcinomas.12 And a meta-analysis that included 11 case-control studies and 10 cohort studies or nested case-control studies on the use of tomato, tomato products, or lycopene found that, compared with nonfrequent users of tomato products, consumers of high amounts of raw tomatoes had an 11% reduced risk of prostate cancer, and those with a high intake of cooked tomato products experienced a 19% lower risk.13
In the 2011 update of a Summary of Research on Tomatoes/Lycopene and Disease Risk, prostate cancer was identified as the subject of substantial research attention. Britt Burton-Freeman, PhD, director of the Center for Nutrition Research at the Illinois Institute of Technology, reviewed 86 studies related to tomato and lycopene intake and prostate cancer in her summary, reporting that, overall, the data support a protective relationship between the consumption of tomato and tomato-based foods and a lower risk of prostate cancer, but that lycopene supplementation doesn’t improve disease status, as measured by PSA levels.14
Tomatoes always have been one of those foods that taste better in combination with other ingredients—whether they’re simmered with onions, olive oil, and basil in a sauce or eaten in a salad with green vegetables. So it’s interesting to discover that antioxidant-rich foods combined with tomatoes may have added cancer-protective effects. Erdman has found such effects when combining tomato powder with both broccoli powder and soy germ in rat studies. “Research is definitely still ongoing and with mixed results in this area. But it does continue to show benefit in laboratory studies of animals, especially when tomato powder is combined with broccoli powder, showing decreased development of prostate cancer,” says Karen Collins, MS, RD, CDN, nutrition advisor of the American Institute for Cancer Research (AICR).
While earlier research has focused on prostate cancer prevention, newer studies are looking at early treatment and slowing the disease progression, according to Erdman. In another NIH-funded study, Erdman’s team is investigating dietary manipulations that can slow the rate of cancer and metastasis in TRAMP (transgenic adenocarcinoma of the mouse prostate) mice that are used in research because they spontaneously develop prostate cancer. “We haven’t published our results yet, but the effects of tomato products look very promising,” Erdman says. “This has practical implications when you’re looking at prostate cancer; men don’t pay attention to this disease until their PSA levels increase.”
Though human research is needed, Erdman reports many barriers. “It’s very difficult to do a clinical trial for prostate cancer. These studies take a lot of time and money.” Additionally, he says a good biomarker to measure cancer risk is lacking. “PSAs are a hot debate in prostate cancer; levels can change if something has gone awry, such as an infection. A reduction in PSA isn’t proven to reduce the risk of prostate cancer.”
However, the evidence on tomato products and prostate cancer prevention is promising enough for health organizations to promote the benefits of consuming tomato products for prostate cancer protection. In a comprehensive scientific analysis of cancer prevention and causation, an expert panel of scientists for the AICR reviewed more than 4,000 trials, studies, and reports to create the organization’s Second Expert Report — Food, Nutrition, Physical Activity, and the Prevention of Cancer: a Global Perspective. The report noted a substantial amount of evidence on tomato products, and that food containing lycopene probably does protect against cancer, in particular providing a convincing decreased risk of prostate cancer.15
Incorporating Tomato Products Into the Diet
While we have much more to learn about how tomatoes fight prostate cancer, most experts agree it’s a good idea to recommend eating more of them as part of the overall strategy to increase fruit and vegetable intake.
“The research is still unclear, and it doesn’t support overdosing on tomatoes or overrelying on tomatoes as a strategy in itself. This should be part of an overall health-promoting strategy that includes regular physical activity, maintaining a healthful weight, eating a diet with an abundance of plant foods, and limiting red meat—especially meat cooked at high temperatures or to very well-done doneness, when carcinogens especially form,” Collins cautions. However, she does recommend lycopene-rich foods such as tomatoes, adding, “Regular consumption probably lowers risk of prostate cancer, based on conclusions from the AICR expert report. According to Erdman, “One can’t say that you can treat or prevent prostate cancer with tomatoes, but two to three servings per week from an epidemiological standpoint appears to be enough.”
Considering how popular tomatoes are in our diets, two to three servings per week isn’t hard to consume. While fresh tomatoes in season offer many simple, delicious meal offerings, tomato products—with more bioavailable lycopene—are shelf stable, economical, and convenient all year long.
The following tips can help guide your patients to increase their tomato intake:
Fresh Tomatoes
• Slice tomatoes for breakfast and serve them as a side with eggs, hash browns, or toast.
• Include fresh tomato slices in sandwiches, pitas, and wraps.
• Dice tomatoes into salsas and dips such as bruschetta.
• Add into salads, tacos, pilafs, and pasta dishes.
• Try heirloom tomatoes from the farmers’ market or your own garden, which are delicious served au naturel.
• Prepare sliced tomatoes with basil and a drizzle of olive oil and black pepper.
• Pack cherry tomatoes for a portable snack or sack lunch component.
• Bake or broil tomato halves with a splash of olive oil and herbs.
• Grill fresh tomato halves or use cherry tomatoes on kebabs.
• Add cherry tomatoes to fresh vegetable platters.
Processed Tomatoes
• Stock the pantry with various tomato products (no salt added), such as canned tomatoes, diced tomatoes, tomato sauce, pasta sauce, tomato soup, salsa, and ketchup.
• Serve tomato soup to accompany meals.
• Make tomato-based vegetable soups with canned tomatoes—serve it hot in the winter and cold (think gazpacho) in the summer.
• Cook a pot of chili using canned tomatoes, beans, and diced vegetables.
• Serve whole grain pasta dishes with tomato sauce.
• Prepare traditional Mexican favorites such as enchiladas and tacos using tomato sauce or prepared salsa.
• Create baked pasta dishes such as lasagna with tomato sauce.
• Dust off the slow cooker to create a savory stew using canned tomatoes.
• Enjoy tomato or vegetable juice (no added salt) as a beverage.
• Bake a stewed tomato casserole with canned tomatoes, breadcrumbs, and herbs.
• Pour tomato sauce over favorite dishes, such as chicken cacciatore, meatloaf, or Swiss steak.
• Try a creamy tomato-based curry with brown rice.
• Create a healthful pizza with whole grain crust, tomato sauce, and lots of veggies.
• Add canned tomatoes to grain dishes such as rice, couscous, quinoa, or bulgur.
• Enjoy sun-dried tomatoes as a snack or use in salads, vegetable platters, and cooking.
— Sharon Palmer, RD, is a contributing editor at Today’s Dietitian, a freelance food and nutrition writer in southern California, and author of the forthcoming book The Plant-Powered Diet.
Home-Style Turkey Vegetable Lasagna
This classic lasagna is bursting with bold flavor and nutrition but is lighter in fat and calories. It’s destined to be a family favorite on your dinner table.
Serves 10
Ingredients
1 T olive oil
1 medium onion, chopped
3 cloves garlic, minced
1 lb (93% lean) ground turkey
1 28-oz can diced tomatoes
1 6-oz can tomato paste
1 tsp each: dried basil, dried oregano, and dried thyme
Salt and pepper to taste (optional)
2 1/2 cups low-fat cottage cheese
1 10-oz package frozen spinach, thawed, squeezed dry
1/2 tsp dried parsley
1/4 tsp black pepper
1/2 cup parmesan cheese, finely grated
12 lasagna noodles, cooked according to package directions
1 cup skim milk mozzarella cheese, grated
Nonstick cooking spray
Directions
1. Preheat oven to 400˚F.
2. Heat olive oil in large skillet over medium-high heat. Add onion and garlic, stirring until translucent, 2 to 3 minutes. Add ground turkey, browning and breaking it into small pieces. Add tomato products, basil, oregano, and thyme and simmer over low heat for 15 minutes. If sauce is too thick, add up to 1/2 cup water and simmer to desired consistency. Add salt and pepper to taste (optional).
3. In medium bowl, stir together cottage cheese, spinach, parsley, black pepper, and 1/4 cup parmesan cheese.
4. Coat a 13- X 9-inch baking dish with nonstick cooking spray. Spread the bottom of the dish with 1/3 of the meat and tomato sauce mixture. Arrange four noodles over the sauce; top with 1/3 of the cottage cheese mixture and 1/2 cup mozzarella cheese. Top with a second layer of 1/3 of the meat and tomato sauce, four noodles, and 1/3 of the cottage cheese mixture. Layer with remaining meat and tomato sauce, four noodles and remaining cottage cheese mixture. Top lasagna with 1/2 cup mozzarella and 1/4 cup parmesan cheese.
5. Bake in center rack of the oven for about 25 minutes, until sauce is bubbling and cheese is starting to brown. Let stand 10 minutes before serving.
Nutrient Analysis per serving: Calories: 408; Protein: 29 g; Carbohydrates: 31 g; Fat: 16 g; Sat fat: 7 g; Sodium: 770 mg; Fiber: 4 g
— Recipe courtesy of Tomato Products Wellness Council, www.tomatowellness.com
References
1. Stones M. Tomato compounds enlisted in fight against prostate cancer. Nutra Ingredients-USA.com website. http://www.nutraingredients-usa.com/Research/Tomato-compounds-enlisted-in-fight-against-prostate-cancer. December 2, 2010. Accessed March 16, 2012.
2. The tomato had to go abroad to make good. Aggie Horticulture website. http://aggie-horticulture.tamu.edu/archives/parsons/publications/vegetabletravelers/tomato.html. Accessed March 16, 2012.
3. Power up on tomatoes, the easy vegetable. Tomato Products Wellness Council website. http://www.tomatowellness.com/static/uploads/Powerupontomatoes.pdf. Retrieved January 4, 2012.
4. Vegetable crops. Purdue University Department of Horticulture and Landscape Architecture website. http://www.hort.purdue.edu/rhodcv/hort410/tomat/to00001.htm. Retrieved January 4, 2012.
5. Khachik F, Carvalho L, Bernstein PS, Muir GJ, Zhao DY, Katz NB. Chemistry, distribution, and metabolism of tomato carotenoids and their impact on human health. Exp Biol Med (Maywood). 2002;227(10):845-851.
6. Allen CM, Schwartz SJ, Craft NE, et al. Changes in plasma and oral mucosal lycopene isomer concentrations in healthy adults consuming standard servings of processed tomato products. Nutr Cancer. 2003;47:48-56.
7. Shi J, Le Maguer M. Lycopene in tomatoes: chemical and physical properties affected by food processing. Crit Rev Biotechnol. 2000;20(4):293-334.
8. Chen L, Stacewicz-Sapuntzakis M, Duncan C, et al. Oxidative DNA damage in prostate cancer patients consuming tomato sauce-based entrees as a whole-food intervention. J Natl Cancer Inst. 2001;93(24):1872-1879.
9. Bowen P, Chen L, Stacewicz-Sapuntzakis M, et al. Tomato sauce supplementation and prostate cancer: lycopene accumulation and modulation of biomarkers of carcinogenesis. Exp Biol Med (Maywood). 2002;227(10):886-893.
10. Grainger EM, Schwartz SJ, Wang S, et al. A combination of tomato and soy products for men with recurring prostate cancer and rising prostate specific antigen. Nutr Cancer. 2008;60(2):145-154.
11. Edinger MS, Koff WJ. Effect of the consumption of tomato paste on plasma prostate-specific antigen levels in patients with benign prostate hyperplasia. Braz J Med Biol Res. 2006;39(8):1115-1119.
12. Kim HS, Bowen P, Chen L, et al. Effects of tomato sauce consumption on apoptotic cell death in prostate benign hyperplasia and carcinoma. Nutr Cancer. 2003;47(1):40-47.
13. Etminan M, Takkouche B, Caamano-Isorna F. The role of tomato products and lycopene in the prevention of prostate cancer: a meta-analysis of observational studies. Cancer Epidemiol Biomarkers Prev. 2004;13(3):340-345.
14. Burton-Freeman B. Summary of research on tomatoes/lycopene and disease risk, 2011 update. http://tomatowellness.com/report2011/critical-findings/cancer-plasma-prostate.html. Retrieved March 12, 2012.
15. World Cancer Research Fund, American Institute for Cancer Research. Food, Nutrition, Physical Activity, and the Prevention of Cancer: a Global Perspective. Washington, DC: American Institute for Cancer Research; 2007.