AICR's
Foods That Fight Cancer

Tomatoes


tomatoes with white background

Tomatoes

Tomatoes are the second most widely eaten vegetable in the United States, probably because of their sweetness and versatility. You've likely enjoyed tomato slices in sandwiches, cherry tomatoes in salads, and fresh or canned tomatoes in sauces and soups. The nutrition information in this section refers to red tomatoes, but you may also see heirloom varieties in all colors of the rainbow. 

What's in Tomatoes?

tomato nutrition facts

Tomatoes are an excellent source of vitamins C and A (produced from beta-carotene) and one serving provides at least 10 percent of the daily recommended potassium. 

In addition to beta-carotene, tomatoes contain a number of other carotenoids: 

  • Lycopene, an antioxidant that gives tomatoes their red color. Red tomatoes, sauces and other tomato products are by far our top source of lycopene 
  • Phytoene and phytofluene, colorless carotenoids that are precursors of lycopene

Full Glossary for Foods That Fight Cancer

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apples

The Cancer Research

Tomatoes’ cancer preventive potential comes from being a non-starchy vegetable as well as a source of vitamin C and carotenoids. The carotenoid lycopene is especially well studied for its cancer preventing properties, but results linking foods containing lycopene to lower cancer risk are currently inconsistent.

What Current Evidence Shows: AICR/WCRF Expert Report and its updates (CUP)

Tomatoes are a non-starchy vegetable that contain carotenoids. After a systematic review of the global scientific literature, AICR/WCRF weighed the strength of the evidence linking these factors to lower risk for several cancers.

Diets high in:CONVINCINGLY lower risk of the following cancers:
Non-starchy vegetables Mouth, pharynx and larynx
Carotenoids Mouth, Pharynx and Larynx
Lung

Source: Food, Nutrition, Physical Activity, and the Prevention of Cancer: a Global Perspective and the Continuous Update Project (CUP)reports.

Open Areas of Investigation: Laboratory Research

Laboratory studies mainly focus on investigating the link between tomatoes' carotenoids and lower cancer risk. The carotenoid lycopene, which has antioxidant properties, appears to prevent DNA and other cell damage. In cell studies, lycopene stimulates self-destruction and decreases growth and metastasis of several types of cancer cells.

Numerous animal studies show lycopene protects against prostate cancer especially. Yet compared to lycopene alone, animal studies suggest that whole tomato powder links to even lower prostate cancer risk. The tomato powder includes other carotenoids and additional compounds. Several animal studies combining tomatoes and broccoli have also shown lower prostate tumor growth than with lycopene or tomatoes alone, suggesting a protective synergy with the compounds in these two foods.

Open Areas of Investigation: Human Studies

Of the many human studies investigating tomatoes, lycopene and cancer risk, most are observational studies of populations. Studies of breast, colorectal and stomach cancer show a neutral or possibly protective effect. Research in healthy volunteers suggests that intake of tomatoes but not lycopene supplements can help protect DNA from damage. Early research linked tomato consumption and blood levels of lycopene to reduced prostate cancer risk, leading to a focus on the role of tomato consumption and this cancer.

Prostate Cancer: Research from the 1990s and early 2000s suggested strong evidence linking foods containing lycopene to lower risk of prostate cancer, as concluded in the 2007 AICR/WCRF report, Food, Nutrition, Physical Activity, and the Prevention of Cancer. Yet when the 2014 Continuous Update Project report on prostate cancer analyzed the global literature, including new and updated studies, it concluded that the evidence is too inconsistent to make a conclusion.

As the report notes: This does not mean that no link exists between foods containing lycopene and prostate cancer, but rather that if there is a link, the nature of the research conducted - because of variations in diagnosis and classifications of the disease - has made it more difficult to see. To provide more insight, better designed studies are required.

Large studies that have focused on tomatoes and lycopene include The National Cancer Institute's Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial. This study compared men with prostate cancer to those without and found that blood levels of lycopene were unrelated to cancer risk. However, a 2014 Health Professionals Follow-up Study concluded that lycopene intake linked to reduced risk of prostate cancer, especially of the more advanced prostate tumors.

Challenges in the Research: Prostate cancer studies are difficult to interpret because this disease often takes decades to develop, with some tumor types aggressive and others slow growing and possibly not lethal. Studying prostate cancer is also challenging due to PSA, prostate-specific antigens, tests. PSAs are often used as a measure of prostate cancer risk but may also be elevated in non-cancerous prostate hyperplasia or inflammation of the prostate gland. Researchers are continuing to look for more specific indicators, including certain forms of PSA, which may provide more accurate information about overall and aggressive prostate tumor risk.

Impact of tomato consumption may vary depending on type and stage of this cancer, synergy with other foods and the proportion consumed as processed tomatoes, which are linked to greater increase in blood lycopene levels.

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Investigations of tomato and/or lycopene intake in prostate cancer patients are limited and results are mixed. Research is ongoing to determine the therapeutic potential, if any, of tomatoes or lycopene.

tomatoes and puree

In the Kitchen

Select:

  • Choose smooth-skinned plump tomatoes that are firm, but not hard.
  • When fresh tomatoes are out of season, try canned tomatoes. Many chefs prefer those for flavor in cooking instead of tomatoes grown in hothouses or transported long distances.
  • Buy canned whole or diced tomatoes and tomato purée, sauce, juice or soup with no added salt and little or no added sugar.

Store:

  • Tomatoes lose flavor at cold temperatures, so store ripe tomatoes at room temperature out of the direct sunlight. If you can’t use the fresh tomatoes before they spoil, refrigerate them, but return them to room temperature for serving.
  • Store under-ripe tomatoes in a brown paper bag to ripen; add a ripe apple or banana to give off ethylene gas that speeds the ripening process.
  • You can freeze tomatoes to use in sauces or other cooked dishes either chopped or whole. The skins will pop right off when thawed.

Prepare:

  • Add raw tomatoes to salads, sandwiches and snack plates.
  • Enjoy cooked tomatoes on their own by grilling, baking or broiling them and adding cherry tomatoes to kabobs.
  • Add puréed or crushed tomatoes to soup, stew, chili, curry, lasagna, enchiladas, Spanish rice and pasta.  
  • Start with homemade or commercial tomato soup and add leftover vegetables, beans, whole grains and herbs for a one-pot meal.

Spicy Gazpacho

Tomato gazpacho recipe
  • 2 lbs. ripe tomatoes, seeded and diced, with their juice
  • 2 large cloves garlic
  • 1 slice stale white bread, crust removed*
  • 1/2 cup reduced-sodium tomato juice
  • 2 Tbsp. tomato paste
  • 4 tsp. white horseradish
  • 2 tsp. white distilled vinegar
  • 1 tsp. extravirgin olive oil
  • Pinch cayenne pepper
  • Salt and ground black pepper, to taste
  • 1/4 cup finely diced peeled cucumber
  • 1/4 cup finely diced green bell pepper
  • 1/4 cup finely diced red onion
  • 4 Tbsp. whole-wheat croutons

In blender, whirl tomatoes and garlic to a coarse purée. Tear bread into 1-inch pieces and add to tomatoes. Add tomato juice, tomato paste, horseradish, vinegar, oil and cayenne pepper. Whirl until soup is a finely pulpy purée. Season to taste with salt and pepper. Transfer soup to a container, cover and chill 3-4 hours to overnight. It will keep up to two days.

Divide chilled soup among four soup bowls. To each bowl, add 1 tablespoon diced cucumber, pepper and onion. Top with 1 tablespoon croutons and serve immediately.

*If bread is not stale, set it on rack in a 225 degree F oven until dry and hard, about 20 minutes.

Makes 4 servings.

Per serving: 120 calories, 3.5 g total fat (0 g saturated fat), 4 g protein, 4 g dietary fiber, 250 mg sodium.

More Recipes

Below are answers to some of the most frequently asked questions we get asked.

Q: Why did the conclusion change from the major 2007 report that found foods containing lycopene protect against prostate cancer?

A: Research from the 1990s and early 2000s suggested strong evidence linking foods containing lycopene to lower risk of prostate cancer, as stated in the 2007 AICR/WCRF report. New and updated studies on the topic were included in the 2014 Continuous Update Project report, which concluded that the evidence is too inconsistent to make a conclusion. Some link may exist, the report notes, but it may exist with only certain types of prostate tumors and/or other links that are not yet appearant in the overall research. More studies are needed.

Q: I know more research is needed before concluding foods containing lycopene protect against prostate cancers, but is taking lycopene supplements safe? What about eating large amounts of tomatoes and their foods?

A: In clinical trials involving prostate cancer patients, lycopene supplement doses ranging from 10 to 120 milligrams/day for up to one year have been well tolerated with only mild-to-moderate gastrointestinal toxicities. AICR recommends that people do not rely on supplements to prevent cancer. Some studies have shown that high-doses of specific compounds may even cause harm.

Studies that use tomato products as a source of lycopene usually use tomato paste or tomato juice because it is a concentrated source. One cup of tomato juice provides about 22 mg of lycopene. Some people may experience heartburn or other gastrointestinal symptoms from consuming tomatoes and tomato products, but these foods are otherwise safe to consume.

Q: I've heard that lycopene from tomatoes is actually better absorbed when tomatoes are cooked. Is this true?

A: Yes, processing tomatoes  – meaning chopping, cooking or puréeing – softens tomatoes' cell walls, making lycopene more available for the body to absorb, and especially with high heat (used to make tomato juice, tomato paste or tomato sauce, for example), lycopene is changed into a form that is easier for the body to use. Fat used in cooking can also help the body better use the lycopene in tomato products.

Q: Which vegetables and fruits should I be eating?

A: Eat as many different vegetables and fruits as you can. Variety is the key to obtaining the many protective phytochemicals. Each vegetable and fruit has its own profile of health-promoting substances. The phytochemicals found in cantaloupe are different from those in broccoli or leeks or cherries. Try to include a lot of colors on your plate. Aim to eat some bright red, green, orange, blue, purple and yellow vegetables and fruits each day.

Q: Should I buy organic foods whenever possible?

A: There are many reasons to eat organic foods, but currently, there is no convincing evidence that shows a difference between organic and conventionally grown foods related to cancer risk. Studies show pesticide residues on conventionally grown foods are almost always within safety tolerance limits. If you are concerned about pesticide residues and can afford to spend more, organic produce may be a choice for you. Eating generous servings of a large variety of veggies and fruits–whether organic or not–will benefit your health. The advantages of including more vegetables and fruits in your diet outweigh the potential risks from pesticides.

References

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  2. van Breemen, R.B. and N. Pajkovic, Multitargeted therapy of cancer by lycopene. Cancer letters, 2008. 269(2): p. 339-51.
  3. Boileau, T.W., et al., Prostate carcinogenesis in N-methyl-N-nitrosourea (NMU)-testosterone-treated rats fed tomato powder, lycopene, or energy-restricted diets. Journal of the National Cancer Institute, 2003. 95(21): p. 1578-86.
  4. Canene-Adams, K., et al., Combinations of tomato and broccoli enhance antitumor activity in dunning r3327-h prostate adenocarcinomas. Cancer research, 2007. 67(2): p. 836-43.
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  13. Peters, U., et al., Serum lycopene, other carotenoids, and prostate cancer risk: a nested case-control study in the prostate, lung, colorectal, and ovarian cancer screening trial. Cancer epidemiology, biomarkers & prevention : a publication of the American Association for Cancer Research, cosponsored by the American Society of Preventive Oncology, 2007. 16(5): p. 962-8.
  14. Kirsh, V.A., et al., A prospective study of lycopene and tomato product intake and risk of prostate cancer. Cancer epidemiology, biomarkers & prevention : a publication of the American Association for Cancer Research, cosponsored by the American Society of Preventive Oncology, 2006. 15(1): p. 92-8.
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