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Cancer Nutrition Consortium

Organic Foods and Cancer Risk

November 18, 2019

Healthy foods like avocado, carrot, citrus fruits and more

Christina L. DiSegna, MS, RD, CSO, CNSC, LDN
Senior Clinical Dietitian
Dana-Farber/Brigham and Women’s Cancer Center

Organic foods are emerging as a potential strategy for decreasing cancer risk. But does the research support this trend?

Organic foods are those which are grown or produced without use of synthetic pesticides or herbicides and chemical fertilizers. Certain pesticides – malathion and diazinon – as well as the herbicide glyphosate have been classified as probable human carcinogens and have been linked to higher rates of certain cancers in those with workplace exposures such as farm workers. 

However, for the general population, low-level pesticide exposure occurs mostly from diet through conventionally-grown produce. The health consequences of these low-level exposures, including cancer risk, are not clear at this time. Regardless, many people are choosing organic foods as a strategy for decreasing pesticide exposure to, in theory, decrease cancer risk. The research to support this practice has been conflicting thus far.

A recent study published in the Journal of the American Medical Association followed 70,000 adults over a seven-year timeframe; those who reported the highest intakes of organic foods had decreased cancer incidence compared with those who rarely chose organic foods. 

However, the researchers noted that those who reported eating organic foods also engaged in healthier lifestyle behaviors and ate an overall healthy diet which are known to decrease cancer risk. Although the study adjusted for these factors in the analysis, there may be unadjusted factors that contributed to the results. 

Additionally, the study did not measure pesticide residues in any of the participants, so it is unclear if differences in pesticide levels correlated with decreased cancer incidence. One other large study conducted previously in 2014 did not show a decreased cancer risk in those who usually or always consume organic foods. Based on these two studies with differing results, conclusive recommendations on the benefit of organic foods and cancer risk cannot be made.

In contrast, the research surrounding the importance of fruits and vegetables in reducing cancer risk is vast. 

The American Institute of Cancer Research and World Cancer Research Fund have compiled expert reports which assess decades of research, looking at hundreds of studies, to make recommendations on overall diet and lifestyle factors that can reduce the risk of developing cancer. In the most recent report, many studies suggested decreased cancer risk associated with increased consumption of fruits and vegetables. 

The inverse was also true; low intakes of fruits and vegetables were associated with increased risk of certain types of cancers. Therefore, high intakes of a variety of colorful fruits and vegetables are suggested for decreasing overall cancer risk. 

One major problem: For those looking to choose organic as well as increase produce intake, the cost increase can be a barrier for many people and this goal is often cost-prohibitive. Practically, what can consumers do to increase produce intake while also decreasing potential pesticide exposure?

  • First, all produce – both conventional and organic – should be washed thoroughly before being consumed. Washing produce under running water with light friction if needed helps remove dirt, bacteria, chemicals, and pesticide residues. 
  • Second, consider choosing organic when buying produce with the highest pesticide residues. The Environmental Working Group publishes the “Dirty Dozen” and “Clean Fifteen” lists yearly which rank foods based on pesticide levels. Those concerned with pesticide residues may choose to buy organic when purchasing from the “Dirty Dozen” list to reduce exposure while also saving money while choosing conventional produce from the “Clean Fifteen” list. 
  • Third, consider buying locally from farmers markets or directly from farmers. Often, smaller farms are practicing organic farming methods but cannot afford the cost of becoming a certified organic farm. The produce cost may be less than organic in the supermarket but with the same benefits, as well as the added bonus of supporting your local farm. 
  • Lastly, note that “organic” does not mean “healthier”. There are many processed and packaged foods in the supermarket that have the ingredients grown organically but still contain significant amounts of fat, sugar, and artificial ingredients that can be detrimental to health. Overall, diets high in fruits and vegetables – conventional or organic – have significant benefits for both cancer prevention and general health and a variety should be included in your diet daily.

Summary

  • Organic foods are grown or produced without use of synthetic pesticides or herbicides and chemical fertilizers
  • Exposure to pesticides and herbicides may increase risk for certain cancers
  • Choosing organic foods as a strategy for decreasing pesticide exposure may decrease cancer risk but the research at this point is conflicting and unclear
  • Many studies show the benefits of increased intake of fruits and vegetables to decrease cancer risk and a diet high in a variety of fruits and vegetables is recommended

Recommendations

  • Wash all produce with running water prior to consuming
  • If choosing to buy organic, utilize the “Dirty Dozen” and “Clean Fifteen” lists from the Environmental Working Group to prioritize organic purchases
  • Consider local farms and farmers markets for in-season produce with potential cost benefit
  • Organic does not necessarily mean healthy! Choose diets high in fruits and vegetables, whole grains, lean proteins, and healthy fats over organic processed foods.

Dirty Dozen

  1. Strawberries
  2. Spinach
  3. Kale
  4. Nectarines
  5. Apples
  6. Grapes
  7. Peaches
  8. Cherries
  9. Pears
  10. Tomatoes
  11. Celery
  12. Potatoes

Clean Fifteen (2019)

  1. Avocados
  2. Sweet corn
  3. Pineapple
  4. Sweet peas (frozen)
  5. Onions
  6. Papayas
  7. Eggplants
  8. Asparagus
  9. Kiwis
  10. Cabbages
  11. Cauliflower
  12. Cantaloupes
  13. Broccoli
  14. Mushrooms
  15. Honeydew Melon

References:

Baudry J, Assmann K, Touvier M. Association of Frequency of Organic Food Consumption With Cancer Risk. JAMA Intern Med. 2018;178(12):1597-1606

Bradbury KE, Balkwill A, Spencer EA, Roddam AW, Reeves GK, Green J, Key TJ, Beral V, Pirie K and the Million Women Study Collaborators. Organic food consumption and the incidence of cancer in a large prospective study of women in the United Kingdom. BR J Cancer. 2014 Apr 29; 110(9): 2321-2326

Hemler EC, Chavarro JE, Hu FB. Organic Foods for Cancer Prevention – Worth the Investment?. JAMA Intern Med. 2018;178(12):1606-1607

International Agency for Research on Cancer. IARC Monographs Volume 112: evaluation of five organophosphate insecticides and herbicides. Available at https://www.iarc.fr/wp-content/uploads/2018/07/MonographVolume112-1.pdf 

World Cancer Research Fund/American Institute for Cancer Research. Continuous Update Project Expert Reports 2018. Wholegrains, vegetables and fruit and the risk of cancer. Available at https://www.wcrf.org/dietandcancer 

Cancer Prevention Recommendations. American Institute for Cancer Research. Accessed 6 September 2019.  https://www.aicr.org/reduce-your-cancer-risk/recommendations-for-cancer-prevention/index.html 

Shopper’s Guide to Pesticides in Produce. Environmental Working Group. Accessed 6 September 2019. https://www.ewg.org/foodnews