Do Fruits and Vegetables Prevent Cancer?

 

A study that was presented in early 2005 in the Journal of the American Medical Association concluded that there is no connection between eating fruits and vegetables and risk of breast cancer (1). Is this true? How does this fit into the "big picture" of what we know about diet and cancer?

What did the researchers study?

First, the researchers found no difference in the risk of breast cancer when they compared women eating 114 grams or less of fruit per day with women who reported eating 367 grams or more of fruit per day.

  • For reference, a medium apple weighs about 250 grams. In other words, comparing people who eat 114 grams of fruit per day with people who eat 367 grams of fruit per day is like comparing people eating half a medium apple per day with people eating one large apple per day. In summary, this study showed no benefit from eating fruit when the researchers compared women eating about one-half to one serving of fruit per day with women eating about two to three servings of fruit per day.
  • Second, the researchers found no difference in the risk of breast cancer when they compared women eating 109 grams or less of vegetables per day with women who reported eating 309 grams or more of vegetables per day.
  • For reference, a medium green, red, or yellow pepper weighs about 180 grams. In other words, comparing people who eat 109 grams of vegetables per day with people who eat 309 grams of vegetables per day is like comparing people eating one bell pepper per day with people eating one bell pepper and two small tomatoes per day. In summary, this study showed no benefit from eating vegetables when the researchers compared women eating about one-half to one serving of vegetables per day with women eating about two to three servings of vegetables per day.

Finally, the researchers did not see any protective effect against breast cancer for specific categories of vegetables when they compared women eating about 10 grams or less of each specific vegetable category with women eating about 40 to 60 grams of each specific vegetable category.

So knowing that a pepper weighs about 180 grams, comparing people eating 10 grams of vegetables per day with people eating 40 to 60 grams of vegetables per day is like comparing people who eat one floret of broccoli per day with people who eat four florets of broccoli per day.

What Does This Study Tell Us?

Before you decide that eating fruits and vegetables doesn't protect against cancer, think about these important points:

  • This study compared women eating about a serving of fruit or vegetables per day with women eating about two to three, or at most four servings of fruits or vegetables per day.
  • Most health experts feel that to have the best cancer preventive benefits, people need to eat a minimum of five servings of vegetables per day and ideally, most people should eat at least nine servings of vegetables every day.
  • The people in the groups that were ranked as having a "high" intake of fruits and vegetables didn't even meet the minimum amount of these foods that most health experts feel is beneficial for cancer prevention.
  • The study authors stated that people in the study had a "wide range of vegetable and fruit intake." The people in the group with the "highest" intake of vegetables ate more than two times the amount of vegetables when compared with the people eating the lowest amounts of these foods. The people in the group with the "highest" intake of fruit ate more then three times the amount of fruit when compared with the people eating the least fruit.
  • These differences sound impressive, but it's important to keep these numbers in perspective: For example, one person might eat one raisin. Another person might eat six raisins. The second person ate six times the amount of fruit as the first person. It sounds like a big difference, but the second person still is not eating much fruit. The numbers may sound significant, but it doesn't mean that they are.
  • When we consider that the studies compared people eating very low amounts of these foods with people eating low and moderate amounts of these foods, it's not surprising that there was no protective benefit from fruits and vegetables.

In Summary

Even though this study did not show that eating small amounts of fruits and vegetables protects against breast cancer, it is a good study.

  • It confirms that to get the maximum benefits of eating fruits and vegetables, More Is Better. A couple of servings per day is not enough.
  • Despite the study being reported in a prestigious medical journal and on the news, the conclusion that eating fruits and vegetables does not protect against breast cancer is far from accurate.
  • This study was reported as if it conclusively tells us that fruits and vegetables don't reduce breast cancer risk. Yet it is important to remember that to reduce cancer risk, health experts recommend that we eat a minimum of five to nine servings of these foods per day. The people eating the most fruits and vegetables in this study didn't even reach this goal.

Diet Still Matters

This one study did not show a cancer prevention benefit from eating vegetables and fruit. However, dozens of other studies do support this approach for reducing risk of breast and other cancers. Eating a diet that closely matches health experts' recommendations for reducing cancer risk works. Research confirms this.

Keep this in mind and use the following tips to help yourself get at least five, and even better yet, closer to nine servings of fruit and vegetables every day.

  • When you are trying to improve your eating habits, the best place to start is with your attitude.
  • Healthy eating is not a punishment.
  • Healthy eating is a gift to yourself.
  • Healthy eating is not an all or nothing game. You can have a healthy diet and still enjoy "treat" foods.
  • Start by making small manageable changes and build on your successes.
  • It may take several months to change you eating habits noticeably, but by gradually working on your diet now, you can make these healthy changes a permanent part of your commitment to better health.

By focusing on a healthy diet now, you will reap the health benefits today and for many years to come. 

Reference 

  1. van Gils CH, Peeters PH, Bueno-de-Mesquita HB, Boshuizen HC, Lahmann PH, Clavel-Chapelon F, Thiebaut A, Kesse E, Sieri S, Palli D, Tumino R, Panico S, Vineis P, Gonzalez CA, Ardanaz E, Sanchez MJ, Amiano P, Navarro C, Quiros JR, Key TJ, Allen N, Khaw KT, Bingham SA, Psaltopoulou T, Koliva M, Trichopoulou A, Nagel G, Linseisen J, Boeing H, Berglund G, Wirfalt E, Hallmans G, Lenner P, Overvad K, Tjonneland A, Olsen A, Lund E, Engeset D, Alsaker E, Norat T, Kaaks R, Slimani N, Riboli E. Consumption of vegetables and fruits and risk of breast cancer. JAMA. 2005;293(2):183-93.
This content was last reviewed August 15, 2010 by Dr. Reshma L. Mahtani.
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