Can a Food Prevent Cancer? Tips for Evaluating Studies about Foods and Breast Cancer

Phyllis Johnson Health Guide
  • On any given day you can see headlines touting studies that claim a given food will have some miraculous effect on your health.  These studies can be very confusing because often today’s “good” food was yesterday’s “bad” food.


    A recent study published in Breast Cancer Research and Treatment is a good example.  It found that a higher consumption of vegetable protein in girls 9-14 led to a lower risk of benign breast disease in their twenties.  Because the most frequent type of vegetable protein eaten by the girls in the study was peanut butter, the headlines focused on the idea that eating peanut butter improves breast health.  How can you evaluate such claims?  Should you rush out and buy the giant size jar of peanut butter?  Let’s use this study as a guide to some principles to help you sort through the reliability of a study.

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    How large was the study?  This one used 9,000 American girls involved in a study called The Growing Up Today Study recruited between 1996 and 2001.  Beware studies that look at small numbers of people because the results may not be statistically significant.  However, 9,000 is a large enough number, and these 9,000 girls are just part of a much larger, very reputable study started at Brigham and Women’s Hospital in Boston that has led to numerous research studies.


    How credible are the researchers?  Some research into diet is funded by the food industry itself, so a study that finds benefits from Food A is less credible if the Food A Council designed and paid for it.  This study was done by researchers at the Washington University in St. Louis Medical School, and the Growing Up Today Study has ties to many universities and research institutions across the country, so the researchers are authoritative.


    What was the design of the study?  Studying the relationship between food and disease is very complicated.  People’s diets are varied and hard to control, so some studies look at mice or other animals.  The results from an animal study may give a clue about a healthy diet, but mice and human have different dietary needs making a study in humans preferable.  How on earth can scientists look at the connection between a food and a specific disease when they don’t know who will get that disease?  That’s why researchers often ask people with a disease to recollect information about their past habits.  I’ve participated in research studies like that myself, and it can be very hard to remember accurately.  A. Lindsay Frazier and Graham A. Colditz, the senior researchers for this research, had seen previous retrospective studies suggesting a connection between vegetable fats and proteins and improved breast health, so they designed this study to start with young girls and follow them over a period of time.  


    The design of this study was a good one.  The girls filled out food frequency questionnaires from 1996-2001 every year.  The questionnaires were not looking at any one food.  The point wasn’t to prove that peanut butter is good.  It was to find out IF there is a connection between any specific foods and breast health.  Starting in 2005, the questionnaires added questions about whether the women had a biopsy for a benign breast condition.  What the researchers found was that the more vegetable proteins girls had consumed, the lower their risk for benign breast disease.  Girls who ate peanut butter and nuts two times a week were 39% less likely to have benign breast disease by the age of 30 than the other girls in the study.  This held true even in the women who had a family history of breast cancer.


    Does the study make sense?   The researchers should be able to explain a theory of why a particular food is healthy.  We know from heart health studies that too much animal fat is not a good thing.  This study looked at American girls, and the vegetable protein they consumed the most was peanut butter.  The study also found a link with other vegetable proteins like bean, lentils, or corn and better breast health, but apparently the amount of these foods consumed by the girls was too low to be statistically significant.  One might expect that if this study had been done in India, the girls with the highest consumption of lentils might have had the lowest risk of breast disease.  

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    When an American girl makes a PB&J, she isn’t having a corned beef or grilled cheese sandwich, so the amount of animal fat and protein she has is lower.  This study fits with other studies that are finding that nuts, beans, and other plant proteins are healthy foods, so a connection with breast health is not surprising.  This is especially reasonable since there are concerns that the hormones given to animals affect the humans who consume meat and dairy products, perhaps even leading to early puberty, which is known to be a breast cancer risk.  Still there may be more factors involved than diet.  Were the girls who ate more nuts more health conscious in other ways?  Perhaps they exercised more, or watched their weight more carefully.  A connection between Event A (eating peanut butter) and Event B (a lower rate of breast disease) does not prove that Event A is the cause of Event B.


    Are the claims reasonable?  You should be skeptical about any food that purports to prevent or cure cancer.  I frequently see ads that claim that a particular food is a miracle food, but there is no such thing.  This study is modest in its claims.  It concludes, “. . . consumption of vegetable protein, fat, peanut butter, or nuts by older girls may help reduce their risk of BBD [benign breast disease] as young women.”  While benign breast disease is a risk factor for breast cancer, the study doesn’t leap to a “Peanuts-Cure-Breast-Cancer!” conclusion.


    Can you use the information in your own diet?  When the study is about a food that you hate, or a food that is expensive or hard to obtain, you are not likely to use it, no matter how good it is for you.  I’ve known women who have turned their diet upside down and inside out after a cancer diagnosis, but they are rarely able to sustain drastic changes for very long.  Most of us can find ways to add vegetable proteins and fats to what we eat.  If you or your daughter is allergic to peanuts and other nuts, you may decide to focus on the idea of adding beans to your diet, or you might substitute olive oil for butter when sautéing vegetables. 


    Before I could finish writing this article this morning, I went out to breakfast with a friend at our neighborhood coffee shop.  Guess what I had on my bagel instead of cream cheese?  


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    Barrett, A. “The Controversy over added hormones in meat and dairy.” NYU Langone Medical Center.  2012.  Accessed Feb. 15, 2014

    Frazier, A., Colditz, G. et al. Vegetable protein and vegetable fat intakes in pre-adolescent and adolescent girls, and risk for benign breast disease in young women. Breast Cancer Research and Treatment September 2013, Volume 141, Issue 2.  Accessed Feb. 15, 2014

    Paddock, C. “Breast health linked to eating peanut butter and nuts.”  Medical News Today.  Sept. 27, 2013.  Accessed Feb. 15, 2014

Published On: February 15, 2014