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A new study looking at diet and health data from more than 44,000 women found that those who reported consuming the highest amount of fiber during high school, about 28 grams a day, had a significantly lower risk of breast cancer before menopause compared with those who said they ate less than 15 grams a day.
The researchers from Harvard’s T.H. Chan School of Public Health, whose study appears in the journal Pediatrics, analyzed data from a large, ongoing, national study of nurses focused on factors that influence women’s health.
“The results of this study emphasize the role of an early life high-fiber diet on prevention of breast cancer in later life. High consumption of foods rich in fiber such as fruits, vegetables and whole grains in early life may help to reduce breast cancer incidence,” lead author Maryam Farvid, a visiting scientist at Harvard, told CBS News.
The findings showed that breast cancer risk was 12 to 19 percent lower among women who ate more dietary fiber in their youth, depending on how much more they ate. Eating more fiber during adolescence was linked to a 16 percent lower risk of breast cancer overall, and a 24 percent lower risk of breast cancer before menopause.
Farvid said the findings show that each additional 10 grams per day increase in fiber intake during adolescence reduced the risk of breast cancer by 14 percent.
“Having the recommended 25 to 30 grams of fiber daily would decrease the risk by 30 percent and potentially even greater with higher fiber intake,” Farvid said. “Women are doing themselves a huge favor in terms of breast cancer prevention if they increase the amount of dietary fiber intake earlier in life rather than later.”
Healthy high-fiber food choices include apples, pears, raspberries, artichokes, green peas, broccoli, split peas, lentils, beans, whole wheat pasta, whole grain bread, brown rice, bran flakes, and oatmeal.
Why would these foods have such an impact?
In an accompanying editorial, Duke University Medical Center’s Dr. Kimberly Blackwell said there’s longstanding evidence that dietary fiber may cut down on circulating estrogen levels through changes in the gut microbiome.
She said that recently more evidence has come to light suggesting a relationship between dietary fiber and breast cancer risk, and that eating more fiber would be a simple way to reduce risk.
One weakness she pointed out in the study is that the women were asked to recall details about their adolescent diet when they were in their 30s and 40s. Nevertheless, Blackwell said, “It is reasonable for pediatricians to encourage a high-fiber diet and include decreasing breast cancer risk as one of the potential benefits.”
Dr. Stephanie Bernik, chief of surgical oncology at Lenox Hill Hospital, in New York, told CBS News, “It lends support to the fact that we need to encourage people to start healthy habits earlier on.”
Dr. Deanna Attai, assistant clinical professor of surgery at the David Geffen School of Medicine at the University of California Los Angeles, said that while it’s an observational study, not a clinical intervention, its larger point about diet and health is important.
“The sexy headline is eat this and you’ll have a lower risk of breast cancer, but I’d shift the focus to, eat more fiber because it’s better for you and you’ll be a healthier person and you’re less likely to be obese and have chronic inflammation and other things that will reduce your risk for heart disease and cancer along the way,” said Attai.
She added, “The message is a good one as far as increasing fiber, but it also has to be put in perspective. This is just one mechanism by which we can reduce risk and it does warrant further study.”
This story focuses on a recent study from the journal Pediatrics, which found that women who ate more dietary fiber during adolescence and young adulthood had a lower risk of developing breast cancer. The story does a nice job of addressing the strengths and weaknesses of the study — as does a competing story we reviewed from NPR. However, as with the NPR story, this story would have been even better if it had explained that the 16% lower risk of cancer was a relative risk reduction, and that the absolute difference was a mere 0.2 percentage point. Moreover, the story would have been improved by the use of more appropriate language in the headline — this type of study can’t tell us whether fiber “may help cut breast cancer risk,” and the story should’ve reflected that uncertainty in its headline description.
Why This Matters
According to the CDC, breast cancer is the most common cancer in women in the United States, with more than 224,000 new cases reported in 2012 alone. Findings that early life experiences (diet and behavior) affect later chance of malignancy and heart disease are beginning to emerge. This should be intuitive, but is hard to show in studies because of the very long periods between the early life experiences and later health outcomes.
There are a lot of foods you can eat to increase your dietary intake of fiber, and the story lists apples, pears, raspberries, artichokes, green peas, broccoli, split peas, lentils, beans, whole wheat pasta, whole grain bread, brown rice, bran flakes, and oatmeal. We’ll rate the story Not Applicable since most people are aware of the cost of the foods mentioned. However, we wish the story had discussed the fact that many of these healthy sources of dietary fiber are either unaffordable or unavailable to many young women, particularly those from low-income backgrounds who live in food deserts. As we noted with the NPR story, we recognize that this is a story about breast cancer risk, not about food availability. However, if a story focuses on the importance of a healthy diet, there should ideally be at least a brief acknowledgment that many people do not have access to the foods that make up a healthy diet.
We recognize that it would be challenging for any journalist covering this story to report on the absolute risks seen in the study. The study does not report absolute risks, although it is possible to calculate them based on the data provided. One could look at the number of cases in each quintile of dietary fiber (found in Table 2) and divide that by the number of people in each quintile (which is found in Table 1). There are several steps involved, but for the example of early adulthood dietary fiber and breast cancer risk in this cohort, you could do the following calculation:
– 613 cases in quintile 1 / 18,364 women in quintile 1 = 3.3% later developed breast cancer (pre or post menopause)
.– 567 cases in quintile 5/ 18,167 women in quintile 5 = 3.1% later developed breast cancer (pre or post menopause).
– The difference is 0.2 percentage point, which is quite a small absolute risk reduction.
When absolute risk numbers aren’t reported in a study, we think journalists should press their sources to provide these numbers so that they can be disseminated to the public. The issue of absolute risk reduction is key to helping readers understand the impact of changing dietary behaviors. We think it’s important enough to rate any story Not Satisfactory when these numbers aren’t provided.
The story offers a brief description of the study, and notes that it is an observational study rather than a clinical study. It also gets high marks for highlighting the fact that the study required women to “recall details about their adolescent diet when they were in their 30s and 40s.” (Though, worth noting, that sentence should say “…in their 30s, 40s and 50s.”)
The story incorporates input from multiple independent sources who provide valuable perspective on the research. We particularly liked this line from Dr. Deanna Attai. (Full disclosure: Dr. Attai is also a reviewer for HealthNewsReview.org.)
“The sexy headline is eat this and you’ll have a lower risk of breast cancer, but I’d shift the focus to, eat more fiber because it’s better for you and you’ll be a healthier person and you’re less likely to be obese and have chronic inflammation and other things that will reduce your risk for heart disease and cancer along the way,”
And while the story does not address conflicts of interest, there do not appear to be any conflicts of interest to report.
The story does note that increasing dietary fiber consumption “is just one mechanism by which we can reduce risk,” but it doesn’t mention any of the other mechanisms. Exercise, maintaining a healthy weight, getting sufficient sleep and limiting alcohol consumption can also help reduce breast cancer risk.
This study is not the first to examine the possible link between dietary fiber and breast cancer risk. For example, a 2012 paper in the Annals of Oncology looked at 16 earlier studies on dietary fiber and breast cancer risk. There is no discussion of this earlier work, or how the new paper builds on or diverges from the previous research.
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