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How big is the reduction in breast cancer risk linked to a high-fiber diet? 16 percent or 0.2 percentage point?

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These fiber-rich foods altogether offer about 28.5 grams, or a woman's daily recommended intake. Clockwise from top left: one pear, 6 grams of fiber; medium artichoke, 7 grams; 1 ounce of popcorn, 3.5 grams; 1 medium sweet potato, 4 grams; 1 cup edamame, 8 grams.

These fiber-rich foods altogether offer about 28.5 grams, or a woman’s daily recommended intake. Clockwise from top left: one pear, 6 grams of fiber; medium artichoke, 7 grams; 1 ounce of popcorn, 3.5 grams; 1 medium sweet potato, 4 grams; 1 cup edamame, 8 grams.

Morgan McCloy/NPR

If the advice to eat more fiber seems easy to ignore, you’re not alone. Most Americans don’t get the 25 to 38 grams a day that recommended, depending on age and gender.

But if you’re skimping on fiber, the health stakes are high, especially if you’re a teenage girl.

A study published Monday in the journal Pediatrics concludes that eating lots of fiber-rich foods during high school years may significantly reduce a woman’s risk of developing breast cancer.

The findings are based on a long-term study of 44,000 women who were surveyed about their eating habits in high school. The women also completed detailed questionnaires about their dietary habits every four years.

The researchers found that women who consumed high levels of fiber (28 grams per day, on average) had a 24 percent lower risk of developing breast cancer before menopause compared to women who ate low levels of fiber (14 grams per day, on average). For the women on the high-fiber diet, the lifetime risk of developing breast cancer was also cut by 16 percent.

Of course, the idea that high-fiber diets can help keep us healthy is not new. It’s well-known that fiber can prevent constipation and keep the bowel moving by making stools bulkier and absorbing water. Prior studies have shown dietary fiber can protect against colorectal cancer and may lower the risk of diabetes and heart disease. There’s also a growing body of evidence linking fiber to weight management.

This new study provides some evidence of yet another potential benefit.

“This is a really important study … [suggesting] that the more fiber you eat during your high school years, the lower your risk is in developing breast cancer,” saysKimberly Blackwell, a breast cancer specialist at the Duke Cancer Center.

In a commentary accompanying the study in Pediatrics, Blackwell writes, “There is longstanding evidence that dietary fibers may reduce circulating estrogen levels.” And this may help explain the reduced risk of breast cancer.

The authors point to other possible explanations, too. For instance, high-fiber diets may reduce the risk of breast cancer through improving insulin sensitivity, since fiber can slow down the absorption of sugars and help keep blood sugar levels more stable.

Farvid says the influence of fiber on cancer risk may be time-sensitive. Adolescence is “a period when breast cancer risk factors appear to be particularly important,” saysMaryam Farvid, a fellow at the Harvard School of Public Health who is lead author of the study.

One limitation of this new study is that is relies on data from women who had to recall what they ate during high school. They were in their 30s and 40 when asked, so there could be “recall bias” — the women’s memories may be foggy.

“The recollection of dietary habits more than a decade earlier must be questioned,” writes Blackwell. On the other hand, she says, “people’s dietary habits don’t really change a lot … In general, what you eat as a teenager is really formative as to what you eat later in life.”

So, how might the message of this new study linking high-fiber diets to a lower risk of breast cancer be communicated to teenagers?

This is a question Kristi King, a dietician at Texas Children’s Hospital, has thought about a lot.

She says it can be hard to get the attention of teenagers about healthy eating. “Unfortunately for teenagers, they’re [into] instant gratification,” and they’re not necessarily focused on how their actions today will influence their future health, she says.

But, she says, explaining that dietary choices may influence their risk of breast cancer may grab their attention. “Most teenage girls do know someone that has been affected by breast cancer,” says King. “So, I feel like that touches a nerve with them.”

Given the known benefits of high-fiber diets and the growing evidence that fiber may play a role in preventing disease, the government’s Dietary Guidelines for Americans also say most people need to consume more.

Women are advised to consume 25 grams a day. Men are advised to consume 38 grams a day.

So, how best to reach these targets? “Add fiber at each meal,” says King in the form of fuits, vegetables, whole grains, beans, nuts or seeds. Pears are a great bet with 7 grams of fiber apiece.

And check out fiber-rich snacks, like popcorn and edamame.

A Diet High In Fiber May Help Protect Against Breast Cancer

Our Review Summary

iStock_000019323234_SmallThis 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 CBS. However, the story would have been even better if it had used more appropriate language in the headline. This type of study can’t prove cause and effect, and so it can’t really tell us whether fiber “may help protect against breast cancer.” The story also should’ve tried to give readers a sense of the absolute risk reduction seen in those who ate more fiber. While the story reports a 16% lower lifetime risk in the high fiber consumers, this is a relative risk reduction that we believe is misleading. Our calculations suggest that the absolute rate of breast cancer was 3.3% for the lowest fiber consumers vs. 3.1% for the highest fiber consumers, a mere 0.2 percentage point difference.


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. Research findings that identify new ways to reduce the incidence of breast cancer are newsworthy, particularly when the new health measures also have significant ancillary health benefits — as is the case with consuming a fiber-rich diet high in fruits and vegetables.


Does the story adequately discuss the costs of the intervention?

Not Applicable

There are a lot of foods you can eat to increase your dietary intake of fiber, and the story singles out fruits, vegetables, whole grains, beans, nuts and seeds. 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 CBS 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.

Does the story adequately quantify the benefits of the treatment/test/product/procedure?

Not Satisfactory

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’s 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 such results 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.

Does the story adequately explain/quantify the harms of the intervention?

Not Applicable

We’re not aware of any harms from incorporating additional fiber into one’s diet. We’ll rate this not applicable.

Does the story seem to grasp the quality of the evidence?


The story does a good job of describing the study, and also explicitly addresses a potential weakness in the work: namely, that it “relies on data from women who had to recall what they ate during high school. They were in their 30s and 40 when asked, so there could be “recall bias” — the women’s memories may be foggy.” The story would have been even stronger if it had noted that this was an observational study, rather than a clinical study, which means that using causative verbs to describe the results (e.g. fiber “may help protect” against breast cancer) is not justified. Stories on studies like this should always state the dietary element is “associated with” or “linked to” a beneficial outcome.

Does the story commit disease-mongering?

Not Satisfactory

In its second paragraph, the story says “…if you’re skimping on fiber, the health stakes are high, especially if you’re a teenage girl.” That’s scary language. This study is an interesting one, and possibly an important one, but it is also just one study addressing one risk factor for one disease. Granted, breast cancer is a scary disease. But the language here appears to be unduly alarming about the consequences of not eating a fiber-rich diet as a teenager. Also, since the absolute risk reduction is 0.2 percentage point there is no cause for alarm here.

Does the story use independent sources and identify conflicts of interest?


The story only quotes two researchers in regard to the study. One was the study’s lead author, and the other was the author of a commentary on the study that was published in the same issue of Pediatrics. A third source is quoted in regard to what can be done to get teens to eat more fiber, but that source doesn’t address the study in question. We’ll give the story credit for reaching beyond the authors of the study, but we think the story would be much stronger if it had incorporated more expert analysis on the study itself.

Does the story compare the new approach with existing alternatives?

Not Satisfactory

The story doesn’t discuss other risk factors for breast cancer at all, much less other lifestyle choices that can reduce risk, such as maintaining a healthy weight, exercising, limiting alcohol consumption or getting enough sleep. Perspective is needed about ways we can stay healthy overall and reduce later cancer risk.

Does the story establish the availability of the treatment/test/product/procedure?

Not Applicable

There are no new products or services at issue in this story, and we addressed access to healthy foods under “Cost,” so we’ll rate this not applicable.

Does the story establish the true novelty of the approach?

Not Satisfactory

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.

Does the story appear to rely solely or largely on a news release?


The story went well beyond a news release, incorporating significant additional information — particularly in regard to how to communicate the findings to adolescent and young adult women.

Total Score: 3 of 7 Satisfactory


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