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Can Fiber Really Cut Breast Cancer Risk?
Harvard study sees a lifelong high-fiber habit as a particularly powerful ally

02/25/2016 By Macaela McKenzie and Craig Weatherby
One in every eight American women will battle breast cancer during her lifetime.
 
Breast cancer rates are not on the rise ... except among African-American women.
 
And few people know that far more women die from heart disease than breast cancer.
 
Nonetheless, several aspects of breast cancer combine to make it a particular focus of fear and engagement.
 
One of these fear factors is the wide range of ages affected by the risk for breast cancer.
 
While two of three cases occur in women aged 55 or older, women under 45 are at significant risk.
 
Harvard study pinpoints fiber as a key ally
New findings suggest that high-fiber diets may be one the few ways women can reduce their risk.
 
But the findings from Harvard suggest that it's critical to start a high-fiber habit early, and keep it up lifelong.
 
The Boston-based researchers analyzed data collected from women participating in the Nurses' Health Study II.
 
That landmark study massive, lengthy study – which began in 1991 – involved 90,534 women aged between 27 and 44.
 
The participating women completed questionnaires about their diets and their health status at the start of the study, and every four years thereafter.
 
In 1998, a subgroup of participants – 44,263 in all – were asked to recall their diets during high school years, and their responses provided the basis for the new analysis.
 
How much was risk reduced, and how much fiber was needed?
The Harvard team's analysis of the women's self-reported diet and health data produced several conclusions:
  • The apparent protective effects of fiber were linked most strongly to diets rich in both fruits and vegetables. 
  • Women eating high-fiber diets from their teen years on were 12-19 percent less likely to develop breast cancer at any time.
  • Feasting on fiber early in life may lower overall risk by 16 percent, and the risk of pre-menopausal breast cancer by 24 percent.
  • For each additional 10 grams (1/3 ounce) of fruit and vegetable fiber a young woman eats daily, her lifelong risk for breast cancer drops by 13 percent.
To put their last finding in practical terms, you'd get 10 grams of fiber by eating one apple and one cup of cauliflower.
 
Visiting Iranian scientist Maryam Farvid, Ph.D. – the study's lead author – said their findings suggest that fiber is one of the very few "potentially modifiable risk factors for pre-menopausal breast cancer."
 
Why fiber seems to help prevent breast cancer
What's the link between fiber intake and breast cancer risk?
 
Fiber-rich foods lower estrogen levels, and high estrogen levels are associated with greater risk for developing the deadly disease.
 
Chronically high blood sugar levels have long been linked to increased cancer risk – including breast cancer – and high-fiber diets help stabilize blood sugar levels.
 
Coincidentally, a study published last month by researchers from the M.D. Anderson Cancer Center found that feeding mice an amount of sugar proportional to the typical American diet raised the animals' risk for breast cancer and its spread (metastasis).
 
The M.D. Anderson study pinpointed fructose as the type of sugar responsible. And it didn't matter whether the mice were fed cane sugar or corn syrup (both sweeteners are half fructose and half glucose).
 
Prior studies bolster Harvard findings
The first studies linking higher fiber intakes to lower breast cancer risk surfaced in the 1990s.
 
A small 1994 study found that dietary fiber seem to exert protective effects against breast cancer among Australian women … though the results focused mostly on post-menopausal women.
 
Then, a 2012 review covering 16 studies found that fiber's apparent anti-breast-cancer effects apply to all of the common types … including fruit fiber, vegetable fiber, soluble fiber (as in beans), and insoluble fiber (as in whole grains).
 
But the authors of another evidence review – published the same year by British researchers – concluded that not all types of fiber are equally effective.
 
The British team arrived at two conclusions:
  • Diets that included ample fiber from fruits or from both fruits and veggies reduce the risk of breast cancer.
  • Vegetables alone do not exert significant protective effects … a finding that contradicts the results of the recent study from Harvard.
So what's a woman to do, exactly?
 
First and foremost, it's important to eat plenty of fiber, which is found only in plant foods.
 
But it pays to mix things up, and not focus on any one type of fiber.
 
Make sure you get a healthy mix of high-fiber fruits (like apples, bananas and raspberries), veggies (like cauliflower, broccoli and beans) and whole grains.
 
 
Sources
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