Fiber
Inadequate fiber consumption may also be a risk factor for breast cancer. Researchers at Yale University and elsewhere found that premenopausal women who ate more than about six grams of fiber a day (the equivalent of about a single cup of black beans) had 62 percent lower odds of breast cancer compared with women who consumed less than around four grams a day. Fiber’s benefits appeared more pronounced for estrogen-receptor-negative breast tumors, which are harder to treat: Premenopausal women on a higher fiber diet had 85 percent lower odds of that type of breast cancer.
How did the researchers arrive at these figures? The Yale study was what’s called a case controlled study. Scientists compared the past diets of women who had breast cancer (the cases) to the past diets of similar women who did not have breast cancer (the controls) to try to tease out if there is something distinctive about the eating habits of women who developed the disease. The researchers found that certain women with breast cancer reported eating significantly less soluble fiber on average than the cancer-free women. Hence, soluble fiber may be protective.
The women in the study weren’t getting their fiber from supplements, though; they were getting it from food. But this could mean that eating more fiber is merely evidence that the cancer-free (so far) women are eating more plant foods, the only place fiber is found naturally. Therefore, fiber itself might not be the active ingredient. Maybe there’s something else protective in the plant foods. “On the other hand,” noted the researchers, “an increased consumption of fiber from foods of plant origin … may reflect a reduced consumption of foods of animal origin … “ In other words, maybe it’s not what they were eating more of but what they were eating less of. The reason high fiber intake is associated with less breast cancer may be because of more beans – or less bologna.
Either way an analysis of a dozen other breast cancer case-controlled studies reported similar findings, with lower breast cancer risk associated with indicators of fruit and vegetable intake, such as vitamin C intake, and higher breast cancer risk associated with higher saturated-fat intake (an indicator of meat, dairy and processed food intake). And according to these studies, the more whole plant foods you eat, the better it is for your health: Every twenty grams of fiber intake per day was associated with a 15 percent lower risk of breast cancer.
One problem with case-control studies, though, is that they rely on people’s memory of what they’ve been eating, potentially introducing what’s known as “recall bias.” For example, if people with cancer are more likely to selectively remember more of the unhealthy things they ate, this skewed recall could artificially inflate the correlation between eating certain foods and cancer. Prospective cohort studies avoid this problem by following a group (cohort) of healthy women and their diets forward (prospectively) in time to see who gets cancer and who doesn’t. A compilation of ten such prospective cohort studies on breast cancer and fiber intake came up with similar results to the dozen case-control studies mentioned above, a 14 percent lower risk of breast cancer for every twenty grams of fiber intake per day. The relationship between more fiber and less breast cancer may not be a straight line, though. Breast cancer may not significantly fall until at least twenty-five grams of fiber a day is reached.
Unfortunately, the average American woman appears to eat less than fifteen grams of fiber per day – only about half the minimum daily recommendation. Even the average vegetarian in the United States may only get about twenty grams daily. Healthier vegetarians, though, may average thirty-seven grams a day, and vegans forty-six grams daily. Meanwhile, the whole food, plant based diet used therapeutically to reverse chronic disease contain upward of sixty grams of fiber.