A similar story emerges when you look at the research on this disease.
Some researchers think fiber might reduce the risk of breast cancer, perhaps by influencing the body’s hormone production. There were some studies to back this up, including one that found eating a lot of high-fiber foods, especially vegetables, might lower the risk of breast cancer slightly.
But other researchers found no such link, and again, as the number of studies grew, the theory became weaker.
One theory is that fiber might prevent this disease by affecting hormone levels, like with breast cancer.
Other experts think fiber's effect on something called "insulin sensitivity" might play a role. Insulin is a hormone your body makes after you eat. It lets blood sugar enter your cells and be used for energy. When blood sugar levels rise, insulin levels tend to spike. But fiber, especially the soluble kind like oatmeal, can soften this effect by slowing the absorption of sugar in the bloodstream.
The few studies on fiber and prostate cancer are inconclusive, though.
There's just not enough strong evidence to say for sure that fiber protects (or doesn't protect) against breast, prostate, or colon cancer.
But there's plenty of research on how it helps you in other ways. It's best known for keeping your bowel movements regular, and it can also stave off more serious conditions. That includes type 2 diabetes and heart disease.
Fiber helps with losing weight, too -- and staying at a healthy weight is one of the best things you can do to lower your risk for lots of diseases, including cancer.