 A quarter century ago, a theory was put forth as to why those eating plant-based diets have lower cancer rates. Vegetarians have up to three times the level of lignans circulating within their bodies. Thanks to the grains and other plant foods they were eating, these anti-cancer compounds. See, back in 1980, a new compound was described in human urine, a compound X, originally thought to be a new human hormone. But later identified to be from a large group of fiber-associated compounds widely distributed in edible plants, known as lignans. Population studies suggest that high intake reduces breast cancer risk, but where is it found? Seeds, whole grains, vegetables, fruits, berries? And with that kind of list of healthy foods, why isn't this just like the fiber store, where lignan intake is maybe just a surrogate marker for healthy plant food intake? Well, in a Petri dish, lignans do directly suppress the proliferation of breast cancer cells, but only after the plant lignans are converted into human lignans by the good bacteria in our gut. That's why we want to use antibiotics judiciously, because a few days on antibiotics dramatically drops your body's ability to make these anti-cancer compounds from the plants we eat. And it can take weeks for our good bacteria to recover. That's why women with urinary tract infections may be at higher risk for breast cancer, because every time they took a course of antibiotics they may be stymying their good bacteria's ability to take full advantage of all the plants they were eating. Though this remains a little more than a hypothesis or educated guess at this point. This is the National Cancer Institute study that provided the strongest evidence to date that there may indeed be something special about the lignan class of phytonutrients for breast cancer prevention. They took a bunch of young women at high risk for breast cancer, meaning they had a suspicious breast biopsy, showing either pre-cancerous changes or carcinoma in C2, or already had breast cancer in the other breast, and gave them a teaspoon of ground flax seeds every day for a year before getting repeat needle biopsies to see if there were any changes. Yes, there are lignans and, you know, sesame seeds, nuts, whole grains, legumes, certain fruits and veggies, but they're most concentrated in flax seeds. They could have instead asked women to eat 10 cups of strawberries a day for a year, but they'd probably get better compliance with just their teaspoon of ground flax seeds. So what happened by the end of the year? The primary endpoint was the expression of a proliferation biomarker associated with cancer called KI67. In 9 of the 45 women it went up, those in red, but in the other 80% of the women it went down, and overall they found less cellular proliferation in their breast tissue and fewer pre-cancerous changes. For those who don't like the taste of flax seeds, sesame seeds may work just as well. Even though flax seeds have significantly more lignans than sesame, you appear to produce about the same amount of lignans from them, though this was comparing them whole, and when you feed people whole flax seeds, some may not get chewed up and may pass right through you, so, you know, ground flax seed may be the best source overall.