Oats (Avena sativa) are an excellent source of avenacosides, avenanthramides and manganese, and a very good source of dietary fiber, thiamin (vitamin B1) and zinc. Oats also incorporate some ferulic acid, iron and melatonin. Avenanthramides, polyphenols found only in oats, have been shown to exhibit anti-inflammatory and anti-cancer properties, as well as anti-itch activity in the skin.
Consumption of oats or β-glucan (the main soluble fiber in oats) has been shown to reduce cholesterol (thereby reducing the risk of heart diease), improve colon health, and reduce high blood pressure. β-Glucan extracts have also been reported to reduce tumor cell proliferation.
Whole grain consumption has also been shown to be associated with greater insulin sensitivity and lower body mass index in adolescents, especially among the heaviest. A diet containing 10% oat lipids was found to reduce the incidence and size of carcinogen-induced rat liver tumors in one study. In addition, high consumption of oats has been reported to be associated with lower risk of colon cancer.

Breast cancer-related effects of eating oats

High intake of oats and dietary fiber have both been found to be associated with reduced risk of breast cancer. Oats are not estrogenic. Oat avenanthramides have been reported to have anti-breast cancer activities.

Oats in diet

One Finnish study reported that women with persistent high consumption of oatmeal during adolescence and midlife had a reduced risk of breast cancer in old age. A Danish study found that high consumption of oats (oatmeal, muesli) before diagnosis was associated with lower all-cause mortality in women with breast cancer. However, not all studies have found a link between oat intake and reduced breast cancer risk or mortality.

Avenanthramides

Oats are the only foods incorporating avenanthramides, a group of polyphenols with powerful anti-inflammatory, antiproliferative, and anti-irritant activities (which gives them a role in some topical products designed to reduce radiotherapy-induced skin reactions).
Most of the research concerning avenanthramides and cancer have focused on demonstrating their effectiveness in inhibiting proliferation, inducing programmed cell death, and reducing migration of colon cancer cells, without harming normal colon cells. However, several avenanthramides were shown to induced cytotoxic effects in triple negative (ER-/PR-/HER2-) breast cancer cells in a time- and dose-dependent manner in one study. Another study found that a synthetic analog to a naturally occurring avenanthramide suppressed cell invasion pathways in hormone receptor positive (ER+/PR+) breast cancer cells.

Dietary fiber

Oats incorporate both soluble and insoluble fiber in approximately equal portions. Soluble fibers (pectins, gums, mucilages) dissolve in water and form a gel, which slows digestion. Insoluble fibers (the cellulose and lignins contributing to the rigidity of plant cell walls) do not dissolve in water; they add bulk to the diet and speed up the passage of food and waste.
Diets rich in whole grains and/or soluble fiber have been found to be protective against breast cancer in some studies. Generally speaking, this protective effect appears to be derived from the following factors:
  • Consumption of fiber increases bowel motility, which has been linked to lower breast cancer risk since it increases estrogen excretion.
  • High fiber intake reduces serum cholesterol levels. There is some evidence that high cholesterol promotes breast cancer.
  • Diets high in fiber reduce circulating C-reactive protein (CRP), a marker of inflammation. Inflammation is thought to increase breast cancer risk and worsen its subsequent prognosis.
  • Fiber intake reduces weight gain for similar levels of calorie intake. Overweight postmenopausal women are at increased risk of breast cancer and recurrence compared to normal weight women.
  • A high intake of dietary fiber, particularly soluble fiber, improves blood sugar control and reduces excess circulating insulin (hyperinsulinemia) in patients with type 2 diabetes. Hyperinsulinemia is associated with increased risk of breast cancer and its recurrence.

Selecting oat products

Since a variety of foods are available that can provide the anti-cancer benefits of dietary fiber, we focus below on identifying the oat-based foods with the highest avenanthramides levels. Avenanthramides are found in the groats, bran, and outer layers of the oat kernel. Oats are consumed primarily as oatmeal, breakfast cereal, granola, and baked goods such as oatmeal cookies. Note that sweetened oat products such as granola can have high cancer-promoting sugar levels and should be limited.
Whole oats are best
Oat groats are whole oats that have been hulled to remove their inedible hulls, leaving the intact germ, endosperm, and bran. Steel-cut oats are groats that have been cut into two or three pieces. Rolled oats are made by steaming oat groats and then rolling or crushing them into flakes and lightly toasting them. Steaming and processing oat groats has been shown to result in modest to moderate loss of avenanthramides. Oat groats and steel-cut oats are the best choices, followed by oatmeal. Instant oatmeal is not recommended since the oat groats are steamed for a longer period, resulting in greater loss of avenanthramides.
Other oat products have lower avenanthramides content
Generally speaking, oat milk has a more favorable anti-cancer profile than almond milk or soy milk, but its avenanthramides content is lower than that of whole oat products. Dry boxed oat-based breakfast cereals have far lower avenanthramides content than whole oat products.
Below are links to recent studies concerning this food and its components. For a more complete list of studies, please click on oats.