Monounsatured fat can cut in half a woman's risk for breast cancer, according to an article in the January 12, 1998 issue of the American Medical Association's Archives of Internal Medicine.

Alicja Wolk, Ph.D., from Karolinska Institute in Stockholm, Sweden, studied 61,471 women between the ages of 40 and 76 from 1987 to 1990. Data were collected on the participants' eating habits and their other risk factors for breast cancer. The Swedish Cancer Registry reported who among the group developed breast cancer during the study period.

The researchers found that monounsaturated fat reduced the risk of breast cancer by 45%, polyunsaturated fat increased the risk by 69% and saturated fat had no association.

There is growing evidence that monounsaturated fat might be protective against breast cancer. Many of the studies have focused on olive oil and the Mediterranean diet and found a decreased risk of breast cancer. This study is important because it found that the protective benefit lies with monounsaturated fats as a category, rather than specifically with olive oil.

While the study doesn't specifically mention it, peanut oil has 6.3g of monounsaturated fat (4.3g polyunsaturated) compared to 10g monounsaturated (1.1g polyunsaturated) in olive oil and 8g monounsaturated (4g polyunsaturated) in canola oil.