Fat and Hormonal Effects

The Physicians Committee

Fat and Hormonal Effects

Several of the most common forms of cancer are linked to sex hormones. This is true of cancers of the breast, uterus, ovary, prostate, and perhaps other sites. The amount of hormones in our bodies and their actions are determined, in large part, by the foods we eat.

Fatty foods affect the body in many ways and have a strong influence on hormonal activity in the body. First, high-fat diets increase the amount of estrogens, the female sex hormones, in the blood. It is known that many breast tumors are "fueled" by estrogens. Estrogens are normal and essential hormones for both women and men, but the more estrogen there is, the greater the driving force behind some kinds of breast cancer. On high-fat diets, estrogen levels increase. When women adopt low-fat diets, their estrogen levels drop noticeably in a very short time.31-33 Vegetarians have significantly lower estrogen levels than non-vegetarians, in part because of the lower fat content of their diet. In addition, they have more of certain carrier molecules, called sex hormone binding globulin, which circulate in the blood and have the job of holding onto sex hormones, keeping them inactive until they are needed. Fatty foods do the reverse: they increase estrogens and reduce the amount of the carrier molecule that is supposed to keep estrogens in check.

Animal fats are apparently a bigger problem than vegetable oils. Paulo Toniolo of the New York University Center compared the diets of 250 women with breast cancer to 499 women without cancer from the same province in northwestern Italy. The two groups ate about the same amount of olive oil and carbohydrates. But what made the cancer patients different was that they had eaten more meat, cheese, butter, and milk. Women who consumed more animal products had as much as three times the cancer risk of other women.34

Even though cross-cultural comparisons have pointed a finger at animal fat as the principal problem, vegetable oil is also under some suspicion. Vegetable oils can probably affect estrogen levels and, as we will see below, increase the production of cancer-causing free radicals. So it is no good just replacing fried chicken with fried onion rings. The best diet eliminates animal products and keeps vegetable oils to a minimum as well.

Certain foods have special benefits. Soybeans, for example, contain natural compounds, called phytoestrogens. These are very weak estrogens which can occupy the estrogen receptors on breast cells, displacing normal estrogens. The result is less estrogen stimulation of each cell. Soybeans are a mainstay of Asian diets and may be an additional reason why these countries have low cancer rates.35

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