During and after menopause women experience many physical and emotional changes. Unfortunately, along with the physical changes comes an increased risk of heart disease, osteoporosis, and breast cancer. This is partly due to changes in estrogen production that occur during menopause, and also to the types of food eaten in the years leading up to and including menopause. In other words, what we eat affects our risk of getting certain diseases.

Reducing the risks of breast cancer and easing the symptoms of menopause

Because the risk of getting breast cancer is related to a woman's lifetime exposure to the estrogen circulating in her body, many studies have looked at ways of lowering the estrogen that is thought to help cancer cells grow. For example, breast cancer cells have estrogen receptors on their surface where estrogen molecules can "land" and in some way, help the growth of these cells.

An area of expanding growth and interest is the role that foods with natural estrogens can play in reducing the risk of getting breast cancer and in easing the symptoms of menopause. These natural estrogens that occur in plants are called phytoestrogens and are found naturally in a wide variety of foods, or they can be made by bacteria in the intestinal tract.

Types of phytoestrogens

There are 3 classes of phytoestrogens: lignans, isoflavones, and coumestans. All 3 can be obtained from a wide variety of foods, particularly fruits and vegetables.

Lignan is found in the cell walls of plants. When plant lignans reach the bacteria in the intestines, the bacteria break down the plant lignans to produce 2 lignans that the human body can use. These are called enterolactone and enterodiol.

The following is a list of human lignans produced from different foods (in descending order of lignan content):

  • flaxseed meal
  • flaxseed flour
  • lentils
  • dried seaweed
  • soybeans
  • oat bran
  • kidney beans
  • wheat
  • garlic
  • squash
  • asparagus
  • pears
  • rye
  • plums

Isoflavones have been the most studied among the 3 classes of phytoestrogens. There are 2 major forms of isoflavones: genistein and daidzein. Both of these are found mostly in soybeans and soy products.

The following is a list of isoflavones (in descending order of isoflavone content):

  • roasted soybeans
  • textured vegetable protein
  • green soybean
  • soy flour
  • tempeh
  • tofu
  • soy hot dog
  • soy noodle (dried)
  • peas
  • beans
  • red clover
  • herbs

Coumestans, such as coumestrol, are found in a variety of plants. Their effects on health have been studied the least among the 3 classes of phytoestrogens.

The following is a list of food sources high in coumestans:

  • alfalfa
  • clover sprouts
  • lima beans
  • pinto beans
  • split peas

It is not known whether phytoestrogens have an effect on the risk of breast cancer. However, studies have shown that phytoestrogens may promote breast cancer cells to grow in people with estrogen-sensitive breast cancer. Therefore, supplements containing high amounts of phytoestrogens are not recommended for people with estrogen-positive breast cancer.

Because phytoestrogens are 1,000 times weaker than the body's own estrogen, it was thought that when they occupy the space on the cell there is less estrogen for use by the cancer cell. In other words, because they are weaker, they do not give the cancer cell what it needs to grow. In this way, phytoestrogens may slow or prevent the growth of breast cancer cells. However, studies have not shown a decrease or increase in the risk of breast cancer in women who consumed phytoestrogens as part of their diet.

Phytoestrogens have been investigated for their ability to lessen the symptoms of menopause. As the body's own estrogen production declines, the weaker plant estrogens may provide a source of estrogen to the body. However, studies overall have not been able to link high phytoestrogen intake with the relief of menopausal symptoms.

There are no daily recommended amounts for dietary phytoestrogens since current studies have not found an impact on breast cancer risk reduction or menopausal symptoms linked to its use. The best strategy may be to eat a wide variety of foods as recommended in Canada's Food Guide to meet your dietary needs for overall health.

Ingrid Verduyn, RDN 
in association with the MediResource Clinical Team