Cancer, Hormones & Weight
by Connie Guttersen, RD PhD,
author of the Sonoma Diet
The estimated 203,500 new cases of breast cancer expected to occur among US women this year is staggering. Even more devastating is that 40,000 women are not expected to survive this disease. Scientific experts relate the risk of breast cancer to obesity, insulin resistance and hormones. Hormones, such as estrogen, testosterone and insulin, plus growth factors, are of special interest since they appear to play a promotional role in the development of breast cancer. Women with higher levels of these hormones appear to have a higher incidence of breast cancer. Hormones, height, weight, diet, exercise and family history have all been found to influence the age of puberty. Since rapid growth rate leads to an earlier age at puberty and menarche, it appears that the younger a woman's age at menarche, the higher her risks of breast cancer.
Among post-menopausal women, both obesity and adult weight gain have been associated with increase risk for breast cancer. In addition to excessive body weight, there is evidence that greater height is independently associated with an increased risk of breast cancer. A recent study by Petrelli et al, confirmed an increased breast cancer mortality with increasing body height up to 66 inches in women as compared to those women less than 60 inches.  This study also confirmed a breast cancer death rate which was three times higher among women with a body mass index (BMI) greater than 40 as compared with those women whose a body mass index was less than or equal to 18.5. Women of short stature may have been exposed to lower levels of insulin like growth factor, IGF-1. This hormone, IGF-1, is a potent mitogen for breast cancer cells when examined in vitro studies or laboratory studies. The Harvard-based Nurses Health Study confirmed that higher levels of IGF-1 in blood are found in women with breast cancer. Scientists are now investigating if IGF-1 is just present at higher levels in breast cancer patients or if it has a role in increasing the risk for the disease.
 Cancer & Obesity
This year's annual meeting of the American Association for Cancer Research in San Francisco suggests there may be more than one reason why obesity can increase a woman's risk of breast cancer after menopause. Previous research has confirmed that factors related to being overweight such as high estrogen levels and insulin resistance are links to breast cancer. EPA and DHA are derived from omega 3 rather than the omega 6 derivative, arachidonic acid. EPA and DHA are important for proper communication between the neurotransmitters in the brain and are necessary for structural and functional roles in the brain cells. Omega 3 fatty acids also affect cellular function.
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Diet and Phytoestrogens
A growing area of interest among nutritionists lies in the discussion of phytoestrogens. Phytoestrogens are a group of chemicals found in plants that can act like the hormone estrogen. They are found in more than 300 types of different foods such as soybeans, tofu, whole grains, fruits and vegetables, and certain spices and herbs. Phystoestrogens are quickly broken down in the body and may prevent estrogen levels from increasing in the body, thus offering a protective role. Two major phytoestrogens under study are the isoflavones and the lignans. After consumed, the isoflavones and lignans undergo metabolic conversions in the gut, resulting in the formation of hormone-like compounds, known as phytoestrogens. These weak phytoestrogens bind to estrogen receptors without a pro-carcinogenic effect and at the same time block the binding of more potent estrogens to the site. Phytoestrogens are structurally similar to the potent anti-estrogen tamoxifen, which has been successfully used in breast cancer treatment.
Animals that were given soy phytoestrogens developed fewer breast tumors in many of the studies reviewed. The decrease in the tumor formation was dependent on the age at which the animals were given the soy. Animals given the soy phytoestrogen before sexual maturity had about half as many tumors as animals given a soy phytoestrogen as adults. The results of the case controlled human studies of the connection of eating soy products and breast cancer are conflicting. Some studies have reported no link and others report a decrease in the risk of breast cancer among women eating soy compared to women who did not eat soy. Most of these studies are limited to women from Asia, who may have eaten soy all of their lives and may have other factors contributing to their lower rates of breast cancer. One recent study of Chinese women suggests that eating large amounts of soy during adolescence may reduce the risk of breast cancer. These human epidemiological studies may suggest that the effectiveness of soy may also be related to period of life that when they are eaten. (Looking for new ways to add soy? Try Seared Moroccan Tofu with Olives or Tofu 'n Olive Entrée Loaf.)
There is much to learn about foods containing phytoestrogens or other protective nutrients and their role in breast cancer risk. Women can take the best precaution by eating plenty of fruits, vegetables, whole grains, beans and healthy fats. In addition, it is important to maintain a healthy body weight and active lifestyle. The research continues to come in, but at this stage, diet, lifestyle and regular mammogram exams appear to be the best prevention.
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C-peptide & Insulin Resistance
A new report from the Harvard Nurses Health Study finds an additional marker of breast cancer, a substance known as C-peptide. At elevated levels, C-peptide is a known marker for insulin resistance. Insulin resistance has been previously looked at as a link to breast cancer since insulin can lead to elevated levels of estrogen and IGF-1. In this study of 1200 women, those with the highest levels of C-peptide had a 70% greater risk of breast cancer than those with the lowest level. An additional observation was that the C-peptide levels increased drastically in women with higher body weights. Women who were physically active tended to have lower levels of C-peptide. Only a limited number of epidemiological studies have directly investigated the association of blood insulin and C-peptide with breast cancer risk. One epidemiological study examined the relationship between C-peptide levels and breast cancer risk from participants in the Shanghai breast cancer study. The incidence of breast cancer among women in urban Shanghai has been increasing at an alarming rate. Shanghai's rapid economic development has been accompanied by substantial changes in diet and lifestyle, including increased consumption of animal foods, decreased levels of physical activity and an increasing prevalence of obesity and type II diabetes. The information gathered in this large population based study showed that women who had elevated levels of C-peptide had an increased risk of breast cancer, and that this association was independent of body weight, body fat distribution, and menopausal status.
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Cancer & Diet
As populations move to a more westernized approach of eating, the risk of breast cancer appears to also increase. This is even more evident in the many studies that confirm a protective influence from the Mediterranean diet. The consumption of olives and olive oil may be associated with a significant decrease in the risk of breast cancer.
These studies were done in Mediterranean countries where women may have a total fat intake of as much as 40% of their total calories. This total fat intake is comparable to or even higher than that seen in the US. However, the incidence of breast cancer is lower in the Mediterranean countries as compared to the US. An explanation for this may be that olives and olive oil contain phenolic and flavonoid compounds, along with other antioxidants that are not present in other common sources of monounsaturated fat. Also, in recognition of the role insulin resistance may have in the promotion of breast cancer, the substantial information supporting the protective effects of monounsaturated fats against insulin resistance may be another protective feature of olive oil and olives.
A recent study by Trichopoulou, published in Cancer Epidemiology, Biomarkers and Prevention, confirmed a lower incidence of cancer, particularly for the breast, colon and prostate in the Mediterranean countries. These forms of cancer are linked to dietary factors, such as the amount of fruits and vegetables, as well as the amount of red meat consumed. The current study calculated that up to 25% of the incidence of colorectal cancer, 15% of breast cancer, and 10% of prostate cancer could be prevented if populations of highly developed western countries would shift to the traditional healthy Mediterranean diet. In conclusion, the Mediterranean diet could reduce the overall incidence of cancer in Northern Europe and North America by up to 10%.
(For recipes, Download Pasta, Vegetarian, and Tapas recipe flyers.)
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