The power of pretty colors

Did you know . . .

that certain foods and dietary habits have been linked to reduced risk of breast cancer recurrence?  In this series of articles, we will review the current literature on diet and breast cancer.


The power of pretty colors (Part 1)

From ancient history, we have reports of the healing power of plants.  The Ayurvedic tradition, the oldest recorded medical treatments, have long used diet as an important component of healing and wellness.  Cato, of ancient Rome, writes of using cabbage leaves to heal breast ulcers (probably breast cancer).  Studies of Japanese women emigrating to North America show startling increases in the rate of breast cancer incidence when the Japanese diet is changed to an American diet.  Indeed, cancer rates are significantly higher in industrialized regions with their attendant “fast food” diets.


But does diet play a role in breast cancer recurrence?  Is there anything specific that we, as breast cancer survivors, should be doing when it comes to how and what we eat?  The Women’s Healthy Eating and Living study (WHEL), was designed to address this question by looking for interactions between diet, exercise, and breast cancer outcomes (Pierce et al, Journal of Clinical Oncology 25:2345-51, 2007).  In this study, approximately 3000 women who had been diagnosed with early stage breast cancer within the past 4 years were randomized to diet and exercise counseling vs. no intervention.  Exercise and eating practices were tracked by telephone calls and questionnaires.  Initially, no significant differences in outcome were seen between those who had the diet/exercise counseling and those who didn’t.


However, looking at the group as a whole, there were clear associations between specific dietary habits and breast cancer recurrence.  First, the amount of fat and fiber in the diet didn’t seem to matter.  However, the number of fruit and vegetable servings per day WAS linked to survival.  Women who ate 5-7 servings of fruits/vegetables per day had better survival than those who had less than 3.4 servings.  Furthermore, combining fruits/vegetables with exercise resulted in the best outcomes – the absolute survival benefit at 10 years was 6% for the group who ate 5 or more servings of fruits/veggies per day and exercised.  This is NOT subtle!  A 6% absolute survival benefit ranks up there with some of the most successful medical interventions for breast cancer.


The investigators of the WHEL study next asked whether specific fruits/vegetables provide the benefit (Thompson et al, Breast Cancer Research and Treatment 125:519, 2011).  They looked at cruciform vegetable intake (broccoli, bok choy, Brussels sprouts, cauliflower, cabbages, dark greens, mustard greens/radish family).  Compounds found in cruciform vegetables had been shown in the laboratory to have activity against breast cancer cell lines, and also had interactions with tamoxifen that helped tamoxifen kill tumor cells.  Indeed, cruciferous vegetable intake was associated with improved outcomes.  Women who ate more cruciferous vegetables (top half) and more vegetables (top third) had HALF the risk of recurrence compared to those who ate less of these vegetables.  Furthermore, consistent with the laboratory studies, the benefit was greatest in women taking tamoxifen.


OK.  So we know that fruits and veggies are good for us, but why, exactly?  It may be because they are packed with phytochemicals.  These are bioactive compounds that are not macronutrients (fats, carbs, protein) nor micronutrients (vitamins, minerals).  They are compounds that have been conserved through evolution that help plants to fight diseases and pests.  They are often responsible for the bright colors and strong tastes of certain vegetables and fruits.  We are only beginning to tap the surface of our understanding about these diverse molecules.  You can read more in the excellent book by Richard Beliveau and Denis Gingras “Foods to Fight Cancer” published by DK Publishing.


Getting back to the WHEL study, cruciferous vegetables are very high in glucosinolates.  The glucosinolates store isothiocyanates and indoles, which are released when the plants are crushed and mixed with an enzyme found in another compartment.  Therefore, chew your cabbage well.  These beneficial compounds are also destroyed by prolonged cooking, and soluble in water.  Therefore, do not boil – steam or stirfry instead.  Finally, the blanching process in freezing also reduces the content of glucosinolates; use fresh vegetables preferentially.  Broccoli and broccoli sprouts are some of the best sources of glucosinolates.  Eat these dark greens.


Let’s dig a little deeper, then, into the biology behind the anticancer activity of cruciforms.  As mentioned, the glucosinolates store isothiocyanates.  The isothiocyanates have been shown in laboratory studies to reduce the occurrence, number, and size of breast tumors in laboratory mice.  They do this, at least in part, by inducing apoptosis (programmed cell death) in breast cancer cells.  Apoptosis is a very potent mechanism of anti-cancer activity of some of the most active chemotherapeutic agents.


Indole-3-carbinol is another product of glucosinolates, but produces its anti-cancer effects via a different mechanism than the isothiocyanates.  Indole-3-carbinol has anti-estrogen effects; it modifies the structure of estradiol so that it reduces its ability to promote the growth of breast cancer cells.  Indole-3-carbinol is found in high levels in broccoli and Brussels sprouts.


And there are other phytochemicals that have activity against breast cancer found in certain vegetables and fruits.  The WHEL study looked at effects of carotenoids by measuring carotenoid levels in some of the women participating in the study.  They divided women into 3 groups based on their carotenoid levels (low, medium, and high).  They found that women in the diet intervention group were more likely to fall into the medium and high groups over time, indicating that eating a diet with more vegetables and fruits can make a difference in carotenoid levels.  Importantly, they also found that those in the medium and high carotenoid level groups had a reduced risk of breast cancer recurrence, with 33% fewer recurrences.  This translates in a 3% absolute reduction in the risk of recurrence, from 19.5% in the group with low carotenoid levels to 15.2% in the group with high levels of carotenoids (Rock et al, Cancer Epidemiol Biomarkers Prev 18:486-94, 2009).  Furthermore, the benefit was the same for both estrogen receptor positive and negative tumors. 


So eat your carotenoid-containing veggies!  These would be foods containing lycopenes – tomatoes, citrus, watermelons.  Also, those containing beta-carotene – carrots, yellow and orange squashes, pumpkins, yams, sweet potatoes.  Eat these reds, oranges, and yellows.