LIFESTYLE CAN INFLUENCE YOUR BREAST CANCER RISK. What you eat can influence your weight, increasing your chances of suffering from breast cancer. For those with breast cancer, weight gain may increase your odds of cancer returning. But today, I want to focus on breast cancer and diet.
But does the evidence show that choosing a healthy diet — such as a Mediterranean one or an approach incorporating lots of vegetables, whole grains, chicken, and fish — boosts your chances of dodging (or dying from) breast cancer?
We begin with soy. It contains phytoestrogens, so does soy increase breast cancer risk?
1. Soy
The most common diet question I receive from my patients with breast cancer is this: “Do I have to avoid all soy products?”
Soy contains phytoestrogens, natural plant substances with a chemical structure similar to estrogen (specifically, 17-beta estradiol). Phytoestrogens contain:
- isoflavones (in high quantities in soybeans and other legumes)
- lignans (in a variety of fruits, vegetables, and cereal products)
Let’s quickly look at a 2014 meta-analysis of 35 studies examining the association between soy food consumption and breast cancer risk.
Soy isoflavone intake may lower breast cancer risk for pre-and post-menopausal women in Asian countries. However, for women in Western countries, pre- or post-menopausal, there is no evidence of an association between soy isoflavone intake and breast cancer.
In summary, soy foods or products are rich sources of isoflavones — offering both weak estrogenic and anti-estrogenic effects. While soy consumption may lower breast cancer risk in Asian populations, we do not have much proof that soy-rich diets in Western women lower breast cancer risk.
2. Red meat
Do red and processed meats increase breast cancer risk? The answer is not clear. The United Kingdom Biobank study discovered that processed (but not red) meat appears to be associated with a higher breast cancer incidence.
3. Dietary fat
Is adopting a low-fat eating pattern associated with better breast cancer outcomes?
A low-fat diet pattern for postmenopausal benefit appears to reduce the risk of dying of breast cancer, at least among those with a breast cancer diagnosis. Proposed mechanisms for this improvement include reducing estrogen (estradiol) and metabolic syndrome components.
The Women’s Health Initiative Dietary Modification Trial randomly assigned nearly 49,000 postmenopausal women (with no history of breast cancer) to 1) a usual diet versus 2) a low-fat dietary pattern, with every three-week group sessions in year one and quarterly maintenance sessions throughout the 8.5 year intervention period.
The lower dietary fat group reduced fat intake to 24 percent of calories from fat. The intervention group, on average, lost three pounds with more fruit, vegetable, and grain consumption.
After a follow-up of nearly 20 years, the researchers found fewer deaths from breast cancer in the dietary group, with a 21 percent relative drop. But in absolute numbers, the improvement is less impressive: 0.04 versus 0.05 percent deaths in the control and dietary groups, respectively (four versus five in 10,000). The researchers controlled for weight changes.
4. Fiber
Researchers examining 24 epidemiologic studies report that dietary fiber consumption is associated with a one-eighth (12 percent) drop in breast cancer incidence.
While this drop by one percent does not sound impressive, a dose-response analysis showed that every 10 grams per day increment in dietary fiber intake is associated with a four percent relative risk reduction in breast cancer. We need randomized clinical trials to confirm these observations.
5. Caffeine/Coffee
There is no association between caffeine consumption and breast cancer risk. A large, prospective study of nearly 200,000 mostly white, postmenopausal women showed coffee intake was not associated with breast cancer risk. Caffeinated versus decaffeinated coffee intake did not seem to matter.
This study of 198,404 women is one of the largest cohorts to date to have evaluated the association between coffee intake and breast cancer risk. The study has flaws: First, the researchers did not collect information on the coffee brewing method. A recent Swedish report suggested that associations with breast cancer risk differ between filtered and boiled coffee.
6. Alcohol
I have written extensively about alcohol and breast cancer, including this recent piece:
https://newcancerinfo.com/2021/01/22/does-putting-alcohol-aside-make-you-healthier/
7. Antioxidants
Do you take vitamin A, C, E, or beta-carotene? There is no evidence that taking these substances lowers breast cancer risk.
8. Vitamin D and calcium
Observational studies and meta-analyses suggest that higher blood levels of vitamin D may be linked with a lower breast cancer risk among post-menopausal (but not premenopausal) women. Randomized clinical trials of vitamin D have not shown that supplements reduce breast cancer risk.
The Women’s Health Initiative randomized trial included more than 36,000 postmenopausal women. Individuals assigned to 1000 milligrams of calcium with 400 internal units of vitamin D3 did not have a lower risk of invasive breast cancer. However, the intervention was only seven years, and the follow-up was not quite five years.
Exploratory analyses found lower vertebral fracture and in situ breast cancer incidence in supplement users.
The vitamin D dose seems on the low end of the range (and subjects did not take vitamin K to help with vitamin D absorption). Finally, might supplements help those with known low vitamin D levels?
Thank you for joining me today in this brief look at diet and breast cancer.
The information I provided in this blog is for educational purposes only and does not substitute for professional medical advice. Please consult a medical professional or healthcare provider if you seek medical advice, diagnoses, or treatment. I am not liable for risks or issues associated with using or acting upon the information in this blog. Thank you.
