Peer-review research is full of controversial information on the influence of specific foods items on breast cancer risk.
This is hardly surprising because scientists mostly base dietary advice on findings from observational studies that typically analyse self-reports of participants’ diets. We know this is highly inaccurate because participants may lie about what they eat or genuinely forget.
Moreover, many of these studies are conducted in Caucasian populations, poorly representing other ethnic groups with different genetics and diets.
That said, the current evidence on how specific food items influence breast cancer is inconclusive for most foods except alcohol, which almost certainly increases breast cancer risk irrespective of ethnicity.
Do you have a family history of breast cancer, or are you a survivor who’s extremely confused about how and what to eat to minimise your risk of developing or redeveloping breast cancer?
You’ll find this post useful!
Before we jump in, let’s cover some basics.
What is breast cancer?
Breast cancer is a disorder of breast tissue that arises when breast cells begin to grow out of control. It is caused by DNA damage or inherited genetic mutations that are sometimes sensitive to oestrogen exposure.
Different subtypes of breast cancer exist based on the cells they originate from and the hormones they express. For example, some cancers begin in the ducts that carry milk to the nipple (ductal cancers), while others start in the glands that make breast milk (lobular cancers) (Alkabban and Ferguson, 2020). In addition, some cancers express a combination of oestrogen, progesterone and human growth factor proteins or none of them.
Breast cancer is the most common cancer in women and the second most common cancer worldwide. It affects women in Western Europe and North America more frequently, although its prevalence in developing countries is rising rapidly due to dietary changes, longer lifespans, and urbanisation.
According to breastcancer.org, “Caucasian women are slightly more likely to develop breast cancer than Black, Hispanic and Asian women. But black women are more likely to develop more aggressive, more advanced-stage breast cancer that is diagnosed at a young age.”
Survival rates have dramatically improved from 63% in 1960 to 90% presently. However, the risk of recurrence after remission remains high.
Breast cancer risk factors
- Age: Breast cancer risk increases significantly with age, reaching its peak during menopause before declining or remaining constant after that (Thakur et al., 2017).
- Gender: Breast cancer is predominant in women and rare in men; it affects no more than 1% of men (Giordano et al., 2002). When it affects men, it typically affects older men who have had hormonal imbalances, radiation exposure, or a family history of breast cancer due to mutations of the BRCA2 gene (Abdelwahab, 2017).
- Age of menstruation onset: women who start their periods before 12 have a two-fold higher risk of developing breast cancer than women who begin later (Thakur, 2017).
- Genetic predisposition: People with BRCA1 and BRCA2 have a higher risk of cancer than people without those mutations. Up to 65% of people with BRCA1 and 45% of people with BRCA2 mutations develop breast cancer (Cobhain, Milliron and Merajver, 2016).
- Late menopause: Women who start menopause over 55 years have a higher risk of breast cancer (Momenimovahed and Salehiniya, 2019).
- Age at pregnancy over 30 years: Having a baby at a younger age reduces breast cancer risk by up to 23%, while older age (over 30 years) increases risk six-fold. Furthermore, women who have their babies before 33 weeks of gestation have a higher risk of breast cancer (Thakur, 2017).
- No history of breastfeeding: Breastfeeding is protective against breast cancer. And the length of breastfeeding is also protective. A case-control study showed that having at least two children and breastfeeding for at least 13 months can reduce breast cancer risk by up to 50% (Jeong et al., 2017).
- Infertility and not having children: The risk of breast cancer decreases with the number of children women have. Every childbirth reduces the risk of progesterone and oestrogen-positive cancers by up to 10%. However, not having children was associated with large tumours in a prospective (future events) study (Butt et al., 2009)
- Use of contraceptives: Current use of contraceptives is associated with an increased risk of breast cancer, but this diminishes 5-10 years after discontinuation of hormonal therapy (Zolfaroli et al., 2018).
- Hormonal treatment after menopause: Breast cancer risk increases with hormone replacement therapy (HRT) use, and this risk decreases once women stop using it and diminish after five years. Breast cancer risk is higher in women who use oestrogen-progesterone HRT than those who use other HRT methods (Beral, 2003).
- Lifestyle factors, including overweight/obesity, smoking, air pollution, physical activity, sleep and diet (Momenimovahed and Salehiniya, 2019).
Diet may play a role in both promoting and preventing breast cancer. Studies show that it influences breast cancer risk in around 35% of cases (Kotepui, 2016). However, information on the role of specific food items on breast cancer risk is conflicting and confusing.
In the section below, we’ll explore current evidence on
The influence of individual foods and nutrients on breast cancer risk
1 | Fruits and Vegetables
Scientists believe that diets rich in fruits and vegetables lower breast cancer risk because they contain large quantities of anticancer nutrients, including polyphenols (Farvid et al., 2019).
Polyphenols – antioxidants that lower inflammation and oxidative stress – block oestrogen, which plays a role in cell overgrowth and cancer development (Vitelli-Storelli et al., 2020). The fibre in fruits and vegetables can also prevent cancer by binding to oestrogen and reducing its concentration in blood (Touillaud et al., 2007).
While some studies show that higher intake of fruits and vegetables, specifically cruciferous and yellow/orange vegetables may reduce breast cancer risk (Farvid et al., 2019), other studies have found only a weak association between fruit and vegetable intake and breast cancer risk (Aune et al., 2012).
The European Prospective Investigation into Cancer and Nutrition (EPIC) found that high consumption of leafy and fruiting vegetables, including tomatoes, is associated with a lower risk of breast cancer (Masala et al., 2012).
One study found an association between high intakes of blueberries, strawberries and peaches/nectarines with reduced breast cancer risk (Fung et al., 2013). Still, another one found no association at all (Farvid et al., 2019).
2 | Red meat
Red and processed meat are risk factors for breast cancer because of their high iron content, their ability to form carcinogenic compounds during high-temperature cooking (Inoue-Choi et al., 2016), and because in some countries, cattle are fed hormones, including oestrogen to promote growth (Nachman and Smith, 2015).
Administering hormones to cattle is banned in the UK, but with the new change in UK guidelines that allows the importation of meat from countries that allow it, it’s a worry. But this is a topic for another day.
One study found that women with consistently high intakes of well-done meat had a 4.6-fold increased risk of breast cancer (Sinha et al., 2000). But in a large prospective study, there was no link between meat intake and breast cancer in Black women (Genkinger et al., 2013).
Observational studies have found unprocessed red meat increases the risk of breast cancer by 6%, while processed meat increases it by 9% (Farvid et al., 2018).
A large study in the UK with over 262,000 women showed a link between processed meat intake and breast cancer in postmenopausal women but not in premenopausal women (Anderson et al, 2018). But they also found that the cooking method, rather than the meat itself, was a potential cause for increased risk.
3 | Dairy products
Dairy products contain a mixture of components, including saturated fat, calcium, vitamin D, short-chain fatty acids and conjugated linoleic acid that influence breast cancer risk in opposite directions (De Cicco et al., 2019).
Some studies show no significant association between total dairy fluids or solids and breast cancer risk (Missmer et al., 2002). Other larger studies show that high low-fat dairy intake (without milk) might lower breast cancer risk in premenopausal women (Dong et al., 2011; Zang et al., 2015).
This protective effect occurs potentially because vitamin D prevents breast cancer development. High intakes of calcium and vitamin D are moderately related to lower BC risk, especially in premenopausal women (Cauley et al., 2013). However, dairy products also contain saturated fatty acids, Insulin-like growth factor and other contaminants that might increase BC risk.
The heterogeneous composition of dairy products makes the net effect of dairy consumption on BC prevention challenging to settle.
4 | Soy
Soy is a source of isoflavones, compounds that have weak oestrogenic activity. They have similar structures to oestrogen and compete with oestrogen receptors (De Cicco et al., 2019).
Soy induces the growth of breast cancer cells in cell culture and rodent studies. However, soy has many anticancer and antioxidant properties and the ability to destroy and limit blood flow to cancer cells (Messina and Wood, 2008).
Some meta-analyses have shown that high soy isoflavones are inversely associated with BC risk in postmenopausal Asians, but no association has been found in Western populations (Qin et al., 2006; Wu et al., 2008; Dong et al., 2011). But this could be because Asian women eat substantially higher quantities of soy products (45.9mg isoflavones daily) throughout their lifetime than Western women (3.2mg isoflavones daily) (DeCicco et al., 2019).
5 | Alcohol
Regardless of alcohol type – beer, wine or spirits – alcohol is strongly associated with increased breast cancer risk in pre- and postmenopausal women (DeCicco et al., 2019). For every 10g of alcohol consumed daily, breast cancer risk increases by 5 and 9% in pre-and postmenopausal women, respectively (DeCicco et al., 2019).
Alcohol is known to increase oestrogen concentration, which then induces abnormal overgrowth of breast cells leading to cancer (Liu, Nguyen and Colditz, 2015). Besides, heavy drinkers have poor intakes of several nutrients including folate.
Folate is crucial for DNA production and repair, thus maintaining genomic stability. Alcohol is also well-known folate blocker, reducing the bioavailability of folate for DNA production and repair (Seitz et al., 2012).
6 | Carbohydrates, glycaemic index, and glycaemic load
A recent study showed an inverse relationship between carbohydrate quality and breast cancer risk, with high quality carbohydrates (whole, unprocessed carbohydrates) reducing breast cancer risk (Romanos-Nanclares et al., 2021).
Overall, there is a weak association between glycaemic index (GI), glycaemic load (GL) and breast cancer risk. However, there seems to be a strong association between high GI and GL diets and breast cancer in pre-and postmenopausal women with hormone receptor-negative (oestrogen and progesterone negative) breast cancer (Schlesinger et al., 2017).
The positive association might be due to increased insulin serum levels after eating carbohydrates. Insulin raises growth hormone levels and insulin-like growth factor 1, which speeds tumour growth and prevents their destruction (Kaaks and Lukanova, 2001; Helle and Lonning, 1996; Key et al., 2010).
While the association between carbohydrate intake, GI and GL and overall breast cancer risk is weak, it is wise to eat a low GL diet (De Cicco et al., 2019).
7 | Dietary Fat
Postmenopausal women who eat diets high in total, saturated and polyunsaturated fats might have a higher risk of hormone-positive breast cancer, but not hormone-negative types (Sieri, 2014).
However, dietary fat is protective against breast cancer in premenopausal women (Turner, 2011).
8 | Omega-3
Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) omega-3 fats in seafood are known to reduce breast cancer risk in a dose-dependent manner – 5% lower risk for each 0.1 g/day increase (Zheng et al., 2013).
Omega-3 fats make cancer cells more sensitive to chemotherapy. They can also integrate into cancer cells and once they do, cancer cells lose the key proteins they need to survive and subsequently die (Liu and M, 2014; D’Eliseo et al, 2016).
Omega-3 fats can also release proteins called resolvins and protectins that resolve inflammation and protect cells against toxic chemicals, such as chemotherapeutic drugs (Murray et al., 2015).
A small trial showed that omega-3 fats help patients with cancer recover with fewer side-effects and improved remission rates (Bougnoux et al., 2009).
Now you know how specific foods and nutrients influence breast cancer risk, you may be wondering how to eat to lower your breast cancer risk. If so, the following tips should help:
- Keep your weight within a healthy age and avoid weight gain as you age
- Exercise for at 30 minutes daily, including strength-training exercising at least twice a week
- Make wholegrains, vegetables, fruits and beans the predominant part of your diet
- Minimise consumption of fast and refined foods and foods high in saturated fat and sugar
- Eat moderate quantities of red meat such as beef, pork and lamb and avoid processed meat.
- Limit sugar-sweetened drinks
- Limit alcohol
- Avoid using supplements for cancer prevention, aim to meet your nutrient needs via diet
- Breastfeed your baby if you can
You now have all the information you need to keep your cancer risk minimal. So, don’t read and forget, implement!
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