Diet and breast cancer

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After a diagnosis of any cancer it would be very wise to generally improve the diet. Along with other lifestyle issues such exercise and giving up smoking, scientific evidence has showed that a healthy diet  is likely to help to:

In addition a healthy diet could help to improve the quality of life and reduce side effects during active cancer treatments by helping with specific symptoms such as weight gain, weight loss, nausea & poor appetite, diarrhoea, constipation, breathless, altered tasteindigestion and dry mouth.  Apart from these examples, however, for practical reasons, this section addresses people who do not have any or few restrictions on their diet after their diagnosis of cancer. Likewise it doesn’t address any pre-existing long standing dietary requirements.  In general, therefore, it is probably not appropriate for patients with advanced cancer or those who’s tumours or treatments have affected their ability to eat or digest food. In these situation,  patients should seek formal advice from qualified dieticians preferably those attached to a mainstream cancer unit.

In generally a healthy diet means:- 

What to less more of: What to more less of:

There are some other specific issues, not entirely resolved scientifically, which concern breast cancer, largely because they are often sensitive to the female hormone oestrogen:-

Soya products and other phyto-oestrogens. In human diet these are mainly from soybeans. The other other legumes, including peas, lentils and beans. Although many of these also have antioxidant properties they are classed separately from antioxidants because they also have weak female hormone (oestrogenic) properties which may influence hormone related conditions such as hot flushes, osteoporosis, fibroids or endometriosis and hormone sensitive cancers such as breast cancer.

The phytoestrogens and cancer story remains one of the most controversial and disputed subjects among cancer doctors.  Historically, the implication of benefit stems from the finding that populations and cultures that have had a high dietary intake of phytoestrogenic foods such as those from the far east have the lowest incidence of cancer and indeed menopausal symptoms such as hot flushes, and osteoporosis. The positive effect on cancer is thought to arise via their affinity to the oestrogen receptor in breast or uterine tissues and for that matter cancer cells that originate from them. They attach to the receptor but only have weak oestrogenic activity. This means the very much stronger own body’s oestrogen has less influence on the receptor i.e. they dilute the effect of their own body’s oestrogen. Furthermore, studies on genestein have shown that it attaches to the oestrogen receptor in the same way as tamoxifen – inhibiting the oestrogen effect on tumours but stimulating the bones and uterus.

This sounds ideal but evidence is rather cloudy. The anti-cancer benefit may simply be via the antioxidant effect of the healthier food rather that the oestrogenic action and some suggest there may be other factors in the East which are beneficial so simply taking soya products may not translate into a western diet. Furthermore, just because they may reduce the incidence of cancer developing originally, this does not necessary mean they would reduce the severity once breast cancer has established. On a concerning note, animal studies have also shown that phytoestrogens supplements are capable of stimulating tumour cell growth as well as having effects on the bodies normal cells sensitive to oestrogen such as breast and uterine tissues so they may not be that innocent after all.

A study looking at the cancer (good or bad) effects in humans has not been performed (and it would take a very brave team to do one!). There have however been trials of phytoestrogen supplements among patients with breast cancer looking at whether they could reduce their hot flushes and so far they have not shown an increased risk of cancer. As these trials had not set out to examine the cancer effect, in mathematical terms they were not designed to have the statistical power to be comforted by these findings. Interesting and probably of more relevance, none of the trials of phytoeostrenic supplementation actually showed a difference in the main end point – hot flushes. Protagonist against phytoestrogens, therefore have a fair point when they argue that the supplement used in these studies could either have not been powerful enough or patients had not taken at a high enough dose to help their hot flushes. So, they argue, if the supplement had been active against hot flushes they would have more likely risked the stimulation of occult residual cancer cells stimulating relapse. In other worlds, for hot flushes, if phytoestrogens work they could be harmful, if they don’t there is no point taking them anyway! 

With conflicting circumstantial evidence on phytoestrogens, most oncologist agree that it would be unwise to take phytoestrogen supplements particularly in patients with breast cancer. Most agreed that foods containing phytoestrogens such as soya legumes are generally healthy and have lots of antioxidants, essential trace elements, fibre, healthy fats and vitamins and should not be discouraged.


Obesity; A large analysis of USA health professionals who had a high energy and fat intake subsequently were associated with an increased risk of breast cancer. Further research has shown that women who eat more than 90g of fat a day had twice the risk of developing breast cancer than those eating 40g per day. Overweight women also had an increased risk of breast cancer irrespective of their daily saturated fat intake. A large USA study, and others, havedemonstrated a strong association between obesity (adiposity, BMI>30kg/m2) and outcome after treatment for breast and cancer, with the improvement in survival being a result of both decreased cancer and non-cancer related deaths such as heart attacks and strokes. The underlying mechanisms of why high fat intake and obesity affects the risk of cancer include:-

Oestrogen levels. Adiposity influences the production of and availability of the body’s sex hormones including oestrogen, androgens and progesterone. In post menopausal women oestrogen is made in the peripheral body fat whilst in pre-menopausal women it is produced primarily in the ovary. This may explain a higher risk of breast and endometrial cancer for overweight post menopausal women but not pre-menopausal women. Fortunately, oestrogen levels have been shown to reduce following weight reduction programmes.

Insulin and Insulin-like growth factor receptor (IGF-1). The increased risks of cancer or its rate of progression is not just hormone related. We know this because overweight women have a worse prognosis after cancer whether their cancers where sensitive to oestrogen (ER+ve) or not (ER-ve). One mechanism for a non hormone related increased risk of cancer progression is via IGF-1 which is higher in overweight people. Higher levels have also been associated with breast, ovary and prostate cancer. This protein, also higher in sedentary individuals, has been shown to promote cancer cell division (encourage proliferation), inhibit apoptosis (cells don’t die when they should) and encourage them to spread. 

Leptin. This is a multifunctional neuro-endocrine hormone generated primarily from fat cells. There is a direct correlation with the amount of body fat levels and circulating blood levels of leptin. There is also a correlation between leptin and serum insulin, IGF-1 and progesterone levels. Leptin has been shown in several laboratory experiments to promote proliferation, reduce apoptosis and reduce the stickiness of cancer cells encouraging them to spread and metastasise. Higher leptin levels are associated with higher expression of Cycloxidase 2 which also, as described below, encourages cancers to grow faster and spread.

 Progesterone. Another important hormone which would affect women is progesterone. Compared to women with ‘normal’ weight pre-menopausal obese women in particular have reduced serum progesterone. There is a significant body of evidence that progesterone plays a protective role in cancer progression particularly ovary. Progesterone increases in pregnancy which also adds some protection against breast and ovarian cancer. In post menopausal women who are not overweight (BMI < 35kg/m2) the evidence is less clear. The risk of breast cancer, in a one large study from Sweden, was higher in women taking HRT containing progestin than those containing oestrogen alone. On the other hand, another study of postmenopausal women with breast cancer from Boston USA, women with higher blood levels of oestrogen and androgens had a worse prognosis but no such correlation was found with progesterone. It well be therefore, that the protective affect of progesterone is greater in pre-menopausal women.

Fat intake Not all fats are unhealthy . Evidence from two large prospective studies and a smaller case-control study suggests a protective effect of oily fish intake on cancer incidence and risk of dying from it. A unique nutritional component of fish is the long-chain marine omega-3 fatty acids. Cancer cells grown in the laboratory in petri dishes and in mice, as well as small human studies have suggested that marine omega-3 fatty acids or even more importantly the ratio of marine omega-3 to omega-6 fatty acid can modulate cancer progression. The entire reason for this not fully understood but one mechanism appeared to be via the cyclooxygenase-2 (COX-2) pathway. Another healthy fat is olive oil which provided it is not over processed, is predominantly the monounsaturated fatty acid oleic acid having strong antioxidant properties. Olive oil also exhibits a number of other advantageous biological functions, including an ability to reduce blood saturated fat levels. Environmental studies have shown that higher olive oil use correlates to a lower incidence of atherosclerosis, diabetes, inflammatory and autoimmune diseases, skin wrinkling and skin aging. For centuries, Greeks and Egyptians have also used olive oil topically for the treatment of what they termed “erythema” or redness and wealthy Romans would rub it on their skin before a steam bath. More recently, oleic acid, in laboratory experiments, has been shown to suppress a protein on breast cancer cells called Her-2. Over expression of this protein is present in 25% of patients with breast cancer and is the main target for the biological agent herceptin. In general the higher the concentration (over expression) of the HER-2 protein the more aggressive the cancer. Olive oil can enhance the effects of herceptin by promoting apoptosis, reducing proliferation etc. It may have an affect on its own even without herceptin. This natural herceptin is being investigated in further clinical studies.

Harmful fats include the saturated fats. Replacing saturated fats with polyunsaturates, and to a lesser extent, monounsaturates, have been shown to reduce serum blood cholesterol and other unhealthy fat levels. A particularly harmful group of fats are the trans-fats or hydrogenated fats. Hydrogenation is one of the processes that can be used to turn liquid oil into solid fat. The final product of this process is called hydrogenated vegetable oil. It's used in some biscuits, cakes, pastry, margarine, processed foods and particularly the fast food industry. The trans fats found in food have no known nutritional benefits and emerging evidence suggests that their may be worse than saturated fats and as a result, Denmark, Canada and the USA have started labelling foods with their trans-fat content.

Tips to reduce saturated and trans-fat intake: 

Tips to increase unsaturated fats and omega-3:

Xenoestrogens. There are over 350 permitted pesticides allowed in western farming but researches have estimated that over 70,000 other chemicals have been detected in our food chain and most of these have not formally been tested for health risks. These pesticides, herbicides, fungicides, fertilizers and industrial pollution are in our water because of rain erosion runoff from landfills and agricultural lands. They are in our food supply–in plants animals, fish and grains. Although some of these may well have direct carcinogenic affects, of relevance to breast cancer, some of these contaminants also have a chemical structure similar to oestrogen and can cause abnormal hormonal activity by disrupting the normal hormone pathway. These toxic estrogens mimics are called xenoestrogens and are presently found in large quantities in the environment with sources including pesticides, herbicides, fertilizers, car pollution, polychlorinated biphenyls PCB’s. There are worries that xenoestrogen are not contributing to the increased risks of hormone related cancers such as breast, testis ovary and uterus but are affecting the male sperm count and other infertility problems. Switching to a healthier diet, with more fruit, salad and vegetables is clearly healthy may paradoxically mean higher exposure to these chemicals so certain precautions may be necessary to avoid them:

Alcohol and breast cancer. Alcohol is known to increase the risk of some cancers. Some research studies show that drinking a lot can increase risk of breast cancer. Other research studies don't show such a risk and quite correctly argue that the data is confused by other lifestyle factors such as smoking, diet exercise, body weight etc. Some studies however show that even small amounts of alcohol can increase the risk of breast cancer. A group of scientists who analysed almost 100 previous studies found no safe lower limit for alcohol intake. Another study from the USA showed that the mortality from breast cancer was 30 percent higher among women reporting at least one drink daily than among non-drinkers. Another American study found that one drink a day increased the risk of bowel cancer by 70%A Japanese study found that people triple their if they drink three to five units a day, and quadruple their risk if they drink five units or more. Others argue that a little alcohol is healthy as it relaxes and in small amounts improves mood and particularly red wine contains antioxidants. As further studies are required before we understand the alcohol fully the DoH have issues sensible guidelines based on available evidence, although these are largely related to the heart, brain and liver related damage:  14 units per week for women, 21 units per week for men. (A premium pint of lager, beer or cider (5% vol) contains 3 units, A standard 175ml glass of wine (11-12% vol) contains 2 units. A double 35ml shot of spirits (40% vol) contains 3 units.) If you have any doubts and are not particularly bothered about the taste of alcoholic drinks, the safest option would be to avoid them.

Further general information Your doctors and specialist nurses are in an ideal position to give you relevant information on your disease and treatment as they know your individual circumstances. Cancerbackup has a help line (0808 800 1234) and a prize winning video available in English, Italian, Urdu, Bengali, Gujarati & Hindi explaining Radiotherapy & Chemotherapy. has over 500 pages describing cancer, its management, practical tips and tool which patients, their carers and their doctors have found helpful during the cancer journey.

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