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Eating (and drinking) is inextricably woven into the fabric of our lives. For events mundane and extraordinary food and drink play an inevitable role. When there is a diagnosis of cancer it is not uncommon to explore if how and what we eat can help with cancer treatment and living well with cancer.

The past few years have seen an explosion of information – often conflicting – about the relationship between dietary elements and cancer, especially breast cancer. It can be difficult for the layperson (and the health professional) to determine the relevance and significance of variously sourced information, especially when there are so many aspects of diagnosis and treatment to consider. What is incontrovertible is that eating a healthy, plant-centred diet and engaging in appropriate physical activity will help you keep up your strength, tolerate your therapy and improve your sense of well-being, both during active treatment and beyond.

This short paper seeks to address some of the most commonly considered topics for those living with breast cancer. The advice herewith is for information and consideration only. If you decide to make any changes to your diet, or are having problems with appetite, eating or digestion, please speak to your doctor or hospital dietitian. 

Body Weight

For those with secondary disease: Although being at an optimal weight is desirable, overall well-being and energy are of most importance. For some people cutting back on calories and fat can be stressful, tiring or difficult, and without any perceived benefit. If you feel like you need to lose weight discuss this with your doctor or dietitian.

The goal during active treatment is to maintain a stable weight, even if you are overweight. Intentional weight loss can have implications for treatment effectiveness and susceptibility to infection. Post active-treatment, however, it may be important to strive to achieve or maintain a healthy weight for your height and age. You may wish to discuss with your doctor what would be a good weight for you.

Weight Gain

There are numerous factors that can contribute to weight gain during and after treatment for breast cancer.  These include: 

side effects of steroids and hormone therapy drugs

being less physically active, possibly because of the side effects of treatment

comfort eating

fluid retention due to drugs or surgery

the menopause and subsequent metabolic changes

Although deliberately losing weight during treatment is discouraged, eating a healthy low-fat diet and taking some exercise can help maintain your weight, as well as help with some treatment-related side effects. If after treatment you and your doctor decide that it would be helpful to lose weight, try and do so slowly. Quick weight loss, although satisfying, can bring on fatigue and increase the likelihood that you aren’t getting an adequate level of nutrients. The ‘easiest’ way to successfully and safely lose weight is to consider the following:

Planning –healthy and nutritious eating doesn’t happen by accident. Make a weekly meal plan and stick with it.

Cut down or out processed food (even so-called diet foods).

Be mindful of salt, sugar and fat in prepared dishes.

Eat more plant foods (fruit, veg, pulses, beans, whole grains) – health experts suggest at least 3/4 of the diet should be plant foods and 1/4 of animal origin (including dairy). Vegetables are better for weight loss than fruits (less sugar). Gradually does it though: sudden changes in your normal diet can cause digestive upset in many people.

Lower dietary fat (cooking with less oil; choosing leaner meats and dairy products/cutting down on these foods).

Avoid skipping meals (especially breakfast) for better blood glucose and craving control. Breakfast eaters typically weigh less than those who don’t.

Control portion sizes – this can make a big difference, especially with starchy carbohydrates. Using a smaller plate can help us accept smaller portions.

Eat only when hungry not out of habit or visual/olfactory stimulation (e.g. smelling freshly baked bread in the supermarket).

Make healthy choices the first choice, leaving less room for nutritionally inferior foods.

Increase physical activity: aim to build up to 30-45 minute sessions at least 4 days a week.

Join a slimming club if you would benefit from the outside support. Beware of the diet food that is often flogged through these groups though – eat real food but less of it instead of ‘diet’ biscuits and processed cheese things.

Choose foods that are nutritious but also fill you up. Most protein-rich foods are satisfying. Below are a few food tips to help you.

Food to Fill You Up

Eat a small salad or slowly sup a bowl of vegetable-based soup before eating your main course. You will probably eat less and still be satisfied.

Have protein at breakfast, lunch and dinner. An American study showed that women who had 2 boiled eggs for breakfast went on to eat on average 400 calories less during the day than those who ate a bread/cereal-based breakfast of equivalent calories. However, don’t eat two eggs every day! 

Low glycemic  carbohydrates reduce hunger as they are digested slowly and keep a steady supply of blood sugar (which influences appetite and fat storage). Glycemic load (GL) is a way of measuring how our bodies digest, absorb and use different carbohydrates and is based on serving sizes (unlike the GI  – glycemic index – diet). In general the less processed the food the lower the GL. For example, an apple will have a lower GL than stewed apple and both have less than apple juice. Most veg and pulses are low GL. If you stay away from the faddier approaches to GL you’ll gradually lose weight and feel great too. There are plenty of books and websites that explain this approach to eating, and the foods that make it happen.

Breaking Habits

During active treatment you may have eaten more ‘treat’ foods than you would normally: friends’ homebaking, comforting meals to cheer you up, easily swallowed milkshakes and creamy soups. These certainly have their place during treatment when eating what you fancy is the standard – and appropriate – advice from doctors. But post-treatment is for many a time to ‘start as you mean to go’ – eating well for recovery, and beyond. To do this we often need to re-establish helpful and healthy eating patterns.

A good first step is learning to distinguish between true hunger and appetite. Grazing and nibbling may have been the order of the day during treatment, but in the long-term this way of eating divorces us from the needs of our body. The result can be spiralling weight and diminishing energy and mood. If this sounds like you, try this exercise: after a meal go four hours before eating, even if you feel a bit peckish. Let your tummy start to rumble so that you know what true hunger feels like. Do this a few times over the course of a week, jotting down the circumstances and times that you were tempted to eat during the four hours.

What brought food to mind? Were you bored? Did you detect a nice smell? Did your soap opera come on and you reached for the usual packet of crisps? Can you identify any patterns? How long did it take for the desire to pass? Keep track for a few days and note down the things that you would have eaten had you ‘given in’. Tot up the calories, and fat, if possible. This can be a real eye-opener. It is said that breaking ingrained habits takes as little as six weeks. For a month and a half challenge yourself to say no to unneeded snacks and seconds. See if you can break any long-standing unhelpful eating patterns. This can help with weight loss and weight maintenance without resorting to boring old diets. If you are having trouble keeping weight on, obviously ignore all of the above and eat what you ned to be a good weight for yourself: see below for more advice.

Weight Loss

As with weight gain there can be numerous factors that can cause weight loss. The most common ones are:

loss of appetite

side effects of treatment (nausea, taste changes, pain, constipation, diarrhoea)

increased energy demands due to treatment and cancer itself

stress and anxiety


Some of you may be concerned about losing weight or being underweight. Just like trying to lose weight, gaining weight can take time. If your appetite isn’t up to much, add olive oil (it has a more neutral taste than extra virgin) or cold-pressed rapeseed oil (both are very healthy fats) to your servings of food. Small amounts of butter, whole milk products, hard cheese and even hard-boiled eggs add calories and protein. Avocados, bananas, dried fruits, quality energy bars, nuts and nut butters are healthful ways of getting extra calories without saturated fat and extra hormones. Smoothies and freshly pressed juices deliver necessary nutrients without stomach-filling bulk. See my article on Help With Gaining Weight.

You may also wish to use a dietary supplement to add calories and protein. These include powders to add to your food and stand-alone soups and drinks. Your GP or hospital dietitian can advise on the right product for you – there are many taste varieties and nutrient formulations to choose from.  These are available on prescription.

Soy Foods and Phytoestrogen Supplements

Phytoestrogens are a group of compounds found in varying concentrations in numerous plant foods such as whole grains, green vegetables, beans, pulses, flaxseeds and alfalfa sprouts. Soy beans (edamame) and soy products such as tofu, tempeh, miso, soy milk and soy yogurt are particularly high in phytoestrogens. Supplements containing phytoestrogens have much higher concentrations than are found in food sources. The interest in phytoestrogens is due to their similarity to human estrogen. 

Whether or not to include soy in particular in the diet to prevent cancer, prevent recurrence and slow tumour growth is very controversial. There are two opposing opinions:

1) soy is protective against breast cancer and should be consumed preventatively and by those with breast cancer;

2) soy is harmful  for those with a diagnosis of breast cancer or those at high risk for breast cancer.

Unfortunately there is no concrete evidence either way, especially with regard to food. It seems probable from the evidence thus far that soy products consumed in a broad and mixed diet are safe. The general advice from most of the scientific literature is that one serving a day in a mixed diet is fine, but some women with estrogen-sensitive disease may be advised by their treatment team to further limit, or eliminate, soy foods Ask your doctor for advice if this is a concern. Most of the scientific literature shows that naturally phyto-estrogen containing foods in a normal diet do not affect breast cells. But, if you are on Tamoxifen or aromatase-inhibitors you will not want to be eating soy foods. Remember that you are blocking/eliminating circulating estrogens of all kinds. Physto-estrogen-containing foods may generally be eaten freely by those with estrogen-negative disease. But again, check with your doctor.

The view on supplemental phytoestrogen is somewhat clearer: most health professionals currently agree that herbal phytoestrogen supplements should not be used by those with breast cancer. Although some women report menopause symptom relief with these supplements their overall effectiveness and safety is not established; soy protein powders used as meal supplements also fall into this category.  Again, this may be an issue to discuss with your doctor. Those with estrogen-negative cancer should also discuss supplements if this is relevant to you. There are numerous large studies currently examining soy’s impact on cancer so hopefully we will soon have guidelines soon.

Dairy Products

Like soy there is some controversy over the part dairy products play in breast cancer. It is not clear whether potential risks of the naturally occurring growth factors present in milk and milk products outweigh the clear benefit of dairy as our best source of absorbable calcium. It is also unclear whether any demonstrated effect is dose-related. It is known that organic dairy products have less total growth factors than non-organic.

Large observational studies of Asian women who move to the West and consume more dairy and less traditional soy products appear to have an increased incidence of breast cancer compared to those who do not make changes. It is unclear how big a part additional ‘confounding’ factors – such as less exercise and more processed food – play in this generalised finding. 

Calcium is vital for bone health and for other functions in the body. Although dairy products are our best source of calcium, some plant foods and soy products, as well as fish also give us calcium. Good sources to include in the diet include whitebait, tinned small fish (sardines, anchovies) and tinned salmon, some leafy green vegetables (watercress, broccoli, kale), dried figs and apricots, baked beans, ground sesame seeds (try tahini), white bread and breakfast cereals (these are fortified). If you rely on non-dairy sources for calcium it is important to vary your sources as described above. Combined Vitamin D and calcium supplementation is an option for those with a limited diet. Ask your doctor for advice.


Some people believe that cancer ‘feeds’ off of sugar and recommend that people with cancer stop eating sugar (this sometimes includes fruit too). Studies show that people who consume lots of sugar generally do not eat much in the way of fruits and vegetables, and they consume more processed foods and fatty meats. These factors (and others) may account for any apparent increase in cancer risk. 

Highly-refined or sugar-laden foods, which are low in nutrients, low in fibre, and high in simple carbohydrates give us calories and little else. Foods high in refined sugars or refined carbohydrates may also increase insulin resistance. It is not clear whether insulin resistance is important in cancer progression. 

Taking in enough calories and maintaining energy may be your goal during treatment and beyond.  Your doctor or breast care nurse may advise you to include high-calorie foods in your diet in order to meet this goal. Including refined carbohydrates or sugared foods in your diet may help you to maintain weight or gain weight, along with foods that are more typical in a healthy diet. Refined carbohydrates are typically easy to digest and absorb.

Most major cancer centres and research bodies concur that sugar does not cause cancer, nor, despite the claims of some ‘alternative’ practitioners, does it hasten the growth of cancer cells.

Complementary and Alternative Diets

You may have heard or read about some diets or supplements preventing recurrence or stopping cancer in its tracks. Some women feel that they may influence disease control. Although there are numerous theories linking diet causatively and preventatively to breast cancer there is no clear scientific evidence that certain foods or diets will modify disease. The best science-based advice is to strive to be at your optimum weight for your height and age. Although there is interesting anecdotal evidence for some ‘anti-cancer’ diets, it is advisable to consult a dietitian or your doctor about the pros and cons of various diets. Everyone is different and what suits one person may not suit another.

One a cautious note, some diets used in cancer therapies can cause weight loss and weakness. These diets are characterised by being high in bulk, low in calories and protein, fairly tasteless, difficult to prepare and expensive to follow. Additionally, herbal and non-nutrient supplements can have very strong effects and should only be taken on the advice of someone experienced in advising those with a cancer diagnosis. Those considering an alternative diet or herbal therapy while going through treatment should ideally inform their doctor as both may have implications for treatment.


Fatigue during treatment can be related to the cancer itself or to the side effects of treatment. Sometimes there are numerous factors involved. These may include:

Chemotherapy drugs


Some types of hormone therapy

Eating less and not getting adequate nutrition because of other side effects

Dehydration due to side effects

Cancer cells may be competing with normal cells for nutrients, slowing the growth of normal cells and causing fatigue, along with weight loss and decreased appetite

Chronic pain

Side effects of medication used to treat other side effects


It can be important to determine the cause of your fatigue as this helps with treating it. You may wish to discuss this with your treatment team. Some ways you might decrease your fatigue level include adjusting your diet, taking steps to cope with stress, increasing or decreasing your physical activity. Other specific things that may help are:

Planning rest periods to conserve energy

Staggering any energy-demanding tasks 

Letting others help with shopping, cooking, housework, errands – anything that you find increases fatigue

Taking your time to complete tasks; don’t force yourself to do more than you can manage

Incorporate some walking into your daily routine unless this makes your fatigue worse.

Getting enough calories

Keeping up with your protein. Adequate protein helps with tissue building and repair as well as helps to provide energy.

Getting enough vitamins and minerals, directly from food. If you are experiencing eating or digestion-related difficulties for more than a few days at a time you may wish to discuss with your doctor whether it would be beneficial to supplement your diet with prescribed supplement drinks and/or an appropriate multivitamin.

Staying well hydrated, especially when undergoing radiotherapy or if you are vomiting or have diarrhoea. 

Asking for help in dealing with stress, anxiety or depression. 

Talking to the hospital dietitian. He or she will be able to advise on any nutrients that you may be lacking and help to create a diet plan that addresses your current and future needs.

6 thoughts on “Breast Cancer:Treatment-related Nutrition Issues

  1. Tatiana says:

    “Calcium is vital for bone health and for other functions in the body. Although dairy products are our best source of calcium….” ARE THEY REALLY??? I have seen some documentaries that prove exactly the opposite. More than that – milk, cheese and dairy take calcium out of our body!

    Thank you for your caring advises anyway. x

    1. Calcium bound in dairy products is the most absorbable form. Too much can indeed leach nutrients out of bones but so can too much (unfermented) soya and too much whole grains, due to phytic acid. If someone is not completely avoiding dairy we usually advise mixed sources, not relying on dairy.

    2. Absolutely! Calcium can be obtained through plants and nuts. Dairy products will fuel breast cancer. They are loaded with hormones – both natural and injected. Growth hormones. Stress hormones. It causes a body to be acidic, which is an environment that cancer thrives in. And while we’re at it, sugar can cause and does feed cancer. When you go for a scan you are injected with a radioactive die that is mixed with a sugar substance. It is in this way that the technicians and doctors can see where cancer is in the body when there is an increased uptake in any area. I’ve been battling my breast cancer completely naturally for two years. It’s rule number 1 when you are diagnosed with cancer. No sugar.

  2. Holly says:

    This is a terrific site/ blog. We are making small but important changes in my family’s meals and this is a very helpful guide.


  3. Barbara MacLeod says:

    Hi Kellie

    Thanks for today’s event and lunch at Maggie’s by WGH. I enjoyed both.
    I will email again soon!

    Barbara MacLeod

    1. You ‘re very welcome. I’ll see you next week.

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