Remarkably, researchers have found that women placed on a plant-based diet, along with walking every day, improved their cancer defences within just two weeks. At that point, their blood was potent enough to kill 20-30 per cent more breast cancer cells than before.
Yet, unfortunately, even after a breast cancer diagnosis, most women don't make the dietary changes that could help them most.
Another study of nearly 1,500 women found that remarkably simple changes - such as eating just five or more servings of fruit and veg per day along with walking for 30 minutes, six days a week - had a significant effect.
Compared with patients who did none of these things, these women appeared to have nearly half the risk of dying from breast cancer in the two years following diagnosis.
In other studies, sulforaphane - a component of cruciferous vegetables such as broccoli - has been shown to suppress the ability of breast cancer stem cells to form tumours. So if you're currently in remission, eating lots of broccoli may help keep your cancer from returning.
Red wine is fine
What about alcohol? In 2013, scientists published a compilation of more than 100 studies on breast cancer and light drinking (up to one glass a day).
Remarkably, they found a small increase in breast cancer risk even among women who had one drink or less per day. Every year around the world, they estimated, nearly 5,000 breast cancer deaths may be attributable to light drinking.
The only exception was red wine, which contains a compound that may cancel out the damage caused to the body when it breaks down alcohol. This compound appears to suppress the activity of an enzyme called oestrogen synthase, used by breast tumours to fuel their own growth.
So have a glass of red wine if you like. But the best foods for suppressing this enzyme are purple grapes - preferably with seeds - plain white mushrooms, strawberries and pomegranates.
Dark dreams
Most of us know that the hormone melatonin helps regulate our sleep. But it also seems to play another role - suppressing cancer growth. Think of melatonin as helping to put cancer cells to sleep at night. To investigate this theory further, researchers in Boston came up with the clever idea of studying blind women.
The thought was that because blind women can't see sunlight, the brain never gets the signal to stop secreting melatonin into their bloodstreams.
Sure enough, the researchers found that blind women may have just half the odds of getting breast cancer as sighted women.
Conversely, women who interrupt their melatonin production by working night shifts appear to be at increased risk of breast cancer.
Even living on a particularly brightly-lit street may increase the risk. Therefore, it's probably best to sleep in a room with heavy blinds and no lights.
But there's something else you can do to keep up your production of melatonin. Yes, more vegetables!
In 2005, Japanese researchers found an association between higher vegetable intake and higher melatonin levels. Meat, unfortunately, seems to have the opposite effect. In a Harvard University study, the diets of nearly 1,000 women were analysed before their morning melatonin levels were measured.
Meat consumption was the only food significantly associated with lower melatonin production, for reasons that are as yet unknown.
Ditch the barbecue
One of the worst things you can do if you're worried about breast cancer is to cook beef, pork, fish or poultry at a high temperature - which includes frying, grilling and roasting.
Eating boiled meat, therefore, is probably the safest.
This is because meat cooked above 100c produces cancer-producing substances called heterocyclic amines (HCAs). The longer that meat is cooked, the more HCAs form.
This may explain why eating well-done meat is also associated with increased risk of cancers of the colon, oesophagus, lung, pancreas, prostate and stomach.
The HCAs in cooked meat are also thought to explain why women who eat more grilled, barbecued or smoked meats over their lifetimes may have as much as 47 per cent higher odds of breast cancer.
The Iowa Women's Health Study found women who ate their bacon, steak, and burgers "very well done" had nearly five times more chance of getting breast cancer than women who liked meat served rare or medium.
Just add broccoli
Is there any other way to lessen the carcinogenic effect of cooked meat? To find out, researchers measured the levels of HCAs in the blood of people who'd just eaten pan-fried meat.
Over the next fortnight, they added about 500g (just over a pound) of broccoli and Brussels sprouts to their daily diets and then asked the women to eat fried meat again.
As expected, there were fewer HCAs in their blood - because the vegetables had helped the liver detoxify some of them.
At this point, the subjects then stopped eating their veggies and, two weeks later, ate pan-fried meat again.
What happened next was a great surprise. Researchers had assumed that the level of harmful carcinogens in their blood would be just as high as before - but they weren't.
What's more, even weeks afterwards, the HCAs still hadn't climbed back to their previous level.
This finding suggests two things. One, that having broccoli or brussels sprouts with your steak will decrease your body's exposure to carcinogens. Two, that you can shore up your defences before a big barbecue by eating broccoli or sprouts days or even weeks before. (Or even try a veggie burger.)
Moral fibre
Every 20g of fibre intake per day has been associated with a 15 per cent lower risk of breast cancer.
And you may not even need that much.
Researchers at Yale University and elsewhere have done detailed studies on pre-menopausal women who eat more than about 6g of soluble fibre (the equivalent of a cup of black beans) a day.
The result? The women had 62 per cent lower odds of getting breast cancer compared with women who consumed less than around 4g a day.
Cut cholesterol
Breast cancer is thought to use cholesterol to help the cancer migrate and invade more tissue.
In other words, breast tumours may be taking advantage of high cholesterol levels in your blood to accelerate their own growth.
So, if lowering cholesterol can help lower the risk of breast cancer, shouldn't more women be taking statins? Probably not.
The first major long-term study on breast cancer and statins has found that women who have been taking statins for a decade or more have twice the risk of contracting two common types of invasive breast cancer.
So, it's far better to lower cholesterol levels naturally by improving your diet.
Core values
People who eat an apple a day - or even half an apple - appear to have significantly lower risks of getting cancer.
One study found, for instance, that eating less than one apple a day lowers the risk of breast cancer by 24 per cent. The risk of ovarian cancer, laryngeal cancer and colorectal cancer is also lowered by significant amounts.
But don't be tempted to just eat the flesh and throw away the peel! Depending on the variety of apple, the peel's anti-oxidant power may be between two and six times greater than the pulp.
When researchers at Cornell University in New York dripped extracts of apple peel and pulp onto cancer cells, the peel stopped cancer growth ten times more effectively.
Something in the apple peel and pulp appears to reactivate a tumour-suppressor gene which is known as maspin - which helps keep breast cancer at bay.
Soya rules!
Soya seems not only to lower breast cancer risk, but also to help reduce menopausal hot flushes. In addition, five studies have found that, overall, the women who ate the most soya lived significantly longer and had a significantly lower risk of breast cancer recurrence.
In one study, 90 per cent of the breast cancer patients who ate the most soya after diagnosis were still alive five years later.
Yet half of those who ate little to no soya had died.
Magnificent mushrooms
Women who ate just half a mushroom or more per day had 64 per cent lower odds of getting breast cancer - compared with women who didn't eat mushrooms at all.
If the mushroom-eaters also managed to sip at least half a teabag's worth of green tea each day, then their risk of breast cancer would be a whopping 90 per cent lower.
Flaxseeds have around 100 times more of a particular phytoestrogen called lignan than any other foods. And, in a test-tube at least, lignans directly suppress the proliferation of breast cancer cells.
In 2010, a study was done on 45 women at high risk of breast cancer - meaning they'd had suspicious biopsies or had previously suffered from the disease.
Each was given the equivalent of two teaspoons of ground flaxseeds every day.
The result? On average, the women had fewer pre-cancerous changes in their breasts after a year of taking flaxseed than before they'd started.
And 80 per cent showed signs of decreased cell proliferation. This finding suggests that sprinkling a few spoonfuls of ground flaxseeds on your cereal - or whatever you're eating during the day - may reduce your risk of breast cancer.
What about women who already have it?
Another study - a randomised, double-blind clinical trial (neither the researchers or the women with breast cancer knew who was taking what) - found that those who ate a muffin containing flaxseed every day had decreased cell proliferation and an increase in cancer-cell death rates.
In other words, the flaxseeds appeared to make the subjects' cancer less aggressive.
• Daily recommendation: 1 tablespoon of ground flaxseeds, sprinkled on to cereal, soups and salads, or baked into a muffin.
The Daily Dozen
Every day, you should aim to have the recommended number of servings from each section of what I call my Daily Dozen:
1. Cruciferous vegetables, such as broccoli, brussels sprouts, cabbage, cauliflower, kale, spring greens, radishes, turnip tops, watercress. One serving a day: A serving is half a cup chopped or quarter of a cup of broccoli or brussels sprouts.
2. Greens including spring greens, kale, young salad greens, sorrel, spinach, swiss chard. Two servings a day: A serving is one cup raw or half a cup cooked.
3. Other vegetables: Asparagus, beetroot, peppers, carrots, corn, courgettes, garlic, mushrooms, okra, onions, pumpkin, sugar snap peas, squash, sweet potatoes, tomatoes.
Two servings a day: A serving is one cup raw leafy vegetables; half a cup raw or cooked non-leafy vegetables; half a cup vegetable juice; a quarter of a cup dried mushrooms.
4. Beans: Black beans, cannellini beans, black-eyed peas, butter beans, soyabeans, baked beans, chickpeas, edamame, peas, kidney beans, lentils, miso, pinto beans, split peas, tofu, hummus. Three servings a day: That's a quarter of a cup of hummus or bean dip; half a cup of cooked beans, split peas, lentils or tofu; or a full cup of fresh peas or sprouted lentils.
5. Berries: Any small edible fruit, including grapes, raisins, blackberries, cherries, raspberries and strawberries. One serving a day: A serving is half a cup of fresh or frozen, or quarter of a cup of dried.
6. Other fruit, such as apples, apricots, avocados, bananas, cantaloupe melon, clementines, dates, figs, grapefruit, honeydew melon, kiwi, lemons, limes, lychees, mangos, nectarines, oranges, papaya, passion fruit, peaches, pears, pineapple, plums, pomegranates, prunes, tangerines, watermelon.
Three servings a day: One serving is a cup of cut-up fruit, or one medium fruit, or a quarter of a cup of dried fruit.
7. Flaxseeds: Snack on one tablespoon a day.
8. Nuts: A quarter of a cup a day, or two tablespoons of peanut, almond or other nut butter.
9. Spices: A quarter teaspoon of turmeric in addition to any other spices you enjoy.
10. Whole grains: Buckwheat, rice, quinoa, cereal, pasta, bread. Three servings a day: Half a cup of cooked rice or pasta; one cup of cereal; a slice of bread; half a bagel.
11. Exercise: Ideally 90 minutes a day of moderate activity, such as walking.
12. Water: Five large (12oz/340ml) glasses a day.
Physical activity is considered a promising preventive measure against breast cancer - not only because it helps with weight control but because exercise tends to lower circulating oestrogen levels.
Five hours a week of vigorous aerobic exercise can lower oestrogen and progesterone exposure by about 20 per cent.
But do you need to work out that long for it to be protective? Although even light exercise is associated with a lowered risk of some other types of cancer, for breast cancer, it appears that leisurely strolls don't appear to cut it.
Even an hour a day of activities such as slow dancing or light house work may not be of much help.
According to the largest study ever published on the subject, only women who worked up a sweat at least five or more times a week appeared to get significant protection. However, moderately intense activity may offer as much benefit as vigorous exercise.
Walking at a moderate pace for an hour a day is considered a moderately intense level of exercise.
This wasn't put to the test until a study in 2013 reported that walking an hour a day or more is associated with significantly lower breast cancer risk.
