The American Institute for Cancer Research (AICR) Institute has spent over $20million on a research campaign to determine the most cancer protective foods that we can include in our daily diets. This is what it came up with: 

Diets that are based mainly on plant foods, including lots of vegetables, fruit, wholegrains and legumes, are linked to lower rates of cancer. All vegetarian diets (including those which are vegan, include eggs, or include meat or fish up to once a week) are associated with overall lower rates of cancer. 

Vegetarians who frequently eat sweets, refined grains, processed foods and unhealthy added fats, do not show as much health benefit. Those who eat more vegetables, legumes, nuts and seeds show the lowest cancer risk. These foods are high in phytochemicals that may protect cells from damage. 

However, there are confounding factors: vegetarians tend to have a healthier weight, avoid tobacco, consume little or no alcohol and get regular physical activity, and it may be these factors that contribute to lower cancer rates, as much as the diet. 

There is also a strong link between consumption of dairy products, and therefore higher calcium intake, and lower risk of colorectal cancer. 

Avoid or have in small quantities occasionally: alcohol, processed meats (sausages, ham, bacon, salami), red meat, sugar-sweetened drinks. 

The plant foods with the highest cancer-protective activity are: garlic, ginger, licorice, soy foods, carrots, celery, parsley and parsnips. 

The plant foods with the next highest level of cancer protective activity include: linseed, turmuric, onion, brown rice, whole wheat, citrus fruits, all the cruciferous vegetables (broccoli, cauliflower etc), and the solonaceous vegetables (tomatoes, capsicum, potato)

Those with modest cancer protective effect include oats, barley, cucumbers, rosemary, thyme, oregano, sage and basil. 

Fruits with significant cancer protective indications include: cherries, all berries, grapes, citrus, apples. 

The consumption of 30g of nuts a day (eg walnuts, almonds, pecans, macadamias etc) is shown to reduce overall cancer risk by 15%. Nuts are also associated with less weight gain. 

Just by eating a diet that is based mostly on a wide variety of plant foods, including herbs and spices, such as the Mediterranean Diet, Pescatarian Diet, a balanced Vegetarian Diet, or any sort of omnivorous diet that is predominantly plant-based, can help protect against cancer.