Introduction

Ask any woman which disease she fears most and there is a good chance she will say breast cancer. By the time you reach your thirties, or certainly your forties, you will probably know someone who has, or has had breast cancer. It's the most common cancer affecting women in the UK. Each year, there are over 40,000 new cases. One in every nine women in the UK will develop breast cancer at some point in their lives. Although less prevalent, breast cancer occurs in men too, affecting one in 300 men during their lifetime.

It has been widely publicised that the chances of surviving breast cancer have greatly improved. Not so well-publicised is that the chance of developing breast cancer is a good deal higher too than it was in the 1970s. Between 1971 and 2003, the incidence of breast cancer has increased by a staggering 80 per cent. However, the total number of women dying from breast cancer has remained fairly constant.

A number of potential causative risk factors are generally accepted including the early onset of periods, late menopause, having a first child late in life and, of course, genetics. Many people think that their risk of developing breast cancer is beyond their control, that "fate" will decide. This type of genetic fatalism results from the much-publicised link between genes and breast cancer. However, less than 10 per cent of all breast cancers are caused by faulty genes, the vast majority are caused by environmental factors including diet. Despite a growing body of scientific evidence, there is a widespread reluctance to acknowledge the role of diet in breast cancer risk.

Numerous studies link the consumption of red meat to breast cancer. A range of mechanisms by which red meat leads to an increased risk of breast cancer have been proposed including the presence of carcinogens in meat, the hormone treatment of beef cattle (banned in Europe but practiced widely in the US) or a high intake of haem iron (a highly bioavailable form of iron from meat) which can induce tumour growth. Other studies suggest animal fat may be involved as it can raise steroid hormone levels, and high hormone levels are linked to an increased risk of breast cancer.

The role of hormones and growth factors present in cow's milk is also a growing concern for many scientists. The hormone content of milk is very different from that of milk produced 100 years ago as modern dairy cows (including organically farmed cows) are frequently impregnated while still producing milk. In fact, two-thirds of retail milk in the UK is taken from pregnant cows, when the hormone content of the milk is markedly elevated. Cow's milk has been shown to contain over 35 different hormones and 11 growth factors. A recent survey of the published data on the occurrence of hormones in cow's milk and milk products argues that, in the light of modern dairy farming methods, there is a need to update the data concerning hormonal levels in milk and milk products.

Other scientists are concerned about another bioactive molecule found in milk; a growth factor called insulin-like growth factor 1 (IGF-1). This growth factor sends a strong signal in breast milk (including human and cow's) from mother to infant directing fast growth and development. IGF-1 is not destroyed during pasteurisation and may be absorbed across the gut wall into the bloodstream. Higher circulating IGF-1 levels are associated with an increased risk of breast cancer and other cancers.

This is undoubtedly difficult for many people to accept as it is deeply entrenched in the British psyche that cow's milk is a natural and normal drink for people of all ages. However, most people in the world don't drink milk after weaning; they are lactose intolerant. This means they cannot digest the sugar in milk (lactose). For lactose to be digested, it must be broken down in the intestine by the enzyme lactase to its component monosaccharides glucose and galactose. Glucose can then supply energy to the young animal. All young mammals possess the enzyme lactase and can therefore digest lactose, but this ability is lost in most humans after weaning (commonly after the age of two). In global terms lactose intolerance is very common, affecting around 70 per cent of the world's population. So, contrary to popular belief in the West, not drinking milk beyond weaning is the norm.

There is some good news though. Many studies show how plant-based foods may offer a protective role against breast cancer. Increasing your intake of vegetables (especially salad vegetables) may help. Increasing the amount of (cereal) fibre in the diet may also reduce breast cancer risk by lowering oestrogen levels. Fibre also protects bowel health, slows sugar and fat absorption and lowers cholesterol. Good sources include fruit and vegetables, wholegrains, pulses, nuts and seeds. Meat and dairy foods do not contain any fibre.

It is beyond the scope of this report to attempt to review all the scientific studies investigating the role of diet in breast cancer. However, this report aims to provide a representative sample, including some key studies. Two consistent themes are very apparent throughout the scientific literature: animal-based foods (meat, animal fat and dairy foods) are linked to an increased risk of breast cancer and plant-based foods (fruit and vegetables, especially salad vegetables and fibre), are linked to a lower risk of this disease.

In summary, this report presents a substantial and representative sample of the evidence showing how dietary factors make a significant contribution to the risk of breast cancer.

For more information on what is the healthiest diet for prevention of, and for those who have, breast cancer see the the guide A Fighting Chance. A guide to healthy eating to help prevent and overcome breast cancer. For more information on the detrimental effects of consuming cow's milk and dairy products see the Viva!Health's fully-referenced scientific report White Lies.