Premenopausal breast cancer

There is strong evidence that:

• ‘being overweight or obese between the ages of about 18 and 30 years decreases the risk of premenopausal breast cancer’
• ‘being overweight or obese in adulthood before the menopause decreases the risk of premenopausal breast cancer’

Postmenopausal breast cancer

There is strong evidence that:

• ‘being overweight or obese between the ages of about 18 and 30 years decreases the risk of postmenopausal breast cancer’
• ‘being overweight or obese throughout adulthood increases the risk of postmenopausal breast cancer’
• ‘greater weight gain in adulthood increases the risk of postmenopausal breast cancer’

• Excess body weight and weight gain in adulthood are among the factors that increase the relative risk for invasive breast cancer in women
• Obesity is among the factors that increase the relative risk for invasive breast cancer in postmenopausal women

There is limited evidence that:

• ‘consuming non-starchy vegetables might decrease the risk of oestrogen-receptor-negative (ER-) breast cancer (unspecified)^a
• ‘consuming foods containing carotenoids might decrease the risk of breast cancer’
• ‘consuming dairy products might decrease the risk of premenopausal breast cancer’
• consuming diets high in calcium might decrease the risk of premenopausal and postmenopausal breast cancer

• Consumption of dietary fibre is associated with a reduction in the risk of breast cancer. This reduction is sometimes observed from 25 grams per day and more consistently for an intake of 30 grams per day.
• The consumption of fruits and vegetables reduces the risk of breast cancer, with a limited but suggestive level of evidence. 

• ‘No relationship could be determined between the consumption of vegetables and breast cancer’
• A clearly inverse relationship was observed between the consumption of fruits and the risk of breast cancer

'Premenopausal breast cancer

There is strong evidence that:

• ‘undertaking vigorous activity decreases the risk of premenopausal breast cancer’

There is limited evidence that:

• ‘being physically active might decrease the risk of premenopausal breast cancer’

Postmenopausal breast cancer

There is strong evidence that :

• ‘being physically active (including vigorous physical activity) decreases the risk of postmenopausal breast cancer’

• Physical inactivity is among the factors that increase the relative risk for invasive breast cancer in women

There is strong evidence that:

• consuming alcoholic drinks increases the risk of premenopausal and postmenopausal breast cancer'

• Alcohol consumption increases the relative risk for invasive breast cancer in women

There is strong evidence that:

• ‘breastfeeding decreases the risk of breast cancer (unspecified)^a in the mother’

• Breastfeeding decreases the risk of breast cancer overall (i.e. all subtypes of breast cancer combined)

• Women with a family history of breast, ovarian or related (prostate or pancreatic) cancer should be advised to breastfeed if possible because this is likely to reduce their risk of breast cancer, and is in accordance with general health advice.