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Research in women of average risk supports the potential benefits of a healthy diet; however, experts do not know the exact effect of diet on hereditary cancer risk. Proving that specific foods affect cancer risk is challenging, and studies of diet and cancer risk are often inconclusive. Research shows that plant-based, high-fiber foods provide phytochemicals and antioxidants; nutrients that contain beneficial chemicals that may protect cells and help repair DNA damage. Vegetables like broccoli, Brussels sprouts, cauliflower, and fruits and vegetables that are red, orange, or purple contain these compounds.
Researchers are exploring the effects of different foods and phytochemicals on cancer risk in high-risk people; so far, no single nutrient has proven to lower cancer risk in people with hereditary mutations. The American Institute for Cancer Research (AICR) recommends meals that consist of two-thirds or more fruits, vegetables, beans and whole grains, and one-third or less of lean protein. One study that observed women with BRCA mutations found those who ate a varied diet had a lower breast cancer risk.
While many studies on diet and cancer risk look at people at average risk for cancer, some study high-risk families. A 2006 study, for example, examined women from 80 French Canadian families: 89 women had BRCA mutations and cancer, while 48 had BRCA mutations but no cancer. The study correlated increased calorie intake with increased breast cancer incidence. The age at the time of maximum body mass index (BMI) also correlated with elevated incidence. Researchers found no overall link between BMI or weight and increased risk, but increased weight gain after age 18 and age 30 resulted in a significantly higher incidence of breast cancer.
This same population of French Canadians was used in a 2007 study, but focused on how effectively different indices of diet correlated with cancer incidence. This subsequent study used a number of different indices, but two, the "DQI-R" and "CHEI" indices showed significant differences between high and low scorers. The CHEI index is based on Canada’s guide for healthy eating. According to the DQI-R index guidelines, a good daily diet contains all of the following:
Points in this index were given for satisfying the recommended daily allowances for individual food groups: grains, fruit and vegetables, milk, and meat/protein alternatives. Higher scores signify overall food diversity as each food group was scored individually, with a maximum score given when the recommended servings of that group were consumed. Individuals who scored well using the DQI-R or CHEI scales had a significantly reduced cancer incidence when compared to carriers with lower scores.
A study among a different cohort of 38 French Canadians in 2009 found that vegetable diversity, but not intake amount, led to decreased likelihood of cancer in BRCA mutation carriers.