Dairy and Cancer connection

A recent article, “Applying the Precautionary Principle to Nutrition and Cancer” (Gonzales, 2014), was published in the Journal of the American College of Nutrition with guidelines for eating and cancer prevention. What is new about the report is the recommendation to limit or avoid milk and dairy products as part of a more plant based diet to prevent cancer. The evidence comes from the 2007 report of the World Cancer Research Fund/American Institute for Cancer Research (WCRF/AICR) and other evidence sources published after the WCRF/AICR report. The authors say that people cannot wait for evidence based consensus and that families have to act now on the best available evidence. So, they developed 6 dietary principles (see box) in which evidence of dietary influence in cancer risk is substantial, even if not conclusive. The report lists 6 guidelines that recommend eating more vegetables and fruits, more soy products, little or no alcohol, little or no dairy and red meats and avoidance of meat that has been fried, grilled or broiled.

SUGGESTED DIETARY GUIDELINES FOR CANCER PREVENTION*:
1.       Limiting or avoiding dairy products may reduce the risk of prostate cancer.

2.     Limiting or avoiding alcohol may reduce the risk of cancers of the mouth, pharynx, larynx, esophagus, colon and rectum, and breast.

3.       Avoiding red and processed meat may reduce the risk of cancers of the colon and rectum.

4.     Avoiding grilled, fried, and broiled meats may reduce the risk of cancers of the colon, rectum, breast, prostate, kidney, and pancreas. In this context, meat refers to red meat, poultry, and fish.

5.      Consumption of soy products during adolescence may reduce the risk of breast cancer arising in adulthood. Soy products may also reduce the risk of recurrence and mortality for women previously treated for breast cancer.

6.     Emphasizing fruits and vegetables in your diet will likely reduce the risk of several common forms of cancer.

* Note that this review specifies suggested dietary guidance in which evidence of a dietary influence on cancer risk is substantial, but not necessarily conclusive



It is not new that there are many advocates for a diet that totally excludes dairy products –milk, yoghurt, cheese and butter- arguing that this helps to stop cancer cells from growing, especially hormone-related cancers such as prostate, testicle and ovarian cancer (see the Milk article in the latest FNM). But, what says the evidence? Studies that investigate a link between dairy and cancer are inconclusive. Some research shows an increase in the risk of developing prostate cancer (Li-Qiang Qin 2009), while others show possible protective role of dairy products on colorectal cancer risk (Murphy, 2013). And, consumption of dairy products has not been identified as a risk factor for breast or other types of cancer (Pala, 2009).

Despite evidence limitations, when it comes to milk and dairy, the article published in the JACN suggest: “Limiting or avoiding dairy products may reduce the risk of prostate cancer”. It was found that eating 35 grams of dairy protein (more than 4 cups of milk) increases the risk of prostate cancer by 32%. It´s believed that the mechanism to increase prostate cancer risk is the ability of a large oral calcium dose to suppress vitamin D activation and the tendency of milk to increase serum insulin-like growth factor-I (IGF-I) concentrations.

The authors acknowledge disadvantages of this recommendation and suggest eating other sources of calcium (leafy vegetables, legumes, and calcium-fortified foods).  As a food and nutrition professional, I believe that the recommendation of limiting dairy for cancer prevention can be risky and confusing for the press and for the public, specially, because dairy products are the main dietary source of calcium, an essential nutrient for bone health and may even prevent colon cancer.  I think that, for now, we should focus on a total diet approach and recommend a healthy, well balanced diet (with more than 5 serving of fruits and vegetables daily). Calcium should be part of that diet, and milk is an important source of calcium. 

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