Reduce the risk of diabetes – and breast cancer

Researchers affiliated with Harvard Medical School and funded by grants from the National Institutes of Health as well as Susan G. Komen for the Cure® recently found that a dietary pattern associated with a lower risk of diabetes is also associated with a reduced risk of breast cancer (Am J Clin Nutr 2020;112:1492-1503).

The research was performed using data gathered for the Nurses' Health Study I and II, both of which are large-scale, long term prospective studies of female nurses. The studies began gathering data in 1976 and 1989, respectively, and include a total of over 238,000 participants. Every 2 years the participants in both studies respond to questionnaires regarding their health and medical history, and diet is assessed with a detailed food frequency questionnaire every 4 years.

In previous research using the same data the authors of this study had identified a dietary pattern associated with an up to 40% lower risk of diabetes that they termed a Diabetes Risk Reduction Diet (DRRD): one that is lower in its overall glycemic index; lower in trans fat, sugar-sweetened beverages, and red or processed meat consumption; higher in cereal fiber, coffee, nuts, and fresh fruit; and with a higher ratio of polyunsaturated to saturated fats.

Noting that insulin resistance, which is linked to type 2 diabetes, has also been linked to breast cancer, the authors wondered if a greater adherence to a DRRD might also reduce a woman's risk of breast cancer.

The researchers devised a scoring system that measured adherence to a DRRD, with scores ranging from 1-5 (lowest to highest risk) for each of the 9 dietary factors of a DRRD, with the lowest overall possible score being a 9 and the highest a 45.

Using the responses to the health surveys from the NHS I and II studies as well as medical information, the authors identified those women who developed breast cancer from the start of both studies to the end of 2016 (for the NHS) and 2017 (for the NHS II). Those women who passed away before 1980 (in the NHS) and before 1991 (in the NHS II) were excluded from their analysis, along with women who reported having cancer at the start of the studies or who provided implausible dietary information in their first surveys.

Comparing the DRRD Score of those women who developed breast cancer with those who did not, the authors found that those with the highest DRRD Score had a not-insignificant reduction in risk of breast cancer of 8% after taking into account multiple variables, including change in weight from the age of 18.

The risk of premenopausal breast cancer was cut by just 4%, but postmenopausal breast cancer risk was cut by 10%.

When the authors analyzed overweight/obese women and women of clinically normal weight separately, they found that the dietary association disappeared for overweight/obese women but the inverse association still applied for women of normal weight.

What this means for you

It certainly isn't lost on us that the Diabetes Risk Reduction Diet shares several elements with a Mediterranean-style diet, including less red and processed meats; higher intake of nuts, fruits, and cereal fiber (whole grains); and a higher ratio of unsaturated to saturated fats. Yet body weight also plays a role. The good news is that if you are working on your weight - or even if you're not - a Mediterranean-style diet is one that you can live with for the long term.

First posted: February 10, 2021