A study from Brigham and Women’s Hospital examined the outcomes of more than 25,000 participants in the Women’s Health Study (WHS), finding that women who adhered to a more Mediterranean (MED) diet had a 30% lower rate of type 2 diabetes (T2D) than women who did not.

Examining several biomarkers to look for biological explanations for these results, the research team found key mechanisms, including insulin resistance, body mass index (BMI), lipoprotein metabolism, and inflammation, according to the study authors.

"Our findings support the idea that by improving their diet, people can improve their future risk of type 2 diabetes, particularly if they are overweight or have obesity," said corresponding author Samia Mora, MD, MHS, of the Brigham's divisions of Preventive Medicine and Cardiovascular Medicine, in a prepared statement. "A lot of the benefit we see can be explained through just a few pathways. And it's important to note that many of these changes don't happen right away—while metabolism can change over a short period of time, our study indicates that there are longer term changes happening that may provide protection over decades."

The WHS enrolled female health care professionals between 1992 and 1995, collected data through December 2017, and was designed to evaluate the effects of vitamin E and low-dose aspirin on risk of heart disease and cancer. Participants were asked to complete food frequency questionnaires (FFQs) about dietary intake when the study began and answer other questions about lifestyle, medical history, demographics, and more, according to the study authors.

The researchers leveraged data from the FFQs and blood samples to investigate the relationship between the MED diet, T2D, and biomarkers that might explain the connection. Each participant was assigned a MED diet intake score from 0 to 9, with points assigned for higher intake of fruits, vegetables, whole grains, legumes, nuts, and fish, moderate intake of alcohol, and lower intake of red or processed meat.

Further, the research team measured a range of biomarkers, including traditional ones such as cholesterol, and more specialized ones that can only be detected using nucleic magnetic resonance. This included lipoproteins and measures of insulin resistance, which is a common precursor to diabetes, according to the study authors.

Out of the approximately 25,000 participants in the WHS, 2307 developed type 2 diabetes. Participants with higher MED intake at the beginning of the study, or scores greater than or equal to 6, developed diabetes at rates that were 30% lower than participants with lower MED intake, or scores less than or equal to 3. This effect was seen only among participants with a BMI greater than 25, which is the overweight or obese range, and not among participants whose BMI was less than 25, which is considered normal or underweight.

Additionally, biomarkers of insulin resistance appeared to be the biggest contributor to lower risk, followed by biomarkers of BMI, high-density lipoprotein measures, and inflammation.

"Most of this reduced risk associated with the Mediterranean diet and type 2 diabetes was explained through the biomarkers related to insulin resistance, adiposity, lipoprotein metabolism and inflammation," said study author Shafqat Ahmad, PhD, in a prepared statement. "This understanding may have important downstream consequences for the primary prevention of diabetes disease."

Although a strength of the study was its length, the study authors noted several limitations, including the study participants being predominantly white, well-educated, and female health professionals. Additionally, dietary intake was self-reported and only examined at the beginning of the study, just as biomarkers were measured.

The study authors emphasized that insights into the biology that explain how the Mediterranean diet may help protect against diabetes could be helpful in preventive medicine and for physicians speaking to patients about dietary changes.

"Even small changes can add up over time," Mora said in a press release. "And there may be many biological pathways that lead to a benefit. One of the best things patients can do for future health is to improve their diet, and now we are beginning to understand why."

Mediterranean diet tied to 30 percent risk reduction for diabetes in Women’s Health Study. EurekAlert! Published November 19, 2020. Accessed November 24, 2020. https://www.eurekalert.org/pub_releases/2020-11/bawh-mdt111820.php