Adherence to Mediterranean Diet Associated with Lower Rate of T2D in Women

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Women who adhered to a Mediterranean-like diet had a 30% lower rate of type 2 diabetes (T2D) vs women who did not, according to a recent study published in the journal JAMA Network Open.

"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, associate professor of medicine, Harvard Medical School, associate physician, divisions of Preventive Medicine and Cardiovascular Medicine, Brigham and Women’s Hospital, in a press release.

"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," continued Mora.

The Mediterranean diet is recommended to reduce the risk of heart disease, T2D, and other adverse health outcomes, but how and why the diet lowers risk of T2D specifically remains unclear.

To examine the association further, researchers selected 25 317 participants from the Women’s Health Study (WHS)—a completed clinical trial that followed female health care professionals for over 2 decades—who provided blood samples and completed a food frequency questionnaire (FFQ) about dietary intake at time of enrollment.

Participants included in the current study were free of diabetes at time of enrollment, the mean age of participants was 52.9 years, and they were followed for a mean of 19.8 years.

Each participant was assigned a Mediterranean diet intake score between 0 and 9. Points were assigned for higher intake of Mediterranean-diet-based foods (eg, legumes, fish, fruits), moderate alcohol consumption, and lower red meat intake.

Out of the 25 317 participants, 2307 developed T2D. Women with higher Mediterranean diet consumption at the beginning of the study (scores ≥6) developed T2D at rates that were 30% lower than women with lower Mediterranean diet scores (≤3). In posthoc analyses, however, this effect was only seen among women with a baseline body mass index (BMI) >25 kg/m² and not among those with a BMI <25 kg/m².

Biomarkers of insulin resistance were responsible for the largest proportion of T2D risk reduction (65.5%), followed by BMI (55.5%), high-density lipoprotein measures (53%), and inflammation (52.5%).

"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 first author Shafqat Ahmad, PhD, researcher, Molecular Epidemiology Unit, Uppsala University, Sweden, in the same press release. "This understanding may have important downstream consequences for the primary prevention of diabetes disease."

Unlike previous studies that have looked at the short-term impact of dietary intake, the WHS followed participants for 25 years—a significant strength of the study. Limitations, the authors point out, include lack of racial and ethnic diversity and an all-female population, self-report of dietary intake, and no follow-up measurement of biomarkers.