Researchers know that a higher dietary inflammatory index (DII) is linked to an increased risk of inflammation, cardiovascular disease, and therefore, mortality. Would a Mediterranean diet help? A new study sought to answer this question through a randomized trial comparing the habitual diet to the Mediterranean diet (HD vs. MD, respectively) in Australian adults.

Study: Adherence to a Mediterranean Diet for 6 Months Improves the Dietary Inflammatory Index in a Western Population: Results from the MedLey Study. Image Credit: Marian Weyo/Shutterstock

Introduction

Inflammation is a physiological response involving multiple cell chemicals, the levels of which act as biomarkers for this phenomenon. They include cytokines, interleukins, tumor necrosis factor (TNF), cell adhesion molecules, and high-sensitivity C reactive protein (hs CRP) in the acute response to potentially harmful exposure.

When the exposure or the inflammatory response continues, chronic inflammation can damage the body. This could contribute to or cause a range of disorders, such as cancers, obesity, atherosclerosis, and metabolic syndrome, many of which are associated with cardiovascular disease (CVD).

Appropriate dietary constituents have been reported to modulate chronic inflammation, such as reduced refined sugar and salt, less added sugar, and a limited intake of processed meat and dangerous fats. These are all known to be more abundant in Western diets and are linked to higher biomarkers of inflammation.

The MD is a plant-based diet with plenty of whole grains, vegetables and fruits, nuts, and olive oil. It is linked to a reduction in hsCRP and other inflammatory markers. in addition, the MD could reduce the risk of cardiometabolic diseases and death due to CVD, perhaps because it introduces a host of bioactive anti-inflammatory components into the body.

Dietary inflammation is assessed using a recently developed tool. This declares the diet pro- or anti-inflammatory, with higher or lower dietary inflammatory index (DII) scores. The index was built based on extant literature in dietetics, ranking foods by their potential to cause inflammation. Such tools could help evolve guidelines and treatment strategies for cardiometabolic disease.

The current study, published in Nutrients, looked at the effects of replacing the habitual diet with the MD for six months in older Australians regarding the DII and energy E-DII scores. In addition, it examined the effects on cognition and cardiovascular health.

The data came from the MedLey study, involving 137 healthy adults with a mean age of 71 years and an average body mass index (BMI) of ~27, which is above the upper limit of normal. The mean glucose and lipid profile were within acceptable limits, with high-normal blood pressure.

What did the study show?

Both groups showed comparable adherence to their diet at baseline, but after the intervention, the MD group had high adherence vs. unchanged levels for the HD group. The DII group was similar for both groups at baseline, but at two and four months from the start, the MD group showed a significant reduction in the DII score.

This traveled from -0.20 to -1.5 over four months of intervention, in contrast to the unchanged DII in the HD group. The E-DII scores did not show this level of significance.

Multiple markers of cardiometabolic risk and endothelial function improved at six months in the MD group compared to the other group. However, cardiometabolic markers did not reflect the changes in the DII scores, even after stratifying the groups by weight.

The DII scores showed a negative correlation with cardiometabolic markers in the HD group if the systolic blood pressure (SBP) was elevated at baseline, but no other associations were noted. The SBP was significantly elevated when the DII was raised, though this was not obvious in the non-energy-adjusted model.

The average BMI at baseline varied significantly from the lowest to the middle of the third DII score tertile, indicating the association of BMI with dietary inflammation. This persisted even after adjusting for E-DII. The same association was observed for body weight and DII tertiles.

Waist-hip ratio, a more accurate measure of visceral obesity, increased in the highest DII tertile compared to the middle one. Average abdominal fat also increased between the lowest to highest tertiles of DII or E-DII.

The average high-density lipoprotein (HDL, “good”) cholesterol showed a significantly higher mean value in the lowest tertile than the middle or highest DII tertile.

What are the implications?

The findings of this dietary intervention study showed that the MD was associated with improved DII and E-DII scores and better anti-inflammatory activity over six months, compared to the HD, in older Australians. Interestingly, this was not reflected in better cardiometabolic outcomes unless in those with higher baseline SBPs.

Differences were noted between those with the most and least inflammatory E-DII scores. Increased dietary inflammation was associated with higher BMI, average body weight, WHR, abdominal fat deposition, and SBP, while they showed lower levels of protective cholesterol.

The cohort showed a considerably lower level of dietary inflammation than American subjects, as shown in the Seasonal Variation of Blood Cholesterol Study (SEASONS), probably due to the different dietary patterns of Australia vs the USA, as well as the effect of age on the DII scores. The Observation of Cardiovascular Risk Factors in Luxembourg (ORISCAV-LUX) study showed anti-inflammatory scores in two of three participants due to the healthier dietary patterns.

Earlier research has shown that adherence to the MD is linked to lower DII scores. One study comparing the MD to a low-fat diet showed that hsCRP and other cardiac risk biomarkers of inflammation were not reduced in the MD group despite a marked lowering of the DII scores.

“Our analyses reveal an association between dietary inflammatory potential and various parameters of obesity including BMI, abdominal adiposity, waist circumference, and WHR.” This corroborates prior research supporting the association between a higher level of dietary inflammation and the DII/E-DII scores, and CVD risk factors and events, and mortality. The lowest scores were linked in this study to lower SBP and higher HDL-C.

The reduction of the inflammatory load of the diet in this trial suggests a mechanism by which a MedDiet pattern could improve cognitive and cardiovascular health. This suggests that increasing compliance with this diet could be reductive or preventative in the elderly for these and other chronic health conditions.”

Larger and more extensive studies over longer intervention periods will be necessary to interpret the results of this trial fully.

Journal reference:

• Clark, J. S. et al. (2023). Adherence to a Mediterranean diet for 6 months improves the dietary inflammatory index in a Western population: results from the MedLey study. Nutrients. doi: https://doi.org/10.3390/nu15020366 https://www.mdpi.com/2072-6643/15/2/366