**4. Discussion**

Our study shows that greater adherence to a Mediterranean diet, as measured by higher mMDS, was favorably associated, as expected, with various anthropometric and biochemical parameters

after adjustment by age and gender. After further adjustment for ethnicity, physical activity, and smoking, a higher mMDS remained associated with a lower total cholesterol/HDL ratio and increased HDL-cholesterol. These results are generally in agreemen<sup>t</sup> with those of our previous larger study in a di fferent Midwest firefighter cohort of 780 career male firefighters. The study sample was representative, as the participants had similar demographics, anthropometrics, and dietary habits to those of their entire fire departments and other mid-Western firefighters [39]. In our former cross-sectional study, the results indicated that a higher mMDS was associated with HDL-cholesterol and with lower LDL-cholesterol when adjusted for age, BMI, and physical activity and that the firefighters who adhere the most to the Mediterranean diet had a 35% lower risk of prevalent metabolic syndrome [39]. Taken together, our findings are biologically plausible based on previous research and lend additional credibility and validity to the mMDS. The PREDIMED study also found similar results for the Mediterranean diet arms of the intervention, where a reduction of carbohydrates and the increase of monounsaturated dietary fatty acids (MUFA) resulted in lower cholesterol levels and increased HDL cholesterol levels [46]. Similar results were reported from another recent randomized control trial from Italy [47]. In summary, the present study is consistent with past research demonstrating that the Mediterranean diet has cardioprotective e ffects by improving HDL-cholesterol levels and the total cholesterol/HDL ratio [19,23,48].

Regarding anthropometrics, our results adjusted for age and gender were consistent with previous findings associating the Mediterranean diet with BMI, waist circumference, and weight loss [19,34,49–52]. However, we found no statistically significant associations, after further adjusting for ethnicity, physical activity, and smoking status. Similarly, several other scores such as the Mediterranean Diet Scale (MDScale), Mediterranean Food Pattern (MFP), MD Score (MDS), Short Mediterranean Diet Questionnaire (SMDQ), and MedDiet score were also not significantly associated with BMI [51,52]. The di fference between our unadjusted and adjusted models may indicate an insu fficient sample size in the current study.

In our study, there was no statistically significant association between the mMDS and glucose levels, consistent with previous research and the most recent RCT meta-analysis studies [23,24,53], although we did find that high consumption of non-alcoholic sugar-sweetened beverages at home was associated with higher glucose levels, as has been shown elsewhere [54,55]. Sweet desserts consumption was associated with a total cholesterol/HDL ratio >6 and with triglycerides levels ≥150 mg/dL. Firefighters with low fruit consumption were more likely to have a total cholesterol/HDL ratio >6. On average, the firefighters were consuming three servings of fruits and vegetables per day, in contrast with the recommendations of five or more daily servings of fruits and vegetables of the American Heart Association (AHA) [56]. Thus, our results highlight the need to increase the consumption of fruits and vegetables, because of their cardioprotective role, as an integral part of the Mediterranean diet [48,57,58]. In a recent study based on how the American population can adopt the Mediterranean diet, it was recommended that the American population should replace their usual desserts such us cookies, ice creams, pies, and sweet and creamy desserts with fresh fruits to optimize their health [59]. Increased fried food consumption was also associated with a total cholesterol/HDL ratio >6 and with triglycerides levels ≥150 mg/dL. It is well documented that the quality of fried food depends on the type of the oil used for frying [60]. Even though the scores for cooking with oils or fats at home and at work were not associated with any of the indices, these scores were below 4, indicating that the consumed fat or oils were mostly oils and spreads other than olive oil (e.g., margarine, corn or vegetable oil, and other spreads). Because at baseline the firefighters were unlikely to use olive oil for cooking, their olive oil consumption was reduced, and they were missing a basic component of the Mediterranean diet which is very important for its anti-inflammatory and antioxidant benefits [61–63].

The major limitation of this study is its cross-sectional nature, which does not allow us to infer causation. Another limitation of our study is that the firefighters were mainly men (94.4%). However, this reflects the current demographic of the US career fire service. Our study was also subject to a

degree of non-response bias, as the lifestyle questionnaires were completed online by firefighters and not during the face-to-face study visits.

One of our study's strengths is that the firefighters' anthropometrics included their body fat percentage and waist circumference, not only their BMI. In fact, BMI may cause some false positives due to the increased muscle mass of some firefighters [64]. Another strength is that all our data were collected using standardized procedures, which limits bias. Also, the mMDS was created so to cover the eating habits of the firefighters at work and at home for better accuracy [39]. Finally, one of the strengths of our study is that the previously validated instrument [43] we used to examine Mediterranean diet adherence was created for the American firefighters, based on their lifestyle, eating habits, nature of work (meals at home and at work), type of drinks, and alcohol consumption and therefore is a good-quality validated instrument for this population, as it is known that the quality of Mediterranean diet scores has been questioned in different populations [38].
