4. Discussion
diabetes, metabolic syndrome, chronic diseases, chronic disease, diabetes
OBESE, CARDIOVASCULAR DISEASE, CHRONIC DISEASES, DIABETES, METABOLIC DISEASE, HYPERTENSION, CHRONIC DISEASE
This randomized controlled trial showed that a 4-month lifestyle intervention based on the Mediterranean diet and moderate physical activity determined a positive change in diet quality and physical activity in healthy, normal-weight, young men.The subjects enrolled in the intervention group, who followed a nutritionist-counseled pathway based on a Mediterranean diet pattern for 4 months, modified their habits, on the average, in a relatively short time (4 months), compared to those in the control group, who received only general recommendations on a correct lifestyle. The latter approach was considered equivalent to a “placebo”, as it has not been found to modify individuals’ habits according to literature.As regards diet, we observed significant differences in food intake changes, from the beginning to the end of the intervention time, between the two groups. Particularly, the mean intake of vegetables, legumes, fruits, nuts and seeds, whole grains, and fish increased, and that of red and processed meat, cheese, sweets, and sweetened drinks decreased significantly more in the INT than the CTRL group. Accordingly, the mean intake of animal protein, saturated fats, and sodium decreased, and that of plant protein, omega-3 and omega-6 fatty acids, fibers, vitamin C, folic acid, beta-carotene, and vitamin E increased in the INT group, with statistically significant differences as compared to the CTRL group. In agreement with the changes in the macro- and micro-nutrient intake, also the PREDIMED mean score increased significantly more in the INT than the CTRL group.Most of the significant differences observed between the INT and CTRL groups at t4 were still present at t8, 4 months after the end of the intervention, although a decline in the adherence to dietary suggestions was found as regards the PREDIMED score and food items. In the same way, the mean physical activity level, measured as the IPAQ score, showed a slight decrease from the end of the intervention to the end of follow-up (from 4 to 8 months since the start) (see The control group showed a lower change in dietary habits than the intervention group, particularly at the 4-month evaluation. However, the control group increased physical activity, similarly to the intervention one, without substantial differences between the two groups. Overall, these findings suggest that participation in the study by itself, with the visits, blood sampling, and interviews, was a sort of “nudge” for the students in the control group, in spite of receiving no more than a leaflet and generic recommendations to follow present guidelines. Furthermore, since both intervention and control group participants were students in the same classes, a potential contamination between the two groups may have occurred, with some control group subjects following the suggestions for the intervention group. Therefore, the “true” efficacy of the intervention may be higher than that which we found when comparing the before–after changes between the two groups (“dilution effect”).The age mismatch between our study and other diet-based RCTs makes a comparison difficult. Usually, RCTs on diet are conducted among adults or old people and focused on making people lose weight, have better control of their chronic diseases, such as hypertension, diabetes, or metabolic disease, or prevent chronic disease occurrence. Overall, dietary intervention studies showed that an increased adherence to the Mediterranean diet has benefits in reducing body weight and/or risk of diabetes, metabolic syndrome, cardiovascular disease, and/or in contrasting risk factors for chronic diseases [The Mediterranean diet has been found to reduce the risk of developing chronic diseases and the overall mortality rate in both experimental and observational studies [The positive results of our trial, even in the control group, are noteworthy when considering the limits of lifestyle interventions among healthy adolescents. Indeed, participants in our trial were high school and university male students, most of whom lived with their parents and therefore had no active role, and probably limited influence, in meal preparation. Furthermore, since they were all healthy subjects, with normal blood pressure, blood parameters, and body mass index, they were less motivated to change their habits than obese or diseased people, who are usually the target of lifestyle interventions, although the volunteer participation in the trial has probably caused a self-selection of young people more interested in their own health than the general student population.This RCT has some strengths, including the use of international standardized questionnaires, the multiple contacts between each participant, and an expert dietician in the intervention group for the whole period, the support of some organic food samples as an incentive to follow the dietician’s suggestions, and the relatively low attrition in the two arms, especially in the intervention group.However, it has some limitations, too. The study design included only a short-term evaluation of the effects of the intervention; therefore, we cannot say if students’ lifestyle improvements will be maintained in the future. The observation at 4 months after the end of the intervention (t8) showed a trend of decreasing adherence to the Mediterranean diet and to a regular physical activity program. According to the main objective of the FASt project, i.e., evaluating the semen quality in adolescents living in polluted areas, only males were enrolled in our study. Therefore, a generalization of the study results to females may be seen as speculative. However, young females are usually more aware of health problems and at least as likely as peer males to follow dietary recommendations. Therefore, we are confident that our findings are of note for women too.The randomization of subjects into the two arms of the study was correct, producing two comparable groups, as shown by the lack of differences between the intervention and control groups for almost all study variables at baseline. However, the RCT was not blinded, which is a limit of almost all dietary interventions, and therefore the assessment of participants’ lifestyle based on questionnaires may be prone to recall bias.Third, a per-protocol analysis, including only the subjects with complete questionnaire data at each observation time, was performed. Even if an intention-to-treat analysis, including also subjects lost at follow-up, is usually performed in RCTs, such analysis was not feasible here, because the subjects withdrawn from the study did not attend the visit and questionnaire sessions. The dropout rates were higher in the control than the intervention group, at both visits, at the end of intervention time (17% and 7%, respectively), and at the end of the follow-up time (30% and 21%, respectively). However, the baseline characteristics of the individuals attending and those not attending the 4th- and 8th-month evaluations were not statistically different for almost all variables and dietary parameters. Therefore, we are confident that no substantial selection bias affected the results of the per-protocol instead of an intention-to-treat analysis, at least at the 4th-month evaluation.