What is the association of Mediterranean diet–based interventions with cardiometabolic biomarkers in children and adolescents?

In a recent study published in the JAMA Network Open, a group of researchers reviewed and meta-analyzed the randomized clinical trials (RCTs) assessing the effects of Mediterranean diet (MedDiet) (Emphasizes fruits, vegetables, whole grains, legumes, nuts, and olive oil)-based interventions on cardiometabolic biomarkers (Indicators of metabolic and cardiovascular health) in children and adolescents. 

Background 

Cardiovascular disease (CVD) prevention should start early, as childhood and adolescent cardiovascular risk factors are linked to CVD in later life. In 2020, metabolic syndrome affected about 3% of children and 5% of adults.

Lifestyle factors, especially diet, significantly influence cardiometabolic health. Unhealthy diets are linked to cardiometabolic issues in children and adolescents, while healthy diets, like the MedDiet, have positive effects.

The MedDiet reduces the risk of noncommunicable diseases. However, its cardiometabolic effects in youth have been studied less. Further research is needed to comprehensively understand the long-term cardiometabolic effects of MedDiet interventions in children and adolescents.

About the study 

This systematic review and meta-analysis followed Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and the Cochrane Handbook for Systematic Reviews of Interventions, registered with International Prospective Register of Systematic Reviews (PROSPERO).

It included studies with participants aged 18 or younger, assessing cardiometabolic biomarkers (diastolic blood pressure (DBP) (Arterial pressure when the heart rests between beats), systolic blood pressure (SBP) (Arterial pressure during heartbeats), high-density lipoprotein cholesterol (HDL-C) (“Good” cholesterol that removes other cholesterol), triglycerides (TGs), total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C) (“Bad” cholesterol that can clog arteries), glucose, homeostatic model assessment for insulin resistance (HOMA-IR), insulin, and glycated hemoglobin (HbA_1c) (Average blood glucose over 2-3 months) through RCTs of MedDiet-based interventions. Excluded were review articles, editorials, and case reports. 

The risk of bias was calculated using the Cochrane risk of bias tool for RCTs, categorizing studies as low, some concerns, or high risk. Evidence quality was assessed with the Grading of Recommendations, Development, Assessment, and Evaluations approach, indirectness, considering limitations, imprecision, inconsistency, and other factors, resulting in downgrading from initially high quality.

Small study effects and publication biases were checked using the Doi plot and Luis Furuya-Kanamori (LFK) index. Effect sizes were calculated using absolute mean differences of biomarker changes between groups, with random-effects meta-analyses and Paule-Mandel adjustment providing overall effect sizes and 95% CIs. Sensitivity analyses ensured robustness by excluding one study at a time. All analyses used R version 4.3.0 and RStudio version 2023.03.1, with meta and metasens packages, considering P 

Study results 

The PRISMA flow diagram illustrates the study selection process, resulting in the inclusion of 9 RCTs with 577 participants (344 girls and 233 boys). The mean age was 11 years (range, 3-18 years), and the mean duration was 17 weeks (range, 8-40 weeks). Intervention groups consisted of 322 participants. Six studies focused on children and adolescents with excess weight, including two targeting nonalcoholic fatty liver disease. One study enrolled children with prediabetes, and two involved apparently healthy children. Most studies included participants of both sexes, except one, which included only girls. MedDiet-based interventions had a minimum duration of 8 weeks.

Adherence to the MedDiet was assessed in four studies using the Mediterranean Diet Quality Index for Children and Adolescents. In seven RCTs, the intervention group received a MedDiet prescription, while in two RCTs, they received nutritional education based on the MedDiet. The control groups included usual care, a standard diet, or a low-fat diet.

MedDiet-based interventions were significantly associated with reductions in SBP (mean difference, −4.75 mm Hg) but not DBP. Significant associations were found for reductions in TGs, TC, and LDL-C, and increases in HDL-C. No significant associations were found for glucose, insulin, or HOMA-IR. A meta-analysis for HbA1c was not conducted due to insufficient studies.

Sensitivity analyses showed no relevant changes in the main results when individual studies were removed, except for certain cases affecting SBP, DBP, HDL-C, and glucose outcomes. The risk of bias was assessed using the Cochrane risk of bias tool for RCTs, and five studies indicated low risk, with four indicating some concerns.

Major asymmetry was observed for SBP, TC, TGs, glucose, and insulin. Minor asymmetries were found for LDL-C and HOMA-IR, while no asymmetry was observed for DBP and HDL-C. The quality of evidence for most biomarkers was classified as moderate. However, the quality of SBP and serum glucose was graded as low and HOMA-IR as very low.

Conclusions 

To summarize, this systematic review and meta-analysis found that MedDiet-based interventions were associated with reductions in TGs, SBP, TC, and LDL-C, as well as increases in HDL-C. However, the limited number of RCTs and variation in intervention types, geographic locations, and control groups necessitate caution in interpreting these results.

The modest reductions in SBP during childhood and adolescence may significantly impact long-term cardiovascular health. The MedDiet’s low intake of saturated fats and high intake of healthy fats likely contribute to its beneficial effects.