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Table 2 Meta-analyses of studies regarding the effects of Mediterranean diet on obesity-associated disorders

From: Mediterranean Diet and Obesity-related Disorders: What is the Evidence?

Source

No. and type of studies

Subjects

Aim

Main findings

Esposito et al. [22]

16 RCTs

3436 subjects

To evaluate the effect of MD on body weight

MD had a significant effect on weight (95% CI −2.86 to −0.64) and BMI (95% CI −0.93 to −0.21). The effect of MD on body weight was greater in association with energy restriction (mean difference, −3.88 kg, 95% CI −6.54 to −1.21 kg), increased physical activity (−4.01 kg, 95% CI −5.79 to −2.23 kg), and follow-up longer than 6 months (−2.69 kg, 95% CI −3.99 to −1.38 kg)

Franz et al. [25]

11 RCTs

6754 adults with overweight or obesity and T2DM

To evaluate the outcomes on HbA1c, lipid (total cholesterol, LDL-C, HDL-C, and TG) and BP (systolic and diastolic) from lifestyle weight-loss interventions resulting in weight losses greater than or less than 5% at 12 months

To evaluate the weight and metabolic outcomes from differing amounts of macronutrients in weight-loss interventions

2 study groups reported a weight loss of ≥ 5%: a Mediterranean-style diet implemented in newly diagnosed adults with T2DM, and an intensive lifestyle intervention implemented in the Look AHEAD trial. Both included regular physical activity and frequent contact with health professionals and reported significant beneficial effects on HbA1c, lipids, and blood pressure

Kastorini et al. [36]

50 RCTs (35 clinical trials, 2 prospective and 13 cross-sectional)

534,906 subjects

To meta-analyze epidemiological studies and clinical trials that have assessed the effect of MD on metabolic syndrome as well as its components

Adherence to MD was associated with reduced risk of metabolic syndrome (log HR −0.69; 95% CI −1.24 to −1.16). Results from clinical studies revealed the protective role of MD on components of metabolic syndrome, like WC (mean difference −0.42 cm; 95% CI −0.82 to −0.02), HDL-C (mean difference 1.17 mg/dl; 95% CI 0.38 to 1.96), TG (mean difference −6.14 mg/dl; 95% CI −10.35 to −1.93), systolic (mean difference −2.35 mm Hg; 95% CI −3.51 to −1.18) and diastolic BP (mean difference −1.58 mm Hg; 95% CI −2.02 to −1.13), and glucose (mean difference −3.89 mg/dl; 95% CI −5.84 to −1.95), whereas results from epidemiological studies also confirmed those of clinical trials

Koloverou et al. [49]

10 prospective studies (1 clinical trial, 9 prospective and 7 cross-sectional)

136,846 subjects

To meta-analyze prospective studies that have evaluated the effect of MD on the development of T2DM

Higher adherence to MD was associated with 23% reduced risk of developing T2DM (combined RR for upper vs lowest available centile: 0.77; 95% CI 0.66 to 0.89). Subgroup analyses based on region, health status of participants and number of confounders controlling for, showed similar results

Schwingshackl et al. [50]

1 RCT and 8 prospective cohort studies

122,810 subjects

To meta-analyze the effects of MD adherence on the risk of T2DM

For highest vs lowest adherence to MD score, the pooled RR for T2DM was 0.81 (95% CI 0.73 to 0.90). Sensitivity analysis including only long-term studies confirmed the results of the primary analysis (pooled RR 0.75; 95% CI 0.68 to 0.83)

Pan et al. [61]

10 RCTs

921 subjects with T2DM

To comprehensively compare the differences between major dietary patterns in improving glycemic control, cardiovascular risk, and weight loss for patients with T2DM

Compared to low-fat diet, MD showed beneficial effects in glycemic control (HbA1c 95% CI –0.55 to –0.34; fasting plasma glucose 95% CI –1.57 to –0.91; weight loss 95% CI –1.99 to –0.37; WC 95% CI –1.26 to –0.19), and cardiovascular risk factors (HDL-C 95% CI 0.04 to 0.11; total cholesterol 95% CI –0.26 to –0.08; TG 95% CI –0.27 to –0.16)

Huo et al. [62]

9 RCTs

1178 subjects with T2DM

To explore the effects of MD on glycemic control, weight loss and cardiovascular risk factors in T2DM patients

Compared with control diets, MD led to greater reductions in HbA1c (mean difference, −0.30; 95% CI −0.46 to −0.14), fasting plasma glucose (−0.72 mmol/l; 95% CI −1.24 to −0.21), fasting insulin (−0.55 μU/ml; 95% CI −0.81 to −0.29), BMI (−0.29 kg/m2; 95% CI −0.46 to −0.12) and body weight (−0.29 kg; 95% CI −0.55 to −0.04). Likewise, concentrations of total cholesterol and TG were decreased (−0.14 mmol/l; 95% CI −0.19 to −0.09 and −0.29 mmol/l; 95% CI −0.47 to −0.10, respectively), and HDL-C was increased (0.06 mmol/l; 95% CI 0.02 to 0.10). In addition, MD was associated with a decline of 1.45 mm Hg (95% CI −1.97 to −0.94) for systolic and 1.41 mm Hg (95% CI −1.84 to −0.97) for diastolic BP

Hansrivijit et al. [67]

4 prospective studies

8467 subjects ≥ 18 years of age without CKD

To assess the association between MD adherence and CKD prevention

With the mean follow-up duration of 20.6 ± 7.0 years, the pooled OR for CKD was 0.901 (95% CI 0.868 to 0.935) for each 1-point increment of MD scale. The incidence of CKD was 0.026 events per person-year (95% CI 0.008 to 0.045)

Becerra-Tomás et al. [84]

3 RCTs and 38 prospective cohort studies

Adults

with type 1 diabetes or T2DM

To evaluate the effect of MD on the prevention of CVD incidence and mortality

Meta-analyses of RCTs revealed a beneficial effect of MD on total CVD (RR: 0.62; 95% CI 0.50 to 0.78) and total myocardial infarction (RR: 0.65; 95% CI 0.49 to 0.88) incidence

Meta-analyses of prospective cohort studies, which compared the highest vs lowest categories of MD adherence, revealed an inverse association with total CVD mortality (RR 0.79; 95% CI 0.77 to 0.82), CHD incidence (RR 0.73; 95% CI 0.62 to 0.86), CHD mortality (RR 0.83; 95% CI 0.75 to 0.92), stroke incidence (RR 0.80; 95% CI 0.71 to 0.90), stroke mortality (RR 0.87; 95% C: 0.80 to 0.96) and myocardial infarction incidence (RR 0.73; 95% CI 0.61 to 0.88)

Schwingshackl et al. [146]

2 RCTs, 51 cohort studies and 30 case–control studies

2,130,753 subjects

To evaluate the effects of adherence to MD on risk of overall cancer mortality, risk of different types of cancer, and cancer mortality and recurrence risk in cancer survivors

Greater adherence to MD was associated with a significantly lower risk of cancer mortality (RR 0.86; 95% CI 0.81 to 0.91), colorectal cancer (RR 0.82; 95% CI 0.75 to 0.88), breast cancer (RR 0.92; 95% CI 0.87 to 0.96), gastric cancer (RR 0.72; 95% CI 0.60 to 0.86), liver cancer (RR 0.58; 95% CI 0.46 to 0.73), head and neck cancer (RR 0.49; 95% CI 0.37 to 0.66), and prostate cancer (RR 0.96; 95% CI 0.92 to 1.00)

  1. RCT randomized controlled trial, MD Mediterranean diet, CI confidence interval, BMI body mass index, T2DM type 2 diabetes mellitus, LDL-C low-density lipoprotein cholesterol, HDL-C high-density lipoprotein cholesterol, BP blood pressure, AHEAD Action for Health in Diabetes, HR hazard ratio, WC waist circumferences, RR risk ratio, CKD chronic kidney disease, CVD cardiovascular disease, CHD coronary heart disease

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