The Combined Effect of Promoting the Mediterranean Diet and Physical Activity on Metabolic Risk Factors in Adults: A Systematic Review and Meta-Analysis of Randomised Controlled Trials

Abstract

Adhering to the Mediterranean diet (MD) and physical activity (PA) public health guidelines have independently been linked to health benefits in adults. These behaviours form essential components of the traditional Mediterranean lifestyle. However, their combined effect on metabolic risk has not been systematically assessed. This systematic review with meta-analysis (PROSPERO; CRD42017073958) aimed to examine, for the first time, the combined effect of promoting the MD and PA compared with no treatment, treatment with MD or PA alone, or a different dietary and/or PA treatment, and estimate its magnitude on metabolic risk factors. Medline, Embase, CINAHL and Web of Science were systematically searched until March 2018 for English language controlled interventions reporting the combined effects of the MD and PA on one or multiple metabolic risk factors in adults. Two researchers independently conducted data extraction and risk of bias assessment using a rigorous methodology. Reporting followed PRISMA guidelines. Quality of reporting and risk of bias were assessed using the CONSORT guidelines and the Cochrane Collaboration’s tool, respectively. Data from 12 articles reporting 11 randomised controlled trials (n = 1684) were included in the qualitative synthesis; across them, risk of bias was considered low, unclear and high for 42%, 25% and 33% of domains, respectively. Between-study heterogeneity ranged from 44% (triglycerides) to 98% (insulin and high density lipoprotein cholesterol (HDL)-cholesterol). Compared to a control condition, there was strong evidence (p < 0.001) of a beneficial effect of promoting the MD and PA on body weight (−3.68 kg, 95% CI (confidence intervals) −5.48, −1.89), body mass index (−0.64 kg/m2, 95% CI −1.10, −0.18), waist circumference (−1.62 cm, 95% CI −2.58, −0.66), systolic (−0.83 mmHg, 95% CI −1.57, −0.09) and diastolic blood pressure (−1.96 mmHg, 95% CI −2.57, −1.35), HOMA-IR index (−0.90, 95% CI −1.22, −0.58), blood glucose (−7.32 mg/dL, 95% CI −9.82, −4.82), triglycerides (−18.47 mg/dL, 95% CI −20.13, −16.80), total cholesterol (−6.30 mg/dL, 95% CI −9.59, −3.02) and HDL-cholesterol (+3.99 mg/dL, 95% CI 1.22, 6.77). There was no evidence of an effect on insulin concentrations. The data presented here provide systematically identified evidence that concurrently promoting the MD and PA is likely to provide an opportunity for metabolic risk reduction. However, due to the high degree of heterogeneity, most likely due to the variation in control group treatment, and the small number of included studies, findings from the pooled analysis should be interpreted with caution. These findings also highlight the need for high quality randomised controlled trials examining the combined effect of the MD and PA on metabolic risk.

Health benefits induced by adherence to the Mediterranean lifestyle components diet and physical activity

“…Moreover, a healthy diet maintains a healthy balanced intestinal microbiota (Cryan & Dinan, 2012;Dash, Clarke, Berk & Jacka, 2015;Johnson & Foster, 2018), and research indicates that this symbiosis establishes an intestines-brain axis, and is of major support to the health of the brain, by influencing the development of the brain, as well as behaviour and mood. Interestingly, in the intestines, the microbial fermentation of host-indigestible dietary fibres produces short-chain fatty acids that act as signals in the host (Kelly, Minuto, Cryan, Clarke & Dinan, 2017;Johnson & Foster, 2018). Supplementation of such fatty acids to mice has been shown to alleviate selective and enduring alterations induced by repeated psychosocial stress (van de Wouw et al, 2018).…”

“…Besides, the following examples emphasize this importance. There is established evidence that altered microbiota populations exist in human patients with autism spectrum disorders, schizophrenia, depression and obesity, compared to unaffected patients and can contribute to (brain) inflammation as well (Cryan & Dinan, 2012;Dash et al, 2015;Kelly et al, 2017;Johnson & Foster, 2018). Another accent comes from a recent large cohort, in which removal of the vermiform appendix − that hosts microbiota, pathogens and immune cells − decades before the onset of Parkinson's disease, lowers the risk of obtaining Parkinson's disease (Killinger et al, 2018).…”

“…Recently, the randomized controlled trials assessing overall health resulting from the combined intervention, physical activity and adherence to Mediterranean diet, were systematically reviewed (Malakou et al, 2018). This meta-analysis identified 11 randomized controlled trials executed between 2003 and 2017, of which the intervention duration lasted from 2 months to 6 years.…”

“…Interestingly, Malakou et al (2018) mention that none of the randomized controlled trials compare the combined effect against control groups receiving only physical activity, Mediterranean diet or no treatment respectively. Only two studies compared the combined intervention results with usual control group (Droste et al, 2013;Dunn, Siu, Freund & Boutcher, 2014) and found a reduced metabolic syndrome risk for the combined intervention.…”

<p>The Relationship Between Abdominal Body Composition and Metabolic Syndrome After a Weight Reduction Program in Adult Men with Obesity</p>

“…16 Weight reduction has been reported to improve cardiovascular risks in subjects with obesity after such a short-term intervention. [17][18][19] A greater loss of subcutaneous fat than of visceral fat was observed in the whole body as well as abdominal area among the majority of weight reduction programs (WRP). 20 However, it is reported that visceral fat was a better predictor of insulin resistance, MetS, and mortality.…”