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Mediterranean [and exercise] Diet Helps Prevent Metabolic Syndrome, Abdominal Obesity, Elevated Lipids, Hypertension - pdf attached
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J Am Coll Cardiol, 2011
"Conclusions:The results of the present meta-analysis suggest that adherence to the Mediterranean dietary pattern was associated with lower MS prevalence and progression. Moreover, greater adherence to this traditional dietary pattern was associated with favorable effects on the MS components. These results are of considerable public health importance, because this dietary pattern can be easily adopted by all population groups and various cultures (65) and cost-effectively serve for the primary and secondary prevention of the MS and its individual components."
"At this point it should be mentioned that abdominal obesity is one of the main causes for the appearance of all the components of the MS, because adipose tissue plays an important role in lipid and glucose metabolism and is responsible for the production of various cytokines influencing the development of the syndrome (54). The present meta-analysis based on results from both observational studies and clinical trials revealed the beneficial effect of the MD with regard to central obesity."..... results of the present meta-analysis suggested that adherence to the MD coupled with physical activity has even more beneficial effects, showing the significant role of an active lifestyle for the prevention of the MS components.
"adherence to the Mediterranean diet was associated with reduced risk of MS:.....The MD is one of the most known and well-studied dietary patterns, which has been shown to be associated with human health, especially decreased mortality from all causes, lower risk for cardiovascular disease, and cancer (8); it is also exerting a beneficial role with regard to type 2 diabetes and obesity (9,10)......present meta-analysis add to the existing knowledge, because they indicate that adherence to the MD has a positive effect on human health through different ways. The MD has a beneficial effect on abdominal obesity, lipids levels, glucose metabolism, and blood pressure levels, all the components of the MS, which are also risk factors for the development of cardiovascular disease, insulin resistance, and diabetes. The antioxidant and anti-inflammatory effects of the MD as a whole as well as the effects of the individual components of the MD and specifically olive oil, fruits and vegetables, whole grains, and fish could offer a possible explanation for the aforementioned findings (9,11-15)...... results from clinical studies (mean difference, 95% CI) revealed the protective role of the Mediterranean diet on components of MS, like waist circumference (-0.42 cm, 95% CI: -0.82 to -0.02), high-density lipoprotein cholesterol (1.17 mg/dl), triglycerides (-6.14 mg/dl), systolic (-2.35 mm Hg) and diastolic blood pressure (-1.58 mm Hg), and glucose (-3.89 mg/dl)
MedPage Today
Published: March 10, 2011
Patients who eat a Mediterranean diet -- rich in fruits, vegetables, whole grains, and olive oil -- lowered prevalence and progression of metabolic syndrome and its components, according to results from a meta-analysis of 50 studies.
Participants who followed the Mediterranean diet had better outcomes for waist circumference, high-density lipoprotein cholesterol, triglycerides, systolic and diastolic blood pressure, and glucose, as well as reduced risk of metabolic syndrome, compared with those on control diets or those who had low adherence to the Mediterranean diet, according to Demosthenes Panagiotakos, PhD, of Harokopio University in Greece, and colleagues.
Researchers looked for outcomes of development or progression of metabolic syndrome or changes in its components.
The diet was associated with a beneficial effect on waist circumference compared against low adherence or a control diet in three observational studies and one clinical trial.
The diet also was associated with beneficial effects on HDL cholesterol levels in 32 studies. Of the studies using a control diet, seven reported beneficial effect of the Mediterranean diet on HDL cholesterol, while two reported benefits for a high-saturated-fat diet.
In all, 29 of the clinical trials looked at the diet's effect on triglycerides; five reported the diet had a beneficial effect, while the remainder reported no significant difference.
"Overall, adherence to the Mediterranean diet was associated with lower triglyceride levels as compared with the control diet," the authors noted. However, they added that "Heterogeneity of the effect measures regarding triglyceride levels was also evident."
Of five observational studies measuring systolic blood pressure relative to adherence to a Mediterranean diet, two reported benefit, while one showed raised blood pressure compared against low adherence to the diet. The diet was not associated with systolic blood pressure levels when compared against a control diet.
An additional 14 clinical trials measured systolic blood pressure and found the diet was associated with lower systolic blood pressure.
When compared against a control diet, the Mediterranean diet also was associated with lower fasting glucose levels in two observational studies and six clinical trials.
The researchers added that the diet showed more prominent effects in Mediterranean countries, possibly due to easier access to associated dietary products, and confounders including genetics and environment. The meta-analysis also found that active lifestyle coupled with the diet had additional preventive effects on metabolic syndrome components.
The authors noted several limitations in the study, including a lack of homogeneity in the characteristics of the Mediterranean diet used in the studies, lack of a standardized dietary intervention in the clinical trials, and considerable heterogeneity among the studies which could affect generalizability of the results.
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The Effect of Mediterranean Diet on Metabolic Syndrome and its Components
A Meta-Analysis of 50 Studies and 534,906 Individuals
J Am Coll Cardiol, 2011
Christina-Maria Kastorini, MSc*,{dagger}, Haralampos J. Milionis, MD, PhD{dagger}, Katherine Esposito, MD, PhD{ddagger}, Dario Giugliano, MD, PhD{ddagger}, John A. Goudevenos, MD, PhD{dagger} and Demosthenes B. Panagiotakos, PhD*,*
* Department of Nutrition Science-Dietetics, Harokopio University, Athens, Greece
{dagger} School of Medicine, University of Ioannina, Ioannina, Greece
{ddagger} Department of Geriatrics and Metabolic Diseases, Second University of Naples, Naples, Italy
Abstract
Objectives: The aim of this study was to meta-analyze epidemiological studies and clinical trials that have assessed the effect of a Mediterranean diet on metabolic syndrome (MS) as well as its components.
Background: The Mediterranean diet has long been associated with low cardiovascular disease risk in adult population.
Methods: The authors conducted a systematic review and random effects meta-analysis of epidemiological studies and randomized controlled trials, including English-language publications in PubMed, Embase, Web of Science, and the Cochrane Central Register of Controlled Trials until April 30, 2010; 50 original research studies (35 clinical trials, 2 prospective and 13 cross-sectional), with 534,906 participants, were included in the analysis.
Results: The combined effect of prospective studies and clinical trials showed that adherence to the Mediterranean diet was associated with reduced risk of MS (log hazard ratio: -0.69, 95% confidence interval [CI]: -1.24 to -1.16). Additionally, results from clinical studies (mean difference, 95% CI) revealed the protective role of the Mediterranean diet on components of MS, like waist circumference (-0.42 cm, 95% CI: -0.82 to -0.02), high-density lipoprotein cholesterol (1.17 mg/dl, 95% CI: 0.38 to 1.96), triglycerides (-6.14 mg/dl, 95% CI: -10.35 to -1.93), systolic (-2.35 mm Hg, 95% CI: -3.51 to -1.18) and diastolic blood pressure (-1.58 mm Hg, 95% CI: -2.02 to -1.13), and glucose (-3.89 mg/dl, 95% CI:-5.84 to -1.95), whereas results from epidemiological studies also confirmed those of clinical trials.
Conclusions: These results are of considerable public health importance, because this dietary pattern can be easily adopted by all population groups and various cultures and cost-effectively serve for primary and secondary prevention of the MS and its individual components.
Abbreviations and Acronyms
CVD = cardiovascular disease
HDL = high-density lipoprotein
HOMA-IR = Homeostatic Model Assessment insulin resistance
MD = Mediterranean diet
MS = metabolic syndrome
NCEP ATP III = National Cholesterol Education Program Adult Treatment Panel III
The prevalence of the metabolic syndrome (MS) is increasing rapidly throughout the world, in parallel with the increasing prevalence of diabetes and obesity; thus, it is now considered as a major public health problem (1). With the National Cholesterol Education Program Adult Treatment Panel III (NCEP ATP III) definition, prevalence of the MS in Europe, Asia, Australia, and North and South America ranges between 9.6% and 55.7%; with the World Health Organization (WHO) definition, prevalence ranges between 13.4% and 70.0%; and with the International Diabetes Federation definition, prevalence ranges between 7.4% and 50% (2-4).
Regardless of the true actual figures, there is undoubtedly a dramatic increase of this condition, and therefore, emerging action should be taken to prevent and control its development. Lifestyle interventions, including dietary changes and physical activity, play a crucial role in the prevention of this condition (5). In fact, the NCEP ATP III has already suggested dietary intervention to prevent this epidemic. Diets rich in whole grain cereals, fruits, and vegetables, with low animal-fat consumption, seem to confer the prevention of cardiovascular disease risk factors, like hypertension, hypercholesterolemia, and obesity (6). The Mediterranean diet (MD) is a dietary pattern that has already shown its cardioprotective effects. The MD was first presented by Ancel Keys in the 1960s (7), and it is characterized by high consumption of monounsaturated fatty acids, primarily from olives and olive oil, and encourages daily consumption of fruits, vegetables, whole grain cereals, and low-fat dairy products; weekly consumption of fish, poultry, tree nuts, and legumes; a relatively low consumption of red meat, approximately twice/month; as well as a moderate daily consumption of alcohol, normally with meals. The beneficial role of the MD with regard to mortality from all causes, cardiovascular disease (CVD) and cancer (8), as well as obesity and type 2 diabetes (9,10) has already been reported from the results of many epidemiological studies and clinical trials. Major bio-pathophysiological mechanisms include antioxidant and anti-inflammatory effects of the foods included in the Mediterranean dietary pattern (9,11-17). However, the influence of the MD on the development of the MS has never been extensively studied. Thus, the aim of this work was to perform a systematic review and a meta-analysis of the findings of published original research articles in which the investigators have assessed the effect of a Mediterranean type of diet on the development of the MS as well as on its components.
Discussion
The present meta-analysis, performed in 50 studies, with an overall incorporated population of approximately one-half million subjects, revealed the beneficial effect of the MD, with regard to not only the MS but also its individual components, namely waist circumference, HDL cholesterol levels, triglyceride levels, blood pressure levels, and glucose metabolism. The significant heterogeneity observed mainly on the effect of the MD on MS components was partially attributed to the location of studies (i.e., Mediterranean or not), the intervention duration, the number of the participants, and the quality of the studies. To the best of our knowledge, this is the first work that has systematically assessed, through meta-analysis, the role of the MD on MS and its components.
The MD is one of the most known and well-studied dietary patterns, which has been shown to be associated with human health, especially decreased mortality from all causes, lower risk for cardiovascular disease, and cancer (8); it is also exerting a beneficial role with regard to type 2 diabetes and obesity (9,10). The results of the present meta-analysis add to the existing knowledge, because they indicate that adherence to the MD has a positive effect on human health through different ways. The MD has a beneficial effect on abdominal obesity, lipids levels, glucose metabolism, and blood pressure levels, all the components of the MS, which are also risk factors for the development of cardiovascular disease, insulin resistance, and diabetes. The antioxidant and anti-inflammatory effects of the MD as a whole as well as the effects of the individual components of the MD and specifically olive oil, fruits and vegetables, whole grains, and fish could offer a possible explanation for the aforementioned findings (9,11-15).
At this point it should be mentioned that abdominal obesity is one of the main causes for the appearance of all the components of the MS, because adipose tissue plays an important role in lipid and glucose metabolism and is responsible for the production of various cytokines influencing the development of the syndrome (54). The present meta-analysis based on results from both observational studies and clinical trials revealed the beneficial effect of the MD with regard to central obesity.
Furthermore, results from studies conducted in Mediterranean countries showed more prominent effects of the Mediterranean-type dietary pattern, possibly due to the easy access of consumers to the Mediterranean products. Nevertheless, these results could be attributed to other potential confounders such as genetics or environmental factors (i.e., physical activity; food sources, enrichment, contamination). In addition results of the present meta-analysis suggested that adherence to the MD coupled with physical activity has even more beneficial effects, showing the significant role of an active lifestyle for the prevention of the MS components. Finally, studies of high quality, longer intervention duration, and higher number of participants showed more prominent results-a fact that can be attributed to the crucial role of the design of a study.
Practical implications. The prevalence of the MS has drastically increased during recent years and is very unlikely to decrease, unless drastic measures are applied. For the delay and prevention of its development, emphasis should be placed on modifiable lifestyle factors. However, in spite of efforts to promote a healthy lifestyle and encourage a healthier diet and increase physical activity, dietary habits in the developed world and in some developing countries are changing toward the opposite direction. Even around the Mediterranean basin, consumption of fat, meat, eggs, dairy products, and sugar has increased, and consumption of cereals, legumes, vegetables, and seafood has decreased. Therefore, encouraging adherence to the MD might be a solution to the problem, because the foods comprising this dietary pattern-apart from its various health benefits-are tasty and it is easy to follow in the long-term.
Study limitations. Certain limitations of this study warrant consideration. The Mediterranean dietary pattern is not homogeneous; however, the basic characteristics of this diet were present in all of the included epidemiological studies. In addition, the MD intervention varied between the clinical trials in terms of hours of intervention, detail of the recommendations given, and macronutrient composition of the diet. In most trials, the control diet was a low-fat, high-carbohydrate diet (21,23,24,42,43,46,47,49,53,55-62), a low-carbohydrate diet (49,63), a prudent diet (30,32), usual patient treatment (22,64), American Diabetes Association diet (45), receiving general healthy dietary information (27,29,31,39,41), high-saturated-fat diet (30,34,46,47,53,58-61), or less counselling on an MD prescription (51). In 9 trials, MD was part of a lifestyle intervention comprising exercise (24,32,43) or a structured plan (smoking cessation, exercise, stress management) (21,22,29,39,41,45). Moreover, significant heterogeneity is present in our analysis, which introduces a warning about the generalization of the present results. More cohort studies evaluating the role of the MD on MS are needed.
Conclusions
The results of the present meta-analysis suggest that adherence to the Mediterranean dietary pattern was associated with lower MS prevalence and progression. Moreover, greater adherence to this traditional dietary pattern was associated with favorable effects on the MS components. These results are of considerable public health importance, because this dietary pattern can be easily adopted by all population groups and various cultures (65) and cost-effectively serve for the primary and secondary prevention of the MS and its individual components.
Results
Sample sizes of the 15 observational studies that were included in the meta-analysis varied between 328 and 497,308 and, for the 35 clinical trials, varied between 8 and 1,224 participants; 35 of the selected studies were conducted in Mediterranean populations, 6 were performed in U.S. populations (20-25), 7 were performed in northern European populations (26-32), 1 was performed in a European population (Mediterranean and non-Mediterranean) (33), and 1 was performed in an Australian population (34).
MD and MS. Eight studies with 10,399 subjects evaluated the role of the MD on the development or progression of the MS. Five of these 8 studies (35-39) reported a beneficial effect of compliance with the MD, as compared with the control diet (i.e., low-fat diet or usual care) or with low adherence to the Mediterranean dietary pattern. Overall, adherence to the MD was associated with a beneficial effect with regard to the MS in 2 of 2 clinical trials, in 1 of 2 prospective studies, and in 2 of 4 cross-sectional studies, as compared with lower compliance with this pattern or with a control diet (i.e., low-fat diet or usual care) (Fig. 2 ). The combined effect of both clinical trials and prospective studies was highly protective (log-hazard ratio = -0.69, 95% CI: -1.24 to -1.16), whereas the combined effect of cross-sectional studies was not significant (log-odds ratio = -0.16, 95% CI: -0.49 to 0.17). No publication bias was observed as indicated by the funnel plot (not presented here).
MD and MS components. Waist Circumference Levels
Three cross-sectional studies (20,33,40) reported a beneficial effect of close adherence to the MD, as compared with low adherence (Table 3). Heterogeneity of the effect measures regarding waist circumference was observed [Cochran's Q = 628.32(4), p < 0.001, I2 = 99.4%]. Moreover, 11 clinical trials with 1,646 subjects (997 assigned to an MD, and 669 assigned to a control diet) evaluated the role of adherence to the MD on waist circumference. Overall, adherence to the MD was associated with a beneficial effect with regard to waist circumference as compared with the control diet (Table 4); but, it should be noted that the previous finding was mainly attributed to 1 study (21) that found a beneficial effect of the MD, as compared with the control diet. No significant heterogeneity of the effect measures regarding waist circumference [Cochran's Q = 8.23(13), p = 0.83, I2 = ~ 0%] was observed.
Lipids Levels
Three studies (14,20,40) reported a beneficial effect of close adherence to the MD on HDL cholesterol levels, as compared with low adherence. Overall, adherence to the MD was associated with higher HDL-cholesterol levels as compared with the control diet (Table 3). Heterogeneity of the effect measures was observed [Cochran's Q = 52.78(6), p < 0.001, I2 = 88.6%]. Moreover, 29 clinical trials with 3,822 subjects (2,202 assigned to an MD, and 1,903 assigned to a control diet) examined the effect of adherence to the MD on HDL-cholesterol. Seven studies (31,39,41-45) reported a beneficial effect of an MD, as compared with the control diet, whereas 2 studies reported a beneficial effect of a high saturated fat diet as compared with the MD (46,47). Overall, adherence to the MD was associated with higher HDL-cholesterol levels as compared with the control diet (Table 4). Heterogeneity of the effect measures was observed [Cochran's Q = 109.99(40), p < 0.001, I2 = 63.6%].
Concerning triglycerides, 3 observational studies (14,40,48) reported a beneficial effect of MD, as compared with low adherence to this traditional pattern. Overall, adherence to the MD was associated with lower triglycerides levels (Table 3). Heterogeneity of the effect measures regarding triglycerides levels was observed [Cochran's Q = 33.18(6), p < 0.001, I2 = 81.9%]. In addition, 29 clinical trials with 3,822 subjects (2,202 assigned to an MD, and 1,903 assigned to a control diet) examined the relationship between compliance with the Mediterranean dietary pattern and triglycerides levels. Five studies (39,42,43,45,49) reported a beneficial effect of an MD, as compared with the control diet, whereas the rest of the studies observed no significant differences. Overall, adherence to the MD was associated with lower triglyceride levels as compared with the control diet (Table 4). Heterogeneity of the effect measures regarding triglyceride levels [Cochran's Q = 89.50(40), p < 0.001, I2 = 55.3%] was also evident.
Blood Pressure Levels
Five observational studies with 15,535 participants were included in the analysis. Two studies (14,40) reported a beneficial effect of close adherence to the MD on systolic blood pressure, as compared with low adherence, whereas 1 study showed higher systolic blood pressure levels for the group more closely following the MD (50). Overall, adherence to the MD was not associated with systolic blood pressure levels, as compared with the control diet (Table 3). Heterogeneity of the effect measures regarding systolic blood pressure levels was also observed [Cochran's Q = 161.28(5), p < 0.001, I2 = 96.8%]. Moreover, 14 clinical trials with 3,060 subjects (1,632 assigned to an MD, and 1,436 assigned to a control diet) evaluated the effect of the MD on systolic blood pressure levels. Three studies (39,42,43) reported a beneficial effect of an MD, as compared with the control diet, and the overall adherence to the MD was associated with lower systolic blood pressure levels as compared with the control diet (Table 4). Heterogeneity of the effect measures regarding systolic blood pressure levels was observed [Cochran's Q = 31.18(15), p = 0.01, I2 = 51.8%].
With regard to diastolic blood pressure levels, no significant associations were observed in observational studies (Table 3). However, in clinical trials (3,060 subjects, 1,632 assigned to an MD, and 1,436 assigned to a control diet) 5 studies (39,41-43,51) reported a beneficial effect of an MD, and the overall effect suggested that adherence to the MD was associated with lower diastolic blood pressure levels as compared with the control diet (Table 4). No heterogeneity of the effect measures regarding blood pressure levels [Cochran's Q = 16.09(15), p = 0.38, I2 = 6.7%] was observed.
Glucose and Homeostatic Model Assessment Insulin Resistance Levels
Two observational studies (40,52) reported a beneficial effect of close adherence to the MD as compared with the control diet, and overall adherence to the MD was associated with lower fasting glucose levels (Table 3). Heterogeneity of the effect measures regarding glucose levels was observed [Cochran's Q = 65.05(7), p < 0.001, I2 = 89.2%]. Moreover, among the 17 clinical trials with 2,373 subjects (1,357 assigned to an MD, and 1,139 assigned to a control diet), 6 studies (39,41-43,45,53) reported a beneficial effect of an MD, as compared with the control diet. Overall, adherence to the MD was associated with lower fasting glucose levels as compared with the control diet (Table 4). Heterogeneity of the effect measures regarding glucose levels was observed [Cochran's Q = 77.49(22), p < 0.001, I2 = 71.6%].
Two observational studies with 3,042 subjects evaluated the role of the MD on Homeostatic Model Assessment insulin resistance (HOMA-IR) levels (40,52). Both studies reported a beneficial effect of close adherence to the MD on HOMA-IR levels, as compared with low adherence (Table 3). Heterogeneity of the effect measures regarding HOMA-IR levels [Cochran's Q = 135.69(2), p < 0.001, I2 = 98.5%] was observed. In addition, 10 clinical trials with 1,742 subjects (1,031 assigned to a MD and 711 to a control diet), examined the relationship between adherence to the MD and HOMA-IR. Six studies (30,39,41,42,44,51) reported a beneficial effect of a MD, as compared with the control diet. Overall, adherence to the MD was associated with lower HOMA-IR levels as compared with the control diet (Table 4). Heterogeneity of the effect measures regarding HOMA-IR levels [Cochran's Q = 118.06(12), p < 0.001, I2 = 89.8%] was observed.
Sensitivity analysis. Heterogeneity of the effect sizes of MD on MS as well as its components has already been reported in the preceding text. Studies included in the present meta-analysis varied in some characteristics with regard to their design. The meta-analysis of clinical trials revealed the beneficial role of the MD on MS, whereas results from observational studies (cross-sectional and prospective) showed a protective but not significant trend (Fig. 2). Moreover, the heterogeneity found regarding the overall effect of diet on MS was not attributed to the weight of each study.
However, heterogeneity was also observed with regard to the effect of diet on MS components. Specifically, differences were revealed with regard to: location of the studied population (i.e., Mediterranean or non-Mediterranean countries), sample size, duration of the intervention, encouraging of lifestyle changes, as well as trial quality. In particular, in studies conducted in Mediterranean countries, the effect of diet was significant with regard to all MS components except for weight circumference, whereas in studies not located in the Mediterranean region the effect of diet was not associated with any of the MS components; similarly, studies with intervention duration more than 3 months showed significant results for all the components studied except for waist circumference, whereas clinical trials with a <3-month intervention showed significant results only with regard to diastolic blood pressure and glucose levels. Moreover, all studies with sample size above the median (i.e., n >66) presented significant associations between diet and all the MS components, whereas studies with <66 participants did not show any significant associations. Studies also encouraging physical activity showed significant associations with regard to all the components studied, except waist circumference; however, studies focusing only on dietary intervention showed significant associations only with regard to blood pressure and glucose levels. Clinical trials of high quality showed significant results between diet and all the components studied, except for waist circumference, whereas clinical trials with low quality showed significant results only with regard to diastolic blood pressure and glucose levels (Table 5). Furthermore, when the control diets were categorized (where this was possible) into "low-fat diet" (i.e., <30% fat),"usual treatment" type (i.e., no further dietary advice apart from that of hospital dietitians or written advice), "high saturated fat diet" (i.e., saturated fat >20%), the subgroup meta-analysis showed that MD was associated with beneficial effects, as compared with the "low-fat diet" (with regard to HDL cholesterol, triglycerides, systolic and diastolic blood pressure, glucose levels) as well as with the "usual dietary recommendations" (with regard to HDL cholesterol and triglyceride levels).
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