Impact of the Traditional Mediterranean Diet on the Framingham Risk Score and the Metabolic Syndrome According to Sex

Abstract

Background:

The traditional Mediterranean diet (MedDiet) has been recognized as a food pattern with beneficial effects on cardiovascular health. However, even if sex-related differences in the cardiovascular response to diet have been previously highlighted, the existence of such differences in the impact of the MedDiet on the global cardiovascular risk has not been yet investigated. This study examined sex differences in the global cardiovascular impact of a 4-week isoenergetic controlled MedDiet using the Framingham risk score and the National Cholesterol Education Program (NCEP) metabolic syndrome criteria.

Methods:

This study included 38 men and 32 premenopausal women (24–53 years) who had slightly elevated low-density lipoprotein cholesterol (LDL-C) concentrations (between 3.4 and 4.9 mmol/L) or total cholesterol-to-high-density lipoprotein cholesterol (HDL-C) ratios ≥5.0. Cardiovascular risk factors were measured before and after the controlled MedDiet.

Results:

A time effect (P=0.04) was found for the Framingham risk score, with both men and women showing a nonsignificant decrease in response to the MedDiet. No time effect was found for the prevalence of the metabolic syndrome and the number of metabolic syndrome criteria that were met by participants (P>0.05). However, a time effect was noted for the continuous metabolic syndrome score (P=0.008), with nonsignificant decreases in both men and women. No sex-by-time interaction was noted for any of variables studied (P>0.05).

Conclusions:

Results from this study suggest that the global cardiovascular impact of the MedDiet, as assessed by the Framingham risk score and metabolic syndrome criteria, is not significantly different in men than in premenopausal women in isoenergetic conditions.

Introduction

Cardiovascular disease (CVD) is a major cause of disability and death in industrialized countries, accounting for 33%¹ and 27%² of deaths, respectively, in the United States and Canada. It is now widely known that sex-related differences exist in the CVD incidence rate because premenopausal women have a lower risk of CVD compared to age-matched men.³ This sex difference could be mainly ascribed to sex steroid hormones concentrations.⁴ In fact, some evidence highlights that endogenous estrogens bring many beneficial effects related to cardiovascular risk factors. More specifically, endogenous estrogens have been identified as contributors of the lower visceral fat accumulation and blood pressure level, lower triglyceride (TG) and cholesterol concentrations, and higher insulin sensitivity found in premenopausal women compared to age-matched men.^5,6

Because cardiovascular risk factors cluster and interact with each other,⁷ different tools combining some well-known cardiovascular risk factors have been created to estimate the global cardiovascular risk of individuals. Two well-recognized and frequently used tools are the Framingham risk score and metabolic syndrome criteria.⁸ These tools have been demonstrated to be good predictors of cardiovascular morbidity and mortality.^9,10 In prevention of CVD, the traditional Mediterranean diet (MedDiet) has been shown as a promising approach to improve cardiovascular health globally. In fact, the MedDiet has been associated with a reduction of the global 10-year CVD risk as estimated by the Framingham risk score.^11,12 Moreover, the adherence to the MedDiet has been associated with a reduced risk of 31% of the metabolic syndrome in a recent meta-analysis.¹³ However, because most of the interventional studies have investigated MedDiet effects in free-living conditions with concomitant weight loss, little is known about the global cardiovascular impact of the adoption of the MedDiet in controlled isoenergetic conditions without the confounding effect of body weight change.

Sex-related differences in the cardiovascular response to diet have been previously highlighted^14,15; however, the existence of such differences in the global cardiovascular risk response to the MedDiet has not been investigated yet in fully controlled conditions. Nevertheless, the adoption of the traditional MedDiet has previously been found to reduce endogenous estrogen concentrations in postmenopausal women.¹⁶ This raises the possibility that women may have limited cardiovascular benefits from the MedDiet compared to age-matched men due to a concomitant decrease in beneficial effects related to estrogens.

Thus, the objective of this study was to investigate sex-related differences in the global cardiovascular impact of a 4-week controlled MedDiet using the Framingham risk score and the National Cholesterol Education Program Adult Treatment Panel III (NCEP ATP III) metabolic syndrome criteria in a sample of women and age-matched men characterized by a slightly deteriorated lipid profile. Previous studies have highlighted that dietary food patterns affect in the same way, but to a greater extent, endogenous estrogen concentrations in premenopausal women compared to postmenopausal women,^17,18 thus we decided in the present study to compare men and premenopausal women to maximize differences due to sex hormones.

Methods

Subjects

The study protocol has been described extensively in a previous publication.¹⁵ Briefly, the study included 38 men and 32 premenopausal women (24–53 years) who had a slightly elevated low-density lipoprotein cholesterol (LDL-C) concentration (between 3.4 and 4.9 mmol/L) or total cholesterol-to-high-density lipoprotein cholesterol (HDL-C) ratio ≥5.0 and at least one of the four following cardiovascular risk factors¹⁹: Waist circumference >94 cm in men and >80 cm in women²⁰; triglyceride (TG) >1.7 mmol/L; fasting glycemia between 6.1 and 6.9 mmol/L; and/or blood pressure concentrations ≥130/85 mmHg. These inclusion criteria were fixed to have participants at risk of CVD in whom primary prevention should be started through the adoption of healthy dietary habits. In women, a follicle-stimulating hormone (FSH) measurement during the early follicular phase confirmed the premenopausal status (FSH <20 IU/L). Exclusion criteria included significant weight change (>2.5 kg) in the 3 months before the study, cardiovascular events, and use of medication that could affect dependent variables under study (namely lipid-lowering, hypoglycemic, insulin sensitizer, and anti-hypertensive medications). Smokers, pregnant women, and women using systemic hormonal contraceptives were also excluded from the study. All subjects gave written informed consent prior to inclusion in the study. All clinical investigations were conducted according to Declaration of Helsinki principles. All aspects of the study were approved by the Laval University Research Ethics Committee on human experimentation, Québec, Québec, Canada.

Study design

Before the experimental MedDiet intervention, participants went through a 4-week run-in period during which they had to comply with healthy eating according to the Canada's Food Guide²¹ as instructed by a registered dietician. The controlled phase was undertaken as a parallel design during which both men and women were assigned to a 4-week fully controlled experimental diet formulated to be concordant with the characteristics of the traditional MedDiet.²² This study design permitted precise evaluation of sex differences in response to the MedDiet. The controlled phase lasted 4 weeks because it has been shown that this duration under controlled conditions is sufficient to obtain significant changes in cardiometabolic variables in both sexes.^23
–25 The experimental diet intervention and its nutritional composition have been described previously.¹⁵ Briefly, the percentages of kilocalories derived from lipids, carbohydrates, proteins, and alcohol were of 32%, 46%, 17%, and 5%, respectively. All foods and drinks were prepared by food technicians at the Clinical Investigation Unit (CIU) at the Institute of Nutrition and Functional Foods (INAF; Laval University) and provided to participants according to a 7-day cyclic menu. Subjects were instructed to consume all foods and drinks provided.

Body weight was measured on weekdays, and energy intake was adjusted to keep each subject's body weight constant throughout the study. Participants were also instructed to maintain their usual physical activity level during this controlled intervention. In premenopausal women, since previous studies have suggested that the phase of the menstrual cycle influences the lipid and lipoprotein profiles,²⁶ glycemia, blood pressure, and adiposity measurements, women's feeding was shortened or prolonged if needed to be able to carry out all tests in the early follicular phase of their menstrual cycle (from the third to the ninth day of the menstrual cycle; mean duration of the feeding period in women, 28.8±4.3 days).

Dietary intakes

To determine whether dietary habits before the controlled MedDiet intervention were similar in men and women, a validated quantitative Food Frequency Questionnaire (FFQ),²⁷ containing 91 items and 33 subquestions, that inquires about food habits during the last month was administrated by a registered dietitian just before the controlled MedDiet intervention (i.e., after the run-in period), reflecting dietary habits during the entire run-in period. A Mediterranean score (MedScore) derived from the FFQ was then calculated as described by Goulet and colleagues.²⁸ The MedScore can vary between zero and 44 points. A MedScore of 44 would imply a food pattern that is perfectly concordant with the traditional MedDiet.

Cardiovascular risk factors assessments

Baseline cardiovascular risk factors were assessed before the controlled MedDiet intervention (i.e., after the run-in period). Cardiovascular risk factors were also measured after the controlled MedDiet intervention. Blood samples were collected from an antecubital vein into vacutainer tubes after a 12-hr overnight fast. Assessments of total cholesterol, HDL-C, and TG were performed according to previously described methods.²⁸ A blood sample was also collected into a vacutainer tube containing EDTA for the assessment of glucose concentrations. Plasma glucose concentrations were measured in a fasting state with the hexokinase-glucose-6-phosphate dehydrogenase method.²⁹

Waist circumference measurement was taken directly on the skin at the mid-distance between the last rib and the top of the iliac crest after a normal expiration. Waist circumference was determined as the mean of three measurements. Systolic and diastolic blood pressures were measured on the right arm using an automated blood pressure monitor (BPM 300-BpTRU: Vital Signs Monitor) after a 10-min rest in the sitting position. Blood pressure was computed as the mean of three readings.

Global cardiovascular risk tools

The Framingham 10-year CVD risk score was calculated using age, total cholesterol, HDL-C, systolic blood pressure, and smoking habits as described in the NCEP ATP III final report.⁸ The metabolic syndrome was defined according to the revised NCEP ATP III criteria.³⁰ Subjects with three or more of the following criteria were defined as having the metabolic syndrome: (1) Waist circumference >102 cm in men and >88 cm in women; (2) TG >1.7 mmol/L; (3) HDL-C <1.03 mmol/L in men and <1.29 mmol/L in women; (4) fasting glucose ≥5.6 mmol/L; and (5) blood pressure ≥130/85 mmHg. We chose the NCEP ATP III definition because it is the most frequently used definition in clinical trials investigating the effects of the MedDiet on the metabolic syndrome,¹³ thereby facilitating the comparison between our results and the literature.

We also calculated a continuous metabolic syndrome score as used in other studies.^31,32 A continuous score was calculated for each metabolic syndrome component using difference between individual subject data and the NCEP ATP III criterion (numerator) and standard deviation (denominator), as suggested by Johnson and collaborators.³¹ A continuous metabolic syndrome score was created as a sum of the five individual scores. A decrease in the score indicates a reduced CVD risk. We decided to include a continuous score in our analyses because (1) CVD risk increases proportionally with levels of metabolic syndrome components³³ and (2) a continuous metabolic syndrome score is more sensitive to overall metabolic changes found in response to lifestyle interventions than a dichotomous approach.^33,34

Statistical analyses

Data were analyzed by using SAS statistical package version 9.2 (SAS Institute Inc., Cary, NC, USA). Data were collected before (i.e., after the run-in period) and after the controlled MedDiet intervention, and results are expressed as means and standard deviation (SD) or standard errors of the mean (SEM). For variables not normally distributed, a transformation was performed to obtain a normal distribution. Differences in anthropometric and metabolic variables between men and premenopausal women before the controlled MedDiet intervention were assessed using the Student t-test. To compare the prevalence of the metabolic syndrome and its components between men and women before the controlled MedDiet intervention, the chi-squared test was used for analyses with five or more participants per cell; otherwise the Fisher exact test was used. The Cochran–Mantel–Haenszel test was used to determine whether sex differences exist in changes in the prevalence of the metabolic syndrome in response to the isoenergetic MedDiet. The chi-squared test was used to evaluate the effect of the MedDiet on the prevalence of the metabolic syndrome in men and premenopausal women taken separately. MIXED procedures for repeated measurements were used to evaluate time and sex-by-time interaction effects on the Framingham 10-year CVD risk score, the number of metabolic syndrome criteria and the continuous metabolic syndrome score in response to the MedDiet. Tukey–Kramer tests were used to determine precisely the location of significant differences.

Results were all adjusted for the slight but significant body weight loss that occurred during the controlled MedDiet intervention (from 91.8±14.0 to 90.6±13.7 kg in men (−1.2 kg or −1.3% of initial body weight; P<0.0001) and from 78.0±14.7 to 77.5±14.3 kg in women (−0.5 kg or −0.7%; P=0.03). Differences were considered statistically significant at P<0.05 (two-sided). One man was excluded from our analyses due to illness, which led to a significant reduction of food intake during several days at the end of the controlled MedDiet intervention. Thus, 37 men and 32 premenopausal women were included in the analyses. A sample size of 69 participants allowed detection of a difference of 1.9% in the change in the Framingham risk score and a difference of 2.2 in the change in the continuous metabolic syndrome score between sexes, considering a standard deviation of, respectively, 2.8% and 3.2% with an alpha risk of 0.05 and a beta risk of 0.20 in two-sided contrasts.

Results

Age and body mass index (BMI) were similar in men and women before the controlled MedDiet intervention (Table 1). Men had higher baseline values for body weight, waist circumference, TG, systolic and diastolic blood pressures, and fasting glucose and lower baseline values for HDL-C than premenopausal women. No sex difference was observed regarding the MedDiet score. The baseline Framingham risk score was significantly higher in men than in women. The prevalence of the metabolic syndrome, the number of metabolic syndrome criteria, and the continuous metabolic syndrome score were not significantly different between sexes before the controlled MedDiet intervention. With regard to components of the metabolic syndrome, no difference was found for HDL-C and blood pressure criteria prevalence, whereas a greater proportion of men had TG and fasting glucose criteria and a lower proportion of men had the waist circumference criterion compared to premenopausal women.

Table 1.

Characteristics of Men and Women Before the Controlled Mediterranean Diet Intervention

	Men (n=37)		Women (n=32)
	Mean	SD	Mean	SD
Age (years)	42.6	7.3	41.2	7.3
Body weight (kg)^a	91.8	14.0	78.0^*	14.7
BMI (kg/m²)^a	29.2	3.2	29.6	5.4
Waist circumference (cm)^a	102.6	10.7	96.4^*	10.5
TG (mmol/L)^a	1.86	1.17	1.36^*	0.63
HDL-C (mmol/L)^a	1.09	0.31	1.30^*	0.26
Systolic blood pressure (mmHg)	117.1	12.6	108.6^*	10.4
Diastolic blood pressure (mmHg)	80.3	9.0	73.5^*	9.0
Fasting glucose (mmol/L)^a	5.89	0.37	5.68^*	0.63
Mediterranean score	24.8	5.9	24.6	4.4
Framingham risk score (%)	3.4	3.2	0.3^*	0.4
Metabolic syndrome score	−0.16	2.89	−0.90	3.44
Number of metabolic syndrome criteria	2.5	1.2	2.0	1.5
Metabolic syndrome [n (%)]^b	17 (45.9)		11 (34.4)
Waist circumference [n (%)]	15 (40.5)		^23 (71.9)^
TG [n (%)]	18 (48.6)		^8 (25.0)^
HDL-C [n (%)]	18 (48.6)		15 (46.9)
Blood pressure [n (%)]	12 (32.4)		4 (12.5)
Fasting glucose [n (%)]	29 (78.4)		^14 (43.8)^

Mean values were significantly different between sexes before the controlled Mediterranean diet intervention by the Student t-test; ^* P<0.05.

Analysis was performed on transformed values.

Metabolic syndrome is defined according to the revised National Cholesterol Education Program Adult Treatment Panel III (NCEP ATP III) criteria.

Prevalence was significantly different between sexes before the controlled Mediterranean diet intervention by chi-squared test; ^** P<0.05.

BMI, body mass index; TG, triglyceride; HDL-C, high-density lipoprotein cholesterol.

A time effect (P=0.04) was observed for the Framingham 10-year CVD risk score (mean change, −0.28±0.13 %) and a nonsignificant decrease was found in both men and women (respectively, −0.38±0.23%; P=0.15 and −0.16±0.08%; P=0.84) (Fig. 1A). No sex-by-time interaction was noted for this variable (P=0.39). Results were similar after adjustment for the baseline Framingham risk score (results not shown).

FIG. 1.

Box plots of the distributions of the 10-year risk of total cardiovascular disease (Framingham risk score) (A), the number of metabolic syndrome criteria that were met by participants (B), and the continuous metabolic syndrome score (C) in men and women before and after the controlled MedDiet intervention. Data are presented as the median and interquartile range; solid lines extend to the extremes of the data. The cross indicates the mean of the data. Metabolic syndrome is defined according to the revised National Cholesterol Education Program Adult Treatment Panel III (NCEP ATP III) criteria. MIXED procedures for repeated measurements were used to evaluate time and sex-by-time interaction effects.

Men experienced a nonsignificant decrease in the prevalence of the metabolic syndrome (from 46.0% before the controlled MedDiet intervention to 32.4% after the controlled intervention; P=0.23), whereas women showed a nonsignificant increase (from 34.4% to 37.5%; P=0.79). However, no significant sex difference was observed for the change in the prevalence of the metabolic syndrome in response to the MedDiet (P=0.32). Moreover, no time (P=0.17) and sex-by-time interaction (P=0.27) effects were found for the number of metabolic syndrome criteria (Fig. 1B). However, a time effect (P=0.008) was observed for the continuous metabolic syndrome score, and a decrease was noted for this variable when the whole sample was considered (Fig. 1C). This is indicative of a reduced risk after the MedDiet (changes ranged from −5.23 to 1.75 for all participants; mean change, −0.49±0.18). When men and women were analyzed separately, changes observed were of similar magnitude as those for the total sample but did not reach statistical significance (respectively, −0.46±0.26, P=0.23, and −0.51±0.24, P=0.21). Finally, no sex-by-time interaction was noted for the continuous metabolic syndrome score (P=0.91).

Discussion

Our results showed for the first time that the impact of the MedDiet on the global cardiovascular risk, as determined by the Framingham risk score and metabolic syndrome criteria, is not different in men than in premenopausal women in an isoenergetic context. This conclusion is supported by the absence of significant sex-by-time interaction for all variables studied. More precisely, we found a significant decrease in the Framingham risk score in response to the MedDiet. Moreover, a decrease in the continuous metabolic syndrome score occurred, indicating a beneficial effect of the MedDiet on the cardiovascular risk factors included in the metabolic syndrome definition; however, this beneficial effect was not reflected by significant decreases in the prevalence of the metabolic syndrome and in the number of criteria that were met by participants. These global beneficial effects, along with the previously reported decrease in LDL-C found in response to the MedDiet in both men and women,¹⁵ support the fact that the MedDiet has beneficial effects on the cardiovascular health, independently of the sex.

Endogenous estrogens have a beneficial impact on total cholesterol and HDL-C concentrations, blood pressure level, and glucose/insulin homeostasis.^4,6 Interestingly, all of these risk factors are included in the calculation of the Framingham 10-year CVD risk score. Thus, because of the decrease in endogenous estrogen concentrations previously found by Carruba and collaborators in women in response to the adoption of the MedDiet,¹⁶ we initially hypothesized that premenopausal women could have a less important beneficial impact on the cardiovascular risk as assessed by the Framingham risk score than age-matched men. However, our results showed a decrease in the Framingham risk score in response to the MedDiet when the whole sample was considered with no sex difference for this variable. Taken together, our results are consistent with observational and uncontrolled interventional studies that highlighted that the adoption of the MedDiet is associated with a global cardiovascular risk reduction as measured by the Framingham risk score in samples including both men and women.^11,12,35 Moreover, our results are in line with those of a well-controlled study that showed a decrease in the Framingham risk score in response to an isoenergetic MedDiet in a sample of men with the metabolic syndrome.³⁶ However, our study brings additional useful information to the previous literature because it is the first to be designed to directly compare the response to the MedDiet between men and premenopausal women with a maximum of control over confounding variables and therefore allowing demonstration that the impact of the MedDiet on cardiovascular risk, as measured by the Framingham risk score, is not different in men and in premenopausal women.

Similar to the Framingham risk score, the metabolic syndrome definition includes cardiovascular risk factors, which can be influenced by estrogen levels. In the present study, we found that, in addition to observing no sex-related differences, participants had no benefit related to the metabolic syndrome from the adoption of an isoenergetic MedDiet when dichotomous criteria were used. Results from Richard and collaborators are in line with our results, as they reported that a controlled isoenergetic MedDiet had no effect on the metabolic syndrome prevalence in men.³⁶ However, our results are inconsistent with those from Esposito and collaborators, who suggested that the adoption of the MedDiet may decrease the number of the metabolic syndrome criteria even after adjustment for the weight loss that occurred during their “real life” intervention.³⁷ Differences in inclusion criteria and study design may explain this divergence between their results and ours. It is relevant to highlight that, in our study, the metabolic syndrome criterion that was the most prevalent in men before the MedDiet intervention was fasting glucose whereas, it was waist circumference in women. Because these criteria are particularly sensitive to weight change³⁸ and the adoption of the MedDiet in uncontrolled conditions usually leads to weight loss, it is therefore possible to suggest that, in a free-living context, the MedDiet could have a significant impact on these dichotomous criteria of the metabolic syndrome. On the other hand, even if no change in metabolic syndrome was observed when dichotomous criteria were used, we noted a decrease in the continuous metabolic syndrome score, a more sensitive tool to reflect changes observed in response to lifestyle interventions than dichotomous criteria. Thus, our results suggest that the MedDiet has a global beneficial effect on metabolic syndrome factors. However, this beneficial effect was not reflected in our study by significant decreases in the prevalence of the metabolic syndrome and in the number of criteria that were met by participants.

It is essential to highlight that participants included in this study were characterized by a slightly deteriorated LDL-C or total cholesterol-to-HDL-C ratio, and are therefore individuals in whom primary prevention should be started in clinical practice through the adoption of healthy dietary habits.^8,39 Therefore, results from this study are highly clinically relevant because they demonstrate that, among these at-risk individuals, the sex has no influence on the effects of the traditional MedDiet on the global cardiovascular risk. A strength of this study is the well-controlled design of the MedDiet intervention in which all foods and drinks were provided to participants and compliance was closely monitored each day. This well-controlled context allowed us to precisely evaluate sex-related differences in response to the MedDiet.

Some limitations should be noted. First the study's “single strand before and after” design does not allow comparisons to a control diet, and therefore nonspecific treatment effects that are not attributable to the MedDiet cannot be ruled out. In fact, as the cardioprotective effects of the MedDiet are well known and have been widely documented,^11
–13 it is important to highlight that this study had as a main objective to investigate sex-related differences in response to the MedDiet, which was possibly due to the parallel design with men and women and the fully controlled nature of the nutritional intervention. Nevertheless, because our study included only premenopausal women, our results cannot be generalized to all women. Moreover, premenopausal women were characterized by a very low Framingham risk score before the controlled intervention, which may have limited the impact of the MedDiet on this global cardiovascular risk assessment tool in women. The nonsignificant effect of the MedDiet on the prevalence of the metabolic syndrome and its criteria may be due to the small sample size of our fully controlled nutritional intervention. Therefore, additional studies with a larger sample size are needed to confirm these results. Finally, sex steroid hormones were not measured in our study, and thus it is not possible to determine whether a decrease in estrogen levels occurred.

In conclusion, results from this fully controlled-feeding study suggest that no sex-related difference exists in the global cardiovascular response to an isoenergetic MedDiet with regard to the Framingham risk score and the metabolic syndrome criteria. The MedDiet is now widely recommended in prevention of CVD by many organizations,^40
–42 thus this study gives additional useful information about the effectiveness of this food pattern, which is independent of the sex, to reduce the global cardiovascular risk even in absence of weight loss.

Footnotes

Acknowledgments

S.L. and S.D. designed the research; A.B. and L.C. conducted the research; S.D. supervised the medical condition of participants; A.B. analyzed data and wrote the paper; all authors read and approved the final manuscript. This research was supported by the Canadian Institutes of Health Research (MOP 84568) and the Heart and Stroke Foundation of Québec (2007-180). A.B. is a recipient of a studentship from Canadian Institutes of Health Research (CIHR). This clinical trial was registered at www.clinicaltrials.gov as NCT01293344.

Author Disclosure Statement

No competing financial interests exist.

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