Breakfast consumption is inversely associated with metabolic syndrome in a sample of Iranian adults

Background: Central obesity, insulin resistance, dyslipidemia and hypertension are the core components of metabolic syndrome (MetS) which is coincident with unhealthy dietary habits in the Middle-Eastern countries. The aim of this study was to explore the association between dietary habits and metabolic syndrome of adult population living in Yazd Greater Area, Iran. Methods: This is a cross-sectional study which uses the data of a population-based cohort study on Iranian adults, known as Yazd Health Study (YaHS). The relationship between dietary habits and metabolic syndrome among adults (n= 2896) were analyzed using multiple logistic regression method. Results: Outcomes from logistic regression examining show that breakfast consumption has a significant inverse effect on the occurrence of metabolic syndrome after adjustment for age, education level, physical activity statue, history of chronic diseases and smoking (odds ratio (OR)= 0.38, 95% confidence interval (CI)= 0.14, 0.97). This effect remains significant even after adjustment for body mass index (BMI) and reveals that odds of having MetS is 69 % lower in breakfast consumers in contrast to non-consumers (OR=0.31, 95% CI= 0.11, 0.87). However, no significant relationship was observed between other dietary habits and MetS after adjustment for all potential confounders Conclusions: This study revealed that eating breakfast has an inverse relationship with metabolic syndrome. Finding out stronger evidence in relation between dietary habits and metabolic syndrome, more researches especially population-based cohort studies are needed to be conducted. smoking


Introduction
With increased risk of diabetes mellitus (DM) and cardiovascular disease (CVD), which are mostly derived from metabolic syndrome (MetS) [1], urgent strategies to prevent its global epidemic are demanded [2]. Central obesity, insulin resistance, dyslipidemia and hypertension are the core components of metabolic syndrome [3]. According to the international diabetes federation (IDF), the rapid increase of MetS has been estimated to be 20-25% globally [4] which is parallel to the growing rate of DM, hypertension, cardiovascular disease and obesity [2]. The prevalence of MetS in different studies varies, depending majorly on the used criteria of different definitions and their compositions (such as sex, age, race and ethnicity) [5]. For example results of recent systematic review and meta-analysis of studies revealed the overall estimation of MetS prevalence in Iran to be 36.9% based on the Adult Treatment Panel guidelines III (ATP III) criteria and 34.6 % according to IDF [6,7]. However, regardless of the criteria used, it has been reported that the prevalence of metabolic syndrome around the world is rising drastically [8,9].
Unhealthy diet and lifestyle are some of the risk factors contributed to MetS [10,11].
Several studies have been conducted to explore the relationship between dietary habits and MetS [12][13][14][15][16][17][18][19]. It has been reported that dietary habits that are more westernized can increase the chances of MetS [19], whereas diets rich in fruits and vegetables [14] might have a reduction effect.
Considering what has been mentioned above, emerging evidence reveals that higher consumption of sugar sweetened beverages consist of energy-containing sweeteners such as sucrose, high fructose corn syrup or fruit-juice concentrates [20] is associated with increasing risks of MetS [21] not only in the US diet [22] but also, in developing countries such as India and China [23]. These findings also have been confirmed by a meta-analyses of cohort studies [24].
Moreover, studies suggests that consumption of out-of-home meals and energy dense fast foods [25] and snacks which contain highly processed meat, total fat (saturated and trans

Study population and data collection
Yazd Health Study (YaHS) recruitment phase data was used for this cross-sectional study.

Dietary Assessment
We aimed at obtaining accurate information on some dietary habits noted by participants via a questionnaire [36]. These items were as follows; i) sweetened drinks (fruit juices, artificially or homemade sweetened beverages) with frequency consumption of not at all, less than once per week, once or more per week, ii) fast foods consumption with frequency of not at all or few times per year, 1-3 times per months, once or more per week, iii) breakfast consumption as not at all in frequency, once per week or more than once per week , iv) sugar cubes with the serving intake of not at all, 1-2 cubes per day and more than 2 cubes per day.

Diagnosis of metabolic syndrome
National Cholesterol Education Program and Adult Treatment Panel III criteria (NCEP) present the definition of MetS in the current study [37][38][39]. To be diagnosed with at least 3 risk factors out of the five following cases, means a participant has metabolic syndrome if: i) Triglyceride (TG) above 150 mg/dl or consuming triglyceride lowering agents (hyperglyceride); ii) high density lipoprotein-cholesterol (HDL-C) level of less than 40 mg/dl in men and less than 50 mg/dl in women or any kind of pharmacological treatment; iii) Systolic blood pressure above 130 mmHg and diastolic blood pressure above 85 mmHg (hypertension); iv) Fasting blood glucose above 100 mg/dl or usage of pharmacological treatment as a control from blood sugar; and v) and waist circumference (WC) above 91.5 cm in men and 85.5 cm in women (adopted for only Iranian population) [40].

Evaluation of anthropometric indices
Weight was recorded with participants wearing lightweight clothing and no shoes using a digital scale (Model BF511, Omron Co. Karada Body Scan, Osaka, Japan) with the precision of 0.1 kg. A non-stretchable tape meter with the precision of 0.5 cm was used to measure height with lightweight clothing and no shoes and with their heels, hip, shoulder and head touching the wall. Body mass index (BMI; weight (kg) / height (m 2 )) was calculated from measuring height and weight. Waist circumference was also measured by a tape in the horizontal plane midway between the iliac crest and the rib cage with the precision of 0.1 cm.

Blood pressure measurement
Systolic and diastolic blood pressures were measured in the sitting position by an automatic digital blood pressure monitor (Reister Germany). Each measurement was repeated for two times after every 5-minute interval.

Laboratory data
Data on serum level of fasting blood glucose (FBG) (mg / dl), total cholesterol, triglycerides, low density lipoprotein-cholesterol (LDL-C) and high density lipoproteincholesterol (HDL-C) were measured and collected. The equipment used in this study included a calibrated Ciba Corning auto-analyzer device (Ciba Corp., Basle, Switzerland (and Pars Azmoon company kits to asses fasting blood glucose and triglyceride after centrifuging and bionic kits as an analyzer for HDL cholesterol.  Table 1 shows the general characteristics of study population. A majority of participants (53.2%) as illustrated were females. Furthermore, a high percent of the participants (24.7%) were between ages of 40-49 years old and had secondary school or lower education (53.5%). The smoking status also demonstrates that a high percent of the volunteers did not smoke (90.0%) and were married (86.9%). Moreover, 51.8% of the participants were active on their physical activity statue.

Results
The prevalence of the metabolic syndrome among the participants was 32.2% as demonstrated in table 2. Additionally, the plurality of the participants (38.6%) were overweight (BMI= 25-29.9). Moreover, 38.8 % met the criterion for hypertriglyceridemia (plasma TG higher than 150 mg/dl) and 29.3% had FBG higher that 100 mg/dl, while 65.8% had low levels of HDL-C (˂40 mg/dl in men and ˂50 mg/dl in women). Furthermore, abdominal obesity which is considered as waist circumference > 91.5 cm for men and 85.5 cm for women afflicted 65.1% of the study population. It was also found that 45.5% of the subjects suffered from high blood pressure (130/85).
Dietary habits among the participants have been presented in table 3. According to our findings, consumptions of sweetened drinks in 77.8% and sugar cubes in 88.5% of participants were as once or more than once per week. 60.6% of the subjects did not consume fast foods at all or few times per year. 93.8% of participants were also breakfast consumers.
Furthermore, after adjusting the confounders, results of the logistic regression examining the association among those who consume breakfast for once per week compared to those who completely skip breakfast shows a significant relationship with odds of metabolic syndrome, which means that these subjects have 62% lesser chance of MetS (odds ratio (OR)= 0.38, 95% confidence interval (CI)= 0.14 to 0.97). This effect remains significant even after adjustment for BMI and reveals that odds of MetS is 69 % lower in breakfast consumption as once per week in contrast to non-consumption (OR=0.31, 95 % CI= 0.11 to 0.87).
Nevertheless, no significant association has been witnessed between other dietary habits including consumption of sweetened drinks, sugar cubes, and fast foods with MetS after adjusting for potential confounders.

Discussion
In the current study, consumption of breakfast can significantly contribute to low chance of MetS. Conversely, consumptions of sweetened beverages, fast foods and sugar cubes have been shown to have non-significant impact on the occurrence of MetS. These relations between dietary habits and MetS were maintained after adjusting for potential cofounders such as age, education level; and physical activity level; history of chronic diseases; smoking and BMI.
Many studies suggest that eating breakfast can associate with an overall better diet quality and healthy lifestyle [44][45][46]. It has been also reported that individuals who eat breakfast frequently have a lower risk of an array of metabolic outcomes comparing to their peers who infrequently or never eat breakfast [47].
Furthermore, consistent to our outcomes, a few studies suggest no significant association between sweetened beverages consumption and higher risk of metabolic syndrome and its components [48][49][50]. A prospective study also, showed that sweetened drinks consumption was not associated with incident of metabolic syndrome in a middle-aged population [51].
This, however, is in contrast with several other studies that report sugar-sweetened drinks intake has significant effect on metabolic syndrome [52][53][54]. Sweetened beverages that were included in this study consist of artificially or homemade beverages. Sweetened beverages in Iran are usually of plant origin which contain beneficial compounds such as polyphenols which are inversely associate with MetS and its components [55]. This issue could be a source of contradiction in this study and others.
Additionally and following the same reasons we could not find any significant association between fast foods intake and metabolic syndrome however many studies suggest that regular fast foods consumption has irreparable effect on general health and can increase the risk of obesity, insulin resistance and other metabolic abnormalities [56][57][58]. There is not a definitive agreement on 'fast foods' definition [59]and differences in ingredients of the fast foods in the different studies could have caused discrepancies in the outcomes.
Moreover, fast foods consumption in our study was generally low (most of the study population (60.6%) did not consume fast foods at all or the intakes were only few times per year.
Many studies suggest that breakfast intake is beneficial to metabolic health which is in This study contains a few limitations. First of all, the design of this study is cross-sectional which does not provide a liable source of causality. Second, the data on dietary assessments were based on self-reported questionnaires. And third, the impact of confounders could not be fully controlled due to unknown or unmeasured factors. Strength points suggest that this study investigates the impact of dietary habits on metabolic syndrome among a relatively large sample in a Middle Eastern country. A large extent of confounders that might affect the metabolic syndrome or its components have been also considered and controlled.

Conclusions
As a conclusion, this study provides evidence that there is in fact an inverse relationship between breakfast intake and metabolic syndrome. No significant association has been seen between other dietary habits and MetS. However, to find out stronger evidence in relation between dietary habits and metabolic syndrome, more studies especially population-based cohort researches need to be conducted.

Competing interests
The authors declare that they have no competing interests.

Funding
No funding was received regarding to the present study.  * Dietary habits for all items were presented as frequency of consumption except for sugar cubes which presented as serving of intake. Table 4. Multivariable-adjusted odds ratios (95% CI) for metabolic syndrome across different frequencies or servings for various dietary habits in a sample of Iranian adults.