Among various factors including race, family history of chronic diseases, age, and gender, diet plays an important role in the development and control of MetS and its components (
Kaur, 2014,
Povel et al., 2012). No specific diet has been introduced to treat MetS. Some studies have shown the beneficial effects of Mediterranean (
Esposito and Giugliano, 2010) and DASH diets (
Azadbakht et al., 2005) on improving components of the MetS. Consumption of some nutrients and food groups (
Casas-Agustench et al., 2011,
Esmaillzadeh et al., 2005) was also reported to reduce the risk factors of this syndrome. In recent years, the combination of macronutrients in the diet of patients with MetS has attracted extensive attention. Since fats have the highest energy density among macronutrients, dietitians recommend individuals to reduce its consumption (
Johnson et al., 2007). However, we should note that a reduction in the percentage of calorie received from the fats is associated with increased calorie intake from carbohydrates. High intake of carbohydrate increases serum triglycerides, decreases serum HDL-C, and impairs glucose metabolism as components of the MetS (
McKeown et al., 2004,
Mittendorfer and Sidossis, 2001). Considering the effect of consuming macronutrients such as lipids, proteins, and carbohydrates on the MetS, the findings of different studies are inconsistent (
Carnethon et al., 2004).
For example, a cross-sectional study on Framingham research found no significant relationship between carbohydrate intake and MetS (
McKeown et al., 2004). Similarly, the results of another study on men and women did not show any association between macronutrients' intake and MetS (
Eilat-Adar et al., 2008). However, the results of a cross-sectional study on 1626 patients with history of cardiovascular diseases showed that high consumption of carbohydrates decreased the prevalence of MetS (
Skilton et al., 2008). Furthermore, the results of a prospective study in this area indicated that high intake of fat was associated with increased risk of MetS (
Skilton et al., 2008).
In this area, the results are controversial and the distribution of macronutrients in diets can determine the successful prevention and treatment of MetS. Moreover, no recommendation has ever been made to set up an appropriate diet for treatment of MetS. So, the current study was conducted to evaluate the effect of macronutrients on MetS and its components in adult population of Yazd city.
Materials and Methods
Participants and design: This cross-sectional study was carried on the data collected by two prospective studies;
Yazd Health Study (YaHS ) and TAghzieh Mardom-e-YaZd (TAMEZ) or Yazd Nutrition Study. The study population included people who lived in Yazd city and were in the age range of 20-69 years. The study design, sampling method, participants' characteristics, and data collection method were published elsewhere (
Mirzaei et al., 2017).
Initially, we studied the data of TAMEZ and YaHS to extract the required information on participants' dietary intake, anthropometric indices measurement, blood factors, blood pressure measurement, and confounding factors including socioeconomic status, history of chronic diseases, and physical activity status. Later, we merged the data of the above mentioned research projects.
Finally, of 3826 available profiles, 383 were excluded due to lack of specific codes (n = 2), lack of nutrition information (n = 332), repeated codes (n = 49), and lack of information on metabolic syndrome (n = 105). Finally, 3338 participants entered the study. In the next stage, we excluded people with a history of cardiovascular disease, stroke, diabetes, and cancer as well as individuals with higher or lower energy intakes (more than 6500 kcal and less than 600 kcal, respectively). Finally, the analysis was conducted on 2221 individuals.
Diet evaluation: Participants' dietary information was collected by completing a semi-quantitative FFQ consisting of 178 food items and 551 questions. The validity and reliability of this questionnaire was measured and confirmed in TAMEZ project (
Mirzaei et al., 2017). In order to complete this questionnaire, we explained the average size of each food item for the participants and asked them to report the amount and frequency of that food. Later, the values related to each food item were determined in grams using guidelines of household scales (
Ghaffarpour et al., 1999). The amount of energy, protein, carbohydrate, and fat intake was also determined.
Diagnosis of MetS: MetS was diagnosed in accordance with National cholesterol education program adult panel III (ATP III) (
Alberti et al., 2009). Accordingly, the MetS was defined as having at least 3 cases of metabolic sub-syndrome factors: 1) Triglyceride above 150 mg/dl; 2) HDL cholesterol level of less than 40 mg/dl in men and less than 50 mg/dl in women; 3) Systolic blood pressure above 130 mmHg and diastolic blood pressure above 850 mmHg; 4) Fasting blood glucose above 110 mg/dl; and 5) waist circumference (WC) above 102 cm in men and 88 cm in women
.
Evaluation of anthropometric indices: The participants' weights were measured using a digital scale (Omron BF511 Inc. Nagoya, Japan) with an accuracy of 0.1 kg. The height was also measured in standing position using the tape meter with an accuracy of 0.1 cm while the participants were leaning against a smooth wall without shoes. Waist circumference was measured with an accuracy of 0.5 cm using a tape measure in the horizontal plane midway between the lowest ribs and the iliac crest. The hip circumference was also measured at the largest part of the hips with an accuracy of 0.5 cm. All measurements were performed three times (before the interview, after completing one third of the questionnaire, after completing two third of the questionnaire). Later, we calculated the body mass index (BMI) by dividing the weight in kilograms by height in meters squared.
Blood pressure measurement: Systolic and diastolic blood pressures were measured in the sitting position after completing two-thirds of the questionnaire, which was after about 40 minutes of rest. The measurements were repeated three times with five-minute intervals using the Richter pressure gauge. Next, average of the second and the third measures was calculated and recorded as the blood pressure.
Laboratory data: Later, we measured the fasting blood glucose (FBG) (mg/dl),
high density lipoprotein-cholesterol (HDL-C), and triglycerides (TG). An auto-analyzer device and kits related to each test (Pars Azmoon) were used for this purpose.
Other variables: Physical activity information was collected using a standard questionnaire (
Mirzaei et al., 2017). Then, the amount of physical activity was calculated in metabolic equivalent of an hour per week. Furthermore, the participants' socioeconomic status and smoking status were collected using questionnaires and interviews (
Mirzaei et al., 2017).
Data analysis: In order to carry out the analyses, we used the IBM SPSS version 22. For quantitative variables, the values were reported in mean and standard deviations and percentages were applied to report the classified variables. Student t-test and chi-square tests were also used to compare the quantitative and qualitative variables, respectively. The intake of macronutrients (grams per day) was adjusted based on the total energy intake and participants were divided into quantiles according to their consumption of macronutrients. These quantiles were then used as qualitative variables in the next statistical analyses. Finally, to evaluate the association of macronutrients' intake with the risk of metabolic syndrome and its components, we run multivariate regression after adjusting for the confounding variables such as age, education, gender, physical activity, smoking status, BMI, and family history of Chronic diseases.
Ethical considerations: both YaHS and TAMEZ studies have ethical approval from the Ethics Committee of Shahid Sadoughi University of Medical Sciences. Informed consents were also obtained from all participants.
Results
A cross-sectional study was carried out on 2221 individuals; 529 were afflicted with the MetS and 1692 did not have it. The general characteristics of the study participants are shown in
Table 1. The BMI, WC, hip circumference, blood pressure, TG, and FBG were significantly higher in people with MetS. Moreover, 71 percent of the individual with MetS were women over 40 years of age.
A significant difference was observed between individuals with and without metabolic syndrome in terms of physical activity, education, marital status, occupational status, home ownership, and the number of family members. However, no significant difference was observed between the two groups regarding smoking status, ethnicity, house in meters, and the history of chronic diseases.
Table 2 shows the odds ratio of MetS and 95 percent confidence interval for intake of macronutrients in the crude model and after adjusting for the confounding factors in three models.
We adjusted for the confounding variables such as age, education, gender, physical activity, smoking status, BMI, and family history of chronic diseases and found that the odds ratio of MetS was significantly higher in individuals with more intake of carbohydrates (OR: 1.67, CI: 1.01-2.75). However, intake of fat and protein did not have any significant association with the probability of developing MetS (OR: 0.97, CI: 0.59-1.60, OR: 0.90, CI: 0.54-1.49).
Furthermore, individuals with higher intake of carbohydrates had more probability of abdominal obesity (OR: 1.89, CI: 1.06-3.34); whereas, higher consumption of proteins reduced the probability of abdominal obesity (OR: 0.45, CI: 0.25-0.79).