The present cohort study revealed that DDS was associated with risk of incident MetS inversely but after adjustment for some confounders such as age, gender, education, WSI, smoking, alcohol and opium consumption and physical activity, total energy intake and total fat intake, the risk of MetS increased in third quartile (18%) and fourth quartile (24%), and after adjusting of BMI, there wasn’t any correlation between DDS and MetS.
Some studies found an inverse association between DDS and Mets. In a prospective cohort study among Korean adults aged 40–60 years with a 12 years follow-up, DDS had an inverse association with MetS and its features in men despite women21.Also a cross-sectional study was conducted on 581 healthy adults in Tehran, indicated an inverse correlation with MetS and its components22. DDS is a good indicator for assessing nutrients intake adequacy, quality of diet and relationship between diet and diseases 23–25. Previous studies have revealed that a more DDS is related to adequate intake of food groups and a healthier diet11,26.
In the present study, after adjusting the confounders, the relationship between DDS and Mets in the third and fourth quartiles was direct. In comparison to other studies, DDS in this study was lower 21–23, that may be due to differences in DDS determining methods. On the other hand, due to lower DDS, the consumption of useful foods such as fruits, vegetables and fiber has decreased, in addition to the increase of some components of MetS such as triglycerides, blood pressure and fasting blood sugar in subjects cause beneficial changes in the diet and can distort the relationship between DDS and MetS, and therefore the existence of these confounding factors can increase the consumption of healthy food, which is related to the increase of DDS.
This study indicated no association between glucose hemostasis and risk of Mets after adjusting of some confounders. But in adjusted model 1 indicated increased risk of Mets. In contrast, previous studies showed that higher DDS was associated with decreased abnormal glucose hemostasis22,27. However In the current study, consistent with some studies, there was a direct association between DDS and BMI. Previous studies showed when DDS increased, the intake percentage of most food groups was increased that may be cause excess energy intake and increasing BMI 28,29. In other study, Mexican men with a more DDS had a higher intake of fat and energy and so overweight30.
In present study, higher DDS associated with excess energy and fat intake. Of course excess energy and total fat may be due to increased consumption of healthy items such as of vegetable oil and whole grain that, there are useful component such as fiber, antioxidants and phytochemicals31,32. In the other hand, contrast with the current study, some studies have showed an inverse association between DDS and BMI15,22. A meta-analysis study of observational studies indicated no relationship between BMI and DDS 33. The contradiction in the studies may be related to the type of study conducted, the method of evaluating and determining food diversity, and the indicators related to its groups and subgroups.
In our results, in line with some studies34,35, men consume higher varied diets than women. In some studies, there is no relationship between DDS and gender36,37, and in Cano-Ibáñez et al. study, contrary to our results, the variety of food in women was more than that of men38. Mood and stress, appetite and genetics are included, and even customs and traditions and culture of each region can have a great impact on food diversity35. For example, the environment under our study is located in an area that uses more traditional foods such as stews and refined grain, which is cooked in a traditional way and can affect people's dietary diversity, as well as traditional sweets that contain a lot of saturated fat and Sugar that is a factor in increasing the incidence of overweight and chronic diseases such as metabolic syndrome 39–42.
In this study, in line with previous studies 43–45, the relationship between education and DDS was direct, so it can be concluded that as the level of education and awareness increases, attention to food diversity and healthy food consumption increases. Low education can reduce people's ability to learn nutritional knowledge and understanding. Also, studying more increases in people with higher education, so nutritional awareness may increase in people with higher education44.
Our study has some limitation. We adjusted the potential confounders but may residue confounders that didn’t adjust and might effect on the Mets risk. Also, this study has some strengths such as large sample size. On the other hand, FFQ was used to assessment of dietary consumption. FFQ may be better for calculating DDS with other tools such as recalls or food records. Analyzing food diversity in each person can help increase the quality of food by increasing the consumption of useful food groups, but according to the results of the studies, it is better to look in the DDS tools and groups and subgroups based on quality, method of processing and the presence of nutrients in them. More studies with higher quality are needed in the future.