In this case-control study based on the population, differences in dietary nutrient intake were evident between the case and control groups. It was observed that participants’ adherence to a healthy diet increased with higher age, BMI, and total energy intake. Notably, a significant association was found between total energy intake and quartiles of unhealthy and mixed dietary pattern scores. Surprisingly, the study discovered that the highest adherence to both healthy and unhealthy dietary patterns was linked to a reduced likelihood of having celiac disease, even after adjusting for BMI and/or energy intake. Additionally, a significant inverse correlation was identified between the odds ratio of CD incidence and the mixed dietary pattern score, even after adjusting for energy intake. Generally, little information exists available on the dietary pattern of CD in the GF diet and whether differences in macro-nutrient, micronutrient intake or dietary quality may be seen in celiac individuals of different ethnicities [20, 21]. To the best of our knowledge, no study has investigated the dietary patterns in Iranian adult patients with CD.

According to our findings, there has been a substantial relation between age, BMI, and total energy intake with quartiles of healthy dietary pattern score. In other words, with increasing age, participants had the highest adherence to the healthy dietary pattern while consuming more calories. Accordingly, as expected, higher consumption of calories was associated with a higher BMI in adults. In line with our study, Taetzsch et al. based on a meta-analysis of seven published studies demonstrated that consuming a GF diet was linked to consuming more energy and fat and substantially less dietary fiber [22]. Another cross-sectional study conducted on 130 Iranian adult patients with CD, illustrated that the mean calorie intake in celiac patients was considerably lower compared with non-celiac people [10]. Ciacci et al. also realized that adults with celiac disease who follow a strict GF diet have considerably lower weight, BMI, fat and lean body mass than a healthy control group. It was further offered that the diet of these patients was imbalanced and they consumed a higher percentage of calories from fat and less from carbohydrates [23]. Mazzeo et al. in line with our study, assessed the daily energy of 100 individuals with CD by a 7-day weighed food record and the modified Italian European Prospective Investigation FFQ. Their finding illustrated the calorie intake was 2,144.0 (269.4) and 1,890.7 (535.7), respectively. Also, 16% of individuals were categorized as overweight (BMI ≥ 25) which was in agreement with our finding in terms of BMI [24].

A prospective study also examined how different durations of a GF diet affected the BMI of Iranian CD patients. Patients were divided based on diet adherence periods: under 6 months, 6 months to 2 years, and over 2 years. Women showed significant changes in both body weight and BMI in all three periods whilst on GFD, while men experienced significant differences after more than 2 years on the diet. Those aged 31–60 had notable changes in BMI under 6 months, while adhering for more than 6 months showed changes for individuals aged 18–60. These differences may stem from varied eating habits among age groups and hormonal disparities [25].

In addition, we observed major differences in energy density and some dietary nutrient intake between groups within the same dietary cluster (healthy eating pattern, unhealthy eating pattern and mixed dietary patterns). The reports of a prior research in this regard Mager et al. highlighted that within the same individual diet patterns (including, western diet-supplement users and higher, fat western diet and prudent diet, lower fat) there were some distinct in terms of energy density, glycemic load (GL), fiber and micronutrient intake between youth with CD and mild chronic gastrointestinal controls. For example, children with CD’s diets were characterized by high energy density, higher fiber, GL and selenium intakes versus gastrointestinal complaints [21]. In a recent case-control study of Iranian children and adolescents with CD, significant dietary patterns were identified. It was observed that among CD patients, half were found to exceed their caloric intake, while a majority displayed higher consumption levels of protein, carbohydrate, thiamin, riboflavin, niacin, vitamin B12, and iron compared to the recommended thresholds. Additionally, based on the Recommended Dietary Allowance (RDA), all subjects within the CD group demonstrated inadequate intake of vitamin D, with half experiencing insufficient intakes of vitamins A and E. Although the healthy control group exhibited overall higher nutrient consumption, both groups demonstrated similar quality of diet, underscoring the necessity for dietary enhancements among CD patients. While the intake of macronutrients and select micronutrients exceeded the RDA in both groups, there remains a need to improve the dietary quality specifically tailored to individuals with CD [26]. In contrast, a recent report indicates that less than half of CD patients are meeting the recommended daily fruit intake, both before and during the COVID-19 pandemic [27]. Apparently, the reported controversial results between these studies are likely to be owing to the difference in included population, the method of defining non-adherence, and the method of evaluation of the diet habits and pattern. Nutritious eating hence becomes significantly more critical for patients especially in children and adolescents on highly restrictive diets, such as the GF diet, which typically lacks adequate nutritional quality by nature [27]. Compliance with a GF diet and the maintenance of a high-quality dietary regimen represent pivotal challenges among children and adolescents diagnosed with CD [26].

Based on our results from regression analysis, the highest adherence to a healthy dietary pattern was related to the lowest odd ratio of CD development. Meanwhile, a negative association between the odd ratio of CD incidence and traditional dietary pattern score was found. When we looked at the consumption of the healthy dietary pattern in our study, individuals with CD were consumers of whole grains, nuts, legumes, white meat, other vegetables, and tea and coffee. As regard to available data, the consumption of these foods is the excellent dietary source of fiber, minerals, and vitamins, protein and micronutrients as well as representing healthier food options [10, 22]. Despite being celiac patients, those in our study primarily consumed whole grains such as Sangak, Barbari, Taftoon, and barley, which are widely recognized and commonly consumed as whole grains in Iran. Besides, CD patients with a healthy eating pattern had a limited consumption of fast food, refined grains, sweets and desserts, and snacks. Conversely, adherence to a mixed eating pattern was related to the high consumption of sweets and desserts, refined grains, fast food, red meats as well as a lower intake of starch vegetables and whole grains. These foods are rich in simple sugars and high-glycemic index and fat (especially, saturated fatty acids or cholesterol) and also low in fiber. The study also observed a connection between moderate consumption of meat and beans and reduced levels of beneficial bacteria, specifically Lactobacillus and Firmicutes, in individuals with CD. High bean intake was particularly linked to lower Lactobacillus abundance. These findings suggest that the consumption of meat and beans might diminish essential gut bacteria, potentially influencing dietary effects and the continuation of CD symptoms through changes in gut microbiota abundance [28]. As a result, this dietary profile could also be harmful and cause the aforementioned insulin resistance, hyperinsulinemia, and cardiovascular disease [20]. A recent study in this field presented that the lower intake of whole grains, plant protein, legumes, and refined grain in Iranian CD patients than that of non-celiac people controls [10].

However, we should note that Iranian celiac patients have insufficient access to available commercial gluten-free alternative sources knowledge regarding adding healthy foods to the GF diet needs to be promoted. Apart from this, unappealing and unacceptability to some patients and the higher cost of a substitute non-gluten source are other reasons not to choose them [10]. Another case-control study displayed that the participants with CD consumed a substantially lower mean daily energy, carbohydrates (CHOs), total protein, and vegetable protein than that of healthy individuals, while the intake of red and processed meat and lipids was significantly higher in individuals with CD versus healthy participants. According to typical Mediterranean foods, their researchers observed that individuals with CD had a lower intake of fruits as compared to healthy participants, while both groups also ate other typical Mediterranean foods in low amounts. As a consequence, a low adherence to a Mediterranean diet contributed to a remarkable increase in the risk of all-cause, non-communicable diseases mortality [29]. In a study conducted on children with CD, Mager identified three diet patterns reflecting a typical Western Diet pattern (characterized by higher fat/simple sugar intakes) and a more prudent dietary pattern (Lower Fat/Higher CHO diet). None of the patterns reflected a Dietary Approaches to Stop Hypertension (DASH) or Mediterranean diet pattern and also addressed no relation between diet quality by dietary pattern method and adherence to the GF Diet [21]. Whereas, a recent cross-sectional questionnaire-based study involving 37 Dutch pediatric patients diagnosed with CD revealed that the majority of children with CD tended to adhere to a healthier diet. Although, there is a need to address potential unhealthy eating habits that might have developed in these patients [27].

While, the findings of the present study should be interpreted cautiously for some limitations. because food groups and dietary intakes were evaluated using FFQ, thus its limitations such as recall bias and underreporting by participants may have affected the present results. Besides, celiac patients are aware of being health conscious. However, the FFQ was validated in the general Iranian population and modified to examine the dietary habits of patients with CD and accomplished by a trained nutritionist. Another limitation was related to the gastrointestinal symptoms caused by celiac individuals were not assessed which might have had effects on food groups and nutrient intake. Our observation showed that dairy products and fruits and vegetables were not reported in healthy and unhealthy eating patterns. Our assuming that celiac individuals tend to decrease the consumption of these types of food groups resulting in lactose intolerance and non-digestible carbohydrates containing fruit and vegetables consumed that could lead to GI discomforts among patients [10]. Which also might have had minimal effects on our results.