In recent decades, notable changes have occurred in dietary patterns across different societies. Using PERSIAN cohort data, we investigated dietary changes among Iranian people in two stages: baseline phase (2015-2017) and reassessment phase (2021-2023). Additionally, the factors influencing these changes will also be examined. The PERSIAN cohort is a multicenter and prospective study comprising 32,000 individuals aged 35-70 years from 18 geographical regions of Iran. The study’s data were collected using a 113-item Food Frequency Questionnaire assessing dietary intake over the past year. The generalized estimating equations (GEE) method was employed to analyze changes in macronutrients and total energy across two time periods. The effects of age, time, gender, place of residence, marital status, education, socioeconomic status (SES), smoking, physical activity, body mass index, DMF (decayed, missing, and filled teeth), sleep duration, hypertension, diabetes, cardiovascular disease, metabolic syndrome, and center were also assessed in the study. Total energy intake in the reassessment phase (2021-2023) was reduced by 250 kcal/day compared with the baseline phase (2015-2017), accompanied by reductions in daily carbohydrate (40.3 g/day), protein (10.3 g/day), and fat (5.7 g/day) intake. In adjusted analyses, women consumed less carbohydrate, protein, fat, and total energy than men: 82.91 g/day, 17.36 g/day, 9.15 g/day, and 485.34 kcal/day, respectively. In addition, there was a lower decline in the intake of all macronutrients in women compared to men. Rural dwellers had significantly higher daily intakes of carbohydrates (11.17 g/day), protein (1.37 g/day), fat (1.57 g/day), and total energy (96.21 kcal/day). Individuals with obesity had a significantly higher average intake of protein (4.82 g/day), fat (3.64 g/day), and total energy (195.62 kcal/day). In the multivariable analysis, individuals in the highest SES group consumed significantly more protein (2.28 g/day), total fat (3.39 g/day), and total energy (47.15 kcal/day) compared to those in the lowest SES group. In addition, all SES received lower intake of macronutrients over time homogenously. Patients with hypertension, diabetes, and cardiovascular disease consumed significantly lower average total energy (31.62, 67.61, and 79.35 kcal/day, respectively) compared to healthy individuals; conversely, those with metabolic syndrome consumed 17.12 kcal/day more energy than their healthy counterparts. Economic challenges and social inequalities have significantly impacted the intake of macronutrients in the Iranian diet, highlighting the need for targeted nutritional interventions to improve dietary balance, particularly among vulnerable populations. Food subsidies for lower-income deciles could be a beneficial intervention.