Introduction: Shift work has become the norm and an absolute necessity in various sectors of public life. Different production processes, technologies, and the nature of certain jobs lead to various health risks. Unhealthy eating behaviors remain common among shift workers across all economic sectors.

Aim: This study aims to compare the eating habits and dietary patterns of shift workers and fixed daytime workers in the Bulgarian machine-building industry, focusing on identifying differences that may influence health outcomes.

Materials and methods: A cross-sectional study was conducted at three work sites of a machine-building enterprise in Bulgaria, involving 309 workers (149 shift workers and 160 fixed daytime workers). Data on eating habits were collected using a 54-item Food Frequency Questionnaire (54-FFQ) adapted for the local population. Descriptive statistics were used to summarize the demographic and dietary data. Group comparisons between shift workers and fixed daytime workers were made using the Mann-Whitney U test for non-normally distributed continuous variables. A p-value of less than 0.05 was considered statistically significant.

Results: The study found significant differences in eating habits between shift workers and fixed daytime workers. Shift workers were more likely to consume white bread (p=0.003), fast food (p=0.045), margarine (p=0.001), fried potatoes (p=0.041), and processed meats (p=0.021) than fixed-daytime workers were. In contrast, fixed-daytime workers had a higher consumption of fruits (p=0.034), vegetables (p=0.047), and alcoholic beverages like beer (p=0.008), wine, and spirits (p=0.005) than shift workers. These differences suggest that work schedules may significantly influence dietary choices and impact workers’ health outcomes.

Conclusion: Shift work disrupts the natural daily rhythm and leads to changes in eating behavior, such as irregular meals, skipping breakfast, and eating late in the evening and at night. Our study highlights how these behaviors are associated with the regular consumption of processed, energy-dense foods rich in carbohydrates and fats but low in fiber and essential nutrients. The eating habits observed in our research are a significant risk factor for developing cardiometabolic diseases.

dietary patterns, health promotion, nighttime eating, public health, shift work

With the rapid growth of industrialization and urbanization, shift work has become a necessary and widely accepted standard globally, especially in sectors such as healthcare, public safety, transportation, machine-building, and other industries that require 24-hour production and service.^[1] According to EUROSTAT data from 2023, about 19% of the workforce in Europe is engaged in shift work. In 2021, approximately 19.8% of the workforce in Bulgaria worked in shifts, representing a significant portion of the country’s total employment. So far, there has been no universally accepted definition and characterization of shift work by health and labor organizations at both national and international levels. Scientific literature often uses the term “non-standard work schedule,” which refers to work outside the standard daytime hours of 7-8 a.m. to 5-6 p.m.^[2] This includes afternoon, evening, night, or early morning work, with schedules that can be either permanent or rotating.^[3] Employees who work on weekends are also considered shift workers, as they work outside standard weekday hours.^[4] It is important to note that shift workers work at night or on weekends as part of their regular schedule, not as overtime. Therefore, shift work should be distinguished from overtime work. A significant portion of the adult population spends about one-third of their day at work, where their health is constantly affected by the work environment. Unhealthy eating habits are common among shift workers in all industries.^[5] Shift workers often exhibit eating behaviors characterized by irregular meals and frequently skipping one of the main meals in the cycle of breakfast, lunch, or dinner.^[6] Eating late in the evening and at night is common, as is the frequent consumption of unhealthy foods such as chips, snacks, wafers, sweets, sugary drinks, and energy drinks.^[7] Unhealthy eating among employees with non-standard work schedules is linked to the presence of vending machines at work, which provide quick and easy access to inadequate and processed yet hunger-satisfying foods and drinks.^[8] Additionally, the lack of proper meal facilities, such as a cafeteria or dining area, is common, especially during night shifts. In these conditions, workers have limited access to healthy food options, which makes proper nutrition more challenging.^[9] This often leads to the regular consumption of processed foods high in carbohydrates, saturated fats, and trans fats.^[7] As a result, their diet is typically low in fiber, essential vitamins, minerals, antioxidants, and polyunsaturated fatty acids (PUFAs).^{[10, 11]} Shift workers are also prone to increased alcohol consumption, often using it as a sleep aid and in some industries, alcohol use is promoted as a way to socialize and relieve stress after shifts.^[12]

Shift work increases the risk of obesity, type 2 diabetes (T2D), and cardiovascular diseases (CVD), likely due to the mismatch between work schedules and typical patterns of work and rest in society.^[13] When sleep, eating, and rest schedules do not align with human chronobiology, it leads to chronic disruptions in circadian rhythms, which are often the primary cause of these health risks.^[14] Poor eating habits, combined with other common factors among shift workers (such as disrupted circadian rhythms, irregular work and rest schedules, reduced sleep, psychosocial stress, and low physical activity), disrupt metabolic balance and increase the risk of developing cardiometabolic diseases, including CVD, T2D, and metabolic syndrome (MetS).‌^{[‌15, 16]} Studies have shown that shift work is associated with a higher incidence of depressive and psychosomatic symptoms among employees.^[17] It is largely attributed to chronic sleep disturbances, which lead to a lower quality of life, disrupted social life, increased tension, depressive moods, high levels of anxiety, and a higher likelihood of abusing alcohol and medications.^[18] This pattern can also worsen the nutritional status and eating habits of shift workers.

The goal of the study is to analyze and compare the dietary habits of shift workers and fixed-daytime workers in the Bulgarian machine-building industry. Specifically, it aims to identify significant differences in the frequency and types of foods consumed, with a focus on understanding the influence of shift working on eating habits. Through this comparison, the study goal is to uncover key differences that could have impact on the health and well-being of the shift workers.

The cross-sectional study was conducted within three work sites of a machine-building enterprise, located in Sopot, Kalofer, and Karnare. A total of 309 workers, both on shift and fixed daytime schedules, participated. The 54-FFQ questionnaire was used to comprehensively assess lifestyle, eating habits, and the frequency of food intake among the workers. The questionnaire is an adapted version of the validated KomPAN^[19] and 72-item SQ-FFQ^[20] questionnaires. The KomPAN (Dietary Habits and Nutrition Beliefs Questionnaire) is designed for individuals aged 15-65 and is available in two formats: one administered by an interviewer and the other self-administered. It assesses dietary habits, frequency of food consumption, nutrition beliefs, lifestyle, and personal data. 72-Item Semi-Quantitative Food Frequency Questionnaire (72-Item SQ-FFQ) is designed to assess the habitual dietary intake of adults by evaluating the frequency of consumption of 72 food items over the past year, providing a comprehensive assessment of energy and nutrient intake. The adaptation process, carried out by the research team, considered local dietary habits and national dietary characteristics. The original list of 72 food items from the Kowalkowska and Lidia Wadolowska questionnaire was reduced to 54 items, removing products that were uncommon or unfamiliar to the Bulgarian population. Additionally, specific types of fruits and vegetables were consolidated into general categories of “fruits” and “vegetables.” The questionnaire consists of eight sections: sections 1 through 7 contain questions related to lifestyle, while section 8 (54 questions) provides a detailed list of the food intake frequency. This section includes various categories such as sugary products, dairy products, meat, cereals, fruits, vegetables, fats and oils, snacks, and beverages. For each food item, participants indicated their frequency of consumption, ranging from “never or rarely”, “once a month or less”, “several times a month”, “several times a week”, “once a day” to “several times a day”.

The study involved 309 workers, with 160 (51.80%) on fixed daytime schedules and 149 (48.20%) on shift schedules. Demographic details of the respondents are shown in Table 1.

The average age of the participants is 44.76±0.66, SD=11.57 (Table 2).

The average total years of employment for participants is 22.51±0.66 years (SD=11.65) and the average number of years in their current job is 12.74±0.59 years (SD=10.34). In assessing participants’ eating habits over the past four weeks, we found that 247 (79.9%) of them did not limit their calorie intake, and 245 (79.3%) did not restrict their salt consumption. Among shift workers, 78.5% did not limit their calorie intake, and 79.9% did not restrict their salt consumption. There were no statistically significant differences between the two groups regarding these dietary practices or in adherence to restrictive diets over the past four weeks (Table 3).

Regarding the three main meals (breakfast, lunch, and dinner), 64.7% of participants reported not following a regular meal schedule. There were no significant differences between the two groups in adherence to these meals (χ²=0.719, df=1, p=0.407) or in the consumption of foods between meals (χ²=6.752, df=4, p=0.150). However, when analyzing the frequency of nighttime eating, significant differences were found between the two groups (χ²=27.887, df=2, p<0.001) (Fig. 1).

Figure 1.

Frequency of nighttime eating in fixed and shift work groups.

In both groups we studied, sugary foods were the most commonly consumed items during nighttime eating, with fruits and vegetables following in frequency (Fig. 2)

Figure 2.

Distribution of food categories consumed during nighttime eating in the study groups.

In the shift work group, the consumption of different food categories was fairly balanced: 34.4% of participants ate fruits and vegetables, 32.3% consumed sugary foods, another 32.3% preferred sandwiches, 21.9% ate snacks like pretzels and crackers, and 10.4% consumed dairy products.

We identified statistically significant differences between the two groups in the types of foods consumed during nighttime eating (χ²=15.639, df=6, p=0.016). Those on a fixed daytime schedule were more likely to eat sugary foods at night, whereas shift workers tended to eat sandwiches more frequently during nighttime. Despite these differences, 96.8% of participants reported that they primarily consume cooked meals.

Additionally, to align with the study’s objective, it was essential to assess the frequency of food intake across various categories of commonly consumed foods and beverages in the Bulgarian population, covering a total of 54 food items. Significant differences between the two groups were observed (Table 4). Shift workers exhibited a higher tendency to consume white (wheat) bread (U=9583.0, p=0.003), fast food (U=10352.0, p=0.045), margarine (U=9552.0, p=0.001), fried potatoes and chips (U=10329.5, p=0.041), and processed meat such as sausages and hot dogs (U=10182.5, p=0.021) compared to those with fixed daytime schedules. In contrast, those on fixed daytime schedules were more likely to consume fruits (U=10230.0, p=0.034) and vegetables (excluding potatoes) (U=10344.0, p=0.047). They also showed a higher preference for drinking beer (U=9988.0, p=0.008), alcoholic cocktails (U=8537.5, p<0.001), and spirits (U=9890.5, p=0.005). Detailed results are presented in Table 4.

This study revealed distinct differences in the eating habits between shift workers and fixed daytime workers. Shift workers were more likely to engage in irregular meal patterns, including skipping breakfast and eating late at night. In contrast with fixed daytime workers, who were found to consume more fruits and vegetables, shift workers exhibit a higher intake of processed, energy-dense foods such as sugary products, fast food, and snacks. The behaviors we observed contribute to a higher intake of carbohydrates and fats, which are linked to increased health risks. On the other hand, despite having a more regular eating schedule, fixed-daytime workers still preferred high-calorie foods, particularly in the evening, along with higher alcohol consumption. Our findings emphasize the need for targeted nutritional interventions for shift workers to address the irregular and unhealthy eating patterns associated with their work schedules. The exact mechanisms by which shift work affects eating behavior remain unclear.^[30] Considering the negative health impacts associated with unhealthy eating patterns during night shifts, employers need to prioritize promoting healthy eating habits among shift workers.^[31] Understanding the dietary profile and eating patterns of shift workers is critical for developing effective nutritional interventions. Specialized programs and recommendations are needed to address specific dietary deficiencies and risks associated with shift work. Implementing and strictly following these measures could significantly improve the health outcomes of shift workers.

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The authors have no funding to report.

The authors have declared that no competing interests exist.