Changes in Body Composition Among University Students During Exam Preparation: The Role of Dietary Habits and Physical Activity

1. Introduction

Thanks to healthy dietary habits, individuals are able to maintain a healthy lifestyle. These habits are closely linked to how we select, process, and consume food, as it must provide the essential nutrients required by our bodies to perform vital functions effectively [1,2]. Achieving a healthy diet depends on several factors, such as food processing methods, timing of meals, and the presence of stress and anxiety. Following a healthy eating pattern can help prevent various diseases, including hypertension, cancer, anemia, obesity, and osteoporosis [3].

From childhood, young individuals develop a set of habits that evolve throughout their lives based on lifestyle choices, which are influenced by culture, customs, and beliefs. These influences shape food preferences and behaviors, which may either support or undermine healthy practices [4,5]. Currently, the population increasingly consumes fast food—highly processed items rich in sugars and fats—and exhibits a more sedentary lifestyle, as most free time is spent engaging with screens, video games, and smartphones. This sedentary behavior has detrimental consequences for both physical and social well-being. Therefore, healthy eating must be accompanied by regular physical activity, performed daily to avoid physical inactivity and sedentarism[6].

Physical activity plays a crucial role in maintaining overall health. As the amount of physical exercise increases, the respiratory system improves, enhancing pulmonary capacity and reducing the likelihood of respiratory illnesses. Exercise also supports mental well-being, helping reduce stress and anxiety. Thus, engaging in physical activity is particularly important during exam periods, as it enhances concentration levels[7,8,9].

Stress is the body’s short-term response to threatening situations. Its onset often disrupts eating habits and physical activity. Stress manifests in two forms: organic and psychological. The latter includes academic stress, which is the focus of this study. Academic stress is defined as a physiological, emotional, cognitive, and behavioral activation in response to academic stimuli and demands[10]. University students are particularly at risk of adopting unhealthy lifestyles[4,11], as they regularly face numerous examinations that induce stress. This stress often stems from competitiveness, goal-setting (e.g., early employment, gaining entry to a desired academic program, managing multiple subjects), or unmet goals that lead to frustration. Academic overload also contributes, as students not only study but must attend internships, seminars, and complete coursework, further intensifying stress. Such accumulated stress can have long-term negative effects.

Body composition refers to the primary components that make up the human body: bone, water, muscle, fat, and visceral tissue. Visceral fat exceeding 12% indicates abdominal fat infiltration, a serious nutritional concern that increases the risk of cardiovascular and metabolic diseases if uncorrected. These components are assessed using bioimpedance analysis, which sends an electrical current through the body (from hand to hand or foot to foot). The time required for the current to travel across the body allows estimation of the amount and percentage of each component[10]. Poor diet and sedentary behavior can significantly disrupt body composition.

As previously described, students experience heightened stress during exam periods. This stress often results in poor lifestyle choices, including unhealthy eating (either excess or insufficient intake of unhealthy foods) and reduced physical activity (due to time constraints). These behavioral changes can negatively affect body composition and increase disease risk.

The aim of this study was to demonstrate how the stress and anxiety experienced by students during exam periods affect their body composition due to poor dietary choices and decreased physical activity. The findings may support the implementation of targeted interventions and raise awareness among young individuals about the importance of maintaining healthy lifestyle habits.

The main objective was to evaluate body composition among university students in relation to their dietary intake and physical activity levels before and during the exam period.

The hypothesis was that students’ body composition deteriorates during the exam period.

2. Materials and Methods

2.1. Study Desing and Population

This study was designed as a prospective, observational, comparative, and longitudinal investigation. The target population consisted of second-year undergraduate nursing students enrolled at the University Complutense of Madrid. Students were recruited through convenience sampling.

This study was approved by the Ethics and Research Committee of Puerta de Hierro University Hospital (ACT 244/23). Access to the study files was password-protected and restricted to the responsible researchers in accordance with current data protection regulations (BOE-A-2018, Regulation 2016). The study was also approved and registered at ClinicalTrials.gov with the identifier: NCT06717620.

2.1.1. Inclusion Criteria

• Age $\ge 18$ years
• Current enrollment in the second year of the nursing program
• Willingness to participate in both evaluation periods.

2.1.2. Exclusion Criteria

• The presence of any physical limitation that prevented bioimpedance measurement.
• Ongoing use of pharmacological treatments that could influence body composition.
• The inability to complete the second assessment (e.g., absence on the exam day).

2.2. Intervention

Participants were assessed at two time points: (1) prior to the start of the exam preparation period (January 2024), and (2) during the exam period, immediately following completion of a major exam (May 2024).

At each time point, the following data were collected:

Anthropometric and body composition measurements: Body weight (kg), height (cm), fat mass (%), muscle mass (kg), and visceral fat (score) were assessed using a validated bioimpedance device (Beurer BF 1000). Participants were instructed to remove footwear and metallic items and to follow standard pre-measurement conditions (e.g., fasting state, avoidance of intense physical activity 12 hours prior).

Dietary habits: Evaluated using a modified version of the Kidmed questionnaire, which assesses adherence to the Mediterranean diet. The questionnaire includes positive and negative dietary items with a scoring system that classifies diet quality into low ($\ge 3$ points), medium (4–7 points), or optimal ($\ge 8$ points).

Physical activity: Measured using the short form of the International Physical Activity Questionnaire (IPAQ-SF). Participants reported the frequency and duration of vigorous, moderate, and walking activities over the past 7 days. Total physical activity was calculated in MET-minutes/week and categorized as low, moderate, or high following standard IPAQ classification criteria (Figure 1).

Additional data on lifestyle behaviors (e.g., caffeine consumption, tobacco use, intake of cola or energy drinks) were also gathered via a structured survey.

2.3. Statistical Analysis

Descriptive statistics were used to summarize sociodemographic and clinical characteristics. Continuous variables were expressed as means and standard deviations, and categorical variables as absolute frequencies and percentages. Paired-sample t-tests were used for normally distributed continuous variables, while Wilcoxon signed-rank tests were applied to non-normally distributed data. Chi-square tests assessed differences in categorical variables. The statistical significance threshold was set at p<0.05. All analyses were performed using IBM SPSS Statistics for Windows, Version 29.0 (IBM Corp., Armonk, NY, USA).

3. Results

3.1. General Characteristics of the Population

In the first phase of data collection, conducted in January 2024 (non-exam period), 142 students who met the inclusion criteria participated in the study. Most participants were female (78.9%), with a mean age of 22.54 years. The mean body weight was 63.32 kg, with a mean BMI of 23.04. Regarding body composition, 42.3% of the students were categorized as having very high body fat, and 50.7% were within the normal muscle mass range.

Diet quality was classified as medium in 48.6% of participants and optimal in another 48.6%. Physical activity was high in 80.3% of the sample during this period (Table 1).

3.2. Comparative Results Between Pre-Exam and Exam Periods

In the second phase of the study, conducted in May 2024 (on the day of the nutrition exam), 72 students completed both data collection stages and were included in the comparative analysis (Figure 2). Of these, 79.2% were female, with a mean age of 21.94 years. (Table 2)

3.2.1. Significant Changes Between the Two Phases

• Fat mass increased from a mean of 25.43% pre-exams to 28.79% during the exam period (p=0.016).
• Muscle mass decreased from 39.70 kg to 36.20 kg (p<0.001)(Figure 2).
• Visceral fat rose from a mean of 2.34 to 3.52 (p<0.001).
• The percentage of students with very high body fat increased from 38.9% to 63.9%, and those with high muscle mass decreased from 36.1% to 8.3%.

3.2.2. Significant Changes Observed in Dietary Habits

• Students consuming a second piece of fruit daily decreased from 52.8% to 33.3% (p=0.018).
• Fast food consumption increased from 48.6% to 52.8% (p=0.024).
• The proportion of students skipping breakfast rose from 13.9% to 51.4% (p<0.001).
• Consumption of pastries for breakfast increased from 23.6% to 45.8% (p=0.005).
• Daily candy consumption increased from 6.9% to 29.2% (p=0.001).
• Optimal diet quality decreased from 45.8% to 20.0% (p<0.001), with a drop in mean Kidmed score from 7.55 to 5.45 points (p<0.001). (Figure 4)

3.2.3. Significant Changes Observed y Physical Activity

• Days of vigorous physical activity decreased from 3.10 to 0.72 days/week (p<0.001).
• Vigorous activity time dropped from 229.02 to 30.69 minutes/week (p<0.001).
• The proportion of students with low physical activity rose from 4.2% to 59.7% (p<0.001), while those with high physical activity dropped from 84.7% to 11.1%.
• Mean sitting time increased from 408.24 to 543.61 minutes/day (p<0.001) (Figure 5).

3.3. Impact of Diet Quality on Body Composition

Students with poor diet quality showed worse body composition parameters, with higher fat mass (30.10%), higher visceral fat (4.14), and lower muscle mass (35.16 kg) compared to those with optimal dietary habits (Table 3) (Figure 6).

3.4. Impact of Physical Activity on Body Composition

Similarly, students with low levels of physical activity had higher fat mass (30.31%), higher visceral fat (3.90), and lower muscle mass (35.25 kg) compared to their more active peers (Table 4).

4. Discussion

The most relevant findings of this study clearly demonstrate the relationship between dietary habits, physical activity, and body composition among university students. The results show that students with poor diet quality and low physical activity levels exhibited increased fat mass, reduced muscle mass, and elevated visceral fat. In particular, the increase in visceral fat observed in students with unhealthy lifestyle habits is concerning, as sustained high levels are associated with a higher risk of developing metabolic disorders such as T2D and cardiovascular diseases, including hypertension and dyslipidemia. Furthermore, the instrument used to assess physical activity in this study, the short form of the International Physical Activity Questionnaire (IPAQ-SF), has been validated in international research and is considered suitable for population-level surveillance. As highlighted by Mantilla Toloza and Gómez-Conesa (2007), the short version is especially recommended for regional and national prevalence studies due to its adequate reliability (r = 0.76; 95% CI: 0.73–0.77) and its practical application across diverse populations. Although the IPAQ-SF does not provide as detailed information as its longer counterpart, it effectively captures essential domains of physical activity—such as walking, moderate and vigorous activity, and sedentary time—which are particularly relevant during periods of lifestyle disruption, such as university exam sessions. Therefore, its inclusion in this study was both methodologically justified and operationally feasible given the academic setting and time constraints of the participants [12].

Another important observation is that body weight and BMI did not differ significantly between the two assessment periods. This can be explained by the balance between increased fat mass and decreased muscle mass. Although body weight remained relatively stable, the underlying body composition worsened, emphasizing that weight and BMI alone are not sufficient indicators of health status. Assessing fat and muscle mass provides a more accurate picture of metabolic and nutritional health.

Previous literature supports the notion that academic stress during examination periods negatively impacts students’ lifestyles[13,14,15]. Increased academic demands often lead to disrupted routines, poorer eating habits[11,16], and a reduction in physical activity levels. Students may skip meals, consume ultra-processed foods, or neglect regular exercise due to time constraints or psychological stress, which, over time, can adversely affect body composition[17] and overall health.[1,6,18]

These findings highlight the need to include stress management strategies within academic environments, such as mindfulness techniques, relaxation exercises, and structured study plans that allow time for self-care. Moreover, educational initiatives focused on promoting healthy eating and regular physical activity should be integrated into university curricula to raise awareness among students about the long-term consequences of unhealthy behaviors.

Despite limitations such as the dropout rate between the two assessment points, the study offers evidence of the detrimental effects of stress-related lifestyle changes on body composition. Although the internal validity of this study is limited due to the homogeneous sample (students from a single university), the external validity is notable, as similar behaviors and stress patterns are likely to affect student populations in other academic settings.

Ultimately, the negative impact of poor habits during exam preparation affects a large portion of the student population. Addressing this issue requires institutional efforts to promote lifestyle interventions aimed at preserving both physical and mental health during high-stress academic periods.

5. Conclusions

Poor dietary habits and a sedentary lifestyle contribute to the deterioration of body composition. Among university students, both diet quality and physical activity levels decline significantly during exam preparation periods, leading to increased fat mass, decreased muscle mass, and elevated visceral fat. These findings underscore the importance of promoting healthy behaviors, particularly during periods of academic stress, to prevent long-term health risks (Figure 8).

6. Limitations

• Limited and homogeneous sample: All participants were second-year nursing students from a single institution (University Complutense of Madrid), which restricts the external validity and generalizability of the findings to other academic disciplines or university contexts.
• Participant attrition: Of the initial 142 students, only 72 completed both stages of the study. This loss may introduce selection bias, as students experiencing higher stress or more unhealthy behaviors may have been less likely to complete the follow-up.
• Lack of objective stress measurement: Although academic stress is hypothesized as a key factor influencing lifestyle changes, no validated tool (e.g., Perceived Stress Scale or Academic Stress Inventory) was used to assess it. This limits the ability to quantify its specific impact.
• Self-reported data: Both dietary habits (Kidmed) and physical activity (IPAQ) were assessed using self-administered questionnaires, which may be subject to social desirability bias and recall errors.
• Observational study design: The study’s correlational and observational nature precludes causal inference. Therefore, it cannot be concluded with certainty that exam preparation or stress directly caused the observed changes in body composition.

7. Future Research Directions

• Incorporate validated stress measurement tools: Future studies should assess perceived stress levels using validated scales (e.g., PSS), allowing for direct correlation between stress and changes in health-related behaviors and outcomes.
• Expand to other academic disciplines and institutions: Replicating the study across different fields of study and universities would enhance the generalizability and robustness of the findings.
• Intervention-based studies: Experimental or quasi-experimental designs could assess the effectiveness of specific interventions (e.g., brief educational sessions, mindfulness, or physical activity programs) implemented during exam periods to mitigate negative outcomes.
• Extended longitudinal follow-up: Investigating whether the changes in body composition are transient or sustained over time could provide insight into their potential long-term health implications.
• Objective measurement of diet and physical activity: The use of accelerometers, 24-hour dietary recalls, or nutritional biomarkers could improve the accuracy and reliability of lifestyle data collection.