1. Introduction
The quantitative assessment of body composition (such as adipose tissue mass, muscle mass, body water bass, fat-free mass, etc.) can be done by an analyser based on the bioelectrical impedance analysis (BIA) technique. BIA is an uncomplicated and non-invasive method based on measuring the resistance (R) and reactance (capacitive resistance Xc) of soft tissues and consequently the tissue’s electrical resistance. An electrical current with low amperage and high frequency is passed through the human body by electrodes placed on the weighing scale platform connected to the feet and in handles held in both hands [
1]. Since the current flows easier through electrolyte solutions than cells, the resistance measured by adipose tissue or extracellular water causes a voltage drop. On the other hand, cell membranes, which are composed of two lipid layers, do not conduct electricity but rather act as a capacitor accumulating electric charges on each side. Therefore, it is possible to measure reactance responsible for the phase shift of the applied electric current expressed as phase angle (PA) [
2]:
A high PA value indicates the high electric potential of a cell membrane, and, therefore, it means appropriate nourishment of body cells, which ensure their proper functioning through their building resources and energy reserves. The PA value should be within 5–7 degrees [
3] (although reference values may vary slightly depending on the studied population [
4]). A decrease in PA indicates a decline in membrane integrity followed by changes in their permeability or amount of extra- and intracellular fluid. Consequently, membranes no longer function properly, which may lead to cellular apoptosis. The efficiency of energy and proteolysis processes, which determine the human health condition, is falling. This may indicate an ongoing chronic or neoplastic disease, malnutrition, high physical exhaustion, or it may happen during a course of sepsis [
3].
Taking into consideration the tissues’ electrical properties, PA values will be determined by many parameters of body composition. Although this subject has been analysed in the available literature, the information obtained is not clear. Previous studies show that the level of PA is influenced by age, sex, and BMI (body mass index). A study by Gonzales et al. [
5] showed that PA is significantly determined by fat-free mass (FFM), height, age, race, and ECW:ICW (extracellular water/intracellular water) ratio. Furthermore, Siddiqui et al. [
6] described the relationship between the PA and body weight, muscle mass, visceral fat, and height. According to Barbosa-Silva et al. [
4] the percentage of fat has a significant influence on PA value. PA can also be a good indicator of muscle performance in both young [
7] and elderly [
8] people. When subjected to physical exercise, older people present an increase in PA, and after their cessation, PA declines [
9]. Generally, there is a higher PA in people who regularly practice sports or athletes than in physically inactive people [
10]. PA is also correlated with mortality: higher values tend to prognose better outcomes for severely ill patients [
11]. However, there is no information on other factors that influence PA—for example lifestyle components. Only the influence of the Mediterranean diet on PA has been investigated already, obtaining a positive correlation [
12].
The aim of the study was to show which parameters of body composition and which lifestyle components correlate with PA values in the group of young people. The obtained result may contribute to a decrease of negative health behavioural patterns among them and therefore improve their quality of life.
4. Discussion
As expected, considering the anatomy and physiology of sexual development, the body composition of men and women differs significantly. Therefore, it is not surprising that the male group had greater values in height, WHR, BMI, weight, BMR, PA, FFM, water mass, muscle mass, and bone mass than in women. In turn, women have higher fat content than men. Those results are natural and result for example from differences in the endocrine system because the amount and distribution of adipose tissue closely relate to oestrogens (such as estrone produced by adipocytes). Women have more and larger fat cells in the subcutaneous tissue, which are mainly located in the gluteal region. On the other hand, although having a greater fat-free mass, men are characterized by a greater fraction of visceral (instead of subcutaneous) adipose cells and have higher WHR [
14]. Men tend to be taller and heavier than women, have greater BMI, and consequently a greater number of cells that increase their PA in comparison to women [
4]. There is also a difference in water content (typically: 60–63%—M and 52–55%—W) [
15]. Since muscles are composed of 75% water, their mass is also greater. The increase in muscle mass improves their capability of work, which relates to an increase in the general metabolism [
16]. According to other research [
5,
17] in our study women present a greater ECW/ICW ratio. This is an integrity of the cell membrane indicator that determines the proper functioning of the cell, its hydration and may be used to assess muscle strength. The ratio is strictly connected to PA: the greater its value, the lower the ECW/ICW ratio [
18]. This is confirmed by the results of our study (negative correlation: r = −0.594; r = −0.475; r = −0.254, for the whole study group, for the men, and for the women, respectively). Due to the higher PA value in the men, their ECW/ICW ratio was lower than in women.
Our research shows that healthy eating behavioural patterns vary significantly by sex. Men drink energy drinks and cola considerably more often, which corresponds to numerous studies [
19,
20,
21]. This may be because advertisements for energy drinks are primarily aimed at young men (mainly athletes [
22]; according to our research, men spent much more time exercising than women: 72 min/24 h vs. 49 min/24 h).
The frequency of alcohol-based beverage consumption varies as well. In men, beer and strong drinks prevail whereas in women it is wine and mixed drinks, which corresponds to numerous research [
23,
24]. Following the recommendations, men drank more water (1.7 L/24 h) than women (1.5 L/24 h), although according to the European Food Safety Authority this amount was still not enough (recommendations are: 2.5 L/24 h—M and 2.0 L/24 h—W) [
25]. Those differences may be caused by the fact that respondents took into consideration only bottled water, not including the intake of other fluids. Male students also had greater intervals between meals and consumed meat and fast foods more frequently. On the other hand, women were more likely to eat fruit and vegetables. This is confirmed by numerous studies that show that women are more likely to follow the rules of proper nutrition [
26,
27,
28].
The development of technology and technical innovations are becoming more and more important in our everyday life, which was also visible in the results of our study. Students tended to spend approximately 4.5 h daily watching television or in front of the smartphone or computer. Men prefer to watch television and to use the computer whereas women choose to spend time with smartphones. Leisure time patterns may vary depending on sex, which is confirmed in literature [
29,
30,
31].
Due to the fact that PA indicated the overall health condition of the body (cell membrane integrity, cell nutrition status, energetic and proteolysis process efficiency), our aim was to research what influences its value: which parameters of body composition or lifestyle components matter. Therefore, numerous correlation analyses were performed to research a relation between PA and studied factors. It shows that the height was strictly correlated with PA—in the case of women only, we obtained a negative correlation. That is, the greater height they achieve, the lower the measured PA value (Gonzales et al. [
5] and Siddiqui et al. [
6] obtained similar results). Moreover, a positive correlation was also present with weight, BMI, BMR, FFM, body water content/weight, bone mass, and muscle content/mass. Relationships for body weight and height result from the somatic development of the body—bone growth, muscle growth, more water mass, which together causes an increase in FFM and, consequently, increase PA value. Furthermore, available sources state that men with a similar height as women and simultaneously higher FFM tend to have greater PA value [
6] (that is the reason for negative correlation: height—PA in females and positive correlation for the whole study group itself in our study). Similar to body weight, BMI was also positively correlated with PA. According to Bosy-Wesphal [
32], with the increase of BMI, the number of cells in the body rises (e.g., muscle cells in athletes) and this is the reason for the PA increase. In addition, a strong correlation of PA with BMR is related to FFM [
33] and muscle mass. With the work of muscles, energy is processed, and metabolism increases [
16] and then PA as well, which as it turns out is also an indicator of this process [
7,
8].
Our study shows a negative correlation between PA and fat mass in the body. It is consistent with the studies conducted by Barbosa-Silva et al. [
4] and Gonzales et al. [
5]. The more fat is present in the body (unfavourable parameter), the greater the risk of civilization diseases (obesity, diabetes, cardiovascular diseases). In addition, with such diseases, the PA values decrease, which supports that correlation.
The obtained results for the relationship between the lifestyle components and PA values showed a weak correlation. Surprisingly, the correlation between PA and drinking cola or energy drinks was positive. Though it is important to mention that such consumption was not very popular among the study group (energy drinks about 1.5/month and cola one time per week), and therefore such small consumption may have a positive impact on PA. The effect of consumption of various types of alcoholic beverages (less than 1 per week) on PA can be similarly explained (only in the case of flavoured alcoholic drinks were the results opposite). This is confirmed by Coehlo et al. [
34], who showed a strong correlation between low PA value and frequent alcohol consumption (>80 g/24 h/5 years) in their research.
As recommended by the Food and Nutrition Institute [
35], students consumed an appropriate amount of bottled water (1.5 L/24 h) and preserved an appropriate interval between meals. On the other hand, their fruit and vegetable consumption were slightly too low (2 times daily) and too often they ate meat (1/daily). It is important to note that consumption of fruit and vegetables had a negative correlation with PA value and meat had a positive. It is possible that respondents did not take into consideration the vegetables present in their sandwiches and rather regarded only vegetables and fruits consumed in salads or separately. Although surprisingly, daily meat consumption increased PA, it should be noted that responders were neither questioned about the type and source of meat nor about the consumed amount of it. This information could resolve doubts about the validity of the obtained results. Nevertheless, meat as a source of wholesome protein provided the body with energy, which may explain its positive effect on PA [
36].
The few studies conducted so far on the influence of nutrition on PA value show that, for example, the Mediterranean diet increases this indicator [
12]. However, analysis of the impact of individual products on the PA conducted by Brazilian scientists [
37] was not so clear. For instance, frequent fruit consumption (at least three portions daily) and low meat consumption (no more than two weekly) increased the risk of acquiring the PA value (similarly to our study). However, after the exclusion of the confounding factor, correct results were obtained—as expected. In addition, the Healthy Eating Index (HEI) was calculated (on the basis of all present nutritional data), which significantly reduced the chance of getting a low PA.
Playing sports has a positive effect on PA value increases muscle mass and burns fat. This is confirmed by numerous studies [
9,
10,
38] including ours, in which we obtained a positive correlation between frequency and length of exercises and the PA value. On the other hand, the decrease of PA was correlated with an increase of time spent on watching television, using the smartphone or the computer for entertainment purposes (negative correlation). This is one of the first studies in which this relationship is statistically significant. Others [
34,
39,
40] confirm the relationship of these parameters, but it is not significant.
However, in the multivariate model concerning the influence of various co-occurring factors on PA value, only height, body weight, fat percentage, and meat consumption frequency were significant. This shows the importance of these variables along with the simultaneous presence of other factors. The obtained results of PA predictors in the multivariate model (height, body mass/BMI) were confirmed in the literature [
5,
6]. In turn, the relationship between body fat content and PA has so far been obtained only in univariate analyses. The relationship between meat consumption and PA value was presented for the first time.
The limitation of this study is the reliance on participants’ declarations regarding their lifestyle. Therefore, the control of these variables might be difficult. Moreover, the extrapolation of the obtained results to other groups of people is limited due to the study of only a small group of students from two different faculties. The bioelectrical impedance method used may also be a limitation in our study, especially when measuring obese people. In their case, there are differences in the body geometry and water distribution in the body compared to people with normal body weight. Therefore, the assumed hydration factor could be inappropriate. In our study, obese people constituted a small percentage of the total number of respondents (12.10%) which minimized the negative impact of the indicated measurement error on the obtained results.