4.1. Influence of Alcohol Consumption on Body Mass
In the present study, adolescent rats consumed more red wine, when compared to beer or ethanol. Despite a simultaneous lower dietary intake than the other groups, there was a significantly higher total energy supply for the red wine group than for the groups with other alcoholic beverages. However, this higher energy intake did not contribute to a higher body weight gain in comparison with the groups on other alcoholic beverages or the control group. The reduced dietary intake in the groups receiving alcoholic beverages was counterbalanced by the energy value of consumed alcohol. Moreover, the resultant total energy supply in the groups receiving alcoholic beverages was not lower than for the control groups.
Though a decrease in weight gain was not observed for the groups receiving alcoholic beverages in our study, some studies have reported this to be caused by prolonged alcohol intake [
24,
25,
26], including the murine studies [
27]. Milat et al. [
28] reported similar observations in a rat model, wherein one-month and three-month-old male rats received white wine (13% ethanol) for four weeks and a significantly lower body mass was recorded in comparison with their control group. According to the authors, non-phenolic compounds in white wine may have contributed significantly to the observed results via their influence on energy metabolism [
28]. However, in this study, red wine, and not white wine, was used and, therefore, the observed differences may be a result of this fact.
Prolonged alcohol consumption may cause disturbances in the metabolism of macro-nutrients and micronutrients, including decreased digestion and absorption of impaired transport and utilization of nutrients, because of the influence of alcohol on the stomach [
29] and intestines [
30]. Simultaneously, alcohol consumption may increase the excretion of nutrients that may increase the risk of deficiency and malnutrition [
24,
31]. Therefore, prolonged alcohol consumption may result in lower body mass gain in animal experiments in comparison with animals that do not receive alcohol [
32].
Regardless of whether acute or chronic intoxication effects are observed, both types of alcohol consumption may cause liver damage and impair amino acid uptake, protein synthesis, and protein transport from the liver [
11]. Furthermore, these processes may influence the body mass.
In general, data on the influence of alcoholic beverages that are characterized by low ethanol content on the body mass are unambiguous and inconclusive. Negrão et al. [
33] did not observe differences in body mass between adult male Wistar rats who were fed an ethanol solution or beer (both containing 5% ethanol) and those given no alcohol for five weeks. Similarly, Rodrigo et al. [
34] reported the absence of between-group differences among adult male rats in a one-month study of ethanol solution or wine (both containing 12.5% ethanol) or those given no alcohol. However, in the study of Cowpland et al. [
35], rats that received red wine containing 5% ethanol for nine weeks were characterized by lower body mass than those that received a solution of 5% ethanol or rats in the control group. This observation corresponds with an observed lower dietary intake in the present study that, nonetheless, did not contribute to a lower body mass due to the additional energy intake associated with the higher intake of an alcoholic beverage.
Furthermore, although young growing rats were studied in the present research work, adult animals are studied in a number of other studies, and that may have contributed to the observed differences between the results. Newbury-Birch et al. [
5] indicated loss of appetite and a decrease in body mass among the consequences of ethanol consumption by young individuals. Although a decrease of body mass was not observed, and appetite was not studied in the present work, differences in dietary intake were observed and, for all the experimental groups, the intake was lower than that for the control group.
The processes of appetite and intake regulation are complex and, thus far, it was reported that ethanol may change the functioning of the nutrostat system by modulating the level of hormones participating in the regulation of dietary intake. Alcohol consumption may stimulate leptin [
36] and decrease ghrelin production [
37], whereas both these changes decrease appetite and may result in a body mass decrease. Simultaneously, in the case of growing organisms, the influence of alcohol consumption on growth hormone level may be especially important and may be decreased by ethanol consumption, with a resultant reduction in bodily growth [
38].
Kokavec et al. [
39] observed that various alcoholic beverages may have different influences on appetite. Red wine may increase appetite, whereas white wine may decrease it. However, at the same time, the potential influence of specific components, such as resveratrol in red wine [
40] or xanthohumol in beer [
41], on the risk of excessive body mass were observed. However, in the present study, whereas the intake of alcoholic beverage and total energy supply in a group receiving red wine was, in fact, higher than for the other groups, the dietary intake was lower. Thus, it may be inferred that a mechanism downregulating intake contributed to the lack of increase in body mass despite the additional energy supply from the intake of alcoholic beverages.
4.2. Influence of Alcohol Consumption on the Liver Antioxidant Defense
This study found that the consumption of alcoholic beverages as well as the experiment duration influenced CAT, SOD, and GST activity as well as the glutathione level in adolescent rats. However, the observed results differed for various alcoholic beverages and changed with the experiment duration, even though no stable trend was identified. Moreover, there were no between-group differences for GPX and GR activity as well as TAS.
The intake of alcoholic beverages has a complex influence on the body. Therefore, the prediction of metabolic changes, without any previous analysis, is not possible, and an explanation of the observed associations may be hindered. Tahir & Sultana [
42] stated that the metabolism of alcohol causes hepatic oxidative stress that may be quantified on the basis of the decreased activity of both enzymatic (CAT, GPx, GR) and non-enzymatic antioxidative components (GSH).
4.2.1. Influence of Alcohol Consumption on CAT Activity
CAT is an enzyme that may be characterized by a peroxidative activity. Therefore, it may catalyze ethanol oxidation. Similarly, after four weeks of experiment in this study, animals consuming beer had increased CAT activity as compared with the control group. Such an influence may be attributed to the influence of some components of beer, which may be different than that of the ethanol itself, and these may have been lacking in red wine. Similarly, in a previous study by these authors, there was an evident lack of influence on the consumption of various wines on TAS [
43]. In the present study, these findings may be inferred to possibly confirm the lack of influence of red wine consumption on some antioxidant defense parameters.
Xanthohumol, which is the major prenylchalcone in hops and beer, with demonstrated high antioxidant activity in inhibiting oxidation [
44] may be responsible for such an influence, since it may take part in the reduction of oxidative stress, with a resulting increase in the activity of antioxidant enzymes.
The specific influence of beer on CAT activity may be confirmed by the lack of such associations in the studies of other alcoholic beverages. In another rodent study where an ethanol solution containing 2, 4, or 6 g ethanol per kilogram of body mass was applied, no differences of CAT activity were observed as compared with the control group one hour after administration [
45]. However, Scott et al. [
45] hypothesized that the lack of observed differences may be attributed to lower alcohol intake because the metabolism of ethanol may not have generated excessive hydrogen peroxide, which is the main activator of the peroxidative activity of CAT.
Furthermore, it may be supposed that the alcohol intake adopted in this study was too low, with the exception of beer where naringenin potentiated the influence. However, it may be inferred that the adaptive potential of the growing organism may have influenced the results we observed. This potential may be confirmed by the increased CAT activity in the control group (the highest, after six weeks of the experiment) that was attributed to intensified oxidative processes in the growing organism [
46]. Moreover, such adaptive potential may have influenced the increase in CAT activity after four weeks of beer consumption, although not after six weeks.
4.2.2. Influence of Alcohol Consumption on SOD Activity
The enzyme SOD participates in the antioxidative defense of the organism and cooperates with CAT. In this study, after four weeks of the experiment, increased CAT activity was reported simultaneously as decreased SOD activity in the group of animals consuming beer. However, a mere two weeks earlier (after two weeks of the experiment), the lowest SOD activity was recorded in a control group, and not in the group receiving beer. This higher SOD activity in all experimental groups, as compared to the control group, after two weeks of the experiment could have resulted from the disturbances of enzymatic mechanisms of antioxidative defense that may be reported even after a short exposure to alcohol. In addition, this was observed in the study of Scolaro et al. [
47] in adult rats, after two weeks of ethanol solution intake, despite being at a higher concentration than in the present study (35% ethanol). The increase in SOD activity due to ethanol exposure may be associated with the prooxidative effect of ethanol, with a resultant increase in the production of reactive oxygen species as well as in the antioxidative defense of the organism [
48]. In the presented study, for the group receiving ethanol for six weeks, the lower SOD activity was stated, which is consistent with the results of the other authors [
49,
50,
51]. The observed situation may be due to an insufficient ability of the liver to remove free radicals, which leads to the oxidative stress. The other reason of decreased SOD activity may be inactivation of the enzyme by the free radicals being generated in the liver during the metabolic pathway of ethanol [
45].
In beer, however, with the exception of ethanol, there are several compounds that may contribute to decreased SOD activity as compared to the other studied groups. Xanthohumol, which is one such example of these compounds in beer, decreases oxidative stress and may reduce the harmful hepatic influence of beer [
52]. The study of Pinto et al. [
52] revealed that an increase in xanthohumol intake for rats receiving ethanol was associated with a decrease in the SOD activity in the liver. Another component of beer that is characterized by antioxidative and anti-inflammatory properties is naringenin, which may influence antioxidative defense of cells by affecting not only SOD, but also other enzymes such as CAT, GPX, and GST [
53].
Rodrigo et al. [
34] did not find an influence of ethanol intake on SOD in adult Wistar rats that received a wine (12.5% ethanol). However, we emphasize that the present study evaluated growing, and not adult, animals. Moreover, differences during the experiment duration were observed that suggests the influence of the process of growth, whereas oxidative processes may have been elevated [
46], which leads to a disturbance in the mechanisms of antioxidative defense that is also observed in the case of adolescents with metabolic disorders [
54,
55].
4.2.3. Influence of Alcohol Consumption on the GSH Level
Another antioxidative compound, GSH, is the main non-protein thiol component. GSH plays a role in enzymatic reactions and, therefore, participates in the regulation of the function and structure of cells [
56]. Gasbarrini et al. [
57] did not observe any influence of beer or ethanol, administered for six weeks (dose 1.1 g/100 g of body mass), on the GSH level in the liver of rats. However, in this study, such differences were observed only after four and six weeks of the experiment, but not after two weeks. The lowest and highest GSH levels were recorded for beer and red wine, respectively. However, compared with the control group, the only differences were reported after four weeks of the experiment and only for the group receiving beer. There was a significantly lower GSH level than for the control group. As previously indicated, the differences observed for beer as compared with other alcoholic beverages may have resulted from the different composition and presence of specific bioactive components of beer. It was observed that some components, such as xanthohumol, may influence the GSH level [
52]. Similarly, the specific results stated for red wine may be attributed to the influence of its specific components, including resveratrol that was observed to cause an increase in the GSH level [
58]. However, they may be associated with the fact that a high dose of resveratrol may act not as an antioxidative compound, but as a pro-oxidant [
59]. Therefore, for young rats, the applied dose may be crucial since it may induce a different effect than for older animals.
Another important issue is the applied dose of ethanol and the age of animals because, compared with the studies of other authors, various doses were applied and may have contributed to different conclusions. Roig et al. [
60] indicated that administration of ethanol solution or sweet wine, both containing 20% ethanol, for six weeks caused a decrease of the GSH level in the liver of rats. In some other studies, lower GSH levels were observed in the liver than in the present study, but for the higher ethanol concentrations [
49,
50,
61,
62]. Authors surmise that the observed effect may be attributed to the binding acetaldehyde by GSH, with a resultant decrease in the GSH level. Furthermore, Das and Vasudevan [
63] indicated that, in general, alcohol consumption induces a decrease of the GSH reserve and, thus, causes a reduction of antioxidative properties. However, DeLeve and Kaplowitz [
64] concluded that a reduction in the GSH reserve of greater than 20% reduces the possibility of protecting cells against reactive oxygen species and causes damage to hepatocytes.
4.2.4. Influence of Alcohol Consumption on GST Activity
Among the enzymes that are dependent on GSH, GST participates in the removal of oxidized GSH from the cell after reduction of hydrogen peroxide. However, this enzyme removes xenobiotics from cells with the use of GSH in a coupling reaction [
65]. In the present study, GST was influenced by the applied intervention and experiment duration. For the experiment duration of four weeks, GST activity differed between groups, and the lowest and highest activities were reported for beer and the control groups, respectively. This difference may be attributed, as previously indicated, to the influence of specific components of beer. However, due to a paucity of related studies, no potential influencing component could be indicated. Moreover, in groups stratified by the experiment duration, GST activity differed significantly for the red wine group, with the lowest activity observed after two weeks of the experiment. Such an observation may be the result of the defense mechanisms in the organism [
60], but could also be attributed to a specific reaction of the developing organism to some bioactive components of red wine (e.g., resveratrol) that have, so far, been reported as being involved in detoxification [
66]. Moreover, the general effect of wine consumption may be attributed to the overall mix of all its components and not to a specific ingredient [
67]. However, this issue requires elucidation in future studies.
The observed changes of the liver antioxidant defense were dependent on both the type of alcoholic beverage administrated and the experiment duration. Moreover, for other factors associated with the liver antioxidant defense, we did not observe any differences. Therefore, the influence of alcohol must be concluded to be multifaceted. Furthermore, it must be emphasized that only one dose of alcohol was assessed and the assessment was conducted for growing animals. Therefore, these results cannot be generalized. Despite the generally observed decrease in the activity of antioxidative enzymes after alcohol administration [
11,
68], it must be indicated that the observed effect depends on the age of animals, applied dose, experiment duration, and type of alcoholic beverage.
However, some limitations of the conducted study should be listed. It would be interesting to observe the energy expenditure of rats and whether their metabolism increased. The metabolic cages should be applied to observe it. For the standard cages in the conducted experiment, such observations were not possible. Taking this into account, further studies are needed.