1. Introduction
Nutritional education is based on the transmission of information and use of tools related to food characteristics and nutritional content with the aim of improving dietary habits and, thus, health status [
1]. Nutritional education is designed to assist and facilitate healthy eating choices and other healthy nutrition-related behaviors [
2]. It has been shown that nutritional education improves the quality and variety of the diet in preadolescents and adolescents [
3,
4,
5], as well as in athletes [
5,
6], leading to a healthy diet. Preadolescence and adolescence are key life periods in terms of biological growth and development. Therefore, during these stages, it is essential to cover all nutritional and energetic demands to allow proper development [
7].
High-performance gymnasts are considered to be at risk for nutritional issues [
8], with a higher risk of suffering from an eating disorder [
9,
10]. Several reasons have been proposed to explain this situation [
11,
12]. Among them is the aesthetic component of gymnastics and the requirement to maintain a low weight, leading to a decreased energy intake [
13,
14,
15,
16]. Furthermore, these athletes are usually engaged in very demanding training schedules with long sessions almost every day. This increases their energy demand, and they are under constant pressure to perform exercises with high precision and strength. Finally, gymnasts are mainly adolescents, or even pre-adolescents, periods that correspond to ages at which optimal performance can be achieved. Therefore, even during normal growth and development gymnasts still need to manage their stressful routines [
7].
The relationship between having an adequate diet and proper performance in sport has been widely demonstrated. Among other requirements are optimal hydration, a good electrolyte balance, and adequate macro- and micronutrient intakes [
17]. It has been suggested that an inadequate food intake combined with intense physical training in female elite gymnasts can, in combination with other factors such as the genetic potential or the hormonal environment, negatively influence the normal pattern of pubertal development (menstrual disorders, amenorrhea), as well as induce a delay in bone growth [
18]. When high levels of physical activity are performed during adolescence, it is even more important to ensure an appropriate nutritional intake. In fact, it has been reported that in adolescent and preadolescent athletes, nutritional interventions become even more important [
19].
The aim of the present study was to determine the effects of implementing a nutritional education program during the sports season on the nutritional status and knowledge of female artistic gymnasts from the Technification Center of the Balearic Islands. The initial nutritional and anthropometrical statuses of the gymnasts as well as changes in anthropometrical parameters during the study were analyzed.
4. Discussion
The main finding of the present study was the low energy intake of gymnasts. However, this low energy intake was not associated with impaired blood parameters or decreased intakes of most micronutrients. The nutritional intervention was not associated with significant changes in the main characteristics of the gymnasts’ diet.
In agreement with previous reports [
13,
14,
15,
16], energy intakes of gymnasts in the present study were below recommended levels for the age group and the level of physical activity performed [
33]. This low energy intake was in agreement with the low intakes of almost all food groups reported in the FFQ. However, even with this low energy intake, gymnasts were not found to be at risk for developing eating disorders, with only one gymnast being identified as at risk. This result agrees with those obtained by Martínez-Rodríguez et al., who reported that only two out of 33 gymnasts of similar ages to the ones in the present study were at risk [
34]. It is noteworthy that studies with female athletes from weight-class sports have been shown to have higher numbers of at-risk participants [
35,
36]. It is possible that sports involving practices to prevent increases in body weight, leading to individuals having to compete in a higher weight category, or strategies to lose weight to compete in a lower weight category, are more stressful than gymnastics, in which aesthetics is the main reason for maintaining a low weight.
While the percentage of energy from carbohydrates was within the recommended range, in agreement with previous results [
37], the low energy intake was associated with a low total intake of carbohydrates. According to specific recommendations for athletes, an intake of up to 5–6 g carbohydrate/kg is necessary, taking into account that the gymnasts follow a very demanding training schedule [
38]. Although carbohydrate increased from 3.2 ± 0.2 to 3.9 ± 0.2 g kg
−1 by the end of the study, this was still not enough to attain recommended levels for these athletes. While a previous study conducted in university athletes reported an increase in carbohydrate intake after a nutritional intervention [
39], in the present study, the reason for this increase may have been it being conducted at the beginning of the more demanding training season, rather than the nutritional intervention. In addition to being low, the carbohydrate intake was characterized by a high proportion of simple carbohydrates. Despite the different nutritional characteristics of simple and complex carbohydrates being established in the nutritional education program, the deviation in the proportion of complex to simple carbohydrates was not corrected by the end of the study. Considering the results of the food group intakes, the sources of this high simple carbohydrate intake were not clear. In this regard, biases due to under or misreporting of, mainly, unhealthy foods are commonly found when dietary records are performed [
40,
41]. Further, pressure from parents and/or coaches can lead to bias in the information provided by the athletes themselves [
42].
The increase in carbohydrate intake contributed to the higher total energy intake observed three months after the beginning of the study, a result also found when energy intake was expressed relative to body weight. It is noteworthy that changes observed in the total energy intake were produced within the initial three months of the study, without additional modifications until the end of the program. This increased energy intake was not associated with the increase in body weight observed at the end of the study. The percentage of energy from fat was within the recommended range both at the beginning and at the end of the study, which is in agreement with previous results [
37,
43]. However, it should be considered that fat intake also increased during the initial study period, mainly due to an increase in unsaturated fat intake. In addition, the percentage of energy produced from proteins decreased, but values remained within the recommended range throughout the study [
44]. This change in the percentage of energy intake from proteins could be attributed to the increases in carbohydrate and lipid intakes, rather than being due to a decrease in protein intake per se. In spite of the higher intake than that recommended for the general population, the protein intake 1.6–1.7 g·kg
−1 body mass could be considered adequate, because daily intakes of between 1.2 and 2.0 g·kg
−1 have been suggested for athletes [
17]. The high proportion of animal to vegetable protein intake observed in the present study could reflect high in meat and egg intakes and low legume and nut intakes. The high phosphorus intake could be also related to the high intakes of foods such as meat and eggs.
Dietary iron is an essential nutrient for human health and for maintaining athletes’ performance [
45]. Low levels of iron have commonly been found, above all, in female, mainly young, athletes with low caloric or iron intakes, and consequently, these athletes have hematological indices below the reference values [
46,
47]. In the present study, and in spite of the decrease observed after the first measurements were taken, iron intake was slightly above the recommended values. Because it has been suggested that the iron intakes of female athletes should be increased by 70% from the estimated average requirement [
17], higher intakes in this group of gymnasts could be deemed adequate. Actually, periods of rapid growth, such as the one being experienced by these gymnasts, can negatively impact iron status [
17]. However, average plasma and blood values related to iron metabolism, namely, hemoglobin and ferritin, were within the normal range, and there were even increased levels of ferritin and transferrin at the end of the study. In fact, as indicated above, at the end of the study period, all participants presented values of the main markers hemoglobin and ferritin that were within the healthy range. Similar results have been obtained in previous studies involving gymnasts [
16,
48], suggesting that gymnasts do not commonly present alterations in iron metabolism, and there is a low incidence of depletion in iron stores [
16,
48,
49]. However, others have reported that poor iron status is commonly found in female athletes in general [
46] and in young female athletes in particular [
46]. In the present study, it is possible that the high intakes of eggs and meat, together with the beneficious interaction between iron and vitamin C intakes [
17], induced a healthier iron status than that found in previous studies [
46,
48].
In addition to the adequate levels of blood iron metabolism related parameters, vitamin levels analyzed in the blood were also within the normal range [
50]. While both vitamin A and vitamin C blood levels reflected adequate intakes, it is striking that vitamin E levels were within the normal range despite intake being below recommended values. In this regard, a poor correlation between intake and plasma levels of vitamin E has been reported because vitamin E is mainly transported by lipoproteins, and, therefore, levels of these lipoproteins could determine plasma vitamin E levels [
51]. In this sense, the decrease in plasma vitamin E observed at the end of the study could have been induced by the decreases in lipoprotein (LDL and HDL) levels observed. The lack of significant changes in the vitamin E concentration in blood mononuclear cells could support the idea that the lipoprotein levels are important determinants of the plasma concentration and could indicate a proper vitamin E status in gymnasts. With regard to the lipoprotein levels in gymnasts, only slightly elevated initial LDL-cholesterol levels were observed, which improved after the aforementioned decrease, leading to values within the recommended range. This decrease in LDL-cholesterol levels is in agreement with the results of a previous nutritional intervention in university athletes [
39]. However, this decrease could have been also induced by the training season, as it has been suggested that in children and adolescents, decreases in LDL-cholesterol are associated with an increased training intensity [
52]. On the other hand, cholesterol levels at the end of the study were similar to the ones found by Guerra et al. [
43]. Therefore, the presence of an adequate lipid intake is in agreement with the results of the serum markers analyzed as well as with the healthy values found for the determined cholesterol ratios, which showed an adequate lipid profile with no cardiovascular risk [
53].
There is an emerging interest in the biomolecular roles of vitamin D in general and in athletes in particular [
17]. In agreement with previous studies conducted on elite gymnasts [
18,
54], the vitamin D intake of participants in the present study was lower than recommended. The low intake of vitamin D could have been associated with the low calcium intake. The low values for calcium and vitamin D could reflect the low intake of dairy products recorded in these athletes. Because plasma levels of vitamin D were not measured, it could not be ascertained as to whether this low intake could induce a deficit. These athletes do not live at latitudes over the thirty-fifth parallel, which has been suggested as being a negative factor in attaining optimal vitamin D levels. However, they primarily train and compete indoors, which could lead to insufficient ultraviolet B exposure. More studies are needed to clarify whether gymnasts are at risk for vitamin D deficit as well as the possible consequences of this deficit.
Previous studies have reported that nutritional education programs induced improvements not only in the nutritional knowledge of athletes [
55,
56], but also in introducing more positive dietary changes [
5,
6]. In the present study, the lack of significant improvements in the gymnasts’ dietary habits could be related to the slight non-significant increase observed in the nutrition knowledge scores. In this regard, it has been suggested that nutritional education can assist and facilitate healthy eating choices as well as healthy nutrition-related behaviors [
2]. However, in the present study, the nutritional education program did not induce a significant improvement in the gymnasts’ nutritional knowledge. This was within individuals with a low level of general nutritional knowledge, which did not reach half of the maximum range score. While nutritional knowledge did not increase, we were unlikely to find significant changes leading to healthy choices. In fact, and in addition to observations indicated above, such as the high intakes of simple carbohydrates and animal protein, the low adherence to the Mediterranean diet indicated low-quality dietary habits of the gymnasts, which did not improve during the study. This result is in agreement with the observation of worse healthy habits in adolescents compared with the general population [
57].
It has been suggested that somatotypes strongly influence sports performance in general and in gymnasts in particular [
58]. Previous studies have shown that gymnasts predominantly have a mesomorphic somatotype (2-6-3), with low values of the endomorphic component [
59,
60], which is in agreement with results from the present study. Despite gymnasts being, at the beginning of the study, in percentiles slightly below the average values [
61], ranging from 10 to 25 (results not shown), they reported an adequate weight in relation to height. At the end of the study, they attained percentiles within the normal range, close to P50, with a significant increase in body weight. This weight increase could be attributed to the increases in height and fat-free mass without increases in fat mass. All of these results are consistent with the body compositions reflected in other studies [
60,
62,
63] and correlate with the evaluated somatotypes [
63]. In this regard, similar results to those obtained in the present study regarding BMI, fat percentage, and fat-free mass have been shown previously [
9,
36,
37]. The low fat mass percentage commonly observed in gymnasts has not been associated with health issues [
63]. In fact, it has been reported that anthropometrical changes observed in gymnasts during growth present a similar pattern to that of the non-athlete female population [
64]. In this regard, it was also suggested that the negative balance between caloric intake and energy expenditure represents short-term data and does not seem to affect normal growth [
65]. Similarly, a previous study performed in young gymnasts and swimmers found no evidence of a negative influence of demanding physical activity from an early age on growth until puberty [
66], and energy deficit has not been commonly associated with slowing down of growth and maturation in gymnasts [
65]. This is in spite of other authors arguing that inadequate food intake combined with exercise can alter the normal pattern of growth and pubertal development [
18].
The present study presented some limitations that should be acknowledged. The main limitation was the study design. We used a “quasi-experimental design” because of the impossibility of finding another group of participants with similar characteristics. Participants in the study were the only group with the characteristics described in Mallorca. Furthermore, the implementation of the nutrition education program to half of the sample, when the benefits of these programs have been supported by previous studies, was considered ethically inappropriate. In addition, a high degree of contamination between groups could be expected. Repetitive measures (pre- and post-intervention, as well as two intermediate measurements) were taken, with each subject being its own control to prevent, in part, limitations derived from the lack of a control group. The small sample size was also a major limitation, and all conclusions of the study were based on this small sample size and may not apply to other subjects. Regarding the methods applied, the use of three 24-h recalls to determine micronutrient intake did not allow proper measurement. In this regard, and as has been indicated above, when dietary records were performed in populations such as that used in the present study, under and miss-reporting biases could be produced [
40,
41]. However, the measurement of blood, plasma, and cell parameters was a more confident way to analyze the micronutrient status of gymnasts.