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15

Original scientific article      UDC: 797.21.034.6:613.2
Received: 2018-04-19

NUTRITIONAL STRATEGIES OF SLOVENIAN NATIONAL 
JUNIOR SWIMMING TEAM

Vesna SIMIČ1, Nina MOHORKO1

1University of Primorska, Faculty of Health Sciences, Slovenia

Corresponding Author:
Nina MOHORKO 

University of Primorska, Faculty of Health Sciences, Polje 42, 6310 Izola, Slovenia. 
Phone: +386 5 66 35 801 

e-mail: nina.mohorko@fvz.upr.si

ABSTRACT

Purpose: The purpose of our study was to assess the nutritional strategies of Slove-
nian national junior swimming team and compare them with recommendations of clini-
cal sports nutrition. Competitive young swimmers, namely, have increased energy and 
nutrient needs compared to general adolescents due to frequent and intense training. 
Despite some physiological differences if compared with adults, adult sports nutrition 
recommendations for macronutrients apply to them. Further, literature reports iron, 
calcium, and vitamin D intake as frequently inadequate. 

Methods: Nutritional strategies of 19 members of Slovenian national junior swim-
ming team were assessed retrospectively through 3-day food and activity diaries, que-
stionnaires, anthropometric data including bioimpedance analysis. Energy availability 
(EA), macronutrient intake and timing, iron, calcium and vitamin D intakes, hydration, 
consumption of sports food and dietary supplement use were evaluated. 

Results: EA in some of male swimmers and in the majority of female swimmers was 
lower than recommended. Carbohydrate intake was adequate in male swimmers and 
two thirds of female swimmers. Although average protein intake exceeded the upper 
recommended limit, some female swimmers did not meet the lower recommended intake 
limit. Total fat intake was lower than recommended, with saturated fat intake on the 
upper recommended level. Calcium and iron intake in male swimmers exceeded recom-
mended values, while female swimmers had lower calcium intake than recommended 
and some had lower iron intake, too. Vitamin D intake was low in all swimmers. Meal 
timing was adequate in the majority of swimmers, who often reached for dietary su-
pplements, mostly omega 3 fatty acids, multivitamins and magnesium.

Conclusions: Low EA in young competitive swimmers is of concern. More success-
ful, personalised nutrition strategies for young competitive swimmers, focusing on hi-



16

Vesna SIMIČ, Nina MOHORKO: NUTRITIONAL STRATEGIES OF SLOVENIAN NATIONAL JUNIOR SWIMMING TEAM, 15–34

ANNALES KINESIOLOGIAE • 9 • 2018 • 1

gher energy intake and healthy food choices, would contribute to the preservation of 
their health and further development into top performers.

Keywords: nutrition, young athletes, sport nutrition recommendation, health, per-
formance.

PREHRANSKE STRATEGIJE PLAVALCEV SLOVENSKE 
KADETSKE IN MLADINSKE REPREZENTANCE 

IZVLEČEK

Namen: Namen naše raziskave je bil ugotoviti ustreznost uporabljenih prehranskih 
strategij plavalcev slovenske kadetske in mladinske reprezentance v primerjavi z velja-
vnimi priporočili klinične športne prehrane. Mladi plavalci, ki tekmujejo, imajo v prim-
erjavi z ostalimi najstniki zaradi pogostih in intenzivnih treningov povečane energijske 
in prehranske potrebe. Kljub očitnim fiziološkim razlikam, ki jih ločijo od odraslih, 
veljajo zanje priporočila za vnos makrohranil za odrasle športnike. Med mikrohranili 
literatura navaja, da so vnosi železa, kalcija in vitamina D pogosto nezadostni. 

Metode: Prehranske strategije 19 plavalcev slovenske kadetske in mladinske re-
prezentance smo retrospektivno ocenili na osnovi 3-dnevnih prehranskih in aktivno-
stnih dnevnikov, vprašalnika ter podatkov antropometričnih meritev, vključno z 
bioimpedančno analizo. Ugotavljali smo energijsko razpoložljivost (ER), vnos in 
časovno razporejanje makrohranil, vnose železa, kalcija in vitamina D, hidracijo, upo-
rabo športne prehrane in prehranskih dopolnil. 

Rezultati: ER je bila pri nekaterih moških plavalcih in pri večini plavalk prenizka. 
Vnosi ogljikovih hidratov so bili primerni pri plavalcih in dveh tretjinah plavalk. Kljub 
temu, da je ugotovljeni povprečni vnos beljakovin presegal zgornjo priporočeno mejo, 
nekatere plavalke niso dosegale spodnje priporočene meje. Celokupni vnosi maščob 
so bili nižji od priporočenih, vnosi nasičenih maščob pa na zgornji meji. Vnos kalcija 
in železa je pri plavalcih presegal priporočene vrednosti, pri plavalkah pa je bil vnos 
kalcija in pri nekaterih tudi vnos železa pod priporočeno mejo. Ritem obrokov je bil pri 
večini ustrezen. Plavalci in plavalke so pogosto uživali prehranska dopolnila, najpogo-
steje maščobne kisline omega-3, multivitamine in magnezij. 

Zaključek: Nizka ER pri mladih plavalcih, ki tekmujejo, je zaskrbljujoča. Bolj 
uspešne individualne prehranske strategije za mlade plavalce, ki bi se osredotočale na 
višji energijski vnos in zdravo prehrano, bi prispevale k varovanju njihovega zdravja in 
razvoju v vrhunske športnike.

Ključne besede: prehrana, mladi športnik, priporočila, zdravje, zmogljivost



17

ANNALES KINESIOLOGIAE • 9 • 2018 • 1

Vesna SIMIČ, Nina MOHORKO: NUTRITIONAL STRATEGIES OF SLOVENIAN NATIONAL JUNIOR SWIMMING TEAM, 15–34

INTRODUCTION

Young athletes who participate in high intensity sports programs have higher nu-
tritional and energy needs than the general WHO recommendations stated for children 
and adolescents (Desbrow & Leveritt, 2015). Competitive young swimmers belong to 
a group of athletes with increased energy and nutrient needs due to frequent and intense 
training (Petrie, Stover, & Horswill, 2004). At the metabolic level, all three energy sy-
stems (the high energy phosphagen system, anaerobic glycolysis and aerobic metaboli-
sm) are involved in all swimming competition disciplines, ranging by duration between 
20 seconds (50 m) and 14.5 minutes (1,500 m) in junior elite swimmers (Federation 
Internationale de Natation, 2018). Although adolescents have specific nutritional needs 
because they differ from adults in energy consumption, substrate consumption during 
exercise, thermoregulation, sweat mechanism and maintenance of fluid balance as well 
as other physiological components (Desbrow & Leveritt, 2015), the sports nutrition 
principles are similar to those for adults. 

For long-term health protection of athletes, adequate energy availability (EA), 45 
kcal/kg of fat-free mas (FFM) or more, must be provided (Desbrow & Leveritt, 2015). 
Sufficient energy and nutrient intake in adolescence is critical for normal growth and 
development, maintaining health and injury prevention. An adequate nutrition intake 
also enables optimization of the training process and successful recovery. Adolescence 
is a crucial period, comprised of intense growth and development, involving the alte-
ration of body composition, metabolic and hormonal fluctuations, maturation of organ 
systems and formation of nutrient storage, all of which has a potential impact on the 
individual’s health in the future (Sawyer et al., 2012). Long-term suboptimal EA, in the 
range between 30 and 45 kcal/kg FFM, or too low EA, under 30 kcal/kg FFM, leads to 
relative energy deficiency in sport (RED-S) (Mountjoy et al., 2014). The latter leads to 
disrupted physiological functions caused by the relative lack of energy, which include 
lowered metabolic rate, disrupted menstrual function, and compromised bone health, 
immunity, protein synthesis and cardiovascular health.

Despite the fact that there are potential differences in the ability to store carbohydra-
tes (CHO) and to use substrates during physical activity between adults and children, 
literature reports that the CHO needs of young athletes do not differ greatly from the 
needs of adults (Desbrow et al., 2014). In moderate to high-intensity endurance train-
ing, which lasts from 1 to 3 hours per day, CHO intake of 6 to 10 g/kg of body weight 
(BW) is recommended and in moderate to high intensity exercise, which lasts 4 to 5 
hours per day, 8 to 12 g CHO/kg BW/ day is recommended (Burke, Hawley, Wong, & 
Jeukendrup, 2011). The recommendations must be individual, dynamic and in accor-
dance with the requirements and goals (Thomas, Erdman, & Burke, 2016). 

Due to the lack of specific research into the protein requirements of adolescent 
athletes, it is suggested to follow the recommendations for adult athletes (1.3 – 1.8 g 
protein/kg BW). Some athletes have increased protein requirements during adolescen-
ce compared to the recommended quantities for their age group, especially if they have 
well-developed muscle mass or if they participate in high intensity exercise programs 



18

Vesna SIMIČ, Nina MOHORKO: NUTRITIONAL STRATEGIES OF SLOVENIAN NATIONAL JUNIOR SWIMMING TEAM, 15–34

ANNALES KINESIOLOGIAE • 9 • 2018 • 1

(Boisseau, Vermorel, & Rance, 2007; Aerenhouts, Deriemaeker, Hebbelinck, & Clarys, 
2011; Aerenhouts, Van Cauwenberg, Poortmans, Hauspie, & Clarys, 2013). 

Dietary fat intake of adolescent athletes should follow general recommendations 
(Desbrow et al., 2014). According to the National Institute for Public Health (2016) 
this means that in the 10- to 14-year old age group, fat should represent between 30 and 
35% of total energy intake (EI), while in the 15- to 18-year old age group, fat intake 
should contribute up to 30% EI, with the note that in physically active individuals this 
share could be increased to up to 35% EI. Saturated fat should not exceed 10% EI (Na-
tional Institute for Public Health, 2016).

Micronutrient deficiencies have negative impact on health and performance beca-
use micronutrients participate in a number of functions in the body. In young athletes, 
special attention must be paid to iron, calcium and vitamin D intakes (Desbrow & 
Leveritt, 2015). Recommendations for iron intake in young athletes do not differ from 
recommendations for the general population, despite the fact that exercise can cause ad-
ditional iron loss through sweating or bleeding into the gastrointestinal system or also 
due to the decomposition of erythrocytes during a long run (Peeling et al., 2009; Koe-
hler et al., 2012). Slovenian adolescent males aged 13 to 18 should therefore consume 
12 mg of iron per day and females 15 mg per day (National Institute for Public Health, 
2016). The only exception are vegetarian athletes who require higher intakes due to the 
reduced bioavailability of non-heme iron (Desbrow & Leveritt, 2015). 

Calcium and vitamin D are key nutrients for the development and maintenance of 
bone mass. Due to intense bone growth during adolescence, calcium needs are increa-
sed in both males and females. For 13- to 18-year olds, the recommended daily intake 
of calcium is 1200 mg (National Institute for Public Health, 2016), which applies to 
adolescent athletes, too, until there is more research available (Desbrow & Leveritt, 
2015). Vitamin D plays an important role in calcium and phosphate metabolism and 
calcium integration into bones and teeth, and in the operation of the immune and mu-
scle systems (Desbrow & Leveritt, 2015). Approximately 90% of our daily vitamin D 
requirements are covered by internal synthesis in the skin after exposure to ultraviolet 
rays; dietary intake contributing only 10% of the requirements (Koundourakis, Avgo-
ustinaki, Malliaraki, & Margioris, 2016). In Slovenia, typical nutritional vitamin D 
intakes (2–4 µg daily) in adolescents in the absence of internal synthesis do not suffice 
to achieve recommended serum concentrations. The difference between the intake and 
the recommended value of 20 µg must be reached through frequent exposure to the 
sun and/or taking a vitamin D formulation (National Institute for Public Health, 2016). 
In latitudes above 35° north, which applies to Slovenia, the sun rays angle in winter 
are too oblique for efficient skin vitamin D synthesis (Holick, 2008), apart from that, 
competitive young swimmers spend long hours practicing indoor also in autumn and 
spring, which poses them at risk for vitamin D deficiency. Geiker et al. (2017) reported 
that 45% of the 29 swimmers (16−24 years old) residing at latitude 55−56° north had 
25-hydroxycholecalciferol below 50 nmol/L in March and April. 

It is known that adolescent athletes have a higher height to body mass ratio (Petrie 
et al., 2004) and a lower sweating rate (Shibasaki, Inoue, Kondo & Iwata, 1997) than 



19

ANNALES KINESIOLOGIAE • 9 • 2018 • 1

Vesna SIMIČ, Nina MOHORKO: NUTRITIONAL STRATEGIES OF SLOVENIAN NATIONAL JUNIOR SWIMMING TEAM, 15–34

adults. A decreased sweating rate is an advantage in maintaining hydration status and 
at the same time decreases the success of thermoregulation. Sawka et al. (2007) pro-
pose fluid replacement during exercise to such a degree that hypohydration exceeding 
2% is prevented. Desbrow et al. (2014) and Smith, Holmes & McAllister (2015), who 
deal with adolescent athletes, recommend the same. Water or milk should not be repla-
ced by sports drinks that contain electrolytes and CHO because sodium losses through 
sweating are smaller than in adults (Meyer, Volterman, Timmons, & Boguslaw, 2012). 
Sports drinks are recommended only in long-term intense physical activity. Drinking 
caffeinated energy drinks is advised against in young athletes (Desbrow & Leveritt, 
2015).

The use of sports food (sports drinks, sports bars, sports confectionery, sports gels, 
liquid meal supplements, …) is justified in adolescents in cases of long and intensive 
training (Desbrow et al., 2014). Replacing nutrients with dietary supplements, such as 
calcium, iron and vitamin D, is also justified when a deficiency is confirmed (Internati-
onal Olympic Committee (IOC), 2011). The use of ergogenics is advised against beca-
use it is inappropriate and unnecessary, and in addition their safe use in all age groups 
has not been confirmed (International Olympic Committee (IOC), 2011).

To fulfil their increased energy requirements, young athletes are recommended 
three main meals and two snacks (Desbrow & Leveritt, 2015). A meal rich in CHO 
(1–4 g CHO/kg BW) is recommended 1–4 hours before activity. During exercise la-
sting 1–2.5 hours, 30–60 g CHO/h should be consumed. The post exercise meal should 
contain 1.0–1.2 g CHO/kg BW and 20 g of protein (Smith et al., 2015). Such a meal, 
consumed directly or as soon as possible after exercise, enables the refilling of glyco-
gen stores, muscle repair and replaces lost fluid. This is especially important in athletes 
who compete several days in a row (e.g. in a tournaments) or train more than once per 
day (Desbrow & Leveritt, 2015). 

The aim of our study was to assess the nutritional strategies of Slovenian national 
junior swimming team and compare them with recommendations. 

METHODS

Data Collection

All members of Slovenian national junior swimming team were invited to parti-
cipate in the study. The eligibility criteria for the national team are determined by the 
Slovenian swimming federation, which also provided us with the list of swimmers (27 
competitive young swimmers). Out of 21 swimmers for whom written consents for per-
sonal data processing were obtained, 2 were excluded from analysis due to inadequate 
food diaries, confining the final sample to 19 competitive young swimmers (Figure 
1, Table 1). The data was collected from October to December 2016 and analysed in 
February 2017. 



20

Vesna SIMIČ, Nina MOHORKO: NUTRITIONAL STRATEGIES OF SLOVENIAN NATIONAL JUNIOR SWIMMING TEAM, 15–34

ANNALES KINESIOLOGIAE • 9 • 2018 • 1

Anthropometric Measurements

We collected weight and height data from anthropometric measurements regularly 
performed during preparation training cycles. Swimmers were weighed to the nearest 
10 g (M 304641-01, AED) and height was measured to the nearest 0.5 cm (Stadiometer, 
M 304641-01 (ADE). Whole body BIA (BIA 101 Anniversary AKERN, Florence, Italy, 
medically approved: EN ISO 13485 − ISO 9001) was performed using an alternating 
sinusoidal electric current of 400 µA at an operating frequency of 50 kHz according 
to recommendations (Kyle et al., 2004) for FFM assessment, that was needed for EA 
calculation.

Dietary Assessment and Energy Consumption Evaluation

Data were collected from food and activity diaries. Swimmers were asked to keep 
3-day weighted food and activity diaries for three consecutive days (including one we-
ekend day). Swimmers were fully briefed on how to complete the diary and asked to 
continue their normal diet and physical activity. They were asked to include food labels 
and recipes for mixed dishes in their record. For each day, they had to record the kind, 
duration and intensity of the physical activity.

The dietary intake was assessed using Open Platform for Clinical Nutrition (OPEN), 
that is an online, freely accessible, dietary assessment and planning tool for the analysis 
of food diary (http://www.opkp.si/en_GB/cms/vstopna-stran). OPEN food composition 
data was taken from the Slovenian food composition database (Golob et al., 2006); or if 
not available there, from the Souci, Fachmann & Kraut Food composition and nutrition 
tables (2008) and/or from the USDA National Nutrient Database for Standard Referen-

Figure 1: Swimmers flow diagram.

http://www.opkp.si/en_GB/cms/vstopna-stran


21

ANNALES KINESIOLOGIAE • 9 • 2018 • 1

Vesna SIMIČ, Nina MOHORKO: NUTRITIONAL STRATEGIES OF SLOVENIAN NATIONAL JUNIOR SWIMMING TEAM, 15–34

ce (http://www.ars.usda.gov/Services/docs.htm?docid=8964). Food composition data 
applied by the OPEN meet the European standard for food data CEN/TC 387, available 
at http://www.cen.eu/. EI, macronutrient intake and calcium, iron and vitamin D intakes 
were evaluated.

To examine the suitability of energy consumption, EA was calculated. EA repre-
sents the energy that is available for body function, growth and development taking 
in consideration exercise energy expenditure (EEE) during planned physical activity 
(Desbrow et al., 2014). 

Metabolic equivalent of task (MET) was used for EEE evaluation, as suggested by 
OPEN. 

Questionnaire

Data from a questionnaire that was developed by nutrition expert in charge of nu-
trition support of national swimming team, were analysed. Swimmers were asked to 
answer the questionnaire on health parameters (number of infections, menstrual cycle, 
growth), nutritional habits, timing of meal intake, use of dietary supplements and sports 
food, as well as type, intensity and the duration of exercise.  

Statistical Analysis

Answers from the questionnaire that refer to sports nutrition recommendations and 
dietary intake compared to recommended values were processed in Microsoft Excel 
(IBM Corp. Released 2011), while anthropometric data and dietary intakes were pro-
cessed with SPSS 20.0 (IBM SPSS Statistics for Windows, Version 20.0. Armonk, NY: 
IBM Corp.). 

The descriptive statistics was used to determine averages, standard deviations and 
minimum and maximum values. The Shapiro-Wilk test was used for assessing the nor-
mality in the distribution of variables, one sample T-test and independent samples T-test 
were used to evaluate the difference from recommended values and difference between 
genders. Statistical significance was set at P < 0,05. Spearman and Eta correlations 
were performed to detect different associations between dietary intakes and frequency 
of infection as well as regularity of menstrual cycle. 

(1)

http://www.ars.usda.gov/Services/docs.htm?docid=8964
http://www.cen.eu/


22

Vesna SIMIČ, Nina MOHORKO: NUTRITIONAL STRATEGIES OF SLOVENIAN NATIONAL JUNIOR SWIMMING TEAM, 15–34

ANNALES KINESIOLOGIAE • 9 • 2018 • 1

RESULTS

Characteristics of swimmers grouped by gender are presented in Table 1. 

Ta
bl

e 
1:

 C
ha

ra
ct

er
is

tic
s o

f s
w

im
m

er
s d

iv
id

ed
 b

y 
ge

nd
er

 
Av

er
ag

e 
(±

 S
D

)
t*

p 
(2

-t
ai

le
d)

*

 
A

ll 
(N

= 
19

)
M

al
e 

sw
im

m
er

s 
(N

= 
6)

Fe
m

al
e 

sw
im

m
er

s 
(N

=1
3)

A
ge

 (y
ea

rs
)

14
,9

5 
± 

1,
22

16
,1

7 
± 

0,
75

14
,3

8 
± 

0,
96

3,
99

0,
00

1

B
od

y 
he

ig
ht

 (c
m

)
17

3,
97

 ±
 7

,7
0

18
1,

92
 ±

 4
,3

2
17

0,
31

 ±
 5

,9
1

4,
28

0,
00

1

B
od

y 
w

ei
gh

t (
kg

)
62

,3
5 

± 
10

,0
7

73
,3

3 
± 

4,
88

57
,2

8 
± 

7,
35

4,
84

0,
00

0

B
M

R
 (k

ca
l/d

ay
) 

(k
J/

da
y)

16
08

,5
0 

± 
18

0,
30

 (6
72

9,
96

 ±
 7

45
,3

8
18

27
,8

8 
± 

91
,5

5
(7

64
7,

85
 ±

 3
83

,0
4)

15
07

,2
5 

± 
10

0,
50

(6
30

6,
33

 ±
   

42
0,

49
)

6,
63

0,
00

0

FF
M

 (k
g)

51
,5

8 
± 

9,
39

62
,9

7 
± 

3,
80

46
,3

3 
± 

5,
62

6,
54

0,
00

0

Fa
t m

as
s (

%
)

17
,4

4 
±3

,7
7

14
,0

8 
± 

1,
75

18
,9

9 
± 

3,
43

3,
28

0,
00

4

Tr
ai

ni
ng

 lo
ad

 (h
/w

ee
k)

20
,7

8 
± 

2,
59

21
,4

2 
± 

3,
52

20
,4

8 
± 

2,
15

0,
72

0,
48

0

E
ne

rg
y 

av
ai

la
bi

lit
y 

(k
ca

l/k
g 

FF
M

) 
(k

J/
kg

 F
FM

)
37

,0
1 

± 
12

,9
9

(1
55

,2
3 

± 
54

,3
5)

43
,4

8 
± 

9,
16

(1
81

,9
2 

± 
38

,3
2)

34
,0

2 
± 

13
,6

9
(1

43
,0

9 
± 

57
,2

8)
1,

53
 

0,
14

4

B
M

R
 –

 b
as

al
 m

et
ab

ol
ic

 ra
te

, F
FM

 –
fa

t f
re

e 
m

as
s  

   
*D

iff
er

en
ce

 b
et

w
ee

n 
m

al
e 

an
d 

fe
m

al
e 

sw
im

m
er

s 



23

ANNALES KINESIOLOGIAE • 9 • 2018 • 1

Vesna SIMIČ, Nina MOHORKO: NUTRITIONAL STRATEGIES OF SLOVENIAN NATIONAL JUNIOR SWIMMING TEAM, 15–34

Nutritional data is presented in Table 2 and graphically for each swimmer (Figure 2), 
coded based on the calculated EA. Female swimmers were assigned codes from 1 to 13 
and male swimmers codes from 14 to 19. Each individual’s code applies to all displays. 

Ta
bl

e 
2:

 N
ut

ri
tio

na
l i

nt
ak

es
 o

f s
w

im
m

er
s d

iv
id

ed
 b

y 
ge

nd
er

Av
er

ag
e 

(±
 S

D
)

t*
p 

(2
-t

ai
le

d)
*

A
ll 

(N
= 

19
)

M
al

e 
sw

im
m

er
s  

 
(N

= 
6)

Fe
m

al
e 

sw
im

m
er

s  
(N

=1
3)

C
H

O
 in

ta
ke

/k
g 

B
W

 (g
/k

g)
7,

24
 ±

 1
,9

2
8,

08
 ±

 1
,3

2
6,

85
 ±

 2
,0

7
1,

33
0,

20
1

Pr
ot

ei
n 

in
ta

ke
/k

g 
B

W
 (g

/k
g)

2.
03

 ±
 0

.7
6

2,
70

 ±
 0

,9
0

1,
72

 ±
 0

,4
4

3,
21

0,
00

5

Fa
t (

%
 E

I)
25

,0
6 

± 
25

,9
8

23
,0

7 
± 

4,
54

25
,9

8 
± 

7,
10

 
-0

,9
16

0,
37

3

Sa
tu

ra
te

d 
fa

t (
%

 E
I)

8,
67

 ±
 9

,0
0

8,
67

 ±
 2

,9
4

9,
00

 ±
 2

,4
8

-0
,2

57
0,

80
0

Ir
on

 it
ak

e 
(m

g)
19

,4
7 

± 
7,

18
25

,7
5 

± 
6,

89
16

,5
7 

± 
5,

35
3,

18
0

0,
00

5

C
al

ci
um

 in
ta

ke
 (m

g)
11

56
,9

9 
± 

51
6,

64
17

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24

Vesna SIMIČ, Nina MOHORKO: NUTRITIONAL STRATEGIES OF SLOVENIAN NATIONAL JUNIOR SWIMMING TEAM, 15–34

ANNALES KINESIOLOGIAE • 9 • 2018 • 1

Figure 2a: Nutritional intake of slovenian junior national swimming team compared to 
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25

ANNALES KINESIOLOGIAE • 9 • 2018 • 1

Vesna SIMIČ, Nina MOHORKO: NUTRITIONAL STRATEGIES OF SLOVENIAN NATIONAL JUNIOR SWIMMING TEAM, 15–34

Figure 2b: Nutritional intake of slovenian junior national swimming team compared to 
recommendations. E Saturated fat intake. F Iron intake. G Calcium intake. H Vitamin 
D intake.

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26

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ANNALES KINESIOLOGIAE • 9 • 2018 • 1

EA of the majority of swimmers was between 30 and 45 kcal/kg FFM, little less 
than of one third under 30 and only 5 above 45 (Figure 2A). 4 female swimmers with 
low EA also had a low CHO intake (Figure 2B). All male swimmers exceeded the upper 
limit for protein intake, while 3 female swimmers did not reach the lower limit of the 
recommendations, 4 were within the recommended values, and 6 exceeded the upper li-
mit of the recommendations (Figure 2C). The intake of fat was below the recommended 
limit for all male swimmers and for 8 female swimmers (Figure 2D), while the intake 
of saturated fat was in accordance with the recommendations in 13 swimmers, whereas 
5 female swimmers and 1 male swimmer had intakes that were higher than recommen-
ded (Figure 2E). 5 female swimmers had inadequate iron intake (Figure 2F). All male 
swimmers and 2 female swimmers exceeded the recommended calcium intake, while 
the remaining 11 female swimmers were under the recommended limit (Figure 2G). 
Vitamin D intake was below the recommended limit in all swimmers (Figure 2H). 

4 female swimmers drank less than 1.5 L of fluid per day, while the majority of 
male swimmers (N = 5) and one female swimmer drank more than 3 L of fluid. The rest 
drank 1.5 − 2.5 L of fluid per day (N = 6) or 2.5 − 3 L (N = 3) on days when they were 
training. Most of the swimmers drank 0.3 − 0.8 L of fluid in one hour of training (N = 
9). 6 swimmers consumed less than that, 3 swimmers drank 0.8 − 1 L, and 1 swimmer 
drank 1 − 1.5 L of fluid in an hour.

The questionnaire gave us the insight in swimmers’ nutritional habits. 17 swimmers (6 
male swimmers and 11 female swimmers) regularly consumed fluid during their training, 
one female swimmer rarely and one never. All swimmers consumed an isotonic bevera-
ge with electrolytes during the exercise, while 17 of them never consumed caffeinated 
energy drinks, and 2 swimmers rarely took them. All swimmers consumed sports food 
(energy bars, gels, …), 15 also took dietary supplements, 3 of which took one dietary 
supplement, 3 took two dietary supplements, 4 took 3 dietary supplements, while 2 took 
4 dietary supplements. The most consumed dietary supplement were omega 3 fatty acids 
(N = 8 swimmers), followed by multivitamins (N = 6) and magnesium (N = 5), 4 took 
iron, glutamine or vitamin C and 3 took vitamin D. Vitamin B, creatine, Q10 or branched 
amino acids were taken by 1 swimmer each. 

The majority (N = 15) consumed five meals or more per day. Others consumed four 
(N = 2) or three (N = 2) meals per day, but none less than that. The majority of swimmers 
(N = 14) also always consumed a balanced meal 2 – 3 hours before training, 4 rarely and 
1 never. The majority (N = 12) consumed a CHO rich meal one hour before training. Al-
most all (N = 18) regularly consumed a meal rich in CHO and protein within an hour after 
training, while one swimmer rarely did so. To the question “Do you consume a protein 
supplement within an hour after training?” 6 swimmers answered “always”, 5 answered 
that they “rarely consumed protein in the form of a supplement” and 8 answered “never”.

We also determined the frequency of infections in competitive young swimmers. 
The majority (N = 13) fell ill 1 – 2 times per year, 4 more frequently and 2 never. Only 3 
female swimmers had a regular menstrual cycle. 2 females in the group who had never 
had a period (N= 6) were over 15 years old. 4 female swimmers had an irregular men-
strual cycle. The frequency of infection was not statistically significantly associated 



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Vesna SIMIČ, Nina MOHORKO: NUTRITIONAL STRATEGIES OF SLOVENIAN NATIONAL JUNIOR SWIMMING TEAM, 15–34

with energy availability (ρ = -0.223, p = 0.360), CHO (ρ = 0.099, p = 0.686), protein (ρ 
= -0.066, p = 0.787) nor fat (ρ = -0.354, p = 0.138) intake. The regularity of menstrual 
cycles in females was not statistically significantly associated with energy availability 
(η = 0.186, η2 = 0.340, p = 0.839), CHO (η = 0.264, η2 = 0.070, p = 0.696), protein (η 
= 0.543, η2 = 0.295, p = 0.175) nor fat intake (η = 0.444, η2 = 0.197, p = 0.333), either. 

DISCUSSION 

The first systematic insight into the nutrition status of young competitive athletes 
in Slovenia showed some inadequate intake of nutrients that may influence the perfor-
mance and health of young athletes.

Some exceptionally low EA values (min. = 15.1 kcal/kg FFM) and the fact that 
almost three quarters of the swimmers did not achieve the recommended EA values 
indicated that the EI in some young male swimmers and mostly in female swimmers 
were too low and needed improvement, because long-lasting low relative EA influences 
a number of organic systems and may in the short and long-term compromise health 
and performance (Mountjoy et al., 2014). The calculated low EA may also be due to 
methodological causes. It is known that in determining dietary intake with the use of 
a food diary, inaccuracies may occur that may be the consequence of a changed diet 
due to recording into the food diary itself, incorrectly recording foods that are or are 
not desired in order to improve the impression on what was eaten, or actual errors that 
occur in the weighing or description of consumed quantities (Burke, 2001). It is also 
known that as many as 80 % of participants report too low quantities of food intake, 
with reported quantity being up to 20 % lower than actual intake (Black et al., 1993). 
Another problem could be the EEE, because it was not measured but calculated based 
on reported time and type of exercise, using MET. The small sample of swimmers and 
unequal representation of genders also represented an additional restriction.

Based on reported training load, 18 swimmers required CHO intake of 6 to 10 g /kg 
BW, while one swimmer had higher requirements due to a higher exercise load (8 – 12 
g/kg BW). While all male swimmers had adequate CHO intake, 4 female swimmers did 
not reach the lower recommended intake limit. Inadequate intake leads to inadequate 
glycogen stores and the onset of fatigue, which, in connection with low EA that was 
identified in all of them, has a negative effect on health and performance (Loucks, 
Kiens, & Wright, 2011). An adequate intake of CHO also prevents protein catabolism. 
Burke et al. (2011) define CHO availability as a dynamic measure of suitable CHO in-
take, both on daily basis and on strategic time points around important exercise sessions 
as high CHO availability provides CHO for muscle and nervous system and has thus the 
potential to enhance performance and recovery at key times. We examined the adequa-
cy of meal timing and composition around training with a questionnaire. 14 swimmers 
followed the recommendations and always consumed a balanced meal, including CHO, 
2 – 3 hours prior to training. In addition, 12 consumed one more meal rich in CHO wi-
thin one hour prior to exercise, which is an effective strategy for ensuring an additional 



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ANNALES KINESIOLOGIAE • 9 • 2018 • 1

energy source for working muscles and the central nervous system (Jeukendrup & Cro-
nin, 2011). During their exercise, all swimmers replaced fluids, CHO and electrolytes. 
As many as 18 swimmers consumed a CHO and protein rich meal after training. All 
the above shows that top young Slovenian swimmers mainly use nutrition strategies in 
accordance with recommendations before, during and after training. However, since 
CHO availability covers both, daily intake and meals around exercise, inadequate daily 
CHO intake in 4 female swimmers means low CHO availability, which means their 
glycogen stores are not optimally replenished which can affect performance, both on 
training and competition (Burke et al., 2011). More emphasis should therefore be pla-
ced on adequate daily CHO intake in female young swimmers. This would enable them 
to reach adequate CHO availability and EA and consequently adequate glycogen stores 
and prevent them from fatigue and muscle catabolism.

The protein intake of all male swimmers and 6 female swimmers exceeded the upper 
recommended limit, 1.8 g/kg BW/day, despite EA being too low in 4 male swimmers 
and 3 female swimmers. The literature reports that young athletes who have adequate EA 
reach or exceed protein intake recommendations (Petrie et al., 2004; Heanley, O’Connor, 
Giifford, & Naughton, 2010; Gibson, Stuart-Hill, Martin, & Gaul, 2011). After training, 
3 male swimmers and 3 female swimmers always consumed protein in the form of a 
supplement, 1 male and 4 female swimmers did so occasionally, while the others did not 
consume protein in the form of supplements. The use of protein supplement in young at-
hletes could be justified merely due to their practicality, however, food sources of protein 
would be a better choice, especially because protein needs can be fulfilled within normal 
EA. On the other hand, 3 female swimmers (all 3 with low EA) did not reach the lower 
recommended protein intake, 1.3 g/kg BW/day. An inadequate protein intake or a low 
EA, where part of the protein is used as a substrate in the process of energy acquisition, 
could potentially lower the amino acid availability for basic physiological functions (Pe-
trie et al., 2004; Campbell et al., 2007). Therefore, low protein intake is problematic, and 
even (too) high intake in the context of low EA does not guarantee appropriate protein 
availability. The average EA in female swimmers was lower than the recommended limit, 
and therefore they were more prone to protein deficiency in our sample than male swim-
mers. To prevent protein and energy deficiency, we would suggest to fulfil protein needs 
by increasing EI through normal food.

No guidelines or recommendations mention the absolute fat content in an individual‘s 
diet, the values refer to the percentage of EI provided by fat. Our swimmers had low 
fat intake, contrary to literature reports (Croll et al., 2006; Juzwiak, Amancio, Vitalle, 
Pinheiro, & Szejnfeld, 2008), which state that the fat intake in young athletes usually 
exceeds 30 % of EI. This lack of fat may be the cause of the low EA that was noticed 
mainly in female swimmers, which is why we, in line with other authors, recommend 
that young athletes be encouraged to eat fish and unsaturated fats from plant sources 
and to avoid the consumption of saturated fats from fried foods and baked goods as 
well as fats of animal origin (Desbrow et al., 2014) which contribute to higher saturated 
fat intake. Indeed, the intake of saturated fat in some swimmers was above the upper 
recommended value.



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Vesna SIMIČ, Nina MOHORKO: NUTRITIONAL STRATEGIES OF SLOVENIAN NATIONAL JUNIOR SWIMMING TEAM, 15–34

Three key micronutrients for young athletes can be identified from the literature: 
iron, calcium and vitamin D (Desbrow et al., 2014; Smith et al., 2015). The average 
iron intake in female swimmers was sufficient, but individual intake was insufficient in 
5 female swimmers. The findings partially correspond to the findings of other authors 
who state that the dietary intake of iron in young male athletes exceeds the recommen-
dations, while in females they are within the recommended limits (Juzwiak et al., 2008; 
Heanley, et al., 2010; Gibson et al., 2011; Martinez et al., 2011). Since low iron stores 
are usually observed in female swimmers, regular supervision of iron status is neces-
sary as well as early detection of low iron stores and appropriate intervention in order 
to increase iron intake or to increase the iron bioavailability. Taking iron as a dietary 
supplement is justified only in cases of proven deficiency (Desbrow et al., 2014).

The literature states that young athletes achieve only one half of the recommended 
calcium intake (Gibson et al., 2011; Juzwiak et al., 2008), which was not the case in 
our study. Calcium intake was above the recommended values in male swimmers, but 
under the recommended limit in female swimmers, which is in line with Martinez et 
al. (2011). Encouraging milk and dairy consumption would not only improve calcium 
intake, but also fat and protein intake and EA (Fayet, Ridges, Wright, & Petocz, 2013).

The estimated dietary intake of vitamin D was lower in female swimmers than in 
male swimmers. A comparison with recommendations was not possible as they define 
vitamin D requirements that may be met through dietary intake as well as through 
internal synthesis. Serum concentrations of 25-hydroxycholecalciferol would give us 
a better insight into vitamin D status, however considering our latitude (above 35th 
parallel north), long hours spent indoors due to training and the low dietary intake of 
vitamin D in female swimmers, we can suspect that this group is at risk of vitamin D 
deficiency. Due to the high physical load we are concerned that the current nutrition 
strategies of some competitive female swimmers together with calcium deficiency and 
low EA may have a negative impact on bone health, which is further exacerbated by the 
physical activity in water which lowers the workload against gravity (Gomez-Bruton et 
al., 2017). Regular monitoring of vitamin D status is necessary in athletes at increased 
risk of deficiency and suitable supplementation should be advised in case of discovered 
inadequacy (Desbrow et al., 2014). 

Fluid intake was assessed using a questionnaire as we were not able to assess it ba-
sed on the food diary due to insufficient data. The problem with sufficient fluid intake 
is that there are noticeable individual differences between athletes, due to which the-
re are no concrete fluid intake recommendations. Reference values for nutrient intake 
(German nutrition society (DGE), 2004) state that moderately active 15-year-old ado-
lescents or younger should consume 1330 mL of fluid daily, while those over 15 years 
old should consume 1530 mL. From the questionnaire, we discovered that 4 female 
swimmers drank less than 1.5 L of fluid per day on training days, which we can certa-
inly assess as inadequate as that is the recommended intake for non-active individuals. 
Adams et al. (2016) discovered that as many as 67 – 78 % (depending on the method) 
of swimmers aged 8 to 17 came to morning training in a hypohydrated state. Due to 
significant differences between individuals and physical activities, Australian dieticians 



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ANNALES KINESIOLOGIAE • 9 • 2018 • 1

and sports nutrition specialists (Desbrow et al., 2014) recommend regular monitoring 
of fluid intake needs by weighing before and after training. We do not have the data on 
individual weight losses during exercise and cannot estimate the quantitative adequacy 
of fluid replacement. Drinking energy drinks containing caffeine is not recommended 
in this age group (Desbrow & Leveritt, 2015). Only 2 young swimmers (10.5 %) re-
ported consuming energy drinks, which is a good result, as O’Dea (2003) found that in 
the age group between 11 and 18 years old as many as 42.3 % of otherwise moderately 
active children consumed energy drinks. 

All the competitive young swimmers in the sample consumed sports food, which 
is justified considering their heavy training load. They also often used dietary supple-
ments (78.8 %), possibly including more than one supplement (up to four), which is a 
little more than reported by McDowall (2007), who found the prevalence between 22 % 
and 71 %. The competitive young swimmers most commonly took omega-3 fatty acids, 
multivitamins and magnesium. The supplementation of nutrients is considered justified 
when a deficiency is discovered or if needs cannot be met through nutrition. Based on 
our results, competitive young swimmers should consider supplementing vitamin D. 
Even though the use of ergogenic aids for better performance is inappropriate and unne-
cessary and their safe use has not been confirmed in this age group, we discovered that 
1 swimmer used creatine. Competitive young swimmers should be familiarized with 
the risks of using dietary supplements because they may not be safe, may be disallowed 
or ineffective or even contaminated with banned substances (Desbrow et al., 2014). 
They should be encouraged to meet their nutritional requirements through the correct 
choice of foods and not through supplements.

It is known that low EA is a risk factor for low immune function and increased 
susceptibility to infection (Montenero, Lopez-Varela, Nova, & Marcos, 2002). Despite 
the fact that there was the possibility that the reported intake was too low, the low EA 
that we noticed in 14 of the competitive young swimmers indicated an increased risk 
of infection that we did not manage to prove in our sample of 19 swimmers. We also 
did not manage to determine a correlation between the frequency of infection and the 
intake of other macronutrients that are connected with immune system function.

Low EA influences the regularity of the menstrual cycle and causes functional 
hypothalamic menstrual dysfunction, which has a negative impact on bone health as 
it leads to decreased formation of new bone tissue and increased resorption of existing 
bone tissue, which represents the second largest protein store after muscles (Loucks et 
al., 2011). Low EA in our female swimmers is of concern, as only 3 female swimmers 
had reported regular menstrual cycle. In the group of 6 female swimmers that had never 
had their period, there were 2 swimmers over the age of 15, thus expressing primary 
amenorrhea. For those with irregular menstrual cycles (N = 4), we did not manage to 
acquire the information on the length of the absence of their period, so we cannot di-
scuss secondary amenorrhea in our swimmers. We did not find a statistically significant 
correlation between EA, intakes of CHO, protein and fat and menstrual cycle regularity. 
Nevertheless, we find alarming to identify 4 young female swimmers (nearly 1/3 of 
female swimmers) with low EA, low CHO intake (one also with low protein intake) 



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Vesna SIMIČ, Nina MOHORKO: NUTRITIONAL STRATEGIES OF SLOVENIAN NATIONAL JUNIOR SWIMMING TEAM, 15–34

as well as low calcium and vitamin D intake. Only one of them stated that she had a 
regular menstrual cycle. Since female swimmers, due to their high training load, belong 
in the group with a high risk of RED-S, and consequently of functional hypothalamic 
menstrual dysfunction, which may also have long-term negative effects on health, we 
believe that the menstrual cycle must be monitored in competitive young swimmers 
and measures be taken in cases where a dysfunction is discovered. Measures include an 
increase in EI, a decrease in EEE or both (Mountjoy et al., 2014; De Souza et al., 2014). 

Hereby, it is important to emphasize the necessity of adaptation of strategies to 
specific individual, for they have to be aligned with their individual goals, their ability 
to execute and potential intolerance for certain specific nutrients. Those strategies must 
take into consideration the athlete‘s favourite foods as well as individual responses to 
strategies themselves (Thomas et al., 2016).

CONCLUSIONS

Comparison of applied nutrition strategies with the current recommendations of 
clinical sports nutrition in young Slovenian competitive swimmers enabled us to iden-
tify dietary deficits, especially among female swimmers, where too low EI leads to 
insufficient macronutrient and micronutrient intake and too low EA, which can lead 
to a decline in performance and even seriously compromise their health. The acquired 
information can enable dietitians to prepare more successful, personalised nutrition 
strategies for young competitive swimmers, hence contribute to the preservation of 
their health and their development into top athletes. 

Acknowledgement

The authors thank Slovenian Swimming Federation, coaches, swimmers and their 
parents for showing a high level of support for the research.

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