Effect of caloric restriction with protein supplementation on weight, adipose mass, and muscle mass in professional male soccer players: a controlled randomized trial

doi:10.21203/rs.3.rs-4919749/v1

Background

Achieving optimal body composition can be advantageous for athletes in terms of competitive performance. To date, there is no research examining the effects of caloric restriction (CR) on body composition in male professional soccer players.

Purpose

This study aims to investigate the impact of 6 weeks of CR with protein supplementation on body composition and the maintenance of changes after stopping CR for the next 6 weeks.

Methods

The study was a controlled, randomized, parallel-group, experiment involving 28 participants. The experimental group received a CR diet (2650 kcal/d) and the control group received a normal caloric (NC) diet (3500 kcal/d). The intervention lasted for 6 weeks, followed by 6 weeks without intervention and provision of ad libitum diet in both groups. Body composition was assessed using anthropometric measurements.

Results

The study participants were aged 27.6 ± 4.4 years on average. After 6 weeks, the CR group showed a significant reduction in body weight compared with the NC group (− 0.33 kg for CR vs. −0.08 kg for NC; p < 0.05). Both groups experienced a reduction in adipose mass after 6 weeks (p > 0.05), but only the CR group continued to decrease body fat after stopping CR (p < 0.05). Throughout the study, there was an increase in muscle mass, and no significant difference was observed between the two groups (p > 0.05).

Conclusions

CR with protein supplementation improves body composition in male professional soccer players by reducing weight, promoting fat loss, and enhancing muscle mass.

Soccer player

caloric restriction

body composition

muscle mass

adipose mass

Soccer is characterized by intermittent changes in movements, speeds, directions, and technical tasks. These demands require physiological adaptations from soccer players [1]. The body composition confers soccer players competitive benefits and contributes to high performance [2]. A satisfactory body composition in soccer players can prevent injuries, improve fatigue resistance during games and training, reduce post-match recovery time, and maintain player performance (e.g., strength, endurance, and jump-sprint ability) [3]. The specific body composition requirements for the performance of elite soccer players vary by playing level and position, for instance, adipose mass varies between 10% and 12%, goalkeepers tend to have greater body fat than outfielders, and midfielders have less body mass than players in other positions [1, 4].

Manipulating body composition is important for preseason, in-season, and off-season training [5]. To achieve optimal body composition, specific training programs coupled with nutritional interventions are employed [1, 4]. One of the dietary strategies employed to reach optimal body composition is caloric restriction (CR) [6, 7]. CR is the restriction of dietary energy intake while maintaining sufficient nutrient supply to guarantee optimal nutrition status and avoid malnutrition. By starting a CR of ~ 12%, the supply of glucose decrease and fatty acid oxidation is required to provide the demand for ATP [8–10]. Correspondingly, CR induces metabolic mitochondrial energy efficiency, reduces oxidative damage, and decreases energy expenditure during physical activity. These adaptations have positive effects on body composition, such as body weight reduction, adipose mass loss, and lean body mass gain [7, 9, 11, 12].

The impact of CR on the body composition of elite male soccer players has been scarcely studied. A study conducted with 15 male professional soccer players who underwent CR found a significant decline in weight, adipose mass reduction, and preservation of lean mass [13]. However, there is insufficient data on the effects of CR on the body composition of male professional soccer players. Therefore, this study aims to evaluate the effect of CR with protein supplementation on body composition in a group of male professional soccer players. Additionally, we aimed to determine if intervention outcomes persisted for 6 weeks after treatment cessation.

Experimental design

The study was a controlled, randomized, parallel-group experiment with a 1:1 allocation. The experimental group was provided with a CR diet in preseason matches. The control group was given a normal caloric (NC) diet across the study. The participants underwent baseline measurements, followed by a measurement at 6 weeks and another in the subsequent 6 weeks, with ad libitum diet in-season matches. This report follows the recommendations of the Proper Reporting of Evidence in Sport and Exercise Nutrition Trials -PRESENT- statement [14].

Ethical disclosure

All participants read and signed the informed consent document. The study was approved by the research ethics committee of the Autonomous University of Madrid (CEI 100–1873) (21-06-2019) and met the standards for the use of human participants in research, as outlined in national and international normativity.

Participants

The sample size was estimated for the difference of independent means at the end of the intervention, considering a Confidence Interval of 95%, Power of 80%, Sample Size Ratio 1 and difference of 2 kg. The calculated total sample size was 20 subjects. Through block randomization, they were assigned to receive either the CR diet or NC diet. The distribution of players in a game position was equal between both groups, which included goalkeeper, central defense, wing defense, midfielder, forward, and outside midfielder. The players had no knowledge of the group they were assigned to. During the study, four players withdrew: two due to injury and two due to team changes Fig. 1.

The study involved 32 male professional soccer players who participated in the highest category of a professional soccer league. Players with a sum of six skinfolds (triceps, subscapular, supraspinal, abdominal, mid-thigh, and calf) > 60 mm; metabolic diseases (e.g., cardiovascular, respiratory, gastrointestinal, thyroid-related, etc.); weight change ± 2 kg in the last month following special diets (e.g., vegan diet, restrictive diet, etc.); consumption of nutritional supplements in the last month; and use of medications to control blood lipid or glucose were excluded. Additional exclusion criteria were failure to comply with all the measurements (physical, physiological, nutritional, and laboratory evaluations) and missing > 5% of the scheduled training sessions. During the study, the players were encouraged to maintain their normal and constant training programs (8 h training/week).

Body composition outcomes

Body composition was assessed using anthropometric measurements. Body composition was determined by Ross & Kerr’s five-components model [15] and AntropoS2.8. version software. Lean body mass was obtained by subtracting adipose mass from total body mass. An anthropometrist Instructor level III of The International Society for the Advancement of Kinanthropometry -ISAK- realized 15 anthropometric measures: weight, height, skinfolds (triceps, subscapular, supraspinal, abdominal, thigh, and calf), and perimeters (arm relaxed, arm flexed and contracted, forearm, waist, hips, thigh middle, and calf). Technical measurement error was 1.17%. The anthropometric variables were measured earlier in the morning, fasting for at least 8 h, and without previous training.

Dietary intervention

Recommended energy intake (REI) was individually calculated based on physical activity; training, competition, or rest days; and resting metabolic rate. Cunningham’s equation was used for resting metabolic rate, incorporating lean body mass from anthropometric measures and daily physical activity. For daily physical activity (e.g., stay at home and study), a factor of 1.25 was employed. The addition of energy expenditure per sports was 5 METS (Metabolic Equivalent of Task) by training and 9 METS by competition [16]. The CR group received − 25% of REI [17, 18]. In order to safeguard the athlete's body composition and performance, this restriction has been implemented [6]. The average REI of the CR group was 2650 kcal/d, whereas that of the NC group was 3500 kcal/d.

All soccer players were given a dietary plan with an equal macronutrient percentage distribution of REI: 18–22% protein (CR: 2.3 g/kg/d; NC: 2.6 g/kg/d), 22% fat (1 g/kg/d), and 56–60% CHO (5–7 g/kg/d). The plan was low in saturated fat, free of trans fats and sugar, and encouraged intake of unsaturated fats [5, 19].

The players were provided with 27 g of a whey protein supplement, which lacked carbohydrates or fats, immediately after their morning training. In the evening, 13.5 g of the whey protein supplement was provided to promote muscle recovery and rest [5, 19]. All soccer players followed the dietary plan prescribed at home and during the concentration period in the team facilities.

Dietary assessment and adherence

Dietary assessment was conducted at baseline, 6 weeks, and 12 weeks by a trained nutritionist. A standard menu and diet referrals were prescribed, based on the energy and nutrient calculation for each group and menu. To assess dietary adherence, a 24-h habitual consumption recall and food consumption frequency questionnaire were used for the following: day with regular training, day without training, and day with only strength or recovery training. The portions were quantified through food models, vessels, measuring spoons, and direct observation during meals [20, 21]. The diet was quantitatively analyzed in an Excel sheet, using national nutritional content tables.

Biochemical parameters

During the initial stage of the study, a range of nutritional blood biomarkers were measured to evaluate nutritional status. These included hemoglobin, hematocrit, leukocytes, lymphocytes, ferritin, total protein, albumin, and globulin. All blood samples were collected in the morning after an 8-h fast with no prior exercise. The samples were processed on the day of collection at a reliable clinical laboratory.

Statistical analysis

Results were described as mean, standard deviation, frequency, or percentage. Normal distribution of quantitative variables was tested by the Shapiro–Wilk test. An independent samples t-test and ꭓ² test were used to test baseline differences between CR and NC groups. The Mann–Whitney U test was used for cases that lacked normal distribution. Student’s t-test or Wilcoxon signed-rank test of dependent samples was used for intragroup comparison. All differences were considered significant at p < 0.05 and with Bonferroni’s adjustments for multiple comparisons (p < 0.002). Statistical analyses were performed in Stata 12 software.

Characteristics and dietary adherence

The study involved 28 male professional soccer players with an average age of 27.6 ± 4.4 years. At the beginning of the study, both groups had similar nutritional intake (calories, protein, fat, and carbohydrates) and nutritional status biomarkers (Table 1). After 6 weeks, the CR group had a lower intake of calories, fat, and carbohydrates, which remained low for the next 6 weeks of ad libitum diet. High protein intake was observed in both groups (Table 2).

Body composition changes

Our study revealed a significant increase in muscle mass and a reduction in adipose mass for both groups (Figure 2). The CR group experienced a decrease in body weight throughout the study, with a notable reduction at the 6-week mark. Both groups showed a decrease in adipose mass at 6 weeks, and the CR group continued to exhibit a reduction in body fat at 12 weeks. Both groups had an increase in muscle mass throughout the study (Table 3).

CR is an effective intervention that has demonstrated favorable effects on body composition in athletes [13, 22–24]. Our findings in professional male soccer players show that after 6 weeks of CR, weight and adipose mass was lost with a gain in muscle mass. Even after cessation of intervention for 6 weeks, the CR group continued to experience fat loss and muscle gain.

CR brings benefits for professional soccer players, contributing to weight reduction, adipose mass loss, and muscle gain. CR reduces the availability of energy, which inhibits lipogenesis and forces the body to utilize fatty acid oxidation for energy, resulting in decreased body fat [10, 18, 25]. These benefits can be attributed to the negative caloric balance created by CR, which triggers a series of physiological, molecular, and cellular, mechanisms, such as metabolic pathways and formation of stress-activated advanced glycation end-products [11, 26].

Mild CR with protein supplementation stimulates muscle gain by using oxidation of free fatty acids as fuel [27], inhibiting gluconeogenesis, and stimulating protein synthesis by preserving mTOR [26, 28]. Indeed, adequate protein intake is essential for building and maintaining muscle mass [29, 30]. Consuming protein pre- and post-training prevents muscle protein breakdown during exercise, preserves muscle mass, and promotes fatty acid oxidation [28, 30, 31]. Therefore, during exercise, mild CR with protein supplementation maintains the beneficial effect of protein consumption on muscle mass.

Studies have not delved into the maintenance of bodily changes after discontinuing CR intervention. Our hypothesis is that the loss of adipose mass and gain of muscle mass after CR cessation can be attributed to the lasting metabolic adaptations of CR attached to nutritional education and acceptance of dietary plan. This is supported by the fact that the intervention of nutrition education used to implement CR has enhanced dietary intake quality [32], and CR was successful for participants to achieve physical, psychological, and environment needs [5, 25]. It is crucial for athletes to decide their body composition goals between the player, trainer, and medical staff [5].

To our knowledge, this is one of the first studies on CR in professional soccer players. The findings are similar those of a pre-post trial including 15 male professional soccer players, with CR − 20% for 4 weeks, without protein supplementation [13]. The trial demonstrated a reduction in body mass (− 2.4 kg; p < 0.05), reduction in adipose mass (− 0.6%; p < 0.05), and preservation of lean mass. According to Hammouda [13], these changes can be attributed to decreased daily energy intake and lipid use during restriction.

Our findings are consistent with those of others using CR in other sport disciplines. A systematic review was done in resistance-trained male athletes using CR with protein supplementation. The study found decreased body fat percentage in all studies and an increase or maintenance of fat-free mass in 50% of the studies [33]. A study in 17 resistance-trained males found that CR with protein supplementation reached fat loss and maintained lean mass [34]. In a study with male-trained participants, CR of 40% and high protein supplementation demonstrated an increase in lean body mass and adipose mass loss [35]. Thus, CR with protein supplementation in male professional soccer players, as well as in players in other disciplines, can contribute to reducing weight and adipose mass while increasing muscle mass.

Future directions

Skinfold thickness and anthropometric methods are a popular and reliable surrogate method for measuring adiposity and muscularity. We followed a high quality protocol to ensure that the data were unbiased [5, 6, 18]. Evidence indicates possible differences between anthropometry with bioelectrical impedance analysis and dual-energy X-ray absorptiometry to estimate adipose mass percentage and fat-free mass kilogram [2]. For instance, our findings should be corroborated by studies using other body composition assessment techniques, such as dual-energy X-ray absorptiometry or bioelectrical impedance analysis. Furthermore, we demonstrate continuous improvement of body composition after cessation of intervention. Therefore, studies must focus in describing the physiological mechanism involved in maintaining changes.

Limitations

Our main strength was testing mild CR with protein supplementation during competition season and follow-up after cessation of CR. An important limitation includes sample size, which prevented in-depth subgroup analyses. Current research has emphasized the influence of a player’s physiology, field position, and playing style on their body composition [1, 5]. Therefore, future studies should consider a larger sample size for detailed statistical analysis, according to soccer player characteristics.

CR with protein supplementation improves the body composition of male professional soccer players by reducing weight, promoting fat loss, and increasing muscle mass. These changes are maintained for up to 6 weeks after cessation of intervention. Studies must focus on the physiological mechanisms of prolonging the benefits after CR cessation, employ different body composition methods, and increase the number of participants.

Practical implication

Body composition confers competitive benefits and contributes to achieving high performance among soccer players. Therefore, manipulating body composition through mild CR with protein supplements could increase muscle mass and decrease adipose mass in male professional soccer players.
After 6 weeks, body weight was significantly reduced in the CR group compared with the NC group (− 0.33 kg for CR vs. −0.08 kg for NC; p < 0.05). Both groups experienced a reduction in adipose mass after 6 weeks.
Six weeks after cessation of CR, only the CR group showed a continued decrease in adipose mass. Muscle mass increased throughout the study.

BIA Bioelectrical Impedance Analysis

CR caloric restriction

DXA dual-energy X-ray absorptiometry

Kg kilogram

mm millimeter

NC normal caloric diet

REI recommended energy intake

RMr resting metabolic rate

SD standard deviation

Funding details

The authors did not receive support from any organization for the submitted work.

Competing interest

The authors have no relevant financial or non-financial interests to disclose.

Authorships

Conceptualization: G.G., A.N., J.D.C., and C.T.G.

Data curation: G.G., G.D., and A.N.

Formal analysis: G.G., G.D., and A.N.

Funding acquisition: G.G.

Investigation: G.G. and A.N.

Methodology: G.G., J.D.C., and C.T.G.

Project administration: G.G., and A.N.

Resources: G.G.

Supervision: G.G., J.D.C., and C.T.G.;

Validation: G.G. and A.N.

Analysis: G.D. and G.G.

Visualization: G.G., M.P.B.M, F.B-A, and A.C.

Writing – original draft: G.G., M.P.-B.M, F.B-A, and A.C.

Writing – review & editing: all authors.

Ethics approval

All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. The study followed ethical research practices and received approval from the research ethics committee at the [Anonymous institution for peer review] (CEI 100-1873) on June 21, 2019.

Consent to participate

Informed consent was obtained from all individual participants included in the study.

Data availability statement

Data availability is subject to request by email to the corresponding author.

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Table 1. Characteristics of the 28 professional male soccer players included in the study.

Calorie restricted diet

n = 12

Normal caloric diet

n = 16

p value

Age, years, mean (SD)

27.8 (4.4)

27.5 (4.6)

0,86

Position, n (%)

Goalkeeper

Center back

Wing back

Center

Winger

1 (8.3)

2 (16.7)

4 (33.3)

3 (25.0)

1 (6.3)

2 (12.5)

5 (31.3)

6 (37.5)

Nutritional intake, mean (SD)

Calorie (kcal/kg/d)

Protein (g/kg/d)

Fat (g/kg/d)

Carbohydrates (g/kg/d)

41.0 (4.0)

2.1 (0.3)

1.0 (0.1)

6.1 (0.7)

41.5 (4.0)

2.1 (0.3)

1.0 (0.1)

6.0 (0.7)

0.6258

0.9254

0.8850

0.6080

Nutritional status biomarkers, mean (SD)

Hemoglobin (g/dL)

Hematocrit (%)

Ferritin (ng/mL)

Total proteins (g/dL)

Albumin (g/dL)

Globulins (g/dL)

15.0 (0.8)

45.3 (2.6)

163.5 (69.4)

7.0 (0.4)

4.2 (0.3)

2.7 (0.5)

14.9 (0.9)

46.1 (2.7)

158.1 (58)

7.1 (0.6)

4.3 (0.4)

2.8 (0.4)

0,949

0,443

0,837

0,454

0,413

0,879

SD: standard deviation

Significance difference (p < 0.05) and Bonferroni’s adjustment (p < 0.002).

Table 2. Nutritional intake and adherence assessment to intervention at 6 and 12 weeks of follow-up.

Calorie restricted

diet

n = 12

Normal caloric

diet

n = 16

p value

Calorie intake (kcal/kg/d), mean (SD)

6 weeks

12 weeks

30.3 (3.7)

33.4 (4.4)

46.9 (4.0)

45.6 (4.3)

0.0001

Protein intake (g/kg/d), mean (SD)

6 weeks

12 weeks

2.1 (0.3)

2.3 (0.3)

2.5 (0.2)

2.6 (0.2)

0.0012

0.0001

Fat intake (g/kg/d), mean (SD)

6 weeks

12 weeks

0.8 (0.2)

1.0 (0.2)

1.1 (0.1)

0.0003

0.0621

Carbohydrate intake (g/kg/d), mean (SD)

6 weeks

12 weeks

3.5 (0.5)

4.0 (0.5)

6.7 (0.7)

6.4 (0.8)

0.0001

SD: standard deviation

p values in bold are statistically significant at p <0.002

Table 3. Body composition of the 28 male professional soccer players included in the study at baseline and after 6 and 12 weeks.

Calorie restricted diet

n = 12

Mean (SD)

Normal caloric diet

n = 16

Mean (SD)

p value

Body weight, kg

Baseline

6 weeks

12 weeks

76.9 (6.2)

76.3 (6.1)

76.6 (6.4)

74.1 (4.8)

74.4 (4.9)

74.1 (5.1)

0.1435

0.3409

0.3068

BMI, kg/m²

Baseline

6 weeks

12 weeks

24.3 (0.9)

24.2 (0.9)

24.2 (1.0)

23.5 (1.1)

23.6 (1.1)

23.5 (1.1)

0.0482

0.0814

0.0567

6-fold sum, mm

Baseline

6 weeks

12 weeks

52.0 (6.4)

46.3 (7.1)

44.3 (7.4)

38.4 (5.3)

33.0 (5.3)

33.1 (6.3)

0.0001

0.0009

Adipose mass, kg

Baseline

6 weeks

12 weeks

16.5 (1.9)

15.4 (1.7)

15.1 (1.9)

14.0 (1.0)

13.2 (1.2)

13.0 (1.2)

0.0007

0.0013

0.0029

Adipose mass, %

Baseline

6 weeks

12 weeks

21.4 (1.8)

20.2 (1.7)

19.6 (1.8)

18.9 (1.4)

17.8 (1.6)

17.6 (1.7)

0.0010

0.0022

0.0062

Muscle mass, kg

Baseline

6 weeks

12 weeks

40.1 (3.9)

40.5 (4.0)

41.0 (3.8)

39.6 (3.3)

40.2 (3.5)

40.4 (3.7)

0.6259

0.8892

0.6424

Muscle mass, %

Baseline

6 weeks

12 weeks

52.1 (1.9)

53.0 (1.6)

53.6 (1.6)

53.3 (1.7)

54.1 (2.0)

54.5 (2.2)

0.0432

0.0701

0.1143

kg: kilogram

mm: millimeter

SD: standard deviation

p values in bold are statistically significant at p <0.002

No competing interests reported.

Effect of caloric restriction with protein supplementation on weight, adipose mass, and muscle mass in professional male soccer players: a controlled randomized trial

Status:

Version 1

Abstract

Background

Purpose

Methods

Results

Conclusions

Figures

Introduction

Methods

Experimental design

Ethical disclosure

Participants

Body composition outcomes

Dietary intervention

Dietary assessment and adherence

Biochemical parameters

Statistical analysis

Results

Discussion

Future directions

Limitations

Conclusions

Practical implication

Abbreviations

Declarations

References

Tables

Additional Declarations

Status:

Version 1