The Role of Whey Protein in Maintaining Fat-Free Mass and Promoting Fat Loss After 18 Months of Bariatric Surgery

Abstract

Introduction: Adequate protein intake is essential for maintaining lean body mass during weight loss, particularly for patients undergoing bariatric surgery (BS). Whey protein supplementation may help meet daily protein requirements. This study aimed to assess the effects of whey protein supplementation on weight loss and body composition in women during the medium-term postoperative phase following BS. Methods: In a double-blind, controlled study over four weeks, 24 women received 30 g of whey protein (Whey group), while 19 received 30 g of maltodextrin (Malto group). Body composition, energy expenditure, muscle thickness, muscle strength, walking performance, and dietary intake were evaluated. Results: Compared to the Malto group, the Whey group showed greater reductions in body weight (median: −0.6 kg vs. −0.2 kg, respectively) and fat mass (median: −1.1 kg vs. −0.25 kg, respectively), along with an increase in fat-free mass (−0.7 kg vs. 0.6 kg, respectively). Muscle thickness improved in the Whey compared to the Malto group in the abdominal (0.07 mm vs. −0.04 mm, respectively) and thigh (0.4 mm vs. −0.15 mm, respectively) regions. Additionally, muscle mass reduction was less pronounced in the Whey group (−3 kg vs. −0.13 kg). No significant differences were observed in handgrip strength, gait speed, or nutrient intake. Conclusions: Whey protein supplementation may be beneficial, as it enhances weight loss and preserves fat-free and muscle mass more effectively than a diet without this supplementation in women during the stabilization phase or late postoperative period of BS.

1. Introduction

Clinical obesity is a chronic, systemic illness characterized by tissue dysfunction due to excess adiposity [1]. Low-grade inflammation is a condition associated with obesity, involving several immune and metabolic disorders. Its etiology is complex and multifactorial, involving genetic and environmental factors. Bariatric surgery is considered the most effective strategy in patients with severe obesity to achieve lasting weight loss, improve quality of life, and reduce comorbidities [2,3]. Mixed techniques associate intake restriction with lower food absorption, like Roux-en-Y gastric bypass [4,5]. The pattern of weight loss following bariatric surgery varies based on the type of procedure, preoperative weight, nutritional support, physical activity levels, and various other factors [6]. Numerous studies indicate that patients tend to experience weight loss primarily within the first 12 months, after which their weight tends to stabilize. Specifically, total weight loss after Roux-en-Y gastric bypass is reported to be approximately 27% by the third postoperative month, with a stabilization of around 32% after one year [7,8,9]. Previous research conducted by our group, which involved a population treated at the same facility as the current study, suggests that the most significant weight loss occurs during the first year following surgery, with minor additional losses observed up to 18 months. Beyond this period, weight tends to stabilize, although a slight regain may occur. Consequently, between 18 and 24 months post-surgery, both weight and dietary patterns become more consistent compared to the rapid weight loss phase within the first year or the potential weight regain phase after 24 months.

The loss of lean mass follows a similar trajectory. A meta-analysis found that at 12 months post-surgery, the reduction in lean body mass and skeletal muscle mass was approximately 8.13 kg and 3.18 kg, respectively. Notably, around 55% of the lean mass loss occurred within the first year, with the majority of the loss happening in the first three months post-surgery, followed by a more gradual decline until the one-year mark. This reduction in lean mass may decrease daily energy expenditure, subsequently contributing to a slower rate of weight loss. Therefore, implementing strategies to minimize lean mass loss could have several beneficial effects. These findings align with our earlier studies, which revealed significant lean mass loss up to 12 months after surgery, followed by a slight decrease until the two-year mark.

Protein malnutrition after bariatric surgery is a serious complication and leads to significant morbidity. Low protein intake is prevalent among patients undergoing bariatric surgery, despite receiving dietary advice. Earlier studies have shown that protein intake and physical activity are key factors in maintaining fat-free mass during weight loss. Additionally, inadequate protein intake and returning to the pre-surgical dietary pattern with high-carbohydrate and high-fat diets can reduce weight loss or even trigger weight regain [4]. Thus, protein supplements can help patients achieve protein intake recommendations after bariatric surgery and, therefore, can contribute to preserving fat-free mass. However, protein deficiency and supplementation are generally prescribed in the short-term postoperatory time due to the frequent meet intolerance and gastric volume restriction. Protein supplementation is sometimes neglected after 18–24 months of BS postoperatory. Whey protein is one of the most popular protein supplements due to its easy digestibility and high concentration of branched-chain amino acids, particularly leucine, which plays an important role in muscle protein synthesis [10]. This interventional, double-blind, placebo-controlled study aims to evaluate whether whey protein supplementation enhances weight loss and improves body composition in women following 18–24 months of bariatric surgery.

2. Methods

The project was approved by the Research Ethics Committee of UFMG (COEP/UFMG, under protocol #75415317.8.0000.5149) and registered in the Clinical Trials registry under protocol #NCT04510389. This was a double-masked, placebo-controlled, matched group trial. The patients were selected from two bariatric surgery services accredited by the SUS in Belo Horizonte (Santa Casa de Misericórdia and Hospital das Clínicas da Universidade Federal de Minas Gerais). Female patients between 20 and 59 years of age, 18 to 24 months after bariatric surgery, treated at hospitals integrated into the project with regular follow-up, were included. Patients with debilitating chronic diseases, vomiting, undergoing other surgical procedures before 18 months postoperatively, carrying prostheses, or using immunosuppressants were excluded. All patients signed an informed consent form.

2.1. Study Protocol

The volunteers were matched by BMI and age in the following groups: Whey: Whey (intervention group) and Malto: Maltodextrin (placebo group). Data were collected in the initial (T0) and final (T4) weeks. This study was conducted using a double-blind methodology. An individual not directly involved in the study handled coding the envelopes and assigning participants, ensuring that the researcher conducting the measurements remained unaware of group allocation.

We evaluated weight, height, body mass index (BMI), fat mass (FM), free fat mass (FFM), handgrip strength, muscle thickness by ultrasound, biochemical tests, a walk test, and a food record at each meeting. Whey protein or maltodextrin supplements were delivered at the initial collection and after 4 weeks. The supplements had equivalent energy composition. They were provided in individual sachets containing 30 g of each metalized package, without identification, and with a total of 30 sachets per month for each volunteer. The composition of both supplements is presented in

Table 1. Nutritional composition of maltodextrin and whey protein supplements.

Composition:	Maltodextrin		Whey Protein
	In 100 g	In 30 g	In 100 g	In 30 g
Energy Value	372 kcal	111.6 kcal	375 kcal	112.5 kcal
Carbohydrate	93 g	27.9 g	0 g	0 g
Protein	0 g	0 g	87 g	26.1 g
Fat	0 g	0 g	0 g	0 g
Sodium	0 g	0 g	155 mg	46.5 mg

Source: Nutricium Indústria LTDA.

.

Maltodextrin has a neutral or slightly sweet taste and a mild aroma, lacking distinct characteristics. Whey protein, which is derived from milk serum, has a slightly milky taste. Its aroma is also mild. Since they had not tried either, they were hardly able to predict or recognize the taste of maltodextrin or whey protein. The volunteers were instructed to consume the supplements at any time of day, preferably not close to consuming main meals, in a single dose or divided into two doses. In addition, they were instructed to return the sachets of supplements that were not consumed and were contacted weekly to assess supplement intake, adherence to physical activity, and review the food diary.

A total of 63 patients were evaluated for eligibility. However, six volunteers did not attend the first data collection, and one was excluded because she did not meet all the inclusion criteria. Among the 56 matched patients, 12 volunteers quit the study due to the COVID-19 pandemic. Thus, 43 participants were considered in the intention-to-treat analysis: 19 belonged to the Malto group and 24 to the Whey group (Figure 1).

2.2. Body Composition

Weight was assessed using a platform scale with a capacity of 150 kg and a precision of 100 g (Tanita BC-601, Tanita Corporation, Tokyo, Japan). Participants were instructed to maintain an upright posture, with arms extended, and to remove any coats, hats, shoes, or accessories that could interfere with the measurement. For height measurements, individuals were instructed to stand with their feet together and their bodies upright. Measurement was conducted using the stadiometer from a Filizolla^® scale (Técnica Industrial Oswaldo Filizola Ltd.a, São Paulo, Brazil), ensuring that the plane was tangential to the vertex of the head. Body fat mass (FM) and fat-free mass (FFM) were measured by bioelectrical impedance (TBW310e). Data on resistance, reactance, fat mass, fat-free mass, and phase angle were collected. Muscle mass was calculated using the estimation equation: [(height²/BIA resistance) × 0.401] + [gender × 3.825] + [age × −(0.071)] + 5.102 (141). The musculoskeletal index was classified according to the cut-off point for women ≤ 6.76 kg/m² [11].

2.3. Food Intake

Participants were instructed to keep a daily food record throughout the 4 experimental weeks. The food diary was used to assess food intake, estimated from three records, one of which referred to the weekend. Nutrients were calculated using Brazilian software AVANUTRI version 4.0.

2.4. Indirect Calorimetry and Physical Activity

Energy expenditure was assessed by indirect calorimetry (MetaCheck Calorimeter Model 7100, Korr Medical Technologies, Salt Lake City, UT, USA). Participants were instructed to abstain from caffeine and alcohol the day before the test, avoid intense physical activity for 24 h, and drink water 1 h before the test. The test was conducted after a 10 min rest. The average energy spent per minute was then calculated.

2.5. Physical Activity

Information on physical activity practices was collected on the frequency, duration, intensity, and type of physical activity practiced by the participants before starting the intervention through a questionnaire adapted from VIGITEL [12]. Patients were instructed to maintain the same level of physical activity throughout the intervention. They were considered active if they engaged in light or moderate physical activity for at least 150 min per week or intense physical activity for at least 75 min per week. At each visit, the level of physical activity was investigated [12].

2.6. Muscle Thickness Assessment

Muscle thickness was assessed using BodyMetrix BX2000 portable ultrasound IntelaMetrix, Inc, Brentwood, CA, USA. The points scanned by ultrasound (US) included the triceps, pectoralis, suprailiac, subscapular, abdominal, axillary, and thigh, using the measurement points described by Wagner, 2013 [13]. All measurements were performed by a single investigator trained directly by the ultrasound provider, BodyMetrix. Each participant underwent a minimum of two measurements, with the result calculated as the average of these two. If the measurements varied, a third measurement was taken, and any outlier values were discarded.

2.7. Muscle Strength

Muscle strength was assessed based on handgrip strength using the manual hydraulic dynamometer recommended by the American Society of Hand Therapists (ASHT). Three measurements of both arms were collected at a one-minute rest interval between them, using the highest value obtained [14].

2.8. Statistical Analysis

The results are presented as the differences observed between the data obtained at the final time point (T4) and those at the initial time point (T0). Dietary intake is expressed as the mean and standard deviation. Normality was assessed using the Kolmogorov–Smirnov test. To compare the variations between T4 and T0 across groups, Student’s t-test was used for parametric variables, while the Mann–Whitney test was applied for non-parametric variables. For dietary data, a two-way repeated-measures ANOVA was conducted. Physical activity data were analyzed using the chi-squared test. Statistical analyses were performed using IBM SPSS Statistics 19 and GraphPad Prism 8. A p-value of <0.05 was considered statistically significant. Graphs were generated using GraphPad Prism 8.

3. Results

Table 2. Baseline characteristics of women before and after 1 year of Roux-en-Y gastric bypass (RYGB).

Parameters	Malto T0		Whey T0
	Mean	SD	Mean	SD
Age (years):	47.60	7.45	46.00	8.26
Height (m)	1.63	0.05	1.60	0.06
Pre-surgical weight (kg):	125.5	21.35	126.7	15.63
1 BMI at surgery (kg/m2):	48.72	7.30	48.17	5.79
1-year post-surgical weight (kg):	89.51	23.91	88.15	11.24

Data presented as means ± SD. ¹ BMI = body mass index.

shows the baseline characteristics of all participants. Participants had similar pre- and 12-month post-surgical age ranges and body weights.

After 4 weeks of supplementation, the Malto group showed superior weight, fat mass (kg), and adiposity gains compared to the Whey group. Still, it exhibited reduced fat-free mass, whereas the Whey group experienced a modest gain in fat-free mass (Figure 2).

There was no significant difference in energy expenditure between groups, as well as in waist and hip perimeter. Regarding skeletal muscle thickness assessed by ultrasound in different regions, we found that the Whey group presented an increase in muscle thickness in the abdominal and thigh regions compared to the Malto group. In the other areas, the variation in muscle thickness was similar between groups (Figure 3).

The increase in muscle thickness in the chest and abdominal regions is consistent with the improvement in total muscle mass and skeletal muscle index. Despite these results, we did not observe any improvement in handgrip strength or gait speed test after Whey supplementation compared to the Malto group (Figure 4). However, we observed an increase in the phase angle in the group supplemented with whey. However, less than half of them performed more than 150 min per week. Only 10.5% and 8.3% of the participants in the Malto and Whey groups, respectively, performed anaerobic strength exercises.

The frequency of physical activity during this study was similar between the groups (

Table 3. Frequency and type of physical activity of patients in the postoperative period of bariatric surgery receiving 30 g of maltodextrin (Malto) or 30 g of whey protein (Whey) supplementation for 4 weeks.

Parameters	Malto			Whey
	No Activity	<150 min/wk	>150 min/wk	No Activity	<150 min/wk	>150 min/wk
Frequency	42.2%	31.5%	26.3%	37.5%	37.5%	25%
Aerobic Exercises	-	21%	15.8%	-	29.2%	16.7%
Anaerobic Exercises	-	10.5%	10.5%	-	8.3%	8.3%

Data analyzed by the chi-squared test.

): approximately 57.8% and 62.5% of the Malto and Whey groups. Participants reported walking as their main physical activity.

Food intake: Food consumption was similar across groups and over time. There was no difference between the groups during this study in terms of daily protein and energy intake, as well as the percentages of lipids, proteins, and carbohydrates in total energy intake (Figure 5).

4. Discussion

Protein intake is recognized as a crucial factor in regulating body weight [15]. A high-protein diet may be beneficial in preventing and treating obesity, as protein induces a higher level of diet-induced thermogenesis compared to fat and carbohydrates [15]. Additionally, during weight loss, protein can help preserve lean body mass, thereby preventing a decrease in resting energy expenditure [16]. Moreover, dietary protein induces the release of intestinal peptide hormones, such as glucagon-like peptide-1 and the YY peptide, which have satiogenic effects, increasing satiety and thus reducing food consumption [17]. In short, a high protein intake can favor a negative energy balance by increasing energy expenditure and decreasing energy intake. Both may be beneficial for body weight normalization [18]. However, the effects of protein supplements on weight stabilization during the post-surgical phase (18–24 months after bariatric surgery) are still unclear. Evidence on the impact of protein supplementation or a high-protein diet on preserving fat-free mass is still scarce. Few studies have evaluated protein supplements after Roux-en-Y bypass surgery [16,19,20,21,22,23,24].

In a previous study [19], analyzing patients between 2 and 7 years after RYGB showed that resistance training associated with whey protein supplementation increased 1.46 ± 1.02 kg in FFM and 0.91 ± 0.64 kg in skeletal muscle mass compared to the control group (maltodextrin), there was an average reduction of 0.24 ± 1.64 kg in FFM and an average increase of 0.08 ± 0.96 kg in MME. This study analyzed patients after 24 months of surgery, when the plateau effect or weight regain occurs. In our study, although women were included 18–24 months postoperatively, a period with slower weight loss, we found an improvement in FFM even without a difference in physical activity.

A meta-analysis [21] including 10 trials showed that, as occurred in our study, protein supplementation led to greater changes in weight, muscle mass, fat-free mass, and fat mass but did not significantly affect BMI.

Schollenberger et al. [16] evaluated patients undergoing BS who received a daily protein supplement over 6 months after surgery. In the group that received the protein, the body fat mass loss was greater than in the control group, while the loss of lean body mass was less pronounced. Like our results, blood proteins and handgrip strength did not differ between the two groups at any time. Although we observed higher fat-free mass in the Whey group, we did not observe an improvement in handgrip strength or gait speed after supplementing with whey. Possibly, 4 weeks of supplementation were insufficient to induce a significant increase in muscle strength, especially gait speed, as these individuals often have chronic knee and hip injuries that can impact gait speed.

It is important to note that the frequency and type of physical exercise performed by the volunteers were evaluated; however, no significant difference was found between the groups. Most volunteers engaged in only aerobic exercises, with walking being reported as the primary physical activity. However, less than half did more than 150 min per week. Only 10.5% and 8.3% of the participants in the Malto and Whey groups, respectively, performed anaerobic strength exercises. To date, there is no defined physical training protocol for the different follow-up stages after bariatric surgery. Among the few studies available in systematic reviews related to bariatric surgery, the variability of training protocols associated with the type, duration, and frequency of the intervention makes it difficult to draw a definitive conclusion about the results [25,26].

Our study analyzed muscle thickness using a portable ultrasound (US). Our findings showed an increase in abdominal and thigh thickness in the Whey group after 4 weeks, compared to the Malto group. This increase was likely due to the improved supply of branched-chain amino acids, such as leucine, in the group supplemented with whey protein, and to the more frequent muscle activity in these regions, which can stimulate protein synthesis or reduce muscle catabolism.

The phase angle (PhA) has been proposed as an indicator of the number, integrity, and function of cells. Higher PhA values represent a large number of intact cell membranes and a high body cell mass, while lower values indicate impaired cell function and membrane integrity [27]. It has been evaluated in some clinical situations and decreases after BS, but its relevance is still unclear. The data suggest that at a one-year follow-up after bariatric surgery, lower PhA values might indicate a concomitant loss of visceral protein and a worsening of protein nutritional status [28]. However, higher values are found in physically active individuals or exercisers. Our study observed an increase in phase angle after protein supplementation. Similarly, our study and that of Cereda et al. [20] found that in patients undergoing chemotherapy, whey supplementation combined with counseling improved the phase angle compared to nutritional counseling alone.

Regarding food intake, surprisingly, there was no significant difference between the groups or across the weeks. There was no significant difference in protein and daily energy intake, as well as macronutrient percentual distribution. Although the Malto group did not receive protein supplementation, protein intake was similar between the groups, reaching the minimum recommendation for bariatric patients of 60 g/day [29] in approximately 53% and 59% of the Malto and Whey groups, respectively. These data suggest that participants in both groups adhered to their protein and energy recommendations as a result of weekly diet monitoring by the research team. However, since almost half of the protein ingested in the Whey group was whey protein that had a high biological value and was rich in branched-chain amino acids, it was possible to suggest that protein quality, rather than quantity, was associated with improved body composition, with a greater loss of fat mass and lower loss of fat-free mass.

A meta-analysis revealed that whey supplementation led to favorable changes in lean body mass compared to a control group without whey protein. Similar results were observed when whey was compared with carbohydrate controls [21]. The systematic review results indicate that whey supplementation improves body composition in adult women without obesity, modestly increasing lean mass without influencing changes in body mass. However, the authors agree that whey protein may be more beneficial for improving body composition when included as part of a weight loss program, as in our study, where caloric intake is about 1000 to 1300 kcal/day.

Our study has certain limitations. Due to participant withdrawals following concerns about the pandemic, the intervention duration was reduced to only four weeks. This shortened timeframe may have limited the observation of more subtle clinical modifications. Moreover, this study was conducted as a matched-group, non-randomized clinical trial. While this approach allows for group comparisons, it does not provide the same level of robustness as a randomized trial in determining whether one intervention is superior to another. The assessment of physical activity in this study was based on self-reported data, which may introduce bias. This approach is susceptible to recall errors, which may compromise the accuracy of the reported activity levels.

In conclusion, our results suggest that, in patients already in a phase of weight stabilization following bariatric surgery, whey protein supplementation may be beneficial, as it enhances weight loss and preserves fat-free and muscle mass more effectively than a diet without this supplementation. Future studies of whey protein supplements are suggested, with a larger sample size, in patients undergoing bariatric surgery.