A few previous studies indicate that protein supplementation increases gains in muscle mass and strength during a resistance exercise program. The purpose of this study was to investigate whether whey protein supplementation results in greater increases in lean body mass, muscle strength and physical function in elderly individuals during 12 weeks of resistance exercise when compared to isocaloric carbohydrate supplementation.
A total of 161 men and women, 65–91 years old, participated in a randomized, controlled, double-blind intervention study, involving dietary supplementation and a 12-week resistance exercise program, designed to increase muscle mass and strength of all major muscle groups. Participants exercised three times a week and received either 20 g of whey protein (n=83) or isocaloric carbohydrate (n=78) in liquid form immediately after each workout. Data were obtained at baseline and end point.
The primary outcomes, lean body mass, strength and physical function increased significantly during the course of the study. Type of dietary supplementation did not influence gains in lean body mass (P=0.365), quadriceps strength (P=0.776) or performance during a 6-min walk (P=0.726) or a timed up-and-go test (P=0.151). Twenty participants discontinued the intervention.
Ingestion of 20 g of whey protein immediately after resistance exercise three times per week, does not lead to greater gains in lean body mass, strength and physical function in elderly people with sufficient energy and protein intakes when compared to isocaloric carbohydrate.
Sarcopenia, the loss of muscle mass and strength during aging, is one of the main reasons for the functional decline frequently observed among elderly people.1, 2 Therefore, it is considered very important to establish therapies that prevent or delay sarcopenia.
Regular resistance training is an effective way to increase muscle mass and strength in elderly people.3 It has also been suggested that increased protein intake4, 5 and/or supplementation with essential amino acids (EAAs), in particular leucine6, could maximize gains in muscle mass or strength during a resistance exercise program. In that regard, research has been directed towards whey proteins due to their high quality.7 Studies in young people indicate that whey protein ingestion directly after exercise stimulates muscle protein synthesis or accretion more than other protein sources.8, 9, 10
The beneficial effect of whey protein is thought to occur primarily due to their very high concentration of EAAs, particularly leucine (up to 14%).11 In general, studies suggest that ingestion of EAAs is an effective way to stimulate muscle protein synthesis in both young12, 13 and elderly individuals,14 whereas non-EAAs appear to have no detectable effect.14, 15 Therefore, it seems reasonable to assume that ingestion of whey protein supplements, with their high amount of EAAs, would result in greater gains in muscle mass after a period of resistance exercise in elderly people than, for example, isocaloric carbohydrate supplements. However, it is unclear whether findings from short-time experiments on muscle protein accretion or synthesis can be extrapolated to a long-term increase in muscle mass or strength.
It is of great importance to investigate how to optimize the benefits of resistance exercise with regard to gains in lean mass, strength and improvement in physical performance in healthy elderly individuals. Research lays the groundwork for effective strategies that could prevent or delay sarcopenia. In the current randomized, controlled, double-blinded intervention study, we compared the effects of post-exercise whey protein and isocaloric carbohydrate supplements in elderly people who participated in a 12-week resistance exercise program. We hypothesized that whey protein supplementation would result in greater gains in lean body mass, muscle strength and physical function than isocaloric carbohydrates.
Materials and Methods
The Icelandic National Bioethics Committee (VSNb2008060007/03–15) and the Icelandic Data Protection Authority (S4018/2008) approved the study, which followed the Helsinki declaration guidelines. Informed written consent was obtained from all participants prior to data collection. Outcome measures were obtained at baseline and again at the end of the study.
A total of 161 participants (age=65–91 years), 67 men and 94 women, were recruited by advertisements in the capital area of Iceland and were randomly assigned to receive either a whey protein supplement or isocaloric carbohydrates (Table 1). Exclusion criteria were age less than 65 years, low cognitive function (Mini-Mental State Examination <19 points), major orthopedic disease and pharmacological treatment with exogenous testosterone or other medications known to influence muscle mass. Furthermore, all participants had to be free of any musculoskeletal disorders or other disorders that could have affected their ability to complete their training and testing. Enrolled subjects were apparently healthy, although some had hypertension, hyperlipidemia or diabetes type II.
The resistance exercise program was designed to increase strength and mass of all major muscle groups. All measurements were obtained at baseline and again at the end of the study. Subjects exercised for three non-consecutive days per week for 12 weeks in groups of 20–30 individuals. The first week was used to teach correct exercise techniques at lower loads (60% of one-repetition maximum). Thereafter, resistance training involved three sets, where each exercise was repeated 6–8 times, at 75–80% of one-repetition maximum. The training load was systematically increased by 5–10% each week in order to keep the number of repetitions per set between six and eight. Ten different exercises were performed in weight machines during each training session; seated leg extension, seated leg curl, seated leg press, seated chest fly, seated row, seated pull-down, seated biceps curl, seated triceps curl, seated lower back extension and seated abdominal curl. Each exercise session started with a 10–15 min warm-up followed by resistance training, and stretching exercises were performed at the end of each session. All sessions were supervised by study staff, an athletic trainer and occasionally a physiotherapist.
Participants were assigned to one of two different supplement drinks, developed and produced by an Icelandic dairy producer (Mjolkursamsalan Ltd., Reykjavik, Iceland). The whey protein drink was based on sweet whey concentrate and contained 20 g protein, 20 g carbohydrates and 1 g fat per portion (250 ml, 169 kcal), whereas the carbohydrate drink contained 40 g carbohydrates and 1 g fat per portion (250 ml, 169 kcal). Participants ingested the drinks under supervision of the study staff immediately after each workout.
Randomization and masking
Treatment assignment was randomized and double-blinded. Participants were randomly allocated to treatment groups following a stratified randomization procedure based on a computer-generated list of random numbers. Randomization was stratified by gender to make the proportion of men and women in each group equal. The supplement drinks were provided in identical brick-style cartons and each of the two supplements had a specific three-digit-labelling. Investigators and other staff were kept blind to supplement assignment by the producer of the supplement until the intervention was completed. Furthermore, the supplement drinks were strawberry-flavoured to mask the contents. One of the leading investigators generated the allocation sequence, enrolled participants, assigned participants to interventions and took outcome measurements in collaboration with other staff.
Body composition was assessed by dual energy X-ray absorptiometry (DXA, Hologic QDR-2000 plus, Hologic Inc., Waltham, MA, USA). The DXA measurements were conducted at the Icelandic Heart Association, Kopavogur, Iceland.
To evaluate muscle strength, knee extensor muscle strength was measured. Quadriceps strength (maximum voluntary isometric contraction) was tested with an isokinetic dynamometer (Kin-Com 500H Chattanooga). The participants performed three submaximal trials and then four maximum voluntary isometric contraction tests for 5 s each, with a 50 s rest between tests. The greatest output was recorded as the peak torque expressed in Newtons (N).
Timed up-and-go test
During the timed up-and-go test the subject was instructed to rise from a chair with a seat height of 43 cm, walk 3 m, turn around, return and sit down again, wearing ordinary footwear and using customary walking aids if necessary.16
6-min walk for distance
The 6-min walk-for-distance was performed indoors in a spacious gym hall and conducted according to the guidelines from the American Thoracic Society (2002).17
Participants weighed and recorded their food intake for 3 consecutive days; 2 week-days and 1 weekend day. The food records were analyzed using an online program (www.hvaderimatnum.is) based on the Icelandic food composition database.
Physical activity and smoking
All participants answered questionnaires regarding leisure-time physical activity and smoking. Leisure-time activities were converted into metabolic equivalents.
Participants were instructed to avoid strenuous exercise and alcohol consumption the day before the drawing of fasting-blood samples at baseline and end point. The blood samples were centrifuged, aliquoted and stored at −80 °C until they were analyzed at the laboratory of the Icelandic University Hospital, Reykjavik, Iceland. The blood samples were analyzed for blood glucose (mmol/l), insulin (mU/l), triglycerides (mmol/l), total cholesterol (mmol/l), high-density lipoprotein (mmol/l) and insulin-like growth factor I (IGF-1) (mU/l).
Insulin was measured with electrochemiluminescence immunoassay on a Modular Analytics E170 system from Roche Diagnostics (Manheim, Germany). Plasma triglycerols, total cholesterol and glucose were analyzed using an enzymatic colorimetric assay and an automated analyzer (Hitachi 911; Roche Diagnostics). High-density lipoprotein was determined using polyethylene glycol-modified enzymes and dextran sulfate. Insulin-like growth factor I was analyzed with a solid-phase, enzyme-labeled chemiluminescent immunometric assay on a Immulite 1000 system from Siemens Healthcare Diagnostics (Tarrytown, NY, USA).
Analyses were conducted using SPSS for Windows version 20.0 (SPSS, Chicago, IL, USA), and the level of significance was set at P<0.05. Data are shown as mean±s.d. and the distribution was tested for normality using the Kolmogorov–Smirnov test.
The baseline characteristics of the whey protein and the carbohydrate group were compared using an independent t-test for parametric variables and Mann–Whitney U-test for non-parametric variables.
According to a priori power calculations, a sample size of at least 63 participants in each group was required to detect a difference of 1 kg in lean body mass between groups as significant (s.d.=2 kg, power=0.8, P=0.05).
Changes in main outcome variables (lean body mass, appendicular skeletal muscle mass, quadriceps strength and physical function) during the intervention were compared between the whey protein and the carbohydrate groups using an independent t-test for parametric variables and a Mann–Whitney U-test for non-parametric variables.
Changes in the main outcomes were also compared between the groups using a general linear model that adjusted for gender, age and baseline values of the dependent variables.
The baseline variables are presented in Table 1. They were not significantly different between the two groups. Figure 1 shows the number of participants that were assessed for eligibility, excluded from participation and randomly assigned to groups.
Body mass index (BMI)
Forty-two percent of participants were classified as overweight according to a BMI of 25–29 kg/m2, and 38% were classified as obese with BMI over 30 kg/m2. The highest BMI was 43 kg/m2 and the lowest 20.5 kg/m2.
Physical activity and smoking
Eighty-two percent of participants reported regular physical activity prior to the study and about two-thirds reached the recommended level of 30 min per day.18 Only 6% of participants were current smokers and 54% had smoked in the past. Rate of smoking and level of physical activity, expressed as metabolic equivalents, were equally distributed between the groups.
Dietary and supplemental intake
Baseline energy intake was on average 1659 kcal per day. Average protein intake was 79 g per day or 1.0 g per kg of body weight per day. According to the records of food intake, protein intake among 36% of participants was 1.0 g of protein for each kg of body weight per day, the current Nordic Nutrition Recommendations for the elderly population.19 Energy and protein intake did not increase significantly during the course of the study (Table 2). Forty-four percent of participants took vitamin supplements.
During the course of the study, lean body mass, appendicular skeletal muscle mass, muscle strength and physical function increased significantly (P<0.001). On average, lean body mass increased by 0.8 kg, appendicular skeletal muscle mass by 0.6 kg and quadriceps strength by 55 N. The results of 6 min walk increased on average by 37 m and the results of the timed up-and-go test improved by 0.6 s.
Gender differences in main outcome variables were considerable. Total lean mass, appendicular skeletal muscle mass and quadriceps strength were significantly greater among men. Furthermore, increase in total lean mass during the course of the study was higher among men, whereas women showed a greater improvement in 6-min walk-for-distance (Table 3). Gains in lean body mass, appendicular skeletal muscle mass, strength and function during the course of the intervention were not significantly different between treatment groups (Table 4).
According to the linear models, with age and baseline values as covariates, and gender and treatment group as fixed factors, there were no significant differences in gains in lean body mass, appendicular skeletal muscle mass, quadriceps strength and physical function between treatment groups (Table 5).
Retrospective sample size calculations based on our own data (s.d. for delta lean mass=1.0 kg for carbohydrate and 1.5 kg for whey) showed that the sample size was sufficient to detect a difference of ∼0.7 kg as statistically significant. In order to detect the non-clinically relevant difference of 180 g (according to Table 5) as significant, we would have needed around 500 participants in each group.
To our knowledge, this is the first randomized controlled trial including a large number of elderly participants of both genders, testing the effects of whey-protein intake during a resistance exercise program. The primary objective was to investigate the effects of whey proteins and isocaloric carbohydrates on gains in lean mass, strength and physical function during a 12-week resistance training program among community-dwelling elderly people.
We hypothesized that participants ingesting whey-protein concentrate immediately after exercise sessions would experience greater gains during the study period than those ingesting carbohydrate supplements. However, despite significant overall gains in all main outcome measures, treatment assignment did not influence any of them significantly. These results were unchanged when using multivariate analysis with adjustment for gender, age and corresponding baseline values.
Our results are in agreement with several studies that have investigated the effects of supplementation with protein or EAAs on the efficacy of resistance training in groups of healthy, middle-aged or elderly people.20, 21, 22, 23, 24 Studies reporting a beneficial effect of protein supplementation during a period of resistance exercise in elderly subjects are few. A study in middle-aged women found a greater improvement in strength and muscle-mass gain with protein supplementation,25 and another study in frail elderly subjects reported an increase in strength.26 Beneficial effect of protein supplementation on physical performance has also been reported in frail elderly subjects not partaking in resistance exercise.27 However, the results of the present study cannot be extended to frail elderly people or to cases where supplementation is given without concomitant resistance exercise.
In young people, there is also conflicting evidence for the additional benefits of protein supplementation during resistance exercise, with some studies showing an added benefit,8, 28, 29, 30 whereas others do not.31, 32 Conflicting results can probably be accounted for by differences in study design and the characteristics of the study population. A recent meta-analysis resolved some of this discrepancy by concluding that protein supplementation improves the benefits of resistance exercise in both the young and elderly populations.5
Several factors may have influenced the results of the present study. First, protein synthesis in the skeletal muscle of elderly people may not be sufficiently stimulated by low doses (∼7 g) of EAAs.14 Higher doses (10–15 g) appear to be needed to increase muscle protein synthesis to a similar extent as in young people.33, 34, 35 Most protein sources of animal- or plant-based origin contain ∼5–8 g of EAAs per 20 g of protein.36 Whey proteins are, however, of excellent quality and contain ∼9–11 g of EAAs (45–55%) per 20 g of protein.37 In the current study, participants ingested 20 g of whey protein immediately after exercise, which might have been too little to promote increases in lean body mass or strength. Post-prandial muscle protein accretion in old men has been found to be higher following an ingestion of 35 g of whey protein when compared to 20 g.38 However, 20–25 g of protein per meal is generally considered sufficient to stimulate post-prandial muscle protein synthesis.10, 14, 36
Secondly, it has been hypothesized that coingestion of protein and carbohydrate may reduce the anabolic response of muscle to EAAs among elderly people,39 whereas in young people, coingestion of protein and carbohydrate does not seem to have any negative effects on muscle-protein synthesis.40 In the current study, the whey-protein drink contained carbohydrate in the form of sucrose (48% of total energy content).
It is also worth considering that total protein and energy intake, as estimated with 3-day weighed-food records, did not increase significantly from the start to the end of the study. Participants in the group that received whey-protein supplementation increased their habitual protein intake by 6%, whereas the control decreased their protein intake by 3.3%. In some cases, the participants seem to have counterbalanced the extra protein and energy provided by the supplement drinks by reducing their habitual dietary intake. The protein spread theory states that there must be sufficient difference in protein ingestion before and during the study, and between groups, to be able to reveal a benefit from protein supplementation.41 In the current study, the between-group spread in protein intake was 19.1%, which appears to be lower than in most of the studies that have reported a beneficial effect from protein supplementation.41
Furthermore, the effect of the post-exercise protein ingestion was likely diluted, at least to some extent, by the daily protein intake of our participants, which was on average 1.0 g per kg per day. When consumption of protein and dietary status is adequate, extra protein supplementation is unlikely to have a measurable effect on the efficacy of resistance training. However, timed ingestion of protein before or after resistance exercise has been suggested to be able to stimulate muscle-protein synthesis to a greater extent than protein intake at other times.42
Studies indicate that in previously untrained individuals, resistance training causes increases in muscle mass regardless of the nutrition during the first months of training, if protein and energy intake is sufficient.43 Although many of our subjects participated in endurance exercise or moderate resistance exercise prior to starting the intervention, the results might have been different with a group of strength-trained individuals.
In summary, supplementation with 20 g whey-protein concentrate mixed with simple carbohydrates, ingested immediately after exercise, does not provide greater gains in lean mass, strength or physical function beyond what is achieved with an isocaloric dose of carbohydrates among community-dwelling-, physically active elderly people with adequate energy and nutrient intakes. The results cannot be generalized to sarcopenic and/or malnourished individuals. Further studies are needed to demonstrate the effect of protein supplementation in the aforementioned groups.
The study was funded by the Icelandic Technology Development Fund (No. 071323008), Research Fund of the University of Iceland, Landspitali University Hospital Research Fund and the Helga Jonsdottir and Sigurlidi Kristjansson Geriatric Research Fund. The trial is registered at the US National Library of Medicine (Nr. NCT01074879).
About this article
Journal of Nutrition in Gerontology and Geriatrics (2019)