Literature Review:  How Important Is Protein for Fighting Muscle Loss As We Age?

As we age, loss of muscle mass and muscle function occur naturally, but can be exacerbated if we don’t do anything to fight it (Santilli et al., 2014). This is referred to as ‘sarcopenia’, which is a syndrome correlated with loss of physical function and even poor quality of life (Santilli et al., 2014). Although sarcopenia is more commonly seen in elderly people, 60 years and above, the onset of muscle loss occurs as early as in our 30s (Santilli et al., 2014). To delay the onset and reduce the need for long-term care, we should aim to prevent and postpone the loss of muscle mass as much as possible (Santilli et al., 2014).

This review examined studies involving elderly men and women, between the ages of 60 and 96, with the number of participants ranging from 31 to 380. Most participants were community dwelling, only a small number of studies were performed in assisted living settings. The studies were conducted in a total of 13 European, Asian, and American countries, with participants ranging from healthy and active to sarcopenic and frail. The purpose of this review was to examine the importance of dietary protein for fighting sarcopenia. We are going to look at the current problem and then the effects of protein supplementation on sarcopenia, of protein supplementation in combination with vitamin D and protein supplementation in combination with physical activity. The literature review is broken down into the following sections:

• Introduction to Dietary Protein Recommendations As We Age
• The Current Problem
• Effects of Protein Supplementation on Sarcopenia
• Effects of Protein Supplementation in Combination with Vitamin D on Sarcopenia
• Effects of High Protein Diets in Combination with Physical Activity on Sarcopenia
• The Takeaway

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The full review starts below or scroll down to jump to that section.

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Introduction to Dietary Protein Recommendations As We Age

It seems to be clear that regular physical activity is the only intervention that has consistently been shown to improve functional health, to fight the loss of muscle, and prevent the development of disability (Marzetti et al., 2017). People are also becoming more aware of the importance of dietary protein for building and retaining muscle and physical strength in adolescence and for athletes (Wu, 2016). Because of this, a dietary protein intake of 1-1.6g per kg/bodyweight/day is often recommended, but even 2g per kg of bodyweight appear to be safe for long-term consumption in adults (Wu, 2016).

However, some new evidence suggests that as we grow older we may need even more protein to promote good health and functionality to make up for the age-related changes in protein metabolism (Bauer et al., 2013). It has also been noted that combining a diet high in dietary protein with additional micronutrient supplementation, such as Vitamin D, may provide additional benefits in preventing sarcopenia (Molnar et al., 2016).

It has yet to be established clearly, to which extent dietary protein is necessary for older adults, how important its combination with additional micronutrients is and what the interplay is between dietary protein and physical activity when it comes to fighting sarcopenia. However, this review aims to shed light on the research that has already been done regarding these topics.

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The Current Problem

Nutrition has been identified as a risk factor for loss of muscle/sarcopenia (Hanach et al., 2019). One aspect of this is that dietary protein provides amino acids and can therefore stimulate anabolic activity in the muscle (Hanach et al., 2019). Because of this, insufficient protein consumption has been associated with a greater muscle loss and accelerated loss of physical function in older adults (Hanach et al., 2019). Dairy products are convenient, inexpensive sources of high-quality protein that can make it easier for older adults to consume enough dietary protein, whether through whole foods or by supplementation (Hanach et al., 2019). Lack of physical activity and vitamin D deficiency have been identified as further risk factors for sarcopenia (Molnár et al., 2016).

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Effects of Protein Supplementation on Sarcopenia

        As people age, they often report loss of appetite and struggling to eat enough (Bauer et al., 2015). This can sometimes lead to micro- and macronutrient deficiencies (Bauer et al., 2015). Alongside vegetables and fruit, foods high in dietary protein seem to be among the ones that the elderly fall short on most often (Bauer et al., 2015). Nutritional supplements can be an easy way to prevent nutritional deficiencies or simply a convenient method when people do not want to cook, bite, chew, etc. (Bauer et al., 2015). Protein supplements come in many forms, for example whey protein isolate concentrate, casein protein, plan-based protein powders and so on (Bauer et al., 2015). These nutritional shortcomings and the simultaneous loss of muscle and physical function, could point towards a good reason for protein supplementation (Bauer et al., 2015).

But let’s look at some studies! A larger increase in relative lean body mass (muscle!) was observed in a study involving 116 physically active older adults following 12 weeks of protein supplementation with milk protein, in comparison to the control group that received an iso-caloric placebo, meaning the other group received a shake with the same calories but less protein (Ten Haaf et al., 2019). However, no differences between the two groups were seen when it comes to strength and performance measures (Ten Haaf et al., 2019).

Contrary to the previous findings, supplementing with whey protein did not fight the deterioration of muscle mass in a study with 218 older adults with sarcopenia (Björkman et al., 2020). In this study the test subjects were split into 3 groups of either ‘no supplementation’, an iso-caloric placebo or supplementing with 2 x 20g of whey protein per day (Björkman et al., 2020). The test supplements seemed to have no effect on performance or lean body mass. It is to be noted, that the participants of this study were older than the participants of the milk-protein study, with the age ranging from 75-96 years in comparison to the 67-73 years in the previous study, which could be an indication of a more advanced level of sarcopenia among these participants.

Nonetheless, in a different study with 66 women between the ages of 60 and 80, whey protein supplementation (2 x 200ml with 27g hydrolyzed whey protein) pre- and post-resistance training over the course of 12 weeks, led to increased muscle mass and functional capacity in comparison to the placebo group that received an iso-caloric beverage containing carbohydrates (Nabuco et al., 2018). Findings regarding appendicular muscle mass increase (AMMI) and performance were congruent with a similar study, involving 56 sarcopenic adults that received a leucine enriched whey protein supplementation over the course of 12 weeks (Lin et al., 2021).

A much shorter study, only 10 days in duration, where 31 elderly men (70-75 years old) supplemented with soluble milk protein or casein protein, showed an increase in muscle protein synthesis (Walrand et al., 2016). The participants were split into an ‘adequate protein group’ versus a ‘high protein group’ (Walrand et al., 2016). It is unclear whether the two groups consumed an iso-caloric diet or not.

Lastly, a meta-analysis, so an analysis of multiple studies, by Hanach et al. (2019) examined the mean difference in mean change of appendicular muscles mass (AMM). The 8 trials that were included had a total of 444 participants supplementing with dairy protein and 457 participants in control groups. The results showed a significantly higher increase in AMM in the supplementation group compared to the control group (Hanach et al., 2019). Types of protein supplementations that were included in this analysis were whey protein (ranging from 20-40g per day), milk protein concentrate (30g) or a milk-based protein matrix (33g) in addition to some whole food-based protein interventions (ricotta cheese and skim-milk) (Hanach et al., 2019). All control groups received an iso-caloric supplement (Hanach et al., 2019). What should be noted though, is that not all participants of all trials were considered previously sarcopenic, which means the onset of muscle loss had not officially been diagnosed yet (Hanach et al., 2019).

Even though there are some conflicting findings, most of the research seems to suggest that protein supplementation, whether with milk protein, whey protein, or casein protein may lead to an increase in appendicular muscle mass and strength in elderly individuals.

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Effects of Protein Supplementation in Combination with Vitamin D on Sarcopenia

        As mentioned, vitamin D also plays a significant role in retaining muscle mass and function (Rondanelli et al., 2016). It stimulates muscle protein synthesis, improves strength and balance, improves neuromuscular function, and decreases inflammation, which has been associated with a reduction in muscular strength in the elderly (Rondanelli et al., 2016). Because of this, many interventions that aim to prevent sarcopenia include the supplementation of Vitamin D.

For example, a 12-week randomized, double-blind, placebo-controlled supplementation trial showed that supplementation with whey protein and vitamin D in conjunction to age-appropriate exercise led to significantly higher increases in fat free mass and strength when compared to the placebo group (Rondanelli et al., 2016). The supplement contained 22g of protein and 100IU of Vitamin D3. It is to be noted that the supplement also contained 10.9g of essential amino acids, including 4g of leucine (Rondanelli et al., 2016).

Another randomized, double-blind, placebo-controlled trial also tested the effects of vitamin D and leucine enriched whey protein on measures of sarcopenia (Bauer et al., 2015). The participants (380 older adults) were split into two groups. The protein group received a supplement containing 20g of whey protein and 800IU vitamin D to consume twice a day, whereas the control group received an iso-caloric product (Bauer et al., 2015). After 13 weeks, the conclusion was drawn that the oral nutritional supplement led to improvements in muscle mass and lower-extremity function among sarcopenic older adults (Bauer et al., 2015). Note that the supplement also contained 3g of total leucine and a mixture of other vitamins, minerals, and fibers that the placebo did not contain, which again, could also be influencing these findings.

Vitamin D, leucine and amino acids are not the only additions that have been made to protein supplementations in various studies. Nilsson et al. tested a five-ingredient supplement concerning its effectiveness in overall muscle mass and strength in old age (2020). The 32 men either received a supplement containing 24g of whey protein, 16g of micellar casein, 3g of creatine, 20ml of fish oil and 1000IU of Vitamin D3 or an iso-caloric placebo (Nilsson et al., 2020). The test results after 12 weeks of this nutritional protocol paired with at home-based exercises showed an improvement in lean mass, muscle fiber size, muscle to fat ratio, strength, and performance in older males compared to the control group that completed the same exercise regime (Nilsson et al., 2020).

Furthermore, vitamin E has previously been linked to affecting muscle strength of the elderly (Bo et al. 2019). Hence why it is not surprising, that this was another vitamin added to a whey protein and vitamin D supplement that the participants of a 6-month randomized, double-blind, placebo-controlled trial with 60 sarcopenic older adults received (Bo et al. 2019). The results showed that compared to the placebo group, nutritional supplementation can significantly improve relative skeletal mass index, muscle strength and anabolic markers in older adults with sarcopenia (Bo et al. 2019).

What the previously mentioned studies fail to address is whether an increase or retention in muscle mass and strength can also be achieved without supplementation and through the same protein content through whole food-based nutrition only. Lin et al. evaluated whether a diet with high protein and vitamin D supplementation would lead to better improvements than additional protein intake via diet (2021). The 56 sarcopenic, participating elderly individuals were told to reach a protein intake of 1.2-1.5g per kg of bodyweight per day (Lin et al., 2021). After 12 weeks the conclusion was drawn that, as long as sufficient protein is consumed, appendicular muscle mass can be improved, regardless of whether this is through whole foods or whey protein and vitamin D supplementation (Lin et al., 2021). It is to be noted that in both groups total calorie intake increased in both groups, compared to pre-trial nutrition, which in and of itself could be a contributing factor to muscle mass and performance increase (Lin et al., 2021).

Additionally, Wright at al. assessed in a 12-week isocaloric trial whether a high protein diet containing three whole eggs per day, or a normal protein diet void of eggs had any effect on muscle composition in 22 older adults between the ages of 65 and 75 (2018). The intervention led to a total reduction in body weight in both groups, however lean body mass was only retained in the high protein diet. It was concluded that in a caloric deficit a high protein diet may not lead to an increase in muscle mass in older adults but can be helpful in retaining muscle mass (Wright et al., 2018).

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Effects of High Protein Diets in Combination with Physical Activity on Sarcopenia

        The majority of the research examined so far points towards benefits of a higher protein diet for fighting sarcopenia. However, most of the aforementioned studies also include one other critical component – physical activity.

        Resistance training for example, has been identified as another potent muscle anabolic stimulus, which increases muscle protein synthesis within 2-3 hours after exercise (Makanae & Fujita, 2015). In their review, Makanae and Fuijita lay out the importance of providing both – the muscle building stimulus through the exercise component, and the provision of essential amino acids, for example through whey or casein protein – to achieve an accumulative effect when it comes to stimulating muscle protein synthesis, hypertrophy and preventing sarcopenia (2015).

        These findings were supported in a randomized clinical trial with pre-conditioned older women (Nabuco et al., 2018). These women underwent an initial eight weeks of resistance training only, followed by a resistance training and supplementation phase, to isolate the effects of supplementation (Nabuco et al., 2018). The resistance-training-only phase showed increases in muscular strength, however, these changes were largely attributed to the neurological adaptation component relating to motor learning (Nabuco et al., 2018). The following supplementation phase showed that resistance training paired with supplementation provided a larger increase in muscular strength when compared to the resistance training only phase and compared to an isocaloric placebo (Nabuco et al., 2018). Furthermore, it was noted that training experience may increase the effectiveness of protein supplementation for fat free mass and muscular strength (Nabuco et al., 2018).

        More evidence for the advantage of combining physiotherapy-based resistance training with a nutritional intervention when it comes to increasing muscle strength and improving skeletal muscle mass, was found in a 3-month trial with 34 elderly patients in a long-term care facility, whereas resistance training alone did not result in significant improvements (Molnár et al., 2016). Whether or not the exercise regime takes place at home or in a gym does not seem to play a role. Nilsson et al. demonstrated that a home-based, un-supervised resistance training can be just as effective in some cases (Nilsson et al., 2020).

        Lastly, even low-intensity cardiovascular activity, such as walking, in combination with a high protein diet seems to lead to an improvement in physical performance and an increase in lean body mass, as demonstrated in a 12-week trial with 116 older adults (Ten Haaf et al., 2019).

Although several studies were found that evaluated the effectiveness of combining physical activity with protein supplementation or a higher protein diet, none of them had control groups that were on a high protein diet without a training component, which could be seen as a limitation to the research examined.

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The Takeaway

With this review we conclude that research establishes dietary protein as an important factor for fighting the loss of muscle (sarcopenia) and therefore for the retention or even increase in muscle mass and function in older adults. Maintaining muscle mass and function through dietary protein can be regarded as a successful intervention strategy, helping to enhance quality of life as we age, which is often hinged on independence of the individual and the ability to continue with everyday tasks and recreational activities (Santilli et al., 2014). As evidence mounts that retaining muscle mass and strength through dietary protein is effective, protein supplementation appears to be an easy and efficient way for elderly population to increase protein consumption (Ten Haaf et al., 2019). However, the same results can be achieved through an equivalent protein component of a whole foods diet (Lin et al., 2021).

        The literature also reflects that it may be beneficial to combine a diet high in protein with other micronutrients that elderly people tend to be deficient in. Vitamin D supplementation in particular showed a positive correspondence with the dietary protein when it comes to fostering the retention or growth of muscle mass and function (Nilsson et al., 2020). Other supplements such as vitamin E, omega 3, creatine, or leucine also showed promising results.

        Furthermore, it can be concluded that combining a diet high in protein with physical activity, especially resistance training, appears to be the best intervention strategy by far when it comes to fighting sarcopenia in older adults. It seems clear that stimulating muscle protein synthesis through a training component and then providing the necessary amino acids through diet to build up muscle tissue is a great way to combat the loss of muscle mass and function as we age (Makanae & Fujita, 2015). Resistance training, whether home-based or gym-based, may provide slightly better adaptations, however, even low-intensity cardiovascular activity was found beneficial for retaining muscle mass and function (Ten Haaf et al., 2019).

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