High-Protein Diets: More Than a Tool for Athletes? Older Adults

TL;DR

  • Aging is associated with a reduced MPS response to protein intake, termed “anabolic resistance.”
  • Older adults should aim for a protein intake of 1.2-1.6 g/kg/d to mitigate age-related declines in skeletal muscle mass and muscular strength
  • For both practical and mechanistic reasons, it is advised to evenly distribute total daily protein intake over multiple meals
    • Each meal should contain ≥ 0.40 g of protein/kg body weight
  • Suboptimal doses of protein can be supplemented with 3-5 g of leucine to maximize the MPS response
  • Creatine supplementation can augment the benefits of resistance exercise and may possess beneficial effects independent of resistance exercise through its ability to act as an antioxidant
  • Omega-3 supplementation can enhance the anabolic response to nutrition and physical activity with relatively high doses (3-5 g/d)

Introduction

If you’re new to this series, I encourage you to begin with part 1, as I provided a bit of background on high-protein diets, including their safety and what qualifies a diet as being “high” in protein.

In this installment, I’ll be going into depth on the importance of protein intake for another growing population: older adults. 

Aging is characterized by a decline in skeletal muscle mass and a loss of muscular strength, collectively termed “sarcopenia.” Sarcopenia is a consequence of muscle protein loss resulting from an imbalance between muscle protein synthesis (MPS) and muscle protein breakdown (MPB) and manifests primarily as a reduction in type II muscle fiber size.

The condition begins around the fifth decade of life and the losses accelerate with advancing age. It is strongly associated with an increased incidence of falls, loss of independence, increased risk of age-related comorbidities, and premature mortality. 

With the enlargement of the world’s older population, sarcopenia is becoming a serious global public health problem. To attenuate its direct and indirect impact, it’s critical to define strategies that help to maintain or slow the loss of skeletal muscle mass.

The main anabolic stimuli for skeletal muscle are exercise and protein intake. As alluded to by the title, I am going to be focusing on the role of protein intake. 

While there will be a couple of references to exercise, I will not be going into depth on specific training strategies. As a general guideline, the World Health Organization recommends at least 150 minutes of moderate-intensity physical activity per week as well as resistance exercise at least twice per week.

The Recommended Dietary Allowance (RDA) is the estimated amount of a nutrient per day considered to meet the requirements of 97.5% of healthy individuals in each life-stage and sex group. The protein RDA for adults (including older adults) is set at 0.8 grams per kilogram of body weight per day (g/kg/d).

To be clear, the RDA is by no means the optimal intake. It is the minimum amount to sustain essential functions. To this point, there is a growing body of evidence that suggests the protein RDA is inadequate for older adults (if the goal is to thrive, not just survive, I would argue the RDA is inadequate for all adults).

Anabolic Resistance

Food ingestion strongly increases MPS rates for a period of 3-5 hours, allowing net muscle protein accretion. As such, the postprandial increase in MPS rate is believed to be a key regulatory factor for the maintenance of skeletal muscle mass.

Anabolic resistance is the inability of an anabolic stimulus (e.g., protein intake, muscle contraction) to stimulate MPS and occurs with increasing age. Current research on the topic suggests there are distinct differences in the responsiveness to protein intake between old and young muscle.

A retrospective, cross-sectional study using data from six previously published studies, found that postprandial MPS rates were 16% lower in older (74 years) compared with younger men (22 years). 

In each study, the same absolute amount (20 g) and type (casein) of protein were consumed. Despite it being a greater relative dose (per kg of lean body mass) in the older group, these subjects showed a more than 3-fold smaller capability to elevate MPS rate in response to feeding. 

Corresponding with this, another cross-sectional analysis of six studies by Moore et al. reported that when expressed relative to body weight, the amount of protein at which MPS reached a plateau was ~68% higher in older compared with younger adults. When expressed relative to lean body mass (LBM), the figure rose to ~140%.

In combination, these analyses display that older adults require significantly more protein to maximize MPS at rest. Similar findings have been reported following exercise as well.

Several studies have shown that physical activity performed before protein intake augments the subsequent anabolic response to feeding. 

For example, resistance exercise performed until muscular failure has been shown to confer a “sensitizing effect” and bolster the feeding-mediated MPS response for at least 24-hours post-exercise. 

Additionally, a 45-minute bout of low-intensity aerobic exercise has been shown to improve endothelial function, Akt/mTOR signaling, and muscle perfusion, and ultimately, enhance MPS response to the intake of amino acids in older adults.

Similar to the evidence above, which states that older adults need a greater amount of protein to maximize the MPS response at rest, while 20 g of protein from a high-quality source is sufficient to maximally stimulate MPS in young adults following exercise, it is inadequate for older adults. 

Yang et al. showed that 40 g of whey protein after resistance exercise increased myofibrillar MPS to a greater extent than 20 g. Compared with exercise without feeding, rates of MPS were about 13, 44, and 91% greater with post-exercise ingestion of 10, 20, and 40 g of whey protein, respectively.

Overall, whether at rest or after exercise, a greater amount of protein is needed in older adults to maximize the MPS response. 

Now, mechanistically, why might this be? What physiological changes occur with aging that dysregulates the MPS response to normally robust anabolic stimuli?

Irrespective of reduced physical activity levels with aging (a major factor), anabolic resistance may be a consequence of impairments in protein digestion and amino acid absorption, increased splanchnic amino acid retention (which suggests fewer amino acids are available for MPS), impaired muscle perfusion reducing delivery of amino acids to the muscle, and reduced uptake of amino acids by the muscle.

Additionally, differences in the availability of key regulatory proteins (e.g., mTORC1) may contribute to the reduced capacity of the MPS machinery to sense a nutrient signal in senescent muscle. 

Corresponding with a blunted MPS response, there is some evidence to suggest that sarcopenia may also be related to a reduced sensitivity to the inhibitory effect of insulin on MPB.

Wilkes et al. reported a 12% reduction in MPB  in response to insulin in older adults compared with a 47% decrease in younger adults. 

The authors state, “in real terms, the degree of insulinemia achieved … is comparable with that expected after a ‘healthy’ low-glycemic index meal, yet it would appear from these results that the normal suppression of proteolysis by insulin at this concentration is impaired with aging.”

With unfavorable alterations on both sides of the muscle protein balance equation, it’s essential to ensure adequate consumption of protein on a daily basis in this population. If the RDA is short of optimal, then how much protein should older adults consume to combat the advent of sarcopenia? 

How Much Protein Should Older Adults Consume?

In an acute trial, Kim et al. examined the effects of two different levels of protein intake on whole-body protein turnover and MPS. Older adults were randomized to consume either 0.8 (1RDA) or 1.5 (2RDA) g/kg/d. The use of multiple measurements here is valuable because as mentioned earlier, sarcopenia is a consequence of muscle protein loss resulting from an imbalance between MPS and MPB.

By combining measurements, the researchers were not only able to distinguish between the muscle response of synthesis from the whole-body response, but the rate of protein breakdown, and thus net balance.

Interestingly, it was found that MPB was reduced similarly in all groups, however, the net balance was greater with 2RDA due to increased whole-body protein synthesis and MPS.

These positive findings in the short-term have been observed to translate into clinically relevant benefits in the long-term as well. 

Mitchell et al. compared the effects of the protein RDA to twice this amount (2RDA) on skeletal muscle mass and physical function in men aged > 70 years.

Despite both diets resulting in a slight energy deficit (~200 kcal/day), 2RDA led to increases in LBM (1.49  ± 1.30 kg) and knee-extension peak power output. In comparison, there was a loss of appendicular lean mass of ~600 g in the RDA group. Moreover, decreases in peak power occurred. 

Following suit, a 12-week intervention comparing three different levels of protein intake (0.8, 1.2, and 1.5 g/kg/d) found improved appendicular skeletal muscle mass (ASM) and gait speed with an intake of 1.5 g/kg/d.

Overall, the available evidence indicates that older adults require a greater amount of protein than the RDA. The European Society for Clinical Nutrition and Metabolism recommends at least 1.0-1.2 g/kg/d for healthy older adults, 1.2-1.5 g/kg/d for older adults who are malnourished or at risk of malnutrition, and even higher amounts for those with severe illness or injury.

In my opinion, 1.2 g/kg/d is the bare minimum that all older adults should consume. Based on the above, 1.5-1.6 g/kg/d seems to be closer to optimal and should be the goal if satiety allows.

Dose & Quality

Within the confines of a protein intake of 1.5-1.6 g/kg/d, there are a few factors to consider: the quantity or dose of protein at each meal, the frequency of consumption, and the source of protein. 

In a seminal retrospective analysis by Moore and colleagues, they reported that older adults require roughly 0.40 g/kg of protein to maximally stimulate MPS with feeding, while 0.24 g/kg is sufficient for younger adults with a couple of caveats.

These values reflect the estimated average requirement to maximally stimulate MPS, which led the authors to state, “the acute protein intake may be as high as ~0.60 g/kg for some older men (depending on the presence of potential contributing factors to the anabolic resistance of MPS) and ~0.40 g/kg for some younger men.”

Furthermore, the findings are based on high-quality, rapidly digested animal-based protein. Protein from animal sources provides all nine of the essential amino acids (EAA), whereas protein from legumes, grains, nuts, seeds, and vegetables can be deficient in one or more of the EAA.

Also, animal proteins generally have a higher content of leucine, which as previously discussed in part 1, acts as a “trigger” to stimulate MPS in response to feeding. 

The quantity of leucine in a meal becomes even more critical for older adults. Available evidence suggests that while young adults are responsive to small quantities of ingested leucine (< 1 g), older adults should consume ≥  2.5 g per meal to raise MPS above basal levels

It stands to reason that a large part of why older adults require a higher dose of protein to maximally stimulate MPS has to do with the need for a higher amount of leucine to ignite the process.  

Other important factors to consider outside of the EAA content of a protein source are splanchnic extraction and digestibility.

There may be greater splanchnic extraction of amino acids from plant-based proteins, which can result in a smaller fraction of the amino acids ingested becoming available for MPS. 

Moreover, plant-based proteins generally exhibit lower digestibility. As a result, less of the protein is effectively digested and absorbed, leading to lower postprandial availability of amino acids for MPS.

In light of these factors, animal-based proteins such as whey, casein, and beef have been shown to stimulate postprandial MPS to a greater extent than plant-based protein sources in older adults.

To add, it has been found that roughly twice as much wheat protein hydrolysate is required to stimulate a similar MPS response to whey protein.

For these reasons, vegetarians and vegans, or omnivores consuming a meal primarily composed of plant-based protein sources, should likely target the top-end range of protein intake at meals, consuming upwards of 0.60 g/kg. 

Distribution

In combination, the recommendations for protein dose per meal and total daily protein intake allude to distribution (i.e., frequency of protein feedings over the course of the day) being a crucial factor in the equation to minimize age-related decreases in skeletal muscle mass. 

Many older adults consume low, medium, and high amounts of protein with breakfast, lunch, and dinner. This information suggests that dinner may be the only meal of the day that contains enough protein to induce a robust stimulation of MPS.

Mechanistically, it stands that an even distribution of protein that provides a sufficient dose at each meal (≥ 0.40 g/kg) would be superior to a skewed pattern due to eliciting a maximal postprandial MPS response more frequently.

In contrast to this hypothesis, two randomized controlled trials have reported a benefit of an uneven protein distribution pattern on LBM. However, there’s a bit more to the story. Let’s dig into the details.

In the first, Arnal et al. fed 15 elderly women 1.05 g/kg/d of protein in either a  pulse or spread diet for 14 days. In the pulse pattern, protein intake was distributed across three meals with most of the daily intake provided in one meal (79% at noon meal). In comparison, the protein spread pattern featured four meals with a distribution of 22%, 31%, 19%, and 28% at 0800, 1200, 1600, and 2000, respectively. 

At the end of the intervention, it was found that LBM decreased significantly from baseline in the spread group (-0.33 ± 0.10 kg) and was maintained (0.10  ± 0.11 kg) in the pulse group. Why might this be?

In the spread group, protein intake at each meal was approximately 12-20 g or 0.23-0.33 g/kg, which based on the previously stated evidence, is insufficient to maximally stimulate MPS in response to feeding. 

In contrast, the noon meal contained about 50 g of protein in the pulse group, which would be enough to facilitate a maximal MPS response. This sole difference likely facilitated the meaningful difference in LBM.

Likewise, Bouillanne et al. compared a pulse or spread protein distribution in elderly malnourished or at risk patients for six weeks. The spread group consumed 12, 21, 14, and 21 g of protein at 0800, 1200, 1600, and 1900 h, respectively. At the same times of day, the pulse group consumed 5, 48, 2, and 11 g of protein.

It was found that LBM significantly increased in the pulse group (0.91 kg) and decreased in the spread group (-0.41 kg). Again, it’s plausible that these outcomes may be explained by the fact that only the noon meal in the pulse group contained enough protein to maximally stimulate MPS.

Observational evidence lines up with these findings as well. Data from the 1999-2002 NHANES show that more frequent consumption of meals containing at least 30 g of protein is associated with greater leg lean mass and knee extensor muscle strength. 

Similarly, more frequent eating occasions with ≥ 0.25 g/kg or ≥ 30 g of protein have been associated with a significantly lower physical disability risk.

Meanwhile, controlled interventions comparing an even distribution—with sufficient quantities of per-meal protein—to a conventional skewed intake in older adults are lacking. To my knowledge, there is one study that fits the criteria and the results were equivocal.

In the formerly mentioned trial by Kim et al., they did not observe any effect of protein distribution on net protein balance when consuming 2RDA (i.e., 1.5 g/kg/d). Otherwise stated, an even distribution of protein (33% of total protein at breakfast/lunch/dinner) produced comparable outcomes to a skewed distribution (15/20/65% of total protein at breakfast/lunch/dinner).

Given the adequate per meal dose of protein (~0.5 g/kg) and total daily intake, the findings are puzzling. It has been speculated that the results are a product of the protein being provided in mixed macronutrient meals. Mixed macronutrient meals typically contain proteins of varying quality, and are associated with alterations in amino acid absorption and reduced amino acid availability.

It’s also possible that protein distribution is less important in the context of energy balance. For example, Murphy et al found that a balanced pattern of whey protein distribution (three 25 g servings) stimulated MPS to a greater extent than a skewed distribution (10 g, 15 g, 50 g) during two weeks of mild energy restriction, despite 25 g being an insufficient dose to maximally stimulate MPS.

Based on the available evidence, a hierarchy of importance emerges. First and foremost, an adequate total daily protein intake should be met. Following this, individuals should aim for a sufficient dose of protein at multiple meals throughout the day, and this practice may increase in importance during a period of energy restriction. 

While there isn’t much direct evidence to support it, the mechanistic rationale is strong for an even protein distribution, and at the very least, it is practical. It is more feasible to consume 1.5-1.6 g/kg/d by splitting it up into 3-4 meals containing 30-40 g of protein than to consume > 60 g in a single meal. 

Leucine

Higher protein intakes might not be feasible for older adults for an assortment of reasons, such as reduced appetite, poor dentition, dysphagia, food preferences, food insecurity, etc. As such, it’s important to investigate other nutritional strategies to diminish the rate of skeletal muscle mass deterioration with aging.

As previously mentioned, the leucine content of a protein source, or the total amount of leucine between protein sources at a meal, is a principal concern for older adults. Could supplementing a low-protein diet or a diet composed of low-quality sources with leucine be an effective strategy to overcome anabolic resistance?

It has been shown that adding leucine to a suboptimal dose of protein can enhance the MPS response. For example, adding leucine to 10 g of milk protein elicits a comparable MPS response to a beverage containing 25 g of whey protein isolate

Furthermore, the addition of 2.5 g of leucine to 20 g of casein protein and 3.1 g of leucine to 15 g of milk protein has been shown to enhance acute MPS rates in older adults.

In the short-term, it’s clear that increasing the leucine content of a protein-feeding has a dramatic impact on the MPS response. Specifically, adding leucine to a suboptimal dose of protein can elicit a similar MPS response to that of an adequate dose of protein. 

While results from acute trials are consistent and impressive, it is still necessary to dive into long-term interventions to determine if these findings translate into clinically relevant outcomes such as the preservation of LBM and muscular strength. 

An early study in this line of research with promising findings comes from Børsheim et al. in 2008. In this trial, glucose intolerant older adults ingested 11 g of EAA + arginine twice per day for 16 weeks. The EAA mixture contained 3.95 g of leucine per serving, resulting in an addition of ~8 g of leucine to the subjects’ daily diet.

Over the course of the intervention, there were no reported changes in physical activity or dietary intake, and significant increases in LBM, muscle strength and physical function occurred.

LBM increased gradually, reaching a peak at week 12 (1.14 ± 0.36 kg). There was then a drop, finalizing as a 0.60 ± 0.38 kg increase at week 16. Also, the lower extremity strength measure score (sum of individual knee flexors and extensors 1-repetition maximum) increased by an average of 22.2 ± 6.1%. With that said, this trial had a major limitation: there was no control group.

This work has been followed up by more recent (and higher quality) trials, which have also reported a positive effect of leucine supplementation on various outcomes.

Ispglou et al. randomized elderly men to receive one of the following each day for three months: EAA mixture (20% leucine), EAA mixture (40% leucine), or placebo. For the supplement groups, a relative dose of 0.21 g/kg/d of EAAs was consumed daily and split between two equal doses at breakfast and dinner.

Based on the average body weight reported for each group, this would mean participants in the 40% leucine group consumed ~15.6 g of EAA containing ~6.24 g of leucine daily (~3.1 g with breakfast and dinner). In comparison, participants in the 20% leucine group consumed ~14.8 g of EAA containing 3 g (~1.5 g with breakfast and dinner) of leucine daily.

In comparison to placebo, the 20% and 40% leucine supplement groups significantly improved aspects of functional status. However, only significant gains in LBM occurred in the group consuming the 40% leucine supplement (1.1 ± 1.1%). 

In another study, older adults were randomized to receive either 10 g leucine/day (5 g ingested after lunch and dinner) or a placebo, plus resistance training for 12-weeks. The outcomes of interest were isometric leg strength, functional status, and body composition.

It was found that baseline protein intake was not significantly different between groups (1.25 g/kg/d and 1.20 g/kg/d in the leucine and placebo groups, respectively), and after four weeks, a 16% increase in protein intake was observed in the placebo group. 

Despite greater protein intake, improvements in leg muscle strength and functional status were superior in the leucine group. Although not statistically significant, the authors point out that these changes should be considered clinically significant. Likewise, changes in triceps skin fold and mid-upper arm muscle area were in favor of the leucine group.

Lastly, an eight-week trial in post-stroke older adults with sarcopenia, found that consuming 3 g of leucine within 30 minutes after sit-to-stand exercise led to significantly greater improvements in sit-to-stand performance, handgrip strength, and appendicular skeletal muscle mass.

In opposition to these four studies, other research has failed to find a meaningful impact of leucine supplementation on measures of LBM, muscular strength, and physical function.

For instance, Verhoeven et al. did not observe an effect of ingesting 2.5 g of leucine at each main meal (7.5 g supplemental leucine per day) on whole-body or limb muscle mass over 12 weeks in healthy older adults. Consequently, there were no changes in 1RM leg press or leg extension strength either.

Another study from the same lab assessed the effects of the same leucine supplementation protocol over a longer duration (six months) in older adults with type 2 diabetes. Again, LBM did not change over time or differ between groups, neither did 1RM leg press or leg extension strength.

When interpreting the outcomes of these studies, there are a few factors to consider: the health status of the subjects,  protein intake, and the timing and quantity of leucine ingestion. 

It has been speculated that if habitual daily protein intake is significantly greater than the RDA (≥ 1.0 g/kg/d) then the meal-induced MPS response may already be maxed out and supplemental leucine will not have an additive effect. 

However, over the span of positive and null findings mentioned above, all reported protein intakes were much greater than the RDA, ranging from 0.95-1.4 g/kg/d. Furthermore, the greatest intakes were observed in the trials by Yoshimura et al. (1.4 g/kg/d) and Trabal et al. (1.28 g/kg/d), which both found a benefit to supplementing with leucine. 

A potential caveat is that Yoshimura et al. featured post-stroke patients with sarcopenia. While supplemental leucine may be beneficial with a daily protein intake of 1.4 g/kg/d in this specific population, the same might not hold true for healthy older adults.

In further conflict with the aforementioned theory, Murphy et al. found that 5 g of leucine co-ingestion with daily meals enhances MPS in older men, regardless of whether their protein consumption was 0.8 or 1.2 g/kg/d.

It’s plausible the trials that did not detect a benefit of leucine supplementation failed to provide a sufficient dose. In both cases, 2.5 g of leucine was consumed with mixed-macronutrient meals. It has been proposed that the dose of leucine required to enhance MPS may be greater when added to a mixed-macronutrient meal compared with an isolated protein or EAA beverage. 

The addition of 5 g of leucine to mixed-macronutrient meals has been shown to induce a lower peak plasma leucine concentration (∼450 μM) compared with that induced by the addition of 2.8 g leucine to an EAA-containing beverage (∼700 μM), despite providing almost double the amount of leucine. 

As such, the addition of 2.5 g of leucine to mixed-macronutrient meals is likely insufficient to enhance the MPS response in older adults.

In sum, in order for leucine supplementation to translate into meaningful benefits in older adults, at least 3 g should be consumed with meals, and 5 g may be necessary depending on the quantity and quality of protein co-ingested. 

Bonus Round: Other Supplements

Regular resistance exercise and a high-protein diet are the cornerstones of maintaining muscle mass, physical function, and strength with aging, but there are a plethora of barriers that can make implementing these interventions unfeasible for many. Therefore, new and effective therapies with minimal side effects are needed to protect against sarcopenia.

Creatine is a naturally occurring nitrogenous organic acid that is endogenously synthesized from reactions involving the amino acids arginine, glycine, and methionine in the liver and kidneys. The vast majority of creatine resides in skeletal muscle (~95%) with trivial amounts in the brain and testes. Metabolically, creatine combines with inorganic phosphate to form phosphocreatine, which helps resynthesize and maintain adenosine triphosphate levels.

It’s no secret, creatine supplementation alongside resistance training is a potent combination. Several metaanalyses have been conducted, each displaying impressive effects. Collectively, they indicate that the addition of creatine to resistance training can significantly increase muscle mass (1.21 kg) and maximum strength. 

There is also promise for improving metrics of physical function and reducing the risk of falls. A meta-analysis of six studies found that daily supplementation of 5 g of creatine in conjunction with resistance exercise 2-3 times per week improved sit-to-stand performance (a good predictor of reduced risk for falls) by 23%, while resistance training with placebo improved performance by 16%. 

There are other potential benefits to be derived from creatine supplementation as well and they may be obtained independent of resistance exercise. 

The aging process is associated with damage to mitochondria and elevated and sustained low-grade inflammation otherwise known as “inflamm-aging.” Inflammatory cytokines (i.e., TNF-⍺ and IL-6) are known to inhibit MPS, and MPS in older adults is inversely associated with levels of inflammatory cytokines. 

There are a few reports that have supported the use of creatine as an anti-inflammatory agent. In rodent models, creatine has shown the ability to downregulate inflammatory cytokines. In addition, through its ability to act as an antioxidant, creatine appears to protect against mitochondrial damage caused by oxidation and this may translate to reduced inflammation with aging

A recent review examined the body of evidence on the benefits of creatine supplementation without resistance exercise. It noted that five studies have shown creatine to have a greater effect than placebo, while another five reported a similar effect. 

Ultimately, creatine supplementation should be a no-brainer for older adults, regardless of whether or not they’re performing resistance training. It’s cheap, possesses virtually zero risks, and has a wide variety of potential benefits.

Another group of nutrients with known anti-inflammatory properties that may help attenuate the rate of decline with sarcopenia are omega-3 fatty acids (n-3 PUFA). The two main n-3 PUFA are eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are commonly referred to as fish oil.

While there is a host of research demonstrating that increasing n-3 PUFA can reduce inflammation, they appear to preserve muscle mass and function in older adults via other mechanisms. 

Currently, the primary causal mechanism to explain the anabolic action of n-3 PUFA relates to modifying the lipid profile of the muscle phospholipid membrane and subsequently upregulating the activity of intracellular signaling proteins rather than an anti-inflammatory response. 

Daily supplementation with 4 g of n-3 PUFA (1.86 g EPA and 1.5 g DHA) for eight weeks has been shown to increase activation of the mTOR-p70s6k signaling pathway and enhance the MPS response to amino acids in older adults.  

Higher rates of MPS with daily supplementation of n-3 PUFA (5 g) were also observed during two weeks of leg immobilization in healthy young women, and this difference appeared to be responsible for attenuating skeletal muscle disuse atrophy.

Further, daily supplementation with 4 g of n-3 PUFA (1.86 g EPA and 1.5 g DHA) for six months was shown to have significant positive effects on muscle mass and strength in the absence of resistance exercise. The difference between n-3 PUFA supplementation and placebo for thigh muscle volume and muscle strength was ~3.5% and ~6%, respectively.

These notable findings have not been observed with smaller doses of n-3 PUFA. Daily supplementation with 1.3 g (660 mg EPA and 440 mg DHA) for 12 weeks failed to improve body composition, muscle strength, or physical performance in older adults. The same absolute dose over a longer time frame (six months) also failed to increase muscle strength, but it did have a beneficial effect on walking speed

On par with creatine, n-3 PUFA appears to have the potential to mitigate age-related deterioration of muscle mass and strength without resistance exercise. It also seems to augment the benefits of resistance exercise.

Rodacki et al. reported an additive effect of daily n-3 PUFA supplementation (2 g/d) when combined with resistance exercise in elderly women. While muscle strength (measured as peak torque) and functional capacity improved in all groups, these metrics improved to a greater extent in the groups that supplemented n-3 PUFA (ST90 and ST150).

On top of possessing the potential to bolster strength and functional capacity, daily supplementation with 3.9 g of n-3 PUFA (2.25 EPA:DHA ratio) for 16 weeks was found to decrease mitochondrial reactive oxygen species production, increase postabsorptive MPS, and enhance the anabolic response to a bout of exercise.

Notably, n-3 PUFA enhanced exercise stimulated MPS only in a fraction of individuals, the vast majority of which were women. Interestingly enough, there is other evidence that displays n-3 PUFA supplementation only has an effect in women.

Da Boit et al. reported significant increases in knee-extensor maximal isometric torque and muscle quality (calculated as torque per unit muscle cross-sectional area) in women, but not men supplementing 3 g of n-3 PUFA daily (2.1 g EPA and 0.6 g DHA).

Together, these results suggest that n-3 PUFA supplementation can enhance the anabolic response to nutrition and physical activity in older adults, making it a potentially worthwhile supplement option. However, a relatively high dose (3-5 g/d) is needed to elicit these effects

Conclusion

The aging process is characterized by a decline in skeletal muscle mass and loss of muscular strength collectively termed “sarcopenia.” To attenuate the rate of loss, the best tools available are exercise and protein intake. 

The protein RDA is set at 0.8 g/kg/d for adults, however, a growing body of evidence displays that this amount is inadequate for older adults due to a reduced MPS response to protein intake known as anabolic resistance.

As a consequence, older adults not only need significantly more protein per day than the RDA, but they require a larger dose of protein per meal than younger adults to maximize the MPS response. 

Older adults should strive for a protein intake of 1.2-1.6 g/kg/d, evenly distributed over multiple meals featuring at least 0.4 g/kg. Those who are unable to meet the former, or consume the majority of their protein from plant-based sources, should consider the upper end of the daily intake range and aim for upwards of 0.6 g/kg at meals. Another option is to supplement meals with 3-5 g of leucine.

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