Older adults exhibit higher levels of muscle damage upon exercise compared to younger adults which can hamper them in pursuing an active lifestyle and accelerate sarcopenia (age-induced muscle degeneration).
Daily protein intake is an important factor for muscle repair yet more than 50% of physically active older adults do not reach the recommended protein intake of 1.2 g/kg/day plus an increasing number of individuals avoid animal based products due to environmental concerns.
Studies in young adults have shown that plant-based protein ingestion leads to increases in muscle mass after resistance training, comparable to whey protein. However, no studies have investigated the effect of plant-based protein supplementation on muscle damage markers in older adults after a bout of endurance exercise.
The recent randomised double-blind placebo-controlled trial, funded by the supplement firm NewCare, based in The Netherlands, therefore aimed to assess the effect of pea versus whey protein supplementation in comparison to placebo on exercise-induced increases in muscle damage markers in older adults in the days after endurance walking exercise.
Secondary outcome measures included differences in changes in muscle soreness, muscle strength and muscle mass.
The authors hypothesised that pea protein supplementation would be able to reduce muscle damage after endurance walking exercise in adults comparable to whey.
However they found pea protein did not attenuate exercise-induced muscle damage compared to placebo while the whey protein group showed lower serum creatine kinase (CK) levels. Neither of the applied protein supplementation strategies effected muscle strength, muscle soreness and skeletal muscle mass, likely due to the relatively short supplementation period.
The authors note, in explanation for these findings, that Leucine is known as one of the most important factors of protein synthesisand plant based proteins have a relatively low leucine content (7.1 ± 0.8%) compared to animal-based proteins (8.8 ± 0.7%), plus older adults are less responsive to the stimulus of a low dose of amino acid.
They add: "The effects of long-term plant protein supplementation on exercise induced muscle damage and body composition should be further explored in physically active elderly. Participants may also be exposed to a higher dosage of plant-based protein, whereas the protein quality in terms of digestibility and composition should be taken into account."
A total of 47 participants, aged 60+, were randomly allocated to a whey protein, pea protein or placebo supplement group. Participants were invited for 5 study visits at the department of Physiology of the Radboud university medical center. The exercise bout consisted of a self-selected 20–30 km walk to provoke muscle damage and muscle soreness. Supplement use was continued on the day of the exercise bout and on the three days thereafter.
Supplements were provided by NewCare (Waalwijk, The Netherlands) . Participants were instructed to consume 12.5 g of protein (i.e., 15 g of dry powder) in the morning and 12.5 g of protein in the afternoon/evening (or after exercise).
Measurements included blood samples, muscle soreness, muscle strength (handgrip and leg), and muscle mass, and were performed at baseline (before supplement use), pre-exercise (after a 10 day pre-load period of supplement use) and three times post-exercise (+24 h, +48 h and +72 h).
A total of 15 participants per subgroup completed the study (Participants were predominantly male (80%), aged 70 ± 6 years with a BMI of 24.2 ± 2.8 kg/m2).
The time-dependent exercise-induced increase in creatine kinase (CK) levels were significantly different between the three groups. Peak CK concentrations (+24 h) were significantly lower in the whey (175 ± 90 U/l) versus placebo (300 ± 309 U/l, p = 0.024) and pea supplemented group (330 ± 125 U/l, p = 0.022). No group differences (p = 0.25) or interaction effects (p = 0.54) were observed in LDH levels.
The authors note, in explanation for these findings, that older adults are less responsive to the anabolic stimulus of a low dose of amino acid intake than younger individuals and plant based proteins have a relatively low leucine content (7.1 ± 0.8%) compared to animal-based proteins (8.8 ± 0.7%). Leucine is known as one of the most important factors of protein synthesis and it also inhibits protein degradation. Previous studies have suggested that every protein supplement serving should contain at least 700 mg of leucine.
Given this study's standardised serving volume for every treatment arm, leucine content was lower for the pea versus whey protein supplement (900 mg versus 1150 mg, respectively). The difference of 250 mg of leucine between these supplements may have contributed to the distinct CK-response following exercise, the authors suggest. Fortifying plant-based proteins with leucine may be a promising strategy to limit exercise-induced muscle damage to a comparable extent as is found after whey supplementation.
These findings are contradictory to previous studies using other plant-based proteins, such as soy and oat, as an attenuated exercise-induced increase in CK levels was found compared to the placebo group. Potential explanations, apart from the difference in plant protein source, for these discrepant outcomes, may be the higher dosage of the protein that was used (42 gr/day versus 25 gr/day) and the younger age of study participants (<40 years versus >60 years) in previous work.
The authors note a number of limitations to this study. The protocol used for assessment of 1 RM for leg strength made it difficult to determine 1 RM of participants that reached the maximum of 200 kg or the last attempt which may have hampered the possible effect of protein supplementation on leg muscle strength. The study also had a relatively small population, which could result in less statistical power and the supplementation period could have been too short to have impact on secondary outcomes. Also, the study had a fixed protein supplementation dose (25 g/day) which increased daily protein intake to >1.0 g/kg/day in 93% of our participants. A personalised protein supplementation dose, based on the individual lean body mass may be more effective to achieve a maximal effective dose for all study participants.
They say the effects of long-term plant protein supplementation on exercise induced muscle damage and body composition should be further explored in physically active elderly. Participants may also be exposed to a higher dosage of plant-based protein, whereas the protein quality in terms of digestibility and composition should be taken into account.
Spoelder, M.; Koopmans, L.; Hartman, Y.A.W.; Bongers, C.C.W.G.; Schoofs, M.C.A.; Eijsvogels, T.M.H.; Hopman, M.T.E.
"Supplementation with Whey Protein, but Not Pea Protein, Reduces Muscle Damage Following Long-Distance Walking in Older Adults"