|
Researched
and Composed by
Jacob Wilson, BSc. (Hons), MSc. CSCS
Address correspondence to:
jwilson@abcbodybuilding.com
Journal of HYPERPLASIA
Research 6(3):
Published August 3, 2006
Abstract
Aging
appears to be associated with muscle tissue loss of an average of 0.5 to 2 % per
year after the age of 50. These muscle tissue losses appear to be related to a
loss of aging muscle tissue’s sensitivity to leucine’s stimulating effects on
protein synthesis. Currently research indicates that proper leucine
administration can reverse this lowered deficit back to levels of young
individuals. The purpose of this paper will be to analyze this research and to
provide practical applications for dietary habits for aging athletes.
Introduction
One of
the more frequent questions I receive to my email account and in person is “can
I still gain muscle at this age?” Typically my answer is that the evidence
supports the efficacy at bodybuilding at any age. However this paper will
address the situation from an in depth scientific perspective. Specifically the
paper discusses sarcopenia, which is the normal loss of muscle tissue mass after
the age of 50. It appears that after age 50 muscle tissue is generally lost at
a rate of 0.5-2 % per year, resulting in progressive loss of function in the
elderly.
Reasons for Sarcopenia
A major
area analyzed in sarcopenia is age related differences in indexes of protein
balance. In a classic study, Volpi and colleagues (2001) measured basal
(resting conditions in post absorbative states) rates of protein synthesis and
degradation in young (28 years of age) and elderly (70 years of age)
participants. It was found that leg volume was lower in the elderly than the
young suggesting muscle tissue loss. Surprisingly however no significant
differences were found in basal protein balance. In more detail there were very
small differences in protein synthesis between young and elderly participants.
The elderly tended to have slightly higher rates of protein synthesis (figure 1)
and degradation than the young, which when added together provided an equal
measure of protein balance.
Fractional synthetic rate in young and elderly men.
The
authors concluded that the differences in basal muscle protein turnover between
older and younger men do not appear to explain muscle loss that occurs with age.
However,
research since this time has indicated that it is the response of elderly to a
meal that is blunted with aging. Specifically the elderly respond with lower
protein synthesis and less suppression of protein degradation following a meal
compared to younger individuals, suggesting signaling deficits. For example
Katsanos et al (2005) had eleven elderly subjects (68 +/- 2 y) and 8 young
subjects (: 31 +/- 2 y) consume 7 g of EAAs. Results found no difference
between conditions during basal periods. However following ingestion of the 7
grams of EAAs the elderly had significantly lower protein balance than the young
individuals.
In a
follow up study Katsanos et al. (2006) administered 7 grams of EAAs to the young
and elderly. In condition 1 both groups were given an essential amino acid
mixture that contained 26 % leucine. In this condition protein synthesis was
increased in the young, but did not increase in the elderly. In condition 2 the
elderly were administered a 7 gram mixture of EAAs with the proportion of
leucine increased to 41 %. Results found that protein synthesis and net balance
were restored to levels seen in young individuals. This suggests that muscle
tissue loss in the elderly is related strongly to impaired leucine signaling,
and when leucine levels are increased the deficit in protein balance is
reversed.
It should be noted that the increased leucine did not increase protein synthesis
in the young individuals. The authors postulated that this is because the
increase in leucine was at the expense of lowering other EAAs. This contention
was supported by past studies in which the nearly 3 grams of leucine were
combined with a total mixture of 15 grams of EAAs. In that study protein
synthesis was double what occurred in the Katsanos et al. (2006) study, again
pointing to the supportive role of other EAAs.
Studies
have also compared acute and chronic supplementation of leucines on protein
balance. In an excellent experiment Dardevet et al. (2002) had young and old
rats consume their normal meals and measured Ubiquitin-proteasome dependent
proteolysis. Recall that Ub-proteolysis is the major pathway for the breakdown
of muscle tissue. Results found that the young rats decreased UB-proteolysis by
56 % in response to normal feeding while the elderly rats had no decrease in
degradation. However when the elderly rats were supplemented with 5 % leucine
they decreased markers of the UB-pathway as completely as the young rats!
Therefore it appears that when adequate leucine intake is given that the elderly
can completely reverse age related deficits in the capacity to lower protein
degradation. In a follow up study Rea (2003) found that 10 days of leucine
supplementation still maintained its effects on lowering protein degradation
suggesting the efficacy of chronic supplementation.
How can Elderly
Individuals Raise leucine intakes?
In the above studies elderly individuals and young were compared with levels of
essential amino acids corresponding to 7 grams, which is approximately 15 grams
of protein.
During this protocol the elderly clearly have deficits in protein synthesis and
degradation. However at higher doses this does not appear to be the case. For
example Paddon jones et al. administered 15 grams of EAAs and found that this
increased plasma amino acids by 300 %. These scientists found no significant
difference between the young and elderly in protein synthesis. The rationale is
that higher levels of EAAs and leucine may have saturated the system such that
it elicited a maximal response in the stimulation of muscle protein accretion in
both the young and the elderly.
Therefore it appears that at high enough doses of leucine and other EAAs that
both the young and elderly have similar responses. The implication is that the
elderly should consume a large enough dosage of EAAs each meal to saturate their
protein synthetic signaling pathways. This most likely occurs at around 15 to
20 grams of EAAs, or 30-40 grams of high quality protein per meal.
This contention is also supported in studies examining pulse feeding. Arnal et
al. compared feeding 80 % of an elderly group’s protein in one of their meals
compared to spreading their protein intake equally over all meals. It was found
that the pulse (80 % condition) feeding improved protein balance relative to the
spread pattern. The authors suggested that this was therefore a viable method
to enhance protein balance in the elderly. However it is the contention of the
current author that what was really demonstrated was that the elderly require a
high dose of leucine and supporting EAAs if they are to maximally stimulate
protein balance. It is predicted that if the elderly had consumed high protein
intakes in each of their meals that their protein balance would increase
proportionally to each of these feedings.
Conclusion
Elderly
individuals appear to be deficient to the anabolic signaling effects of food
intake. Specifically they are insensivite to leucine signaling. However when
leucine is supplemented the effects of protein balance are enhanced to levels of
young participants. It was suggested that elderly should consume 15 to 20 grams
of EAAs per meal, or 20 to 40 grams of protein per meal.
Combaret L, Dardevet D,
Rieu I, Pouch MN, Bechet D, Taillandier D et al. (2005). A leucinesupplemented
diet restores the
defective postprandial inhibition of proteasome-dependent
proteolysis in aged rat
skeletal muscle.
J Physiol
569, 489-499.
Katsanos CS, Kobayashi H,
Sheffield-Moore M, Aarsland A & Wolfe RR (2005). Aging is associated with
diminished accretion of muscle proteins after the ingestion of a small bolus of
essential amino acids.
Am J Clin Nutr
82, 1065-1073.
Katsanos CS, Kobayashi H,
Sheffield-Moore M, Aarsland A & Wolfe RR
proportion of leucine is
required for optimal stimulation of the rate of muscle
essential amino acids in
the elderly. Am
J Physiol - Endocrinol Metab
Dardevet
D, Sornet C, Bayle G, Prugnaud J, Pouyet C, Grizard J. Postprandial stimulation
of muscle protein synthesis in old rats can be restored by a leucine-supplemented
meal.
J Nutr.
2002 Jan;132(1):95-100.
Rieu I,
Sornet C, Bayle G, Prugnaud J, Pouyet C, Balage M, Papet I, Grizard J, Dardevet
D. Leucine-supplemented meal feeding for ten days beneficially affects
postprandial muscle protein synthesis in old rats.
J Nutr.
2003 Apr;133(4):1198-205.
© ABC Bodybuilding Company. All rights reserved.
Disclaimer |
