Douglas Paddon-Jones, Ph.D. Associate Professor, Physical Therapy and Internal Medicine The University of Texas Medical Branch Protein Intake and the Preservation of Muscle Mass in Aging Iowa Dietetic Association 2009

Overview  muscle protein metabolism – the science  translating science  clinical practice  protein needs - healthy aging - physical inactivity - exercise

Inactivity Malnutrition Balance Synthesis Breakdown Muscle growth Muscle loss Nutrition Exercise Hormones Maintaining Muscle Mass Illness/Injury

Age and body composition

FrailtyFrailty  lean body mass  fat mass  insulin resistance  visceral fat Decreased muscle mass muscle massDecreased  type 2 diabetes  strength  power  risk of falls  risk of fractures  walking speed

Dietary strategies to maintain muscle Free-form amino acid supplements:  stimulate muscle anabolism  they are effective in all age groups  they can be used clinically

Breakfast LunchDinner How much protein are we getting ?

Muscle Protein Synthesis / Muscle Growth - protein ingestion - Symons et. al. AJCN, Fasting Protein Synthesis (%/h) Young Elderly 30 g protein ?

Protein Ingestion and Muscle Growth - a message of moderation Fasting 30 g protein Protein Synthesis (%/h) Protein Synthesis (%/h) Fasting 90 g protein Young Old ~1.2 g/kg/day for 180 lb individual

Daily protein distribution - typical ? - Total Protein 90 g Catabolism Anabolism 10 g maximum rate of protein synthesis 15 g 65 g A skewed daily protein distribution fails to maximize potential for muscle growth

Daily protein distribution - Optimal - Catabolism Anabolism maximum rate of protein synthesis 30 g Total Protein 90 g Repeated maximal stimulation of protein synthesis  increase / maintenance of muscle mass

FastingProtein meal Protein Synthesis (%/h) Young Elderly Protein + Exercise ??

Bed rest is a defacto treatment modality - if you’re hospitalized you will become inactive - Inactive (0 steps/min) Low Activity (< 15 steps/min) % of Time

Muscle Loss in Bedridden Elders - 10 Days of Inactivity/Bed rest Loss of lean leg mass (g) Young 28 Days Bedrest 2% total lean leg mass Elderly 10 Days Bedrest Paddon-Jones et. al Kortebein et al ?

Muscle Loss in Hospitalized Elders Loss of lean leg mass (g) Young 28 Days Inactivity 2% total lean leg mass Healthy Elders 10 Days Inactivity Elderly Inpatients ~ 3 days ??

Inactivity reduces the ability to build/repair proteins and muscle Day 1Day 10 Protein Synthesis (%/h) * Kortebein et al h muscle protein synthesis during 10 day of inactivity in elders (stable isotope methodology )

What are our older inpatients eating ? per meal

Can we reduce muscle loss associated with injury/inactivity using dietary protein ?

Paddon-Jones et al, 2004 Muscle Mass Change in leg muscle mass (kg) Bedrest Bedrest +Amino acids Paddon-Jones et. al ?

Strength Loss of 1RM Leg Extension strength (kg) Bedrest Paddon-Jones et. al ? Bedrest +Amino acids

Can protein also help elders? - 24 h muscle protein synthesis Day 1 Day 10 Protein Synthesis (%/h) * Normal Diet Normal Diet + Amino Acids # Normal Diet + Amino Acids

Regular meals + Leucine Post-absorptive Post-prandial Day 1 (pre) Day 14 (2 weeks LEU) Protein synthesis: % / hr ?

 Hot topic: Leucine plays a key role  Distribution of protein throughout the day plays a key role  Moderation and common sense are still the key themes  Muscle growth is a slow process, but atrophy can be exceedingly fast  The RDA for protein is not sufficient in many circumstances Summary  ~ 30 g of protein maximally stimulates muscle protein synthesis