{"id":1713,"date":"2026-09-16T19:23:08","date_gmt":"2026-09-16T19:23:08","guid":{"rendered":"https:\/\/epinutrition.org\/?page_id=1713"},"modified":"2026-09-16T19:23:08","modified_gmt":"2026-09-16T19:23:08","slug":"proteins-journey-chapter-11-aging-where-can-the-response-change","status":"publish","type":"page","link":"https:\/\/epinutrition.org\/?page_id=1713","title":{"rendered":"Protein\u2019s Journey \u2014 Chapter 11 \u2014 Aging: Where Can the Response Change?"},"content":{"rendered":"\n<style>.pj{max-width:1080px;margin:auto;color:#203b32;font:18px\/1.7 Arial,sans-serif}.pj *{box-sizing:border-box}.pj a{color:#185c42}.pj .hero{display:grid;grid-template-columns:230px 1fr;gap:36px;align-items:center;background:#f4f3e9;padding:32px;border-radius:14px}.pj .cover{width:100%;height:auto}.pj h2{font:32px\/1.25 Georgia,serif}.pj h3{font:25px\/1.3 Georgia,serif}.pj .actions{display:flex;gap:12px;flex-wrap:wrap}.pj .button{display:inline-block;padding:12px 22px;border:2px solid #185c42;border-radius:7px;text-decoration:none;color:#185c42!important;font-weight:bold}.pj .primary{background:#185c42;color:white!important}.pj section{margin-top:44px;scroll-margin-top:25px}.pj li{margin:9px 0}.pj video{width:100%;aspect-ratio:16\/9;background:#102b26}.pj details{border:1px solid #d2dcd4;border-radius:8px;margin:12px 0;overflow:hidden}.pj summary{cursor:pointer;padding:18px;background:#f6f8f4}.pj .episode-body{padding:20px}.pj .time{display:inline-block;margin-left:12px;font-size:14px}.pj .table-wrap{overflow-x:auto}.pj table{border-collapse:collapse;width:100%}.pj th,.pj td{padding:10px;border:1px solid #ccd8ce;text-align:left}.pj .reference{font-size:16px;overflow-wrap:anywhere}.pj a:focus-visible,.pj summary:focus-visible{outline:3px solid #c3922e;outline-offset:3px}@media(max-width:640px){.pj .hero{grid-template-columns:1fr;padding:22px}.pj .cover{max-width:210px}.pj h2{font-size:28px}.pj .episode-body{padding:12px}}<\/style>\n<div class=\"pj\"><p><a href=\"https:\/\/epinutrition.org\/?page_id=1648#read-book\">\u2190 Book contents<\/a> \u00b7 <a href=\"https:\/\/epinutrition.org\/?page_id=1711\">Previous<\/a> \u00b7 <a href=\"https:\/\/epinutrition.org\/?page_id=1715\">Next<\/a><\/p>\n<p>Two people of the same age can have very different muscles.<\/p>\n<p>One may remain physically active, eat regularly, and recover well from exercise. Another may have experienced illness, reduced appetite, and weeks of limited movement. Their chronological age is similar; the conditions affecting muscle renewal are not.<\/p>\n<p>Aging can alter the relationship between food and muscle, but understanding those changes requires following the entire journey.<\/p>\n<p><strong>Is less protein being eaten? Are fewer amino acids reaching muscle? Does the muscle make less protein in response? Or does the difficulty emerge later, in retention and function?<\/strong><\/p>\n<p>These questions help locate a limitation rather than assume one.<\/p>\n<h3>What anabolic resistance means<\/h3>\n<p>Researchers use the term <strong>anabolic resistance<\/strong> to describe a reduced protein synthetic response to a stimulus such as amino acids, protein feeding, or exercise.<\/p>\n<p>The term describes a response under specified conditions. It does not mean that muscle has stopped making protein, that protein cannot be absorbed, or that every older adult has the same impairment.<\/p>\n<p>In a study involving forty-four young and older men, basal muscle protein synthesis rates were similar, but the older participants showed reduced sensitivity and responsiveness to ingested essential amino acids. Changes in anabolic signaling accompanied the reduced response. [1]<\/p>\n<p>This distinction between the resting state and the stimulated response is important. A muscle can maintain a similar basal rate of synthesis yet respond less strongly when nutrients arrive.<\/p>\n<p>Anabolic resistance is therefore best understood as something demonstrated through a comparison\u2014not diagnosed from age alone.<\/p>\n<h3>Preserved responsiveness also occurs<\/h3>\n<p>Other human studies show that older muscle can retain substantial anabolic responsiveness.<\/p>\n<p>A study of ten young and ten older men selected for good health and leanness found preserved muscle protein synthetic responsiveness in the older group under the exercise and essential-amino-acid conditions tested. The older participants also had higher expression of several amino acid sensors and mTORC1-related activators. [2]<\/p>\n<p>The authors proposed that these differences might help maintain responsiveness. The study established an association, rather than proving that the higher expression caused the preserved response.<\/p>\n<p>Preserved responsiveness in this small, selected group complements the evidence for anabolic resistance in other settings.<\/p>\n<h3>Establish the starting conditions<\/h3>\n<p>Intake and tissue response are separate parts of the assessment. Reduced eating, illness, and inactivity may accompany aging and affect the circumstances in which muscle receives nutrients.<\/p>\n<p>Establishing these conditions helps identify whether a reduced response reflects the amount supplied, its delivery, or events within the muscle. The practical assessment of portions and food choices follows in Chapter 12.<\/p>\n<h3>Absorption and incorporation must be separated<\/h3>\n<p>Age-related muscle loss does not establish that protein absorption is poor. Nor does a high blood amino acid concentration establish that absorption is unusually high.<\/p>\n<p>Blood concentrations reflect arrival, release from existing proteins, and removal by tissues.<\/p>\n<p>As discussed earlier, a study comparing young and older men found that prior exercise increased the use of dietary amino acids for muscle protein synthesis in both groups, without finding impaired digestion and absorption kinetics in the older participants under the tested conditions. [3]<\/p>\n<p>The finding directs attention to the use of available amino acids under those conditions.<\/p>\n<h3>Resting regulation and responsiveness<\/h3>\n<p>The resting signaling measurements discussed in Chapter 8 differ from the nutrient-sensing protein expression measured in the healthy, lean older men described here. [2,4] Expression, phosphorylation, and the response to feeding should remain distinct when explaining age-related changes.<\/p>\n<p>Aging can alter regulation in several ways. Direct measurements of synthesis establish how the muscle responds.<\/p>\n<h3>Inactivity can change the response<\/h3>\n<p>Chapter 9 showed how bed rest can reduce nutrient responsiveness in older muscle. [5] This helps explain why activity history belongs alongside age in the assessment. Illness may also change appetite, movement, and metabolism at the same time.<\/p>\n<h3>Finding the relevant limitation<\/h3>\n<p>A useful way to organize the investigation is to ask a sequence of questions:<\/p>\n<ul><li><strong>Intake:<\/strong> Is the person eating enough food and protein?<\/li><li><strong>Digestion and delivery:<\/strong> Are dietary amino acids becoming available to tissues?<\/li><li><strong>Muscle response:<\/strong> Does feeding or activity stimulate protein synthesis?<\/li><li><strong>Retention:<\/strong> How does synthesis compare with breakdown over time?<\/li><li><strong>Function:<\/strong> Are strength and physical abilities being maintained?<\/li><\/ul>\n<p>These questions distinguish the stages at which difficulties can arise.<\/p>\n<h3>An approach based on responsiveness<\/h3>\n<p>The evidence supports investigating muscle responsiveness as an important part of aging. It also supports recognizing variation and retained capacity.<\/p>\n<p>For EpiNutrition, the goal is to connect suitable meals with the circumstances in which they are eaten and used. Food quantity, meal composition, activity, and recovery belong in the same investigation.<\/p>\n<p><strong>Aging can change the journey from meal to muscle. The useful question is where the response changes in a particular setting\u2014and what evidence shows that it can improve.<\/strong><\/p>\n<p>The next chapter turns to choosing protein within a meal, bringing amino acid composition, food structure, and practical eating considerations together.<\/p>\n<h3>References<\/h3>\n<p class=\"reference\">1. Cuthbertson D, Smith K, Babraj J, et al. Anabolic signaling deficits underlie amino acid resistance of wasting, aging muscle. <em>FASEB Journal<\/em>. 2005;19(3):422\u2013424. <a href=\"https:\/\/pubmed.ncbi.nlm.nih.gov\/15596483\/\">doi:10.1096\/fj.04-2640fje<\/a><\/p>\n<p class=\"reference\">2. Horwath O, Moberg M, Hodson N, et al. Anabolic sensitivity in healthy, lean, older men is associated with higher expression of amino acid sensors and mTORC1 activators compared to young. <em>Journal of Cachexia, Sarcopenia and Muscle<\/em>. Published online 2024. <a href=\"https:\/\/pubmed.ncbi.nlm.nih.gov\/39558870\/\">doi:10.1002\/jcsm.13613<\/a><\/p>\n<p class=\"reference\">3. Pennings B, Koopman R, Beelen M, Senden JMG, Saris WHM, van Loon LJC. Exercising before protein intake allows for greater use of dietary protein-derived amino acids for de novo muscle protein synthesis in both young and elderly men. <em>American Journal of Clinical Nutrition<\/em>. 2011;93(2):322\u2013331. <a href=\"https:\/\/pubmed.ncbi.nlm.nih.gov\/21084649\/\">doi:10.3945\/ajcn.2010.29649<\/a><\/p>\n<p class=\"reference\">4. Markofski MM, Dickinson JM, Drummond MJ, et al. Effect of age on basal muscle protein synthesis and mTORC1 signaling in a large cohort of young and older men and women. <em>Experimental Gerontology<\/em>. 2015;65:1\u20137. <a href=\"https:\/\/pmc.ncbi.nlm.nih.gov\/articles\/PMC4397165\/\">Study available through PubMed Central<\/a><\/p>\n<p class=\"reference\">5. Tanner RE, Brunker LB, Agergaard J, et al. Age-related differences in lean mass, protein synthesis and skeletal muscle markers of proteolysis after bed rest and exercise rehabilitation. <em>Journal of Physiology<\/em>. 2015;593(18):4259\u20134273. <a href=\"https:\/\/pubmed.ncbi.nlm.nih.gov\/26173027\/\">doi:10.1113\/JP270699<\/a><\/p><p><a href=\"https:\/\/epinutrition.org\/?page_id=1648#read-book\">\u2190 Book contents<\/a> \u00b7 <a href=\"https:\/\/epinutrition.org\/?page_id=1711\">Previous<\/a> \u00b7 <a href=\"https:\/\/epinutrition.org\/?page_id=1715\">Next<\/a><\/p><\/div>\n","protected":false},"excerpt":{"rendered":"<p>\u2190 Book contents \u00b7 Previous \u00b7 Next Two people of the same age can have very different muscles. One may remain physically active, eat regularly, and recover well from exercise. Another may have experienced illness, reduced appetite, and weeks of limited movement. Their chronological age is similar; the conditions affecting muscle renewal are not. Aging&#8230;<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"pmpro_default_level":"","_kad_post_transparent":"","_kad_post_title":"","_kad_post_layout":"","_kad_post_sidebar_id":"","_kad_post_content_style":"","_kad_post_vertical_padding":"","_kad_post_feature":"","_kad_post_feature_position":"","_kad_post_header":false,"_kad_post_footer":false,"_kad_post_classname":"","footnotes":""},"class_list":["post-1713","page","type-page","status-publish","hentry","pmpro-has-access"],"brizy_media":[],"_links":{"self":[{"href":"https:\/\/epinutrition.org\/index.php?rest_route=\/wp\/v2\/pages\/1713","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/epinutrition.org\/index.php?rest_route=\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/epinutrition.org\/index.php?rest_route=\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/epinutrition.org\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/epinutrition.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1713"}],"version-history":[{"count":2,"href":"https:\/\/epinutrition.org\/index.php?rest_route=\/wp\/v2\/pages\/1713\/revisions"}],"predecessor-version":[{"id":1739,"href":"https:\/\/epinutrition.org\/index.php?rest_route=\/wp\/v2\/pages\/1713\/revisions\/1739"}],"wp:attachment":[{"href":"https:\/\/epinutrition.org\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1713"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}