#81: Your body doesn't stop working with age. It stops listening

When did you last play something so hard you were gasping for air and still grinning? Maybe a game of badminton, cricket or soccer, or chasing a child around the park. I don’t mean a workout. I mean play.For many adults, the honest answer is years ago. We tell ourselves that is simply what getting older looks like. The body slows, muscle fades, blood sugar creeps up, and we file it all under age. I no longer think it is that simple. At 54, I have more muscle, denser hips (hips don’t lie!) and less visceral fat than I had in my forties. Aging didn’t reverse, but my body moved in the opposite direction from what the calendar would predict. In today’s post (#81), I get into two scientific ideas that helped me understand why: insulin resistance and anabolic resistance.Before I get into the topic, I would like to announce the 6th cohort of the 28-day challenge that begins on October 4th. If you are interested in signing up for it, go to Deadline to sign up for this cohort is October 1st.What is insulin resistance?Insulin is a messenger. After a meal, it tells your muscle, liver and fat cells what to do with the nutrients arriving, including helping muscle and fat pull glucose out of the bloodstream. In insulin resistance, the cells respond less effectively, so the pancreas compensates by producing more insulin to get the same job done. For years that compensation can keep blood glucose looking fairly normal, which is why insulin resistance so often goes unnoticed. Eventually, the pancreas can’t keep up and blood glucose rises.Think of a doorbell. If nobody answers, you ring harder and longer. The bell works perfectly well. The house has simply stopped listening.What is anabolic resistance?Muscle has its own version of the same problem. Protein supplies the amino acids, and lifting something heavy supplies a powerful signal telling muscle to repair and build. Scientists measure part of that response as muscle protein synthesis. As we age, muscle tends to respond less to the same meal, and that blunted response is called anabolic resistance. At 25 you can whisper “build” and your muscles hear you, while at 65 you may need to speak much louder.The encouraging part is that older muscle still responds remarkably well when you do speak louder, especially when resistance exercises and enough protein are combined. Age may turn down the sensitivity of the receiver, but exercise turns up the signal.Are insulin and anabolic resistance connected?They aren’t the same biological process, but they overlap a great deal. Skeletal muscle is one of the body’s main destinations for glucose after a meal, so healthy, active muscle matters enormously for blood sugar control. The same things that make muscle less responsive to insulin, particularly inactivity and poor metabolic health, also blunt its response to protein.One experiment really brought this home for me. Researchers took healthy older adults and cut their activity to around 1,400 steps a day for just two weeks. In that short time, their muscle-building response to a meal fell by 26%, their insulin sensitivity after meals fell by 43%, and they measurably lost lean mass in their legs. In another study, a single night without sleep reduced muscle protein synthesis after a meal by about 18% in healthy young adults.The message isn’t that aging doesn’t matter, because it clearly does. It is that age isn’t acting alone. Its partners are movement, nutrition, metabolic health and sleep, and all of those are things we can change.My body has been my experimentMy story started in 2015, when a coronary calcium score of 266 at age 43 told me I had coronary artery disease, despite being lean and playing soccer regularly. That result changed how I thought about health, and I started measuring. Here is what eleven years of those measurements show. I started tracking muscle in December 2018, so that comparison covers about seven and a half years.The triglyceride-to-HDL ratio is an imperfect but useful clue that tracks with insulin resistance in many populations, and mine fell from 7.0 to 0.6. My HbA1c fell too, from 6.1% to 5.7%, but 5.7% still sits right at the threshold used to define prediabetes, so that one remains a work in progress. On the body composition side, I added 7.7 pounds of skeletal muscle while losing 7.1 pounds of fat between my late forties and mid fifties, and my hip bone density went up rather than down.This is an experiment with a sample size of one, so I don’t present it as scientific proof. But it makes the science very real to me. My age went up, my muscle went up, my fat went down and my hip bones got denser.Does this concept extend beyond muscle and insulin?It does, and bone is a wonderful example. Bone is living tissue whose cells sense mechanical load and adapt to it. In the LIFTMOR trial, postmenopausal women with low bone mass did supervised heavy resistance and impact training twice a week for eight months. Their bone density improved compared with women who didn’t train that way. My DEXA scans tell a similar personal story.Blood vessels respond in much the same way. Increased blood flow stimulates the lining of our arteries, and regular aerobic exercise improves how well arteries widen, even in older adults.Leptin is a hormone made by your fat cells. Think of it as a message to your brain saying, “We have enough energy stored, so you don’t need to keep eating.” But in obesity, even though leptin levels are often high, the brain may stop responding properly to the message. This is called leptin resistance. We know it happens, but we still don’t fully understand why it happens or how easily it can be reversed.The broader principle is simpler and easier to defend. Our bodies adapt to what we repeatedly ask them to do, and just as surely to what we stop asking them to do.What moved my numbers?Lifting two to three times a week. I lift heavy enough that the last few repetitions are genuinely difficult. A lifting session also makes muscle more responsive to protein for up to a day afterward, which is one of the best arguments I know for pairing strength training with protein consumption.Protein per meal, not just per day. Older muscles need a bigger dose at one sitting to switch on building, often around 30 to 40 grams, so I pay attention to each meal and not just the daily total. I average around 100 grams a day.Movement between workouts. That two-week step study stays with me because it shows how quickly inactivity takes its toll. I walk during calls, walk after meals and play soccer. Movement isn’t something I save for the gym.Cardio at different intensities. Comfortable aerobic work and harder intervals provide different stimuli, and both improve how my body handles sugar and how my arteries respond.Sleep. I went from around five hours a night to almost six. It remains my weakest link and the thing I am always working on improving.None of this is exotic, and that is exactly the point. They are just simple lifestyle changes I made consistently over a long time. The above changes are part of the 33 habits from my playbook. If you’d like to see all 33 habits, click on My Playbook. In fact, we are launching the 6th cohort of our 28-day challenge, where we introduce one habit each week, explain the science simply and help you make it stick, while keeping it fun. Longevity Circle community embers told us it became the starting point for transforming their health. By Day 28, it no longer feels like a program. It is simply how you live. If you are interested, sign up for the October 4th cohort by tomorrow's deadline (October 1st) at try28.comSo what is the takeaway?There is an old line, often attributed to George Bernard Shaw, though the attribution is shaky: we don’t stop playing because we grow old; we grow old because we stop playing. Whoever said it, the thought captures something I increasingly believe. Aging changes our bodies, and none of us can exercise our way back to 25. But aging is not acting alone. Muscle and bone respond to load, insulin sensitivity responds to movement, blood vessels respond to exercise, and nutrition and sleep shape how well we adapt to all of it. Doing these doesn’t mean one has reversed aging. It tells us something far more useful: the aging body remains remarkably adaptable. We cannot stop getting older, but we can keep giving our bodies reasons to stay capable.If you want help figuring out where to start, join us in The Longevity Circle community at always, I would love to hear your thoughts and experiences in the comments.Author: Nickhil Jakatdar is the CEO of GenePath Diagnostics and the founder of PreventiveHealth.ai, working to make advanced diagnostics and credible health guidance more accessible, affordable, and actionable. A PhD in EECS from UC Berkeley and the youngest recipient of the UC Berkeley Distinguished Alumnus Award, he has founded and led multiple tech companies. He holds 60 patents, and serves on several academic, healthcare, and innovation boards. To follow his thinking on preventive health, technology, and systems that scale expertise, join his private WhatsApp community and subscribe to his Substack.Disclaimer: Views expressed above are the author's own.