If your 20s are in your rearview mirror and you long for the energy you once seemed to have in abundance, you’re part of a very large club. Those days of powering through workouts, late nights, and packed schedules without much thought? A distant memory. Instead, you’re waking up exhausted, crashing midafternoon, and wondering what on earth happened.
It’s tempting to chalk it up to aging, but for most people, there’s much more nuance to the story, according to Sunjya Schweig, M.D., integrative family physician and founder of the California Center for Functional Medicine. What’s really happening isn’t a sudden loss of vitality, but rather the result of years of small stressors quietly adding up.
“In early adulthood, the body can compensate for poor sleep, high stress, skipped meals, or inconsistent exercise without showing clear symptoms,” he says. “After 30, those same factors and stressors begin to accumulate and overwhelm the body’s ability to adapt.”
Recent research backs this up. In fact, a decades-long study published in the Journal of Cachexia, Sarcopenia and Muscle found that aerobic fitness, strength, and endurance tend to peak in early adulthood and gradually decline after the 30s.
This doesn’t mean energy loss is inevitable, but it does mean the body becomes less forgiving, and habits that once felt optional start to matter more. Ahead, we’ll break down what’s happening in the body that triggers energy dips after 30, and how to rebuild vitality from the ground up.
- ABOUT OUR EXPERTS: Sunjya Schweig, M.D., is an integrative family physician and founder of the California Center for Functional Medicine. Jerry Bailey, D.C., LA.c., is a certified nutritionist, acupuncturist, chiropractor, and functional medicine physician with Lakeside Holistic Health. Brittany Michels, M.S., R.D.N., L.D.N., C.P.T., is a registered dietitian, certified personal trainer, and nutritionist for The Vitamin Shoppe.
What Changes Your Energy After 30 (Aside from “Just Aging”)
Energy changes that pop in as you inch toward midlife aren’t driven by one single shift. Instead, they’re shaped by several interconnected factors that begin to matter more as the body ages and its margin for error narrows. Here are the most common culprits experts see behind persistent fatigue after 30.
1. Muscle Loss
Muscle loss is one of the most overlooked drivers of low energy as you age. “Beginning as early as the early 30s, adults start to lose skeletal muscle each decade unless they actively work to preserve it—and that loss has real consequences for how energized you feel day to day,” explains Jerry Bailey, D.C., LA.c., a certified nutritionist, acupuncturist, chiropractor, and functional medicine physician with Lakeside Holistic Health. “As muscle declines, blood sugar becomes less stable, leading to energy crashes, cravings, and fatigue.”
Without regular resistance training, adults can lose an estimated three to eight percent of muscle mass per decade after age 30. Over time, that loss makes it harder to sustain energy, recover from exercise, and feel resilient throughout the day, Bailey explains. “Fatigue can then discourage movement, creating a cycle of deconditioning that quietly compounds.”
Read More: 6 Major Health Benefits Of Building Muscle
He recommends prioritizing resistance training two to three times per week and eating enough protein (go for 0.7 to one gram per pound of ideal body weight) to support muscle maintenance, both of which can help stabilize energy more than you might expect.
2. Metabolism Changes
As muscle mass declines, metabolism slows down alongside it. Muscle tissue is a major site of mitochondrial activity and insulin-mediated glucose uptake, explains Brittany Michels, M.S., R.D.N., L.D.N., C.P.T., a registered dietitian, certified personal trainer, and nutritionist for The Vitamin Shoppe. Less muscle essentially means the body becomes less efficient at converting food into usable energy.
Contrary to what many of us believe, a slower metabolism doesn’t necessarily mean weight gain, but it does mean energy production becomes less flexible. “The body has a harder time switching between fuel sources, maintaining steady energy between meals, and bouncing back from physical or mental stress,” says Schweig. This reduced metabolic flexibility can leave people feeling fatigued even when they’re eating “well” and exercising regularly, he explains.
Protein intake plays a key role here, so get those grams in! Aiming for 25 to 40 grams per meal can help you meet the mark and support muscle maintenance, Schweig suggests. (More on that in a bit.)
3. Chronic Stress
As anyone in their 30s or older can attest, life often becomes more stressful with the introduction of family life, added caregiving demands, financial pressure, health worries, and the constant mental load of “holding it all together.” Over time, this keeps the nervous system stuck in a low-grade fight-or-flight state in which cortisol signaling becomes dysregulated and normal daily cortisol rhythms begin to flatten, explains Bailey. Instead of a strong morning rise and a gradual decline in the stress hormone (which is the healthy pattern), you might feel drained of energy during the day and more wired at night.
“This stress state suppresses digestion, disrupts sleep quality, interferes with hormone balance and thyroid conversion, and reduces the body’s ability to repair and recover at the cellular level,” Bailey warns. “Even when physical demands are relatively low, accessing energy becomes harder because the body is metabolically overextended and never fully ‘downshifts.’”
Read More: 6 Science-Backed Ways To Lower Cortisol
He recommends shifting your focus from doing more to regulating your nervous system. Think prioritizing consistent sleep and wake times, getting light exposure within 30 minutes of waking to anchor circadian rhythms, and calming habits like slow breathing, short walks, gentle stretching, or meditation. “Boundaries around work and screen time, especially at night, can also be helpful,” he adds. “These small, steady signals tell your body it’s safe to recover, making energy and sleep easier to come by.”
4. Accumulating Sleep Debt
Sleep debt doesn’t require dramatic all-nighters to take a toll. Research suggests that even one night of poor sleep can set off a chain reaction that disrupts nearly every system in your body, leaving you tired, foggy, and less able to recover from workouts or daily stress.
With age, sleep quality may shift due to stress hormones, blood sugar instability, and hormonal changes, explains Bailey. “As a result, total sleep time may look ‘adequate’ on paper, but truly restorative sleep is often lacking,” he says. “Without sufficient deep and REM sleep, energy production suffers at the cellular level and recovery becomes incomplete.”
Your best bet for optimal energy—and health—is to make sleep non-negotiable. The CDC recommends aiming for seven to nine hours per night. Sticking to consistent sleep and wake times seven days a week (weekends included) can make a big difference, Bailey suggests. The same goes for limiting evening light (especially blue light from screens) an hour or two before bed and reducing (or eliminating!) caffeine after noon.
5. Under-Eating Protein
Yep, we’re talking about protein again. It’s just that important! Many adults eat enough calories but not enough of the nutrients their bodies need to produce energy efficiently. Protein gives your body the raw materials it needs to make the brain chemicals that affect mood and focus, clear out waste and toxins, keep your immune system strong, and repair and rebuild muscle, explains Schweig. “When protein intake is insufficient, muscle loss accelerates and mitochondrial enzyme production declines, which directly reduces cellular energy output,” he says.
Protein needs increase with age due to anabolic resistance, which means the body becomes less efficient at using dietary protein to maintain and build muscle. As a result, older adults often need more protein than younger adults to get the same muscle-preserving effect, Schweig explains. “Addressing protein adequacy is foundational for restoring energy, especially in midlife,” he adds.
Start by aiming for that 0.7 to one gram of protein per pound of ideal body weight per day, spread out across your snacks and meals. (Use these tips to pack 30-plus grams of protein onto your plate.) If you’re having trouble hitting the mark, recruit some help from a handy protein powder or grab-and-go fuel like protein bars or ready-to-drink protein shakes.
6. Declining Mitochondrial Efficiency
Mitochondria are essentially your body’s energy factories, responsible for turning food and oxygen into usable energy (ATP), Michels explains. With age, as well as chronic stress, inflammation, and oxidative damage, these cellular “engines” can become less efficient.
“When mitochondria aren’t working well, energy production drops (even if blood work looks normal), and the body starts relying more on quick, short-term energy pathways, which leads to energy crashes, poor stamina, and slower recovery,” says Bailey. “Over time, this also reduces exercise tolerance, making workouts feel harder than they used to.”
The good news is that mitochondrial function is highly responsive to lifestyle interventions, especially exercise. For this reason, Schweig recommends incorporating both aerobic exercise (brisk walking, cycling, or jogging) and resistance training (weights, bands, or machines) into your routine. The Physical Activity Guidelines for Americans recommends at least 150 minutes of moderate-intensity aerobic activity per week, along with two to three strength-training sessions.
How Long Until Your Energy Returns?
If you’re anxious for your energy to return, know that the body responds to healthy lifestyle changes quicker than you might think! “For many people, early improvements show up within two to four weeks of addressing the biggest energy drains (sleep consistency, adequate protein intake, and daily stress regulation),” Schweig says. “These early shifts often look like steadier morning energy, fewer afternoon crashes, clearer thinking, better workout recovery, and less reliance on caffeine or sugar.”
That said, “meaningful muscle gains (and the benefits that come along with them) require eight to 12 weeks of consistent, progressive resistance training combined with adequate protein intake,” says Schweig. So be patient on that front, and you’ll feel better and better over time.
When Should You See a Doctor About Low Energy?
If you notice that your low energy improves when you make lifestyle changes, great! However, when fatigue persists despite consistent foundational support, it’s a signal to look deeper, according to Schweig.
“If someone has genuinely addressed the basics for six to eight weeks, yet still feels depleted, further evaluation is warranted,” he says. “There are also situations in which waiting isn’t appropriate, such as if you’re also experiencing unexplained weight gain or loss, hair thinning, heat or cold intolerance, heart palpitations, shortness of breath with minimal effort, sudden or severe fatigue, fever, or unexplained pain.”
A thorough check-in with a healthcare provider—and, when it makes sense, a registered dietitian or therapist—can help connect the dots, take the guesswork out of what you’re feeling, and point you toward the next right steps.