Why Some People Maintain Energy After 40
I have been working with fitness since 1982, and one thing has become very clear: two people can be the same age on paper but have completely different energy levels. One takes the stairs, exercises, travels and is curious about life. The other feels exhausted after lunch.
It's easy to say that the difference is due to age. But age is only part of the explanation. Energy is the result of how sleep, muscles, fitness, food, hormones, stress and health work together. That's also why a capsule rarely solves the problem.
You don't have to feel like you're 25 to have good energy at 50, 60, or 70. The goal isn't youth – it's capacity. |
First: what do we actually mean by energy?
When someone says “I have no energy,” it can mean several different things. You could be sleepy, mentally exhausted, unmotivated, or physically exhausted. The problems can feel the same but have completely different causes.
Sleepiness is often caused by too little or disrupted sleep. Mental fatigue can result from prolonged stress and too few breaks. Poor physical endurance can be due to low fitness, reduced muscle strength or illness. Therefore, the first question is not which supplement to buy, but what kind of fatigue you actually have.
What changes after 40?
No dramatic biological boundary is crossed on the 40th birthday. However, several small changes often begin to be noticed in the following decades – especially if everyday life has become more sedentary.
Muscle mass and strength become easier to lose. Inactivity costs more than before and the muscles need a clearer training signal.
Fitness declines if it is not maintained. The combined reserve of the heart, lungs and muscles affects how much everyday life takes from you.
Sleep can become more fragile. Stress, alcohol, menopause symptoms, nighttime toilet visits and sleep apnea can result in many hours in bed but too little recovery.
Hormones can affect well-being. Menopause can cause sleep disturbances and fatigue. In men, hormonal changes usually occur more gradually and should not be used as a standard explanation for all low energy.
Recovery is less likely. Hard workouts, travel, illness and lack of sleep can require longer recovery than before.
Metabolism is rarely the culprit at 45
A common explanation is that metabolism “shuts down” in middle age. This is inconsistent with modern research. A large study, with participants ranging in age from eight days to 95 years, showed that energy expenditure adjusted for body size and composition was relatively stable from about 20 to 60 years of age. After that, it began to gradually decline.
This doesn't mean that weight loss is always easy to maintain. We may move less, sleep worse, drink more alcohol, lose muscle and eat just as much as when our daily lives were more active. The experience is real – but the explanation is often a changed lifestyle and body composition, not a suddenly broken metabolism.
Why do some people retain their energy?
Those who seem to have the most energy after 40 don't necessarily have better discipline every day. They often have built a system that keeps their body getting the right signals over and over again.
They maintain their muscles. Strong muscles make every everyday task cheaper. Getting up, carrying, walking and working require a smaller proportion of maximum capacity.
They maintain fitness. When oxygen transport works better, both exercise and everyday movement feel easier.
They protect sleep. They don't try to compensate for chronic sleep deprivation with coffee, sugar, and willpower.
They dose the load and recovery. Full speed all the time is not energy – it can be the path to exhaustion. Capacity is built when load is followed by recovery.
They let habits do the work. Exercise, meals, and bedtime don't have to be renegotiated every day.
They treat problems that are treatable. Sleep apnea, anemia, thyroid problems, depression, medication side effects, and other conditions should not be dismissed as normal aging.
The afternoon dip doesn't always mean something is wrong
Many people experience a natural slump in the early afternoon. It becomes more pronounced after too little sleep, a large meal, a lot of alcohol the night before, or many hours of inactivity. A lunch with a lot of energy but little protein and fiber can also make you hungry again quickly.
Try the simple things first: a reasonable portion size, protein and vegetables in your meal, water, and a ten-minute walk after eating. However, if you fall asleep involuntarily during the day, snore heavily, or wake up with a headache and never feel rested, sleep apnea should be considered.
Seven habits that support energy after 40
Strength train regularly. Two to four well-planned sessions per week can help you maintain muscle mass, strength, and work capacity. More sessions are not automatically better if recovery is not kept up.
Exercise your heart too. Brisk walking, cycling, swimming or other cardio exercises complement strength. The WHO recommends that adults do 150–300 minutes of moderate activity per week, or the equivalent amount of vigorous activity, plus muscle-strengthening exercises on at least two days.
Move between workouts. A gym session doesn't completely make up for a day in the chair. Walking, taking the stairs, and short movement breaks keep your circulation and everyday capacity going.
Eat foods that keep you stable. Build meals around protein, vegetables, high-fiber carbohydrates, and a moderate amount of fat. Breakfast isn't mandatory for everyone, and frequent meals aren't a requirement—choose a rhythm that provides consistent energy and fits your goal.
Use caffeine strategically. Coffee can improve alertness, but late or heavy consumption can impair sleep and create next-day fatigue. If you need caffeine all afternoon, it's often your sleep or workload that needs to be addressed.
Be honest about alcohol and stress. Both can impair sleep quality even when you fall asleep quickly. Planned recovery, daylight, and breaks are not laziness – they are part of the energy system.
Investigate persistent fatigue. Contact a health center if fatigue persists despite reasonable changes, gets worse, or limits daily life. This can then be used to assess sleep, medications, mental health, and relevant tests.
And NMN – is it the solution?
NMN, nicotinamide mononucleotide, is a precursor to NAD+, a substance needed in cellular energy metabolism and many other processes. This makes NMN biologically interesting. However, a plausible mechanism is not the same as a proven health effect.
Small, short-term human studies show that NMN may affect NAD-related blood markers. One study of 25 postmenopausal women with obesity and prediabetes found improved insulin sensitivity in muscles. Other trials have reported occasional improvements in walking tests or physical function, while overall results for performance have been unclear.
My assessment: NMN is an interesting area of research, but we don't yet have robust evidence that it generally increases everyday energy, relieves fatigue, or slows down human aging. The available safety studies are also short and say little about use over many years. I would therefore place NMN far behind sleep, exercise, food, recovery, and medical investigation.
Energy is something you build
You can't promise the same energy at 60 as you did at 25. But the big difference between people of the same age shows that development is not predetermined. You can build more muscle reserve, better fitness, more stable sleep and smarter recovery.
It's rarely the most exotic ingredient that determines how much energy you have. It's what you do often enough to keep your body capable.
After 40, it's not about chasing youth. It's about maintaining the power to live the life you want to live.
All the best,
Kennet Bath
Founder, Bodyweight Diet
Sources and further reading
Please note: The text contains general health information and is not a substitute for individual medical advice, diagnosis or treatment.
Kennet Båth • bodyweight.diet •
