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What happens to your metabolism with age?

Discover how body weight, composition, and lifestyle have greater impact on metabolic rate than age itself.

While many assume weight maintenance gets tougher as years pass, the notion of metabolism slowing down significantly with age is being reconsidered. Recent studies suggest that age-related metabolic shifts may not occur as early as believed, and other influential factors have been underestimated.

Does metabolism slow down with age?

Metabolism isn’t just one process; it’s a complex interplay of biochemical reactions that keep you alive and functioning. At the core of this is your Basal Metabolic Rate (BMR), which is the minimum energy requirement for essential physiological functions like breathing, circulating blood, cellular repair, and waste elimination. According to Harvard Health, for sedentary adults, BMR accounts for 50-70% of total daily energy expenditure. The rest comes from dietary thermogenesis, the energy needed to digest food (10-15%), and physical activities (20-30%).


Contrary to popular belief that metabolism peaks in childhood and steadily declines with age, a groundbreaking study published in 2021 in the journal Science offers a different narrative. Researchers examined 6,421 individuals ranging from 8 days to 95 years old across 29 countries. They found that metabolism spikes within the first year of life, being about 50% faster in infants compared to adults. From there, metabolic rates gradually decrease, plateauing from ages 20 to 60 for both genders, even during pregnancy. Only after 60 does metabolism begin its decline, dropping by 26% by the age of 90.


This research highlights that age-related metabolic changes primarily kick in during the latter part of life. The decline from age 60 onward reflects shifts in tissue-specific metabolism and is associated with a rise in noncommunicable diseases.

How important is metabolism for weight loss?

While genetics play a role in determining metabolism, the aforementioned study indicates that weight gain in middle age is more likely influenced by external factors like diet, physical activity, sleep patterns, and stress.


Calories in versus calories out remains the most credible predictor of weight fluctuations. Popular weight loss programs advocate creating a daily calorie deficit, often referencing the “3,500-calorie rule” to lose 1 pound per week. However, emerging research questions the long-term efficacy of this rule, suggesting that a reduced calorie intake can also lower the resting metabolic rate, thereby obstructing planned weight loss.


Researchers suggest even minor adjustments in daily caloric intake can produce meaningful weight changes over time. For instance, skipping dessert once a week could translate to nearly 6 pounds lost over a year. Consistent monitoring of food intake coupled with incremental increases in physical activity often yield more stable results than drastic weight-loss programs.

While genetics play a role in determining metabolism, research indicates that weight gain in middle age is more likely influenced by external factors like diet, physical activity, sleep patterns, and stress.

Factors that contribute to weight gain

While age itself can’t be a reason for weight gain, the majority of people experience biological and lifestyle changes in middle age that can make them more prone to retaining extra pounds.

Muscle mass loss

The aforementioned research underscores that body composition, particularly fat-free mass, significantly impacts metabolic rate. Of all tissue types, muscle mass burns the most number of calories increasing basal metabolic rate.

Sarcopenia is an age-related, involuntary loss of skeletal muscle mass and strength. Physically inactive people start losing from 3–5% of their muscle mass each decade after the age of 30. By the age of 75–80, this loss can reach up to 50% of lean muscle mass, according to studies.


Sarcopenia ignites hormonal changes that increase the risks of obesity even more. Reduced muscle mass leads to mitochondrial dysfunction that impairs skeletal muscle insulin sensitivity and increases the risk of insulin resistance and type 2 diabetes associated with extra weight.

Less active lifestyle

Poor eating habits and lack of physical activity are considered the 2 main reasons for the obesity epidemic in industrial countries. Global obesity prevalence may reach more than 21% in women and 18% in men by 2025.


Physical activity can be divided into exercise-related activity thermogenesis (EAT) and non-exercise activity thermogenesis (NEAT). EAT refers to any kind of sports training, while NEAT includes all other types of daily activity including physical labor, doing chores, taking stairs, walking, etc. According to statistics, the percentage of the population engaged in regular exercise activity remains low. 36.1% of the studied US population was categorized as sedentary, while a further 47.6% were physically active at low levels.


For busy middle-aged individuals, short, high-intensity exercises like Reduced Exertion HIIT (REHIT) and increased daily movement can effectively elevate energy expenditure.

Unbalanced diet

An unhealthy diet, rich in simple carbohydrates, sugars, and ultra-processed foods, not only disrupts metabolism but also leads to caloric excess. A balanced diet is rich in lean proteins, fibers, healthy fats, and essential nutrients.

Lack of sleep

Sleep deprivation is another important factor in slowing the metabolism. Sleeping less than 7 hours at night decreases insulin sensitivity. Insulin is a key hormone to turn glucose into energy. In addition to that, lack of sleep increases levels of the hunger hormone ghrelin stimulating the desire to eat, especially foods rich in fat and sugar. A systematic review of 36 publications showed that sleep-deprived individuals have a higher risk of concurrent and future obesity.

Stress levels

Elevated stress levels can induce hormonal imbalances that alter metabolism. Stress triggers the production of the stress hormone cortisol which temporarily pauses regular bodily functions to release more energy to the alleged threat. Cortisol is associated with increased appetite and excess abdominal fat storage.


Both epinephrine and cortisol released under chronic stress may increase insulin resistance in the long term.

Cell aging

Cell aging is the only age-related biological mechanism of the metabolism slowdown. Mitochondria are the cell elements responsible for turning nutrients and oxygen into energy. With age, the number of mitochondria reduces and they become less efficient. This process becomes significant after the age of 60.


After comparing changes in the mitochondria between 9 younger adults (average age of 39) and 40 older adults (average age 69), researchers found that older adults had 20% fewer mitochondria. Additionally, their mitochondria were nearly 50% less efficient at using oxygen to create energy.

For busy middle-aged individuals, short, high-intensity exercises like Reduced Exertion HIIT (REHIT) and increased daily movement can effectively elevate energy expenditure.

How to prevent weight gain with age

There are lifestyle changes you can make to level out the factors that negatively impact your metabolism and contribute to weight gain.

1. Do strength training

Resistance training is effective in preserving muscle mass as you age, helping to maintain your metabolic rate.

2. Introduce HIIT to your exercise routine

HIIT is an efficient way to get more physical activity in a fraction of the time. High-intensity workouts engage your fast-twitch muscle fibers that don’t work in other types of training. Additionally, HIIT accelerates your metabolism for hours after training due to the excess post-exercise oxygen consumption (EPOC).


Reduced Exertion HIIT (REHIT) is the next generation of HIIT developed by scientists looking for the shortest, most effective, and accessible way to exercise. A 5-minute REHIT session packs in the fitness benefits of a 20-minute HIIT workout or those of a regular 45-minute steady-state cardio workout.


As you work at supra-maximal intensity during the 2×20-second sprints, your body is pushed into a fight or flight mode and burns significantly more body fat. According to a study, REHIT burns almost twice as many calories per minute as moderate-intensity cardio, with 66% of calories burned after your workout. This is the shortest, most efficient way to exercise for people pressed for time. CAROL Bike is the only bike fully optimized for REHIT— making it easy, effective, and safe. Its AI automatically tailors resistance levels so that you hit your personal maximal capacity during each ride.

3. Practice endurance training

Endurance training significantly improves mitochondrial activity and fights age-related metabolic changes. Even a single bout of endurance exercise is sufficient to increase the number of mitochondria and their activity. According to studies, with prolonged endurance training, mitochondrial volume typically increases as much as 40–50%.


CAROL Bike’s Zone-Based Free Ride is a low-intensity endurance cycling training that you can perform a few times a week.

4. Eat more protein, fiber, and healthy fats

Protein is the primary nutrient for your body to build muscles, organs, bones, and skin. As you age, your body requires more protein to better preserve muscle mass and strength to maintain the same quality of life. Healthy fats provide a stable source of long-term energy, reducing overall calorie intake. Fiber increases satiety levels and helps digestion.

5. Get more sleep

In order to maintain the metabolic equilibrium, you need to get at least 7 hours of sleep per day. In order to get a good night’s sleep, try to maintain a  consistent bedtime, reduce time spent with electronic devices before going to bed, and avoid consuming large meals, caffeine, or alcohol close to bedtime.

6. Practice meditation and breathing techniques

Yoga, meditation, and breathing techniques are efficient stress management tools that reduce cortisol levels and facilitate weight loss in the long term. A study of 92 overweight women during weight loss treatment confirmed that good mental health is an important factor that prevented participants from regaining weight and improved continued weight loss.

Although it may seem that metabolism slows dramatically with age, current research suggests that age-related changes in metabolism are not as significant until after the age of 60. Through mindful lifestyle choices, it’s entirely possible to maintain a healthy weight throughout one’s lifespan. With strategies like REHIT, even time-crunched individuals can effectively manage their weight.

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