How metabolism changes with age when physical activity is missing
Metabolism tends to slow with age, and when regular physical activity is missing this process accelerates-leading to lower calorie needs, loss of muscle, greater fat gain, and higher risk of insulin resistance and related conditions.https://pmc.ncbi.nlm.nih.gov/articles/PMC12675181/
What “metabolism” means here
Metabolism refers to the chemical processes your body uses to convert food into energy and to maintain tissues. Two key parts are resting energy expenditure (how many calories you burn at rest) and the energy used for movement and digestion. As people age, both parts change in ways that reduce total daily energy expenditure.https://pmc.ncbi.nlm.nih.gov/articles/PMC12675181/
Why metabolism slows with age when activity is low
– Loss of muscle mass: Skeletal muscle declines with age unless it is regularly challenged. Muscle is metabolically active at rest, so losing muscle lowers resting energy needs.https://pmc.ncbi.nlm.nih.gov/articles/PMC12675181/
– Lower mitochondrial function: Aging can reduce how well mitochondria (the cell’s energy factories) work, which weakens overall energy metabolism; exercise normally helps preserve mitochondrial health, so inactivity lets this decline continue.https://www.frontiersin.org/journals/aging/articles/10.3389/fragi.2025.1696856/full
– Fat redistribution and inflammation: With age and sedentary behavior, fat tends to accumulate inside the abdomen and around organs. This visceral fat releases substances that promote chronic, low grade inflammation and impair insulin action, raising the risk of metabolic disease.https://pmc.ncbi.nlm.nih.gov/articles/PMC12675181/
– Reduced spontaneous activity: Older adults who are inactive also take fewer daily steps and move less overall, further lowering total daily energy expenditure and creating a feedback loop that favors weight gain.https://www.nature.com/articles/s43856-025-01226-6
Consequences when physical activity is missing
– Easier fat gain and harder weight loss: Lower energy needs plus the same or increased calorie intake mean body fat tends to increase; this makes loosing weight more difficult without increasing activity or reducing calories.https://pmc.ncbi.nlm.nih.gov/articles/PMC12675181/
– Worsening insulin sensitivity: Inactivity with age contributes to reduced insulin sensitivity and higher risk of type 2 diabetes.https://www.frontiersin.org/journals/aging/articles/10.3389/fragi.2025.1696856/full
– Lower cardiorespiratory fitness: Not doing cardio or other aerobic activity reduces VO2 peak and makes everyday tasks more tiring, which can further reduce willingness to exercise.https://pmc.ncbi.nlm.nih.gov/articles/PMC12675181/
– Reduced functional capacity and higher disease risk: The combination of muscle loss, fat gain, and metabolic changes raises the risk of frailty, cardiovascular disease, and decreased quality of life.https://www.nature.com/articles/s43856-025-01226-6
How different types of activity help (and what is missed when they are absent)
– Resistance training maintains or rebuilds muscle mass and helps preserve resting metabolic rate; without it muscle loss proceeds more quickly.https://pmc.ncbi.nlm.nih.gov/articles/PMC12675181/
– Aerobic training or cardio workouts improve mitochondrial function, insulin sensitivity, and cardiorespiratory fitness; skipping regular running, cycling, walking, or other cardio deprives the body of these benefits.https://pmc.ncbi.nlm.nih.gov/articles/PMC12675181/
– High intensity interval training can produce meaningful improvements in glucose metabolism and fitness in older adults when performed safely; absence of higher-intensity efforts means missing those gains, though steady moderate cardio still helps.https://pmc.ncbi.nlm.nih.gov/articles/PMC12675181/
– Breaking up long periods of sitting with short activity bouts helps metabolic markers; continuous sedentary time worsens outcomes even if occasional exercise is performed.https://www.frontiersin.org/journals/aging/articles/10.3389/fragi.2025.1696856/full
Practical actions to slow age-related metabolic decline when activity is limited
– Prioritize any movement over none: Short walks, light resistance moves, or brief cardio sessions are better than long inactivity and help counteract declines in metabolism.