Does Metabolism Really Slow Down With Age?
If you're over 35 and living a busy professional life, you've probably said it: "My metabolism just isn't what it used to be." I hear this almost every week with clients at Griffin Fit Personal Training in Oxford.
But here's the reality - your metabolism hasn't suddenly 'switched off.' It hasn't broken. And it hasn't betrayed you. What's changed is stimulus.
Ageing doesn’t automatically slow metabolism - our behaviour changes, and the body adapts to those changes. Let’s break this down properly.
What Metabolism Actually Is
Metabolism is simply the total energy your body uses in a day, made up of four components:
1. Basal Metabolic Rate (BMR) – Energy used at rest for organs, breathing, and brain function.
2. Thermic Effect of Food (TEF) – Energy used to digest food.
3. Exercise Activity – Planned exercise like lifting, running, cycling or swimming.
4. Non-Exercise Activity (NEAT) – All other movement, such as walking or climbing stairs.
The largest contributor is BMR, and the biggest driver of BMR is lean muscle mass.
Does Metabolism Really Slow Down?
"The short answer: Research shows metabolic rate stays relatively stable from age 20 to around 60. What changes is how much we move, how much muscle we carry, and how hard we train."
Research does indeed show metabolic rate remains relatively stable from age 20 to around 60 when body composition is accounted for. What typically changes is behaviour:
We move less
We lose muscle mass
We sit more
Training intensity drops
Stress and sleep challenges increase
Your body adapts to the stimulus you give it. If the stimulus reduces, energy expenditure reduces.
The Missing Piece in Most Metabolism Conversations
One of the biggest lifestyle changes as people age is a reduction in physical activity.
Even losing a few thousand daily steps can significantly reduce total energy expenditure over time. This is where cardiovascular exercise, such as running, cycling, rowing or brisk walking, can play an important role.
Cardio and Weight Gain: Helpful or Overrated?
Cardio can help manage body fat by:
Increasing daily energy expenditure
Improving cardiovascular health
Supporting insulin sensitivity
Encouraging regular movement
However, cardio alone is rarely the most effective long‑term fat‑loss strategy if resistance training is ignored, as muscle loss can occur and metabolic rate may gradually decline.
The Role of Resistance Training
Resistance training is critical for maintaining muscle mass as we age.
Adults can lose 3–8% of muscle mass per decade without strength training. Maintaining muscle supports metabolic health, strength, bone density and long‑term weight control.
Cardio works best when used alongside resistance training rather than replacing it.
Metabolism in Men as We Age
Common changes for men include:
Gradual testosterone decline
Increased abdominal fat storage
Reduced muscle mass if inactive
Best approach:
Resistance training 3–4 times per week
8–10k daily steps
1–3 cardio sessions weekly
Adequate protein intake
Metabolism in Women and the Impact of Menopause
Hormonal changes during perimenopause and menopause can influence fat distribution, recovery and sleep quality.
However, resting metabolic rate does not dramatically collapse.
The most effective strategy includes:
Resistance training at least 3 times weekly
Adequate protein intake
Cardiovascular exercise for heart health and energy expenditure
Strength training to protect bone density
How to Include Cardio Without Undermining Fat Loss
Cardio works best when structured intelligently. A practical weekly structure:
3–4 resistance training sessions
8,000–10,000 daily steps
1–3 structured cardio sessions such as running or cycling
Cardio should support overall activity without interfering with recovery from strength training.
Final Thought
Ageing does not automatically destroy your metabolism. More often, we simply move less, lose muscle and reduce training intensity.
The solution is simple but powerful:
Daily movement
Intelligent use of cardio
Quality sleep
Consistency
Ageing is inevitable - but metabolic decline is largely optional.
Written by Alan Griffin, qualified personal trainer and founder of Griffin Fit, Headington, Oxford
