- Most calories go to keeping you alive (basal metabolism); daily movement is the biggest variable you control.
- Metabolism stays fairly stable from about 20 to 60, according to a large 2021 study; it doesn’t crash at 40.
- Dieting lowers calorie burn somewhat, more than lost weight alone predicts.
- Muscle, movement and sleep are the practical levers.
“Slow metabolism” gets blamed for a lot. Some differences are real, but they’re usually smaller than people think, and the parts you can change matter more. This guide explains how metabolism works and what research shows.
Where your calories go
| Component | Share of daily burn | What it is |
|---|---|---|
| Basal metabolic rate | About 60 to 70% | Energy to keep organs working at rest |
| Thermic effect of food | About 10% | Digesting food; higher for protein |
| Exercise | Small for most people | Planned workouts |
| Non-exercise activity (NEAT) | Highly variable | Walking, standing, fidgeting, chores |
Age
A 2021 study in Science analysed energy expenditure in thousands of people and found that, adjusted for body size, metabolism stays fairly stable from about 20 to 60, then declines slowly. Weight gain in midlife is more about activity and lifestyle than a metabolic crash.
Genetics
Genes influence appetite, where you store fat and how you respond to diet and exercise. They make weight management easier or harder, but they don’t override energy balance.
Dieting and adaptation
When you lose weight, you burn fewer calories, partly because you’re smaller and partly through adaptation: the body becomes more efficient and you move less without noticing. This is one reason weight loss slows and regain is common. Diet breaks, strength training and keeping daily steps up help.
What you can change
- Daily movement: steps make a bigger difference than most workouts
- Muscle: strength training preserves metabolically active tissue
- Protein: costs more energy to digest and keeps you full
- Sleep: poor sleep increases hunger and reduces activity
Canadian diets
Research using national survey data estimates that close to half the calories Canadians eat come from ultra-processed foods, which are easy to overeat. Canada’s Food Guide emphasizes vegetables, fruit, whole grains and protein foods, cooking more often and eating meals with others.
Thyroid and hormones
Hypothyroidism can lower metabolism and is easily tested. See our guides to thyroid conditions and hormonal imbalances.
Frequently asked questions
Does metabolism slow down with age?
Research shows it’s fairly stable from about 20 to 60, then declines gradually.
Can I speed up my metabolism?
Increasing daily movement, building muscle and eating enough protein have the biggest effects.
Does dieting damage metabolism?
Calorie burn drops somewhat more than expected during weight loss, but it isn’t permanent damage.
Is a slow metabolism why I can’t lose weight?
Differences between people exist but are usually modest; appetite, activity and food environment matter more.
This article is general information for adults in Canada, not medical advice. Talk to a doctor or pharmacist before using any prescription drug, anabolic steroid or research compound, and get bloodwork done. If you’re in crisis, call or text 9-8-8 (Suicide Crisis Helpline) any time.
