Metabolism
Your body's engine. Metabolism is the sum of all chemical reactions that convert food into energy and building blocks. It's not fixed— it's influenced by thyroid function, muscle mass, sleep, stress, and what you eat. A "slow metabolism" usually has addressable causes.
Components of Metabolism
Basal Metabolic Rate
Calories at rest. 60-70% of total. Organs, brain, breathing. Thyroid-controlled.
Thermic Effect of Food
Energy to digest food. ~10% of calories. Protein burns most.
Activity Thermogenesis
Exercise + NEAT. Most variable. Fidgeting, walking, standing count.
What Affects Metabolism
Thyroid Function
T3 sets metabolic rate. Hypothyroidism slows everything. Check thyroid first.
Muscle Mass
Muscle burns more than fat. Strength training builds. Age-related loss.
Sleep
Poor sleep tanks metabolism. Hormones disrupted. Ghrelin rises, leptin drops.
Stress/Cortisol
Chronic stress → belly fat. Cortisol affects insulin. Muscle breakdown.
Age
Drops 2-3% per decade after 20. Largely from muscle loss. Preventable.
Dieting History
Crash diets slow metabolism. Adaptive thermogenesis. Body fights back.
Supporting Healthy Metabolism
Build Muscle
Strength training 2-3x/week. Each pound of muscle burns 6-10 cal/day. Compound exercises.
Eat Enough
Severe restriction backfires. Support thyroid function. Adequate protein.
Prioritize Protein
Highest thermic effect. Preserves muscle. 25-30% of calories or more.
NEAT Movement
Non-exercise activity. Walking, standing desk. Can be 200-500+ cal/day.
Optimize Thyroid
Check full panel. Iodine, selenium, zinc needed. Treat if low.
Cold Exposure
Activates brown fat. Increases metabolic rate temporarily. Cold showers, winter walks.