Metabolism Explained: How Your Body Burns Calories
Complete guide to metabolic rate. Learn what affects metabolism, myths vs. facts, and how to naturally boost your calorie burn.
What is Metabolism?
Metabolism is the sum of all chemical processes in your body that convert food into energy. It's not a single thing but rather thousands of simultaneous reactions that keep you alive—breathing, circulating blood, maintaining body temperature, building cells, and more.
Your "metabolic rate" is the number of calories your body burns just to maintain these basic functions. Some people claim to have a "fast metabolism" or "slow metabolism," but the science is more nuanced.
Components of Your Metabolic Rate
Your total daily energy expenditure (TDEE) consists of four components:
1. Basal Metabolic Rate (BMR) - 60-75%
The calories you burn at complete rest maintaining basic body functions. This is the largest component of TDEE.
2. Thermic Effect of Food (TEF) - 10%
Calories burned digesting food. Protein has the highest thermic effect (20-30%), followed by carbs (5-10%) and fats (0-3%).
3. Exercise Activity Thermogenesis (EAT) - 5-10%
Calories burned during intentional exercise. This varies greatly based on exercise intensity and frequency.
4. Non-Exercise Activity Thermogenesis (NEAT) - 15-30%
Calories burned through daily activities: walking, fidgeting, work tasks, etc. This is often underestimated but significant.
Example: 2,000 calorie TDEE breakdown:
- BMR: 1,400 calories (70%)
- TEF: 200 calories (10%)
- Exercise: 150 calories (7.5%)
- NEAT: 250 calories (12.5%)
Factors That Affect Your Metabolism
Age
Metabolism decreases ~2-8% per decade after 30 due to muscle loss. This is called sarcopenia.
Muscle Mass
Muscle is metabolically active; each pound burns ~6 calories/day at rest. More muscle = higher metabolism.
Sex
Men typically have higher metabolic rates due to more muscle mass. Hormonal differences also play a role.
Body Size
Larger bodies require more energy to maintain, so BMR correlates with weight.
Genetics
Genetic factors account for 20-30% of metabolic variation. Some people naturally have faster metabolisms.
Thyroid Function
Thyroid hormones regulate metabolism. Hypothyroidism slows it; hyperthyroidism speeds it.
Hormones
Estrogen, testosterone, cortisol, and insulin all affect metabolic rate.
Calorie Restriction
Extreme dieting lowers metabolism as your body enters "conservation mode." Moderate deficits don't have this effect.
Temperature
Cold environments increase metabolism as your body burns calories to maintain warmth.
Activity Level
Regular exercise, especially strength training, increases resting metabolism.
Metabolism Myths vs. Facts
❌ Myth: "I have a slow metabolism"
Most people's metabolic rates are within normal range. Weight gain usually comes from eating more, not a fundamentally broken metabolism.
❌ Myth: "Eating late makes weight gain worse"
Timing doesn't matter; total calories do. Your body doesn't process calories differently based on meal timing.
❌ Myth: "Small frequent meals boost metabolism"
Meal frequency doesn't affect metabolic rate. What matters is total calorie intake.
✅ Fact: "Muscle increases resting metabolism"
True. Each pound of muscle burns 6 calories at rest; strength training is the best way to increase long-term metabolic rate.
✅ Fact: "Protein has a higher thermic effect"
True. Your body burns more calories digesting protein than other macronutrients.
✅ Fact: "Sleep affects metabolism"
True. Poor sleep impairs hormonal regulation and slows metabolic rate.
How to Naturally Boost Your Metabolism
- 1. Build Muscle Through Strength Training: Most effective long-term strategy. 3 sessions/week creates measurable metabolic increase.
- 2. Eat Adequate Protein: Increases thermic effect and supports muscle retention.
- 3. Stay Active: NEAT (non-exercise activity) contributes significantly. Take stairs, walk more, fidget!
- 4. Get Quality Sleep: 7-9 hours nightly supports hormonal balance and metabolic health.
- 5. Manage Stress: Chronic stress elevates cortisol, which slows metabolism.
- 6. Stay Hydrated: Even mild dehydration slightly reduces metabolic rate.
- 7. Don't Drastically Cut Calories: Extreme diets slow metabolism. Moderate deficits work better.
- 8. Cold Exposure: Brief cold exposure (cold showers) stimulates metabolism, though effect is small.
- 9. Check Thyroid: If you suspect thyroid issues, get tested. This is fixable with treatment.
Calculate Your Metabolic Rate
Use our calorie calculator to determine your basal metabolic rate and total daily energy needs.
Calculate Your Metabolism →