BMR & Daily Calorie Needs
About BMR (Basal Metabolic Rate) — Detailed Guide
1. What is BMR?
Basal Metabolic Rate (BMR) is the number of calories your body needs each day to maintain vital functions while at rest — breathing, circulation, cell production, temperature regulation and other essential processes. BMR is measured under very specific conditions clinically (fasted, rested, in a thermoneutral environment) and is the baseline energy need.
2. Formula used (Mifflin–St Jeor)
This widget uses the Mifflin–St Jeor equation, commonly used because it performs well across many populations:
Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161
The widget converts imperial inputs (lb, in) to metric before calculation.
3. What is TDEE and activity multipliers?
Total Daily Energy Expenditure (TDEE) is BMR × an activity factor representing daily movement and exercise. Common multipliers used here:
- 1.2 — Sedentary (little or no exercise)
- 1.375 — Lightly active (1–3 days/week)
- 1.55 — Moderately active (3–5 days/week)
- 1.725 — Very active (6–7 days/week)
- 1.9 — Extra active (hard daily exercise or physical job)
4. Example
Say a 30-year-old woman, 65 kg, 165 cm, moderately active (1.55):
BMR ≈ 10×65 + 6.25×165 − 5×30 − 161 = 650 + 1031.25 −150 −161 ≈ 1370 kcal/day.
TDEE ≈ 1370 × 1.55 ≈ 2124 kcal/day (approx maintenance).
5. Factors that change BMR
- Lean body mass: More muscle raises BMR because muscle uses more energy at rest than fat.
- Age: BMR declines with age, partly due to loss of lean mass.
- Sex: Men typically have higher BMRs because of higher average lean mass.
- Hormones: Thyroid hormones, cortisol, and sex hormones influence metabolic rate.
- Genetics & environment: Some people naturally have higher or lower metabolic rates; temperature and recent food intake also affect measurements.
6. How to use the estimate practically
Start with TDEE: Use the estimated TDEE as your maintenance target. Track body weight and body composition for 2–4 weeks to confirm accuracy.
Fat loss: Try a conservative deficit first (≈150–300 kcal/day or about 7–15% below TDEE) and monitor energy levels and exercise performance. Avoid very low calorie diets without supervision.
Muscle gain: Add a small surplus (≈200–350 kcal/day), pair with progressive resistance training and adequate protein (1.6–2.2 g/kg/day).
7. Common FAQs
Q: Is BMR the same as RMR?
A: Resting Metabolic Rate (RMR) is similar to BMR but measured in slightly less strict conditions; values are close, and many people use the terms interchangeably for practical planning.
Q: How accurate is this calculator?
A: Equations like Mifflin–St Jeor give reasonable estimates for most people, but individual variation exists. Use measurements (weight trends, body comp) to fine-tune intake.
Q: I am pregnant or have a medical condition — can I use this?
A: For pregnancy, certain illnesses, or major medication changes, consult a clinician; adjustments are often needed.
8. Safety & best practice
Always prioritise adequate protein, sleep and progressive training when making body composition changes. If you plan to reduce intake significantly or have underlying health concerns, consult a healthcare professional before starting.
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