Question 1

Why does the Mifflin-St Jeor equation use different formulas for men and women?

Accepted Answer

Men generally have more lean muscle mass and higher metabolic rates than women. The equation accounts for this by adding 5 kcal/day for males and subtracting 161 kcal/day for females. These constants were derived from regression analysis of measured resting metabolic rate data in a diverse adult population. On average, men have a BMR 5–10% higher than women of the same weight, height, and age.

Question 2

What does my BMR number mean for weight loss?

Accepted Answer

Your BMR is the minimum calories your body needs for basic survival functions at complete rest. To manage weight effectively, first calculate your TDEE (Total Daily Energy Expenditure) by multiplying your BMR by your activity factor (1.2 for sedentary up to 1.9 for extremely active). Then create a calorie deficit of 300–500 kcal below your TDEE — never below your BMR — for safe, sustainable fat loss of approximately 0.3–0.5 kg per week.

Question 3

Can I use this BMR calculator if I am under 18 or over 80?

Accepted Answer

The Mifflin-St Jeor equation was validated for adults aged 19–80. For ages 15–18, it may provide a reasonable estimate but tends to slightly underestimate BMR during growth phases. For adults over 80, accuracy decreases due to significant changes in body composition. For children under 15, the Schofield equation or FAO/WHO/UNU equations are more appropriate. Always consult a registered dietitian for clinical nutrition planning in these age groups.

Question 4

What is the difference between BMR and TDEE?

Accepted Answer

BMR (Basal Metabolic Rate) is the calories your body burns at complete rest — your baseline energy requirement before any activity. TDEE (Total Daily Energy Expenditure) is BMR multiplied by an activity factor that accounts for exercise, movement, and the thermic effect of food. TDEE represents your actual daily calorie needs to maintain current weight. For a sedentary person, TDEE is approximately 1.2× BMR; for a very active person, up to 1.9× BMR. Always base your calorie targets on TDEE, not BMR.

Question 5

Is the Mifflin-St Jeor equation the most accurate BMR formula available?

Accepted Answer

For most non-athletic adults, yes. A 2005 review published in the Journal of the American Dietetic Association comparing 10 BMR equations found Mifflin-St Jeor the most accurate in 82% of cases, with a mean error of approximately 10% compared to indirect calorimetry (the gold-standard measurement method). The Harris-Benedict equation (1919, revised 1984) has errors of 10–15%. For lean athletes with known lean body mass, the Katch-McArdle formula is more accurate.

Question 6

Does BMR decrease with age, and can I slow the decline?

Accepted Answer

Yes. BMR naturally declines approximately 1–2% per decade after age 30, primarily because of gradual loss of lean muscle mass (sarcopenia) — muscle tissue burns significantly more calories at rest than fat tissue. The most effective strategy to slow this metabolic decline is regular resistance training (weight lifting, bodyweight exercises), which preserves or builds lean muscle mass. Adequate protein intake of 1.2–1.6 g per kg of body weight per day also helps preserve muscle and metabolic rate, especially during calorie restriction.

Question 7

How do I use my BMR to calculate my activity-adjusted calorie needs?

Accepted Answer

Multiply your BMR by the appropriate activity factor: 1.2 for sedentary (desk job, little exercise), 1.375 for lightly active (light exercise 1–3 days/week), 1.55 for moderately active (moderate exercise 3–5 days/week), 1.725 for very active (hard exercise 6–7 days/week), and 1.9 for extremely active (physical job plus hard training daily). The result is your TDEE — the calories needed to maintain your current weight. Subtract 300–500 kcal for gradual fat loss, or add 200–300 kcal for muscle gain.

Question 8

What factors can significantly change my actual BMR from the calculated estimate?

Accepted Answer

Several medical and physiological factors can raise or lower actual BMR substantially. Hypothyroidism can reduce BMR by 20–40%. Hyperthyroidism, fever (each 1°C elevation increases BMR ~13%), pregnancy (increases by 15–20%), and recovery from surgery or illness can all significantly elevate it. High muscle mass from strength training raises BMR because muscle tissue burns 6× more calories at rest than fat. Prolonged caloric restriction triggers metabolic adaptation — a decrease in BMR of 10–30% as the body conserves energy — which is why crash diets often fail long-term.

BMR Hesaplayıcısı — Bazal Metabolizma Hızı

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