Basal Metabolic Rate and Recommended Dietary Allowances
What this domain tests
Basal metabolic rate (BMR) is the energy needed for vital functions at rest, measured after an overnight fast and in a comfortable environment. Recommended Dietary Allowances (RDA) are intake levels that meet the needs of nearly all healthy people in a group. The exam tests BMR factors, calculation and the meaning of RDA.
Core rules
- BMR is influenced by body size, age, sex, thyroid function, pregnancy, lactation, climate and fever.
- A simple rule of thumb is about 1 kcal/kg/hour for men and 0.9 kcal/kg/hour for women, but predictive equations are more accurate.
- Total energy expenditure = BMR × physical activity level (PAL), plus the thermic effect of food.
- RDA is not a minimum requirement; it includes a safety margin for variability within a population.
- ICMR-NIN 2020 gives reference values by age, sex and activity; these must be used rather than old or foreign values.
Worked example
A 65 kg sedentary man: BMR ≈ 65 × 1 × 24 = 1,560 kcal/day. With a PAL of about 1.4, total energy ≈ 1,560 × 1.4 = 2,184 kcal/day, close to the ICMR-NIN 2020 sedentary reference of about 2,110 kcal. Reasoning: BMR is only the resting component; activity raises the total. Using BMR alone would underfeed an active person.
Traps that cost marks
- Measuring BMR after a meal or exercise.
- Treating RDA as the exact requirement of every individual.
- Forgetting to multiply BMR by PAL.
- Ignoring pregnancy, lactation and fever as factors that raise needs.