The document discusses basal metabolic rate (BMR), the energy required for involuntary bodily functions, and the methods for its measurement, such as direct and indirect calorimetry. Factors affecting BMR include body composition, gender, age, sleep, body temperature, and the role of endocrine glands like the thyroid. Key insights include that higher muscle mass correlates with a higher BMR, while thyroid hormones significantly influence metabolic rates.

1. Mrs. R.Subha, M.Sc., M.Phil., D.C.T.,
Assistant Professor of Home Science,
V.V.Vanniaperumal College for Women,
Virudhunagar.
Factors Affecting Basal Metabolic
Rate

2. Basal Metabolic Rate
 Amount of energy required to carry on the involuntary
work of the body is known as Basal Metabolic Rate.
 Measurement of Basal Metabolism:
 Direct Calorimetry – require the subjects to be in human
caloriemeter or respiration chamber – to measure the
amount of heat evolved – Atwater and Rosa respiration
caloriemeter – measures the heat output by the subject.
 Indirect Calorimetry – based on the fact that the oxygen
used and CO2 produced is in proportion to the heat
generated – simple procedure – Benedict and Roth
apparatus – gives more feasible and accurate measure
of heat.

3. Factors affecting Basal Metabolic
Rate
Body Composition
 body tissues are metabolically active and
constantly maintained - their components are
degraded and resynthesised with an accompanying
requirement of energy.
 Muscle, brain and various glands and organs (liver)
– more active and metabolically consume large
amount of oxygen/unit of weight – produce more
heat
 Bone tissues and adipose tissue are relatively
inactive metabolically and requires less oxygen /unit
 Total basal energy requirement/unit of body weight
is higher when muscle tissue is in higher proportion
in total body weight.

4.  Gender: Woman have more adipose tissue and less muscle
tissue compare to men of same height and weight.
 Age :BMR -first 2 years of life – declines throughout
childhood – accelerates slightly in adolescence. When
growth increase, BMR increase – later years muscle tone
decreases when muscle mass reduce. Hence BMR is low.
 Sleep: 10% lower than waking state – also depends on
amount of motion during sleep. The B.M.R. in sleep is
about 5 percent less than in the basal metabolic state.
 Body temperature: elevation in body temperature increases
BMR. 13% for each ◦ C and 7% ◦ F. Increase chemical reaction –
increases temperature.
 Endocrine Glands:
 Thyroid gland – hormone (thyroxine) – iodine – powerful stimulator
of metabolism.
 Hypothyroidism – BMR depressed due to under secretion of thyroxin.
 Hyperthyroidism – BMR elevated to 50-70% above normal level – due
to oversecretion of thyroxin.