BMR is closely dependent on (AIIMS MAY 2011, AIPG 2010,2011)
|B||lean body mass|
a. Energy expenditure in resting state is given by RMR or the Resting Metabolic Rate.
b. The metabolic rate determined at rest in a room at a comfortable temperature in the thermoneutral zone 12–14 hours after the last meal is called the basal metabolic rate (BMR).
c. Katch-McArdleformula is most accurate for its calculatiom on the basis of lean body mass: where LBM is the lean body mass in kg.
d. This value falls about 10% during sleep and up to 40% during prolonged starvation.
e. The rate during normal daytime activities is, of course, higher than the BMR because of muscular activity and food intake.
f. The maximum metabolic rate reached during exercise is often said to be 10 times the BMR.
Factors Affecting the Metabolic Rate
- The metabolic rate is affected by many factors. One of the most important is muscular exertion. O2 consumption is elevated not only during exertion but also for as long afterward as is necessary to repay the O2 debt .
Factors Affecting the Metabolic Rate.
Muscular exertion during or just before measurement
Latest ingestion of food (SDA)
High or low environmental temperature
Height, weight, and surface area
Circulating levels of thyroid hormones
Circulating epinephrine and norepinephrine levels
a. Comparison of the correlation coefficients obtained by both Schofield and by Soares&Shetty (1988) shows that BMR has a stronger correlation with body weight than with any other nutritional anthropometric index used as a single independent variable.
b. Schofield, Soares&Shetty (1986,88) demonstrated an r = 0.80 for body weight accounting for 64% of the variance while BMI had an r = 0.64 and height an r = 0.57.
c. Miller and Blyth assessed different means of adjusting basal metabolic rate (BMR) for different body size parameters. The correlation between BMR and lean body mass(LBM) was r =0.92, greater than that for BSA (r= 0.84) and body mass (r = 0.85).
d. So, we can see that BMR has highest correlation with Lean body mass as compared to Total weight (fat + Lean body weight), BSA & Height.
e. Since BMR is the energy consumption in resting state in metabolic active tissue i.e lean body mass (adipose tissue is metabolically inert) BMR depends very much on LBM. By far the main determinant of resting metabolic rate is fat-free mass (Miller & Blythe, 1953; Webb, 1981)
f. In a very tall thin and short obese person BMR differs but BSA can be similar so low correlation. Same way BMI depends more on Body weight rather Lean body weight so again low correlation.
g. Latestly ingested foods also increase the metabolic rate because of their specific dynamic action (SDA). The SDA of a food is the obligatory energy expenditure that occurs during its assimilation into the body.
h. Another factor that stimulates metabolism is the environmental temperature. The curve relating the metabolic rate to the environmental temperature is U-shaped. When the environmental temperature is lower than body temperature, heat-producing mechanisms such as shivering are activated and the metabolic rate rises.
i. When the temperature is high enough to raise the body temperature, metabolic processes generally accelerate, and the metabolic rate rises about 14% for each degree Celsius of elevation.