Body size – Larger people have high BMR. A weight difference of about 10 kg may affect BMR by 123 Kcal in adult men or women.
Body composition-Adipose tissue has lower metabolic rate than the fat free or lean body mass. Hence, BMR is better expressed in terms of fat free or lean body mass. However, since adipose tissue contributes to body size, the energy cost of physical activity must be calculated considering the body size.
Age- Energy expenditure declines rapidly as age advances. Childhood is characterized by rapid growth and high physical activity.In infants, energy required to maintain the body temperature also increases the energy cost. In adults, there is a decrease in lean body mass and increase in adipose tissue, causing lowered BMR.
Diet-Â It affects the BMR, both immediately as well as over a long period.Post prandial thermogenesis is greater when more proteins are consumed than carbohydrates or fats. For mixed diets (mainly vegetarian) the post prandial thermogenesis may be between 5 to 15 % .
Climate- Temperatures below 25 degrees may increase energy expenditure as well as that above 30 degreesÂ may cause sweating and thereby increase energy expenditure.
Genetic Differences – BMR varies upto 10% due to ethnic, racial and genetic variations.
Hormonal state – Endocrine disorders such as hyperthyroidism and hypothyroidism affect energy expenditure to a very great extent. In hyperthyroidism BMR increases while it decreases in hypothyroidism. In pregnacy there is a Fall in BMR initially while it incraeses at the end of gestation accounting for weight gain. In lactation too BMR falls.
Psychological state- Acute anxiety does increase BMR.
Disease- The catabolic state during disease also increases BMR.
Active substances- Caffeine found in beverages like tea and coffee and other drugs like nicotine, amphetamines etc . increase energy expenditure.