Abnormal basal metabolic rate
Abnormal BMR has physiological and pathological causes.
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A high or low basal metabolic rate (BMR) can stem from either normal bodily processes or from disease. Physiological factors include sex, age, body shape, activity level, and environment: males tend to have a higher BMR than females, and a woman’s BMR may rise during pregnancy or breastfeeding. Infants and children have a high BMR to support growth, while older adults typically have a low one. Tall, thin individuals have a higher BMR than shorter people of the same weight due to greater skin surface area. BMR drops during sleep and rises with exercise; regular exercisers have a higher BMR than sedentary individuals. Both hot and cold environmental temperatures increase BMR.
Pathological causes include fever, which raises BMR by about 7 percent for each degree Fahrenheit increase in body temperature. Thyroid disorders directly affect BMR: hyperthyroidism (excess thyroid hormone) raises it, while hypothyroidism (deficient thyroid hormone) lowers it. Prolonged malnutrition lowers BMR, whereas prolonged overnutrition raises it, helping the body maintain stable weight. Cancer can also increase BMR, likely due to the high metabolic activity of tumor cells.
Quick Facts
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Lore & Background
An abnormal basal metabolic rate is not necessarily indicative of disease; a number of physiological factors can alter the BMR by influencing cellular metabolic activity. For instance, males are more likely than females to have a high BMR, and in women, the BMR may rise to abnormal levels during pregnancy or lactation. An individual's BMR varies greatly with age: infants and children typically have a high BMR, required for growth, while the elderly have a low BMR. Tall, thin people have a higher BMR than their shorter counterparts, even with the same weight, due to the greater surface area of their skin. The metabolic rate also decreases during sleep and increases in exercise, and individuals who exercise regularly have a higher BMR than those who are sedentary. Environmental temperature also has an effect: the BMR is increased in both heat and cold.
Reader's Guide
A common pathological cause for a high BMR is fever, since a rise in body temperature increases the rate of cellular metabolic reactions. It is estimated that for every degree Fahrenheit of rise in body temperature, the BMR increases by 7 percent. Thyroid disease also has a marked effect on BMR, since thyroid hormones regulate the rate of cellular metabolism. Hyperthyroidism—in which there is an increase in the production of thyroid hormones—leads to a high BMR, while hypothyroidism—in which thyroid hormones are depleted—causes a low BMR. Prolonged periods of abnormal nutrition cause an adaptive change in BMR; this helps the body to maintain a stable body weight in response to the change in food supply. In prolonged malnutrition, the BMR declines, while in prolonged overnutrition, the BMR is increased. Cancer sometimes causes an increase in BMR, perhaps because the cancer cells that form tumors have a high level of metabolic activity.
Did You Know?
- Hyperthyroidism leads to a high BMR, while hypothyroidism causes a low BMR.
- Prolonged malnutrition causes a decline in BMR, while prolonged overnutrition increases it.
Frequently Asked Questions
What is Abnormal basal metabolic rate?
It describes a resting energy expenditure that deviates above or below the expected range for a given individual's sex, age, and body composition. The deviation can reflect everyday physiological variation or signal an underlying medical condition.
What are Abnormal basal metabolic rate's causes?
Physiological drivers include sex, age, body size, sleep, exercise, ambient temperature, pregnancy, and lactation. On the pathological side, fever, thyroid disorders, malnutrition, overnutrition, and cancer can all push the rate out of its normal band.
Who is most commonly associated with Abnormal basal metabolic rate?
Males typically run a higher BMR than females, while infants and children show elevated rates to fuel rapid growth. Older adults tend toward a lower rate, and pregnant or breastfeeding women experience a measurable increase.
How does Abnormal basal metabolic rate work in the body?
Greater skin surface area in tall, thin individuals raises the rate compared with shorter people of the same weight, and the rate drops during sleep but climbs with physical activity. Regular exercise training keeps the baseline elevated over time, whereas sedentary living pulls it down.
Why is Abnormal basal metabolic rate important in medicine?
It sits at the intersection of physiology and medicine as a diagnostic clue that separates benign variation from disease. Identifying whether a shift is driven by factors like age or pregnancy versus conditions such as thyroid dysfunction or cancer directly shapes clinical management.
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