Final answer:
When sick, especially with a fever, the BMR can rise significantly due to higher metabolic reactions, with increases up to 50% or more.
Step-by-step explanation:
When you are sick, particularly when you have a fever, your basal metabolic rate (BMR) can increase significantly. An elevation of body temperature by 0.5° C can cause the BMR to rise by about 7%. Consequently, if an individual has a fever of 42° C, which is around 4° C above the normal body temperature, the BMR can increase by approximately 50%.
This response reflects how the body's demand for energy changes in the presence of illness. Other factors like the external temperature, physical exercise, and diet also impact the BMR. Thyroxine and adrenaline secreted from glands also contribute significantly by increasing metabolic activity.
In summary, BMR can rise substantially during illness, particularly in the presence of fever, as the body works harder to maintain health, with potential increases of up to 50% or more depending on the extent of the temperature increase.