Basal Metabolic Rate is the number of calories your body needs to support the vital functions that keep you alive (breathing, digesting etc) while at rest. These functions take up to 60-70% of your daily calorie intake. This makes the BMR the largest contributor to your metabolism. Your BMR does not include the calories you burn for normal daily activities or exercise.
Here are the key factors that play into BMR:
Your BMR is higher when you are younger. This is due to needing calories to supply a growing body. The trend is as you age, weight is gained in the form of fat mass and weight is lost in the form of muscle mass.
A larger individual requires more calories to sustain their body at rest and with any activity that they perform. Taller and larger individuals have bigger organs that require more calories for upkeep.
Muscle is metabolically more active than fat. This means that more calories must be burned to maintain a pound of muscle compared to a pound of fat.When you compare two healthy individuals of the same height, age and weight they can have very different BMR if they have different percentages of lean vs. fat mass. Women tend to have a higher fat mass than men, so they correspondingly have a lower BMR when compared to men of the same weight and height.
Yes, good old genetics! Some individuals are born with a higher or lower BMR than others. This is completely normal. If you suspect that you have a genetic condition that slows down your metabolism, consult a medical professional. This can be something as simple as hypothyroidism and can be treated with medication.
Hormones act like chemical dials in the body that allow your body to turn up your metabolism or down depending on your needs. The two main hormones responsible or this are thyroxine and triiodothyronine. These hormones are responsible for turning up BMR from your thyroid gland. There are other hormones that are indirectly involved to release more or less of these hormones that lead to a change in BMR as well.
Your BMR will be higher if you are fighting off an infection or healing from a major wound. This is because your body requires more calories to accomplish both these tasks.
There are so many factors that introduce so much variability in calculating an individuals BMR. This makes it difficult to measure accurately without having the most high tech equipment. Instead, the BMR is measured generally and is approximated by using an equation. Using this equation has been shown to be the most accurate in predicting the BMR for most healthy adults. The equation approximates your BMR using your body size, gender and age when calculating your daily calorie goal.
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