Metabolic age is a reflection of physical health in the form of a calculation based on the base metabolic rate (BMR). If someone's metabolic age is lower than his or her actual age, it suggests that the body is in good health, while one that is higher than the actual age indicates that someone may be experiencing health problems. This measurement is one among many that can be used to assess health, and people should avoid putting too much weight on it; a more complete assessment of physical health can be obtained from a medical professional, who may also have suggestions to improve health.
A number of different calculations can be used to determine metabolic age, but they all rely on some combination of the subject's height, actual age, and weight. Coming up with a number is a bit more complicated than this, however, since it is affected by activity level, genetics, and a wide variety of other factors. Estimates can vary depending on which formula is used, reflecting the fact that it is a bit difficult to pin down a single number.
As people age, their BMR changes. Older individuals tend to have lower caloric requirements for a variety of reasons, ranging from a reduction in physical activity that reduces the demand on calories for energy to a reduction of muscle, which also reduces the body's need for energy. The BMR plays an important role in metabolic age, making it important to periodically recalculate it to see if circumstances have changed.
Some fitness centers perform this calculation for their clients as a courtesy, and there are also many calculators available on the Internet which allow people to plug in values and obtain their number. People should be aware that health is a complicated issue, and the human body is quite diverse, which means that a calculation may not always be accurate. For example, a young athlete may appear to have a skewed metabolic age and actually be in excellent health. A full physical exam is a much better way to learn about general health.
The BMR can also be used to help people calculate appropriate caloric intake. People who are interested in calorie restriction as a facet of a weight loss program can calculate their metabolic rate and determine how many calories below that number they need to eat to lose weight. Likewise, people who want to bulk up can eat over their BMR. When the desired weight is reached, the subject can return to a maintenance level.