Does BMI Affect Fat Metabolism?

BMI and Fat

BMI doesn't directly calculate body fat percentage. Instead, it gives a rough estimate based on averages, but these averages are not always correct. A very muscular person, for example, might be classified as "overweight" according to BMI because muscle weighs more than fat. To learn how much body fat you have, you'll need to consult a physician or personal trainer, who can accurately calculate your body fat.

Fat Metabolism Basics

The amount of body fat you have doesn't necessarily affect fat metabolism. Instead, fat -- technically called adipose tissue -- is a source for long-term energy storage, so your body burns fat based upon how much energy it needs, not based upon how much fat you have. When you burn calories during exercise, you'll burn more fat as you burn more calories. Cardiovascular exercises such as cycling and running are particularly effective at burning fat.

Muscle and Metabolism

Although a pound of fat and a pound of muscle weigh the same (a pound is a pound), muscle requires more energy to maintain. A calorie is a unit of energy, which means that if you're more muscular, you'll burn more calories. BMI can't measure your muscle mass, so is not an accurate predictor of how quickly you'll burn calories and shed fat. Instead, try asking your doctor or a personal trainer to estimate your muscle mass. By increasing your muscle mass, you can increase your metabolism and shed unwanted pounds more quickly.

Size and Metabolism

BMI can give you a rough estimate of how quickly you'll burn calories, because larger people with larger BMIs tend to burn more calories during activity. Harvard Health Publications, for example, points out that a 125-pound person will burn about 90 calories in 30 minutes of weight lifting, whereas a 185-pound person can expect to burn about 133 calories. Since BMI is based on body size, you can expect to burn more calories during exercise if you have a higher BMI.