Question

Body Mass Index (BMI)

# Can a higher body mass index (BMI) be healthy?

• Body mass index (BMI) is a very rough indicator of fitness. It is used to make a guess about, but it does not distinguish between sources of weight. As a consequence, someone with high muscle density will also register a high BMI. People in this category are not at risk of the same health problems as people with a high BMI because of body fat.
• BMI is an index of a person's weight in relation to height. It is a good tool used to determine health risks and mortality rates associated with excessive body weight. However, BMI does not differentiate between fat and lean body mass. Therefore, an individual who has a large amount of muscle mass may in fact have a BMI that places them in the overweight, or obese categories, even though they clearly have very little body fat. In such cases a high BMI can be healthy. However, a high BMI as a result of excessive body fat is not healthy. Health risks increase when BMI exceeds 25.0.
• There are certain exceptions to high BMI still being a healthy number. Remember that BMI is not a direct measure of body fatness, but is calculated using total weight and height. For example, highly trained athletes can have more muscle than the average person and therefore weigh more because of muscle, not because of fat. This increased total weight will lead to a high BMI. Keep in mind that these are very small percentages of the population. BMI is a strong predictor of body fatness for a vast majority of people. What this means is that if your BMI is high, then your body fat percentage is likely high as well. If you aren’t sure, seek out fitness professionals that use reliable means to measure body fat more directly, such as skin fold calipers.

Yes as long as the person is declared “healthy” after a physical examination. There are many healthy people that have a higher BMI than the suggested healthy range of 18.5-24.9 due to greater muscle mass than overweight individuals.  Since BMI is calculated from a formula involving only height and weight, BMI does not predict well for most muscular individuals. However, it does help determine health risk for the vast majority of the population. For example: Two persons of the same height and weight will have an equal BMI. Now let’s suppose that BMI is 30, which is considered unhealthy, but one person is athletic and muscular with a low body percentage (such as women between 16-24% or men 12-18%) and the other has a much higher percentage of body fat. The latter would be at health risk while the muscular counterpart is probably not only healthy but may even be healthier than many other people with lower BMIs. This of course presumes this muscular person doesn’t have other health problems unrelated to weight.

According the National Institute of Health, a BMI of 18.5-24.9 is considered normal. Another tool that may be of interest to you in preserving your health throughout life is waist circumference (waist to hip ratio can be a measurement of abdominal fat distribution). This, along with BMI, has been shown to correlate strongly with health risks (e.g. heart and metabolic disease). Click Assessing your Risk <http://www.nhlbi.nih.gov/health/public/heart/obesity/lose_wt/risk.htm> from the National Heart, Lung and Blood Institute for more information. And finally, we always prefer using a body fat measurement for assessing health risk related to weight (see below for ranges) but it’s not always practical, which is why other measurements are more commonly used.

• Yes! Adults with a BMI between 25 and 29.9 are considered overweight, but health practitioners consider this to be low risk, since some amount of fat reserve is needed for energy. This extra energy can be helpful during severe, chronic illness or stress.

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• Body Mass index is a weight to height ratio that is used to classify individuals as underweight, normal, overweight, or obese.  This also helps to estimate an individual’s risk of health problems, based on excess weight.
While this is a quick and easy tool, it does have some limitations.  BMI does not take body composition into account (whether your weight is made up of more muscle or fat).  Therefore, a very muscular individual might be heavier than what is normal for their height group, and according to this calculation they could be considered overweight or obese.  Having more lean muscle is certainly advantageous to your health, so this would be one instance in which a high BMI number would actually be okay.