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What a healthy BMI is and how to measure it


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Using a body mass index (BMI) calculator can help a person determine whether their weight is within the recommended range for their height. However, BMI calculations have several important limitations in everyone, including men.

BMI is one measure of body size. It is a calculation of a person’s body mass based on their weight relative to their height.

Doctors generally consider people whose BMI is within the “normal” range to have a healthy BMI. Individuals below this range may have underweight, while those above this range may have overweight or obesity.

However, BMI may not be the most accurate indicator of whether a person’s weight is healthful for several reasons.

This article explores what BMI is and looks at how to calculate it. It also considers the recommended BMI ranges, the potential limitations of using BMI as an indicator of health, and tips to maintain a moderate BMI.

A BMI calculator for men assesses a man’s target weight range based on his height.

Doctors use the same calculator for all people over the age of 20 years. The calculation is the same regardless of age, sex, race, body composition, and other factors.

It is possible to calculate BMI by dividing a person’s weight in kilograms (kg) by their height in meters squared (m2).

For example, a person who is 5 feet 6 inches (or 66 inches) tall has a metric height of 1.6764 m. If that person weighs 150 pounds, their metric weight will be 68.0389 kg. To calculate their BMI:

  1. Square 1.6764 m by multiplying 1.6764 by 1.6764. This produces the answer 2.81031696.
  2. Divide the person’s weight of 68.0389 by 2.81031696.
  3. The answer rounds to 24.2, for a BMI of 24.2.

Many health advocates argue that BMI is not a good measure of whether a person has a moderate weight.

Some argue that even if a person has overweight or obesity, this does not necessarily reveal much about their health.

A handful of recent studies support this claim, so a person should not use BMI as the sole measure of their health.

Some shortcomings of BMI include:

  • BMI does not take into account body composition. As a result, some people with very high body fat but a low overall weight may have a BMI within the normal range. Likewise, people with more dense bones or athletes with high muscle content may fall into the overweight category or even the obese category.
  • While population level studies show an association between a BMI outside the normal range and a higher risk of certain weight-related health problems, these studies do not necessarily reflect the risk for all individuals.
  • BMI does not take into account fat distribution. Some evidence suggests that certain types of fat, such as abdominal fat, present a higher health risk.
  • A focus on BMI may contribute to weight stigma and weight discrimination in healthcare settings.

The BMI ranges are as follows:

  • Under 18.5: A person has underweight and may be at risk of certain weight-related health issues.
  • Between 18.5 and 24.9: A person is within the normal weight range.
  • Between 25 and 29.9: A person has overweight and may be at risk of certain weight-related health issues.
  • 30 and above: A person has obesity and may be at risk of certain weight-related health issues.

BMI does not take into account body composition, age, race, sex, athletic involvement, or other factors. It does not assess lifestyle, diet, or anything else that may help mitigate the potential health effects of having a high body weight.

A person’s ideal BMI does not change with various health conditions. However, certain health issues may affect their ability to maintain a BMI within the recommended range.

For this reason, it is sometimes important to discuss weight changes, diet, and exercise with a doctor.

People should discuss their BMI with a doctor if:

  • it remains outside of the normal range despite them eating a healthful diet and exercising regularly
  • they need help losing or gaining weight
  • they think that their body composition may mean that BMI is not a reliable health metric

Not everyone can maintain a BMI in the normal range, even with a healthful diet and plenty of exercise.

Elite athletes with high muscle mass, for example, may fall into the overweight range.

Similarly, being in the normal range does not necessarily mean that a person is healthy. People who eat unhealthful foods and never exercise may still have a moderate BMI.

For this reason, the best strategy is to focus on promoting general health.

For most people, this will make it easier to attain a BMI in the normal range. People looking to promote their health can try:

  • Exercising most days of the week: The Centers for Disease Control and Prevention (CDC) recommend that adults get either 150 minutes of moderate intensity aerobic exercise, such as walking, or 75 minutes of vigorous aerobic exercise, such as running, each week. Adults should also do strength-based exercises at least twice per week.
  • Eating a healthful, balanced diet: Although it is important to limit the intake of very high calorie or high fat foods, people should avoid crash or fad diets.
  • Talking to a doctor if it is hard to maintain a moderate weight: Sometimes, weight gain signals an underlying health issue, such as a thyroid condition.

BMI is one way to assess a person’s weight and predict how it might affect their health.

In the absence of other measures, however, it does not reveal much about a person’s well-being.

A person who wants a better understanding of the possible effects of their weight on their overall health should discuss these concerns with a doctor or dietitian.



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