Body mass index (BMI) measures body fat based on an individual’s weight and height.
Healthcare providers use BMI as a screening tool to find possible health problems caused by weight.
It is significant because it can provide information about a person’s risk of developing certain health conditions.
However, it’s necessary to note that BMI is just one factor that can affect health. Other factors, such as diet and exercise, also play a role.
How Do I Calculate My Body Mass Index?
You calculate your body mass index (BMI) by dividing your weight in kilograms (kg) by your height in meters (m) squared.
Here is a step-by-step guide for calculating BMI manually:
- Measure your weight in kilograms (kg). If you are using pounds (lbs), you will need to convert your weight to kilograms by dividing your weight in pounds by 2.2. For example, if you weigh 150 lbs, your weight in kilograms is 68.2 kg (150 / 2.2 = 68.2).
- Measure your height in meters (m). If you are using inches (in), you will need to convert your height to meters by dividing your height in inches by 39.4. For example, if you are 5’5″ (65 inches), your height in meters is 1.65 m (65 / 39.4 = 1.65).
- Divide your weight(kg) by your height(m) squared to get your BMI. For example, if you weigh 68.2 kg and are 1.65 m tall, your BMI is 24.4 (68.2 / (1.65 x 1.65) = 24.4).
Alternatively, you can use a BMI calculator to determine your BMI.
Many online BMI calculators, such as this one: BMI calculator, are available.
Enter your weight and height, and the calculator will calculate for you.
Note that BMI is not a perfect measure of body fat, as it does not take into account differences in muscle mass, bone density, or the distribution of fat.
It can, however, give helpful information about a person's weight and possible health risks.
Diagnosing Weight Types With BMI
The BMI puts a person's weight into one of four groups: underweight, normal, overweight, or obese.
According to World Health Organization (WHO) guidelines, a healthy BMI range is between 18.5-24.9.
These guidelines categorize individuals into one of four weight status categories.
Here is a breakdown of the categories:
- Underweight: BMI < 18.5
- Normal weight: BMI 18.5-24.9
- Overweight: BMI 25.0-29.9
- Obese: BMI ≥ 30.0
Who Shouldn’t Use a BMI Calculator?
Some people might not be good candidates to use a body mass index (BMI) calculator.
Here are a few examples:
- Children and adolescents: BMI calculators are not suitable for children and adolescents, as their bodies are still growing and developing. Instead, healthcare providers use growth charts to track children's growth and development and determine if they are at a healthy weight.
- Pregnant women: Pregnant women should not use a BMI calculator, as the calculator does not take into account the additional weight gain that occurs during pregnancy. Pregnant women should contact their healthcare professionals to determine a safe weight range during pregnancy.
- Athletes and bodybuilders: Individuals with a high muscle mass, such as athletes and bodybuilders, may have a higher BMI even if they have a low body fat percentage. It is because BMI does not take into account differences in muscle mass, bone density, and fat distribution.
- Older adults: As individuals age, they may lose muscle mass and bone density, affecting their BMI. For this reason, older adults should discuss their weight and potential health risks with a healthcare provider rather than relying on a BMI calculator.
The BMI calculator isn't the best way to figure out body fat and has several limitations.
If you belong to any of the above groups or need to know if a BMI calculator is right for you, you should talk to a doctor or nurse to determine your weight status and possible health risks.
Limitations of Body Mass Index
The body mass index (BMI) has several limitations.
One of the main limitations of BMI is that it does not take into account differences in muscle mass, bone density, or distribution of fat.
It means that individuals with high muscle mass or dense bones may have a higher BMI, even if they have a lower body fat percentage.
For example, a professional athlete with high muscle mass may have a high BMI but a low body fat percentage.
The BMI also can't tell the difference between fat and lean mass, which includes muscle, bone, and organs.
Individuals with a high BMI may have a higher body fat percentage or lean mass rate.
Also, BMI doesn't consider age, gender, or ethnicity, which can change a person's body composition and health risks.
For example, older individuals tend to have a higher body fat percentage. They may have a lower BMI despite being at a healthy weight.
Similarly, women generally have a higher percentage of body fat than men. They may have a higher BMI even if they are at a healthy weight.
In conclusion, BMI is an excellent way to learn about possible health risks related to weight.
Still, it has several flaws, and you shouldn't use it as a diagnostic tool.
Think about a person's diet, how active they are, and their overall health when determining their weight status and possible health risks.
Relationship Between Body Mass Index (BMI) and Health Risks
A strong relationship exists between body mass index (BMI) and health risks.
According to the WHO, a BMI of 18.5-24.9 is considered healthy.
On the other hand, a BMI below 18.5 means that a person is underweight and may be more likely to have some health problems, including:
- Malnutrition: Underweight individuals may not get sufficient nutrients from their diet, which can lead to malnutrition. Malnourishment can weaken the body's immune system and make sickness more likely.
- Anemia: Underweight individuals may be at higher risk of developing anemia, a condition characterized by a deficiency of red blood cells or hemoglobin. It can lead to fatigue and other symptoms.
- Osteoporosis: Underweight individuals may be at higher risk of developing osteoporosis, a condition in which the bones become weak and brittle. It can increase the risk of fractures.
- Infertility: Underweight women may have irregular menstrual cycles, which can affect fertility.
- Delayed growth and development in children and adolescents: Underweight children and adolescents may have delayed growth and development.
If you have a BMI of 25.0-29.9, you are considered overweight, and if it is 30.0 or higher, you are obese.
Researchers have found that having a higher BMI makes you more likely to get several diseases, including:
- Diabetes: Higher BMI is associated with an increased risk of type 2 diabetes. Too much body fat can result in insulin resistance, raising blood sugar levels.
- Heart disease: Higher BMI is associated with an increased risk of a heart attack. Excess body fat raises the risk of high blood pressure, high cholesterol, and other factors for heart disease.
- Certain cancers: Higher BMI is also associated with an increased risk of some cancers, including breast, colon, and endometrial cancer.
- Osteoarthritis: Higher BMI is associated with an increased risk of osteoarthritis. This condition affects the joints and causes pain and stiffness.
- Sleep apnea: Higher BMI is associated with an increased risk of sleep apnea, a condition characterized by interrupted breathing during sleep.
Tips for Maintaining a Healthy Weight
Here are some suggestions for maintaining a healthy weight:
- Make physical activity a part of your routine: Regular physical activity can help you maintain a healthy weight and lower your chance of developing various health problems. Aim for at least 150 minutes each week of vigorous-intensity cardio or a combination of the two. You can also incorporate strength training exercises at least two days per week to help build muscle mass.
- Make healthy food choices: Choose nutrient-dense foods, including fruits, vegetables, whole grains, lean meats, and healthy fats. Reduce your consumption of processed meals, sugary beverages, and harmful fats.
- Set realistic weight loss goals: If you are trying to lose weight, it's essential to set realistic goals. Aim for 1-2 pounds of weight loss per week since this is a safe and sustainable rate of weight loss.
- Seek support: When attempting to maintain a healthy weight, it can be beneficial to engage the help of friends, family, or a healthcare provider. They can provide motivation, encouragement, and guidance to help you achieve your goals.
Remember, maintaining a healthy weight is vital for overall health and well-being.
It's OK to indulge yourself occasionally, but you must make healthy choices to get and stay at a healthy weight.
Other Helpful BMI Tools
Besides body mass index (BMI) calculators, a few other tools can help people figure out their weight status and possible health risks.
Some examples include:
- Waist circumference: Measuring waist circumference can provide additional information about an individual's risk for certain health conditions, such as diabetes and heart disease. A waist circumference greater than 40 inches or more for men and 35 inches for women is associated with an increased risk of these conditions.
- Body fat percentage: Measuring body fat percentage can provide a more accurate assessment of body fat than BMI, as it takes into account differences in muscle mass, bone density, and fat distribution. Several methods for measuring body fat percentage include skinfold thickness measurements, bioelectrical impedance, and dual-energy x-ray absorptiometry (DXA).
- Nutrition and physical activity tracking apps: Several apps can help individuals track their food and physical activity and provide personalized recommendations for achieving and maintaining a healthy weight.
- Online weight loss programs: Many online weight loss programs offer support, resources, and tools to help individuals achieve and maintain a healthy weight. These programs often include meal plans, exercise plans, and support from healthcare professionals and other individuals working towards similar goals.
There is no single perfect tool. Talk to your doctor about your weight and any possible health risks to figure out the best way to get to and stay at a healthy weight.
It's important to note that BMI is just one factor that can affect health, and other factors, such as diet and exercise, also play a role.
However, maintaining a healthy weight is essential for overall health and well-being.
If you have a higher BMI, talking to a healthcare provider about your weight and possible health risks may be helpful.
They can help you determine the best action to take to achieve and maintain a healthy weight.
- Benjamin Adams (May 2020). Higher BMI is linked to an increased risk of heart attacks in European adults: a Mendelian randomisation study. DOI: 10.1186/s12872-020-01542-w
- World Health Organization (n.d). A healthy lifestyle - WHO recommendations. who.int/europe/news-room/fact-sheets/item/a-healthy-lifestyle---who-recommendations
- Eur J Epidemiol (Sep 2016). High body mass index and cancer risk-a Mendelian randomisation study. DOI: 10.1007/s10654-016-0147-5.
- Cleveland Clinic (n.d). Body Mass Index (BMI). my.clevelandclinic.org/health/articles/9464-body-mass-index-bmi
- NHS (n.d). What is the body mass index (BMI)? nhs.uk/common-health-questions/lifestyle/what-is-the-body-mass-index-bmi/
- Centers for Disease Control and Prevention (n.d). Body Mass Index (BMI). cdc.gov/healthyweight/assessing/bmi/index.html