Understanding body mass index on a deeper level
If you’ve learned about body mass index (BMI) in health class or at the doctor, you may be curious to find out more about what it is and how it’s used. Though BMI is still a part of many standard doctor’s visits and can serve as a helpful snapshot of one’s body composition, it’s far from an all-encompassing measure of overall health.
This article will explain how to calculate BMI, its uses and limitations of BMI, tips for maintaining a healthy lifestyle, and considerations for treating issues related to healthy habits and self-image.
What is body mass index (BMI)?
Body mass index (BMI) is an estimation of body composition based on a person’s height and weight. To calculate BMI, you can divide your weight (in kilograms) over your height (in square meters). However, it’s easiest to use an online calculator to compute BMI.
The calculator will give you a number which corresponds to one of four categories: underweight, normal weight, overweight, or obese. Generally speaking, a higher BMI indicates more body fat, though there may be some variation due to factors like bone density or muscle mass. Despite being a somewhat simplistic metric, BMI values can provide an easy way to identify whether a person might be at an increased risk for certain health problems related to obesity.
Extensive health research indicates that excess weight is associated with a higher likelihood of experiencing health complications including cardiovascular disease, diabetes, liver disease, and cancer. In fact, the World Health Organization estimates that nearly 3 million people die each year as a result of being overweight or obese. Thus, weight management can be a crucial aspect of self-care and well-being.
Is BMI an accurate measure?
For most people, BMI can be a worthwhile metric for gauging obesity-related health risks and providing a general sense of where they stand in terms of body weight categories. However, BMI is only one metric, and accurately assessing an individual’s overall health may require a more comprehensive analysis by a medical professional.
Limitations of BMI
While public health authorities such as the Centers for Disease Control (CDC) and National Institute of Health (NIH) still recommend the use of BMI, it is important to be aware of its limitations. BMI does not factor in lean body mass, bone density, or fat distribution, nor does it take into account race, sex, age and other factors that can influence a person’s body composition.
For example, a person who lifts weights regularly and has higher than average muscle mass may be considered overweight or even obese according to their BMI, although they may have quite a low body fat percentage. Women tend to have more body fat than men at the same BMI, and older adults may have more body fat than younger adults with the same BMI.
For a more accurate estimate of body fat, it may be worth taking some other measurements. Waist circumference, skinfold thickness measurements, and DEXA scans can provide a more nuanced view of body composition. Blood tests and fitness assessments can also give you a more well-rounded understanding of your overall physical health.
Children and teens might need to use a BMI calculator adjusted for age for a more accurate value. Note, however, that rapid growth in a child’s height or weight fluctuations can mean that a healthy BMI may vary somewhat, even for children of the same age. If a child or adolescent has a BMI outside of the healthy range, it may be worth discussing some intervention strategies for identifying and working towards an ideal weight.
Health and worth beyond the scale
If you are considered overweight or obese based on BMI, it is important to remember that a person’s physical health goes far beyond their weight and that there are a wide variety of healthy BMI ranges. If an individual smokes cigarettes, for example, they’re prone to a variety of health risks. If they rarely get exercise, they may be at risk for another set of health complications. A BMI calculator does not evaluate a person for factors like these, which is why it’s generally recommended that you continue conversations with your doctor about your health beyond the number that you see on the scale or the BMI that was calculated.
It’s also important to remember that a person’s value, intelligence, or worth have no correlation with their body fat composition. Even today, people who are viewed as being in the overweight range often face unfair treatment. Bullying, microaggressions, discrimination, and other negative behaviors toward those with larger bodies than what society or the media deem to be average or best are unfortunately common. While the cultural messaging around weight and size can be harsh and harmful, the implications that anyone is less valuable or less worthy of love and respect because of their size are untrue.
Maintaining good physical health
In general, a robust body of research supports a few basic activities that can help keep you healthy at different ages, regardless of your size or body type. These include:
Fueling your body with nutrient-dense foods and limiting your intake of processed foods;
Staying active with physical activity you enjoy;
Getting plenty of quality sleep each night;
Staying hydrated and limiting consumption of sugary drinks;
Finding healthy outlets for managing stress
These activities can not only help with weight management, they can also improve cardiovascular health, enhance mental well-being, strengthen muscles and bones, and increase overall physical and mental resilience.
One example of supportive research is a ten-year longitudinal study of 2,287 middle and high school students. It found that reducing fast food intake and screen time while increasing fruit/vegetable intake, family meals, and moderate-to-vigorous physical activity resulted in 32% of adolescents exiting the BMI category of “obesity” as they progressed into young adulthood. However, you might be surprised to learn that abstaining from dieting as an adolescent was also associated with exiting the “obesity” BMI category.
While healthy dietary habits are a good thing, creating harsh restrictions and inflexible rules surrounding food can end up creating more problems. Instead, it may be preferable to aim for balance and nourishment rather than focusing on numbers like weight and BMI.
Teens and self-image
For teens, BMI may not be the best way to evaluate health because, during the teenage years, a person’s body may change significantly. When thinking about body mass index, teens may experience weight fluctuations, in addition to the physical changes associated with puberty which can make it difficult to use BMI as an accurate representation of health, especially in children. These adjustments can also be challenging to experience, and some may feel insecure as a result. Remember, however, that changes like these are completely normal. While the development of adolescence can be more tumultuous, your body will continue to change over your lifetime.
Cultivating a healthy, accepting relationship with your body can be difficult, however, given the many pressures we’re all exposed to—especially through the media. It’s one reason that disordered eating habits often start during a person’s teenage years. In fact, 95% of people with eating disorders are between ages 12 and 25. Remember that eating disorders are clinical mental health concerns that generally don’t resolve without treatment. If you’re concerned you or your child may have an eating disorder, seeking help is typically important for your well-being. There’s no shame in getting the support you need and deserve for a concern like this, and the right healthcare professional or healthcare provider can help you feel better.
How can therapy help build self-esteem?
The way you feel about your body can have a significant impact on how you feel about yourself overall, and even how you’re able to function or enjoy your life day-to-day. If you’re facing concerns or challenges related to your weight or appearance, speaking with a therapist may help. For those who may be experiencing a mental health condition like an eating disorder, a mental health professional can devise the appropriate treatment plan based on the individual’s unique situation. For those who are experiencing low self-esteem or would like support in learning how to practice more positive self-talk, stick to healthier habits, or set boundaries with those who have negative attitudes about their bodies, a therapist can provide support and guidance with these topics as well.
While studies suggest that both online and in-person therapy offer similar benefits, some teenagers may prefer the online format. For those with mental health concerns related to their body, speaking with a mental health professional via phone and/or chat may help them feel more in control of how they’re perceived—especially if they’ve experienced appearance-based discrimination from healthcare providers in the past. In addition, online therapy is often more available and affordable than in-person office visits.
Research also supports the effectiveness of online therapy in helping people overcome issues with body image. One study suggests that the use of internet-delivered cognitive behavioral therapy for perfectionism (ICBT-P) was effective in helping participants reduce dysmorphic concerns, selective attention abnormalities, body image disturbances, depression, anxiety, stress, and perfectionism. If you’re interested in online therapy, you can get matched with a licensed therapist with your parent’s consent through a virtual therapy platform like TeenCounseling. You can speak with your provider via phone, video call, and/or chat to address your concerns in the way that feels most comfortable for you.
Counselor reviews
Read on for client reviews of TeenCounseling therapists. “My son has been working with Tara for a few months. She is compassionate, professional, kind, and caring. She takes the time to get to know the person and the family. Her methods are gentle and very well-developed. I would recommend Tara to anyone seeking a good counselor for a teen with generalized anxiety, social anxiety, self-image challenges, and more.”
Takeaway
How can you understand the body mass index?
The simplest way to understand body mass index, or BMI, is that it’s the ratio of a person’s weight to their height. A higher BMI means that the proportion of weight to height is greater, while a lower one means the opposite. If two people weigh the same amount but have different heights, the taller person will have a lower body mass index.
This measurement is commonly used as a rough estimate of how much fat a person has. This can give insight into certain kinds of health risks, though it’s not always reliable on its own. The tools used to compute BMI don’t take into account age, percentage of muscle vs. fat, or where the majority of fat is concentrated on the body. These factors can all be significant for determining whether someone’s weight is healthy or unhealthy.
What is BMI and why is it important?
A person’s BMI is a simple metric for assessing how heavy someone is relative to their height. This can be used as a proxy for whether someone has excess body fat. Researchers have found evidence that high adiposity (above-average body fat) is associated with several health conditions, including:
- Cardiovascular disease
- Liver disease
- Type 2 diabetes
- Rheumatoid arthritis and overall inflammation
- Sleep apnea
- A variety of different cancers, including stomach, colon, ovarian, breast, and pancreatic cancer
Although you may not be able to determine your level of adiposity from your body mass index alone, this measurement can give you a partial idea of whether your weight is normal for your height. Studies indicate that a high BMI is linked with a shorter-than-expected lifespan across many different cultures and geographic regions.
That’s not to say that a lower BMI is always better. It’s also possible to be underweight, which can come with serious health complications of its own. People with a lower-than-average body mass index may also be at risk of earlier mortality due to problems such as immune dysfunction, vascular problems, and cancer.
You might also want to keep in mind that what’s considered an “average” weight in a statistical sense may not be an optimal weight for you. A variety of genetic and lifestyle factors can influence what weight is healthy for your body type. It’s often best to consult with a doctor before concluding that you’re overweight or underweight.
How do you calculate body mass index (with an example)?
The basic BMI calculation is fairly simple. To obtain your body mass index, divide your weight in kilograms by the square of your height in metres. For American readers, this may mean doing some preliminary calculations to convert from imperial to metric units.
We’ll go through a quick example so you can see how this is done. An individual who is 5 feet 8 inches tall weighs 150 pounds. Here’s how they would calculate their BMI:
- 150 pounds (lb) times 0.4536 is approximately 68.04 kilograms (kg)
- 68 inches times 0.0254 is about 1.73 metres
- Multiply 1.73 by 1.73 to get the square of the height: about 2.99 metres squared (m2)
- Divide 68.94 kg by 2.99 m2 to get this individual’s body mass index: 23
Since the healthy BMI range falls between about 19 and 25, the person in our example would be considered neither underweight nor overweight.
How do you use a body mass index chart?
Another way to obtain your BMI is to look it up on one of the many tables or charts provided by various health organizations. To use a body mass index chart, locate your height on the left-hand side, then follow that row to the right until you find your approximate weight. The column it falls in will tell you your BMI.
Note that your exact weight may not be listed on the table, so you might need to simply choose the closest entry. For this reason, using a body mass index chart may not give as precise a result as calculating it directly.
How do you define obesity in terms of body mass index?
According to the Centers for Disease Control, a body mass index of 30 or greater is considered an indicator of obesity. As we stated above, BMI alone may not give you a complete picture of your adiposity level and metabolic health. However, if your body mass index is 30 or more, it might be a good time to talk to a doctor about ways to achieve a healthier lifestyle.
What are three ways to maintain a healthy body mass index?
If you’re finding it difficult to stay within a healthy weight category, you’re not alone — many people have a hard time with this, especially as they get older. A wide variety of healthy lifestyle changes may help. In particular, the World Health Organization recommends the following three ways to maintain a healthy body mass index:
- Eat lots of fruits and vegetables. These foods tend to contain more nutrition per calorie, helping you to stay healthy and nourished without consuming more energy than you’re burning.
- Reduce or limit your intake of sugars, fats, and salt. Food items high in these ingredients are often unhealthy, contributing to weight gain without providing much nutritional benefit.
- Exercise regularly. Physical exercise of all kinds tends to help you burn calories, shifting the balance of your body weight toward muscle and away from fat.
It may also be important to check in with a doctor regularly to make sure you’re not overdoing it. While most recommendations for maintaining a healthy BMI are focused on avoiding obesity, rapid or excessive weight loss can also pose health risks.
What are the risks of low BMI?
An overly low BMI (below 19 for women and 20 for men) can put you at higher risk for health concerns like:
- Malnutrition
- Osteoporosis
- Difficulty healing from wounds
- Higher chances of post-surgical complications
- Reproductive challenges and infertility
- Neurological disorders
- Strokes
- Anorexia and other eating disorders
- Vascular dysregulation (poor blood circulation)
- Cancer
A low BMI may increase these risks even if it’s not technically within the underweight range. What constitutes an optimal weight can vary considerably between individuals even if their heights are similar. Consulting with a physician can help you confirm that your body size isn’t putting your health at risk.
How does age affect BMI?
The proportion and distribution of fat in an individual’s body will typically change a great deal between infancy, adulthood, and old age. This means that healthy BMI ranges may not be the same for all ages.
Centers for Disease Control guidelines state that standard adult body mass index calculators should not be used for people under 20 years old. Instead, the BMI of young people is assessed relative to the typical growth patterns for their age and sex.
Body size recommendations may also be different for older adults. Some research indicates that the healthy BMI range may be higher — between 25 and 27 — for people over 65 years old.
How to reduce BMI?
Reducing BMI may require lifestyle changes to ensure you’re not taking in as many calories as you’re using. Different people may use different strategies to achieve this goal, but eating a healthier diet and exercising regularly tend to be among the most effective. Some potentially helpful habits include:
- Reducing consumption of sweets and red meat
- Walking or biking to nearby destinations
- Getting more sleep
- Cardiovascular exercise, such as jogging or swimming
- Eating whole grains rather than starchy foods
- Increasing your water intake
- Getting more of your calories from fruits, nuts, and vegetables
- Avoiding between-meal snacks
- Using olive oil in place of vegetable oils or butter
Working with healthcare professionals while pursuing weight loss strategies can help you reduce your BMI at a healthy pace.
What factors influence the body size of a human?
A person’s BMI can be affected by many things besides the amount of fatty tissue in their body. Several other factors may influence human body size, including:
- Age. As previously discussed, “typical” BMI can depend quite a bit on a person’s age.
- Ethnicity. Your optimal body size may differ depending on what ethnic group you belong to. For instance, Asian people may have a somewhat lower healthy BMI range, while for Black people it may be slightly higher.
- Sex. The healthy weight range for males can be a bit higher than for females.
- Muscle mass. Muscle tissue is denser than fat, so highly muscular individuals may have a higher BMI than would be expected for the amount of body fat they possess.
- Other genetic factors. Researchers are still working to understand the complex interactions between genes that affect a person’s body size. There may be considerable genetic variation in the factors influencing BMI even between two people of the same age, sex, and ethnicity.
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