Body Mass Index (BMI)

Body Mass Index – What’s Your BMI?

Calculating your Body Mass Index (BMI) gives you an idea of whether you’re underweight, overweight or a healthy weight for your height. Healthcare providers often use BMI calculations because they are a quick, easy tool for assessing a person’s estimated amount of body fat, which can be valuable as an indicator for other health-related issues.

What Is Body Mass Index (BMI)?

A BMI is a mathematical calculation based on a person’s height and weight measurements that provides an estimated measure of their approximate amount of body fat. The BMI concept was first developed in 1832 by a Belgian mathematician named Lambert Adolphe Jacques Quetelet, whose original desire was to provide a comparable measure to estimate a population’s overall health with the view to aiding governments in deciding where to allocate health and financial resources.

Today the body mass index is commonly used by health professionals to classify people into four weight-orientated categories - underweight, healthy weight, overweight and obese (more on these below). These classifications are a handy tool for estimating a person’s body fat to help diagnose and predict other health-related issues. However, it is essential to note that a BMI is only an estimate as it is unable to distinguish between body fat, bone density and muscle mass.

What Is BMI Used For?

BMI is used worldwide as a general indicator for weight management and obesity as well as a screening tool for specific health conditions. These conditions include things like gallstones, type 2 diabetes, high blood pressure, heart disease, strokes, breathing problems, high cholesterol, osteoarthritis and certain cancers (including endometrial, breast, ovarian, prostate, liver, gallbladder, kidney, and colon).

Assessing the amount of body fat provides health professionals with information that can be used to better estimate a person’s risk of developing these health conditions. Essentially the higher your BMI, the higher the risk. However, a very low BMI is also an indicator of risk for malnutrition, anaemia, weakened immune system issues, osteoporosis and infertility.

How To Calculate Your Body Mass Index

Your BMI is calculated by dividing your weight (in kg) by your height (in metres) squared.

For example, a man who is 1.8 metres tall and weighs 85 kg has a BMI of 26.23. If you’d prefer to use an automated tool, there are a large number of BMI calculators available online. Just be sure to choose one from a trusted source.

What Is A Healthy BMI?

How do you know what a normal BMI is? Having calculated your Body Mass Index, you can use these ranges to find out where you are on the scale.

  • Underweight Less than 18.5 (high risk of poor health)
  • Healthy weight 18.5–24.9 (low risk)
  • Overweight 25.0–29.9 (low to moderate risk)
  • Obese 30.0 and above (high to extremely high risk)

The World Health Organization (WHO) states a healthy range for an adult’s BMI is between 18.5 and 24.9. However, it is essential to remember that measuring body fat is not a standalone indicator of overall health or a set indicator for developing certain medical conditions. Many other health factors need to be considered, including genetics, race, age, bone density, fitness/activity levels, smoking/alcohol use and any existing health conditions.

Interpreting BMI Charts For Children And Teens

The BMI calculation is understandably interpreted differently for children and teenagers. The formula is the same, except the final figure is expressed as a percentile of the population, so the BMI charts differ while also taking into account whether the child or teen is a boy or girl. It pays to note that BMI calculations for children and teens are much less accurate than for adults. Kids describe the ranges for a child or teens weight under the following percentiles for age, gender, and height:

  • Underweight. Below the 5th percentile.
  • Healthy Weight. At or above the 5th percentile and less than the 85th percentile.
  • Overweight. At or above the 85th percentile, but less than the 95th percentile.
  • Obese. At or above the 95th percentile.

Limitations Of The BMI Test

How accurate is the BMI calculation? Although it is a helpful guideline for most men and women, the usefulness of BMI calculations is limited in its wider sense. The main concerns with the BMI are:

  • The BMI can overestimate body fat in adults with higher than normal levels of muscle mass, such as professional athletes. This is because muscle mass is heavier than fat, and the BMI calculation does not take this into consideration.
  • Following that train of thought, the BMI may underestimate body fat in people who have less muscle mass, such as older people.
  • The BMI measurement tool is not suitable for women who are over 10 weeks pregnant, for children under two years old, or people with certain health conditions. (Some endocrine or genetic conditions).
  • BMI is a less accurate indicator for ethnic groups with a naturally smaller body stature.

Using the BMI calculation along with other indicators such as waist measurements, age and fitness levels is a better way of providing a more accurate picture of a person’s health.

Additional Methods Used To Assess Overall Health

Every patient is an individual, and healthcare providers will require more than one test to determine a person’s level of health. Some of the additional measurements and assessment tools for determining a person’s health alongside using their BMI are:

  • Waist Circumference. Sometimes people are at greater risk of developing chronic disease when they carry a lot of weight around their middle. Generally speaking, a larger waist circumference (greater than 85 cm for women or 101.6 cm for men), the higher the risk.
  • Waist-To-Hip Ratio. Again focussing on weight stores around the middle, a high waist to hip ratio (for women greater than 0.80 and for men greater than 0.95) means increased risk and a low ratio (for women lower than or equal to 0.80, and for men lower than or equal to 0.95) implies lower risk.
  • Body Fat Percentage. This is a measurement of the relative amount of body fat a person has, much like the BMI however it distinguishes between fat and non-fat mass and therefore offers a more accurate representation.
  • Lab Tests. Comparable blood tests and vital sign measurements taken over time can be used to indicate the risk of chronic disease. These might include blood pressure, heart rate, cholesterol, and blood glucose levels tests. Lab tests provide deeper insight into a person’s overall health.

Why The Focus On Fat?

Presently there are more people around the world who are obese than underweight, making obesity one of the most troubling public health challenges of the 21st Century. According to the World Health Organisation, the worldwide prevalence of obesity nearly tripled between 1975 and 2016. While these stats are alarming, it is helpful to know obesity is preventable.

Health professionals use the BMI in conjunction with other tools to aid in identifying those who need to address body fat issues. As mentioned above, measuring a person’s fat levels can help assess the risk factors for certain health conditions. High body fat can mean a higher risk of developing heart disease, stroke and type 2 diabetes for example, and low body fat can be an indicator for malnutrition, infertility and anaemia.

Why is fat so important in the human body? Eating nourishing foods, staying hydrated, exercising regularly, and taking care of your mental and spiritual health are all part of a person’s journey to better health. Excess fat (or not enough fat) can impact the body’s ability to remain in this healthy state for a number of reasons, but most significantly because the right amount of body fat helps vitamins and minerals absorb into your body better while providing a reliable source of energy for your body. Fat also helps maintain body temperatures and protect internal organs. Too much fat and all of the bodily functions can be thrown out of balance making it much more difficult to maintain a consistently healthy lifestyle.

How Can Obesity Be Reduced?

Supportive healthcare environments, community groups and weight loss programs are fundamental in helping people learn to make better choices and therefore helping prevent the prevalence of obesity which is great! But the best thing we can do is help ourselves!

According to the World Health Organisation, a few of the most basic things you can do to aid in reducing fat levels and building a healthier lifestyle are:

  • Limiting fats, salt and sugars, and generally avoiding highly processed food items.
  • Increasing whole food intake such as fruits and vegetables, whole grains and nuts.
  • Engaging in regular physical activity (at least 60 minutes daily for children and 150 minutes spread throughout the week for adults).

It also pays to note weight loss surgery can also be an option when efforts to live a healthier lifestyle are not successful in reducing residual fat levels. In fact, the positive impact surgery can have on your health and wellbeing can make a huge difference to quality of life.

Interested in learning more about surgical weight-loss procedures available here in New Zealand? Contact Christchurch Weight Loss Surgery for a private consultation today. You will find their professional team of health professionals offer range of surgical procedures and ongoing assistance with your weight loss journey.

Please note: All of the information provided in this post is intended as a general guide only, if you have any questions around interpreting your BMI or about your weight, always talk to your healthcare provider.

Wherever you are in life, we’re here to help. Call us on 03 375 4949 Or send us an email