Calculating your body mass index (BMI) works as a general guide to determining risk factors for certain illnesses, including heart disease (New Zealand’s second highest cause of mortality), diabetes, and obesity.
Your BMI also influences your health and life insurance and the premiums you pay. A Policywise adviser can help you understand these issues and find the best insurance plan for your situation.
This article will explain how to use a BMI calculator, the significance of your BMI result, what it means, and its impact on your health. We’ll address its limitations as a tool for health/weight analysis and who should avoid using BMI. We’ll also discuss other health indicators and practical tips for maintaining a healthy BMI.
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How do I calculate my BMI?
BMI is a widely-used measure to determine whether an individual has a healthy body weight in relation to their height. Calculated by dividing a person’s weight by the square of their height, BMI offers a straightforward method to assess body fat.
For example, if you weigh 70 kg and your height is 175 cm, your BMI is 22.9. This value is then compared to a BMI chart, which categorises the result into weight status classes, such as underweight, normal weight, overweight, and obese.
However, BMI does not directly measure body fat or fat distribution, and may not accurately reflect the health of athletes, those with a muscular build, or certain ethnicities.
BMI chart and its categories
|
Category |
BMI Range (kg/m²) |
|
Underweight |
Less than 18.5 |
|
Healthy weight |
18.5 – 24.9 |
|
Overweight |
25 – 29.9 |
|
Obese (class I) |
30 – 34.9 |
|
Obese (class II) |
35 – 39.9 |
|
Obese (class III): ‘extreme obesity’ |
40 and above |
According to the BMI chart, the result can be categorised as per the following breakdown:
- A BMI of less than 5 is considered underweight, suggesting a potential need for nutritional improvements.
- A BMI ranging from 18.5 to 24.9 is considered to be within a normal weight.
- On the other hand, a BMI between 25 and 29.9 is deemed overweight, which may prompt a need for lifestyle modifications to prevent associated health risks.
- A BMI of 30 or above falls into various obesity categories, signalling a higher risk for chronic health conditions, such as heart disease, high cholesterol, diabetes, and hypertension.
Working out your BMI and seeing where it falls on the chart can help you make informed decisions about your health and wellbeing. It’s important to remember that BMI is a general guide and does not account for muscle mass, bone density, and overall body composition, which can vary significantly among individuals.
BMI and your health
Understanding the importance of regulating your BMI to what is considered a healthy zone for your body type is invaluable for maintaining good health.
In New Zealand, one in three adults (or 34.3%) is considered obese - a figure continuing to rise, year on year. A BMI in the overweight or obese range can be indicative of a higher risk for several health conditions, including diabetes, which is also on the rise. In 2023, almost 300,000 New Zealanders suffered type 2 diabetes - a figure expected to increase by 70-90% over the next 20 years. Diabetes itself can create many health complications, such as kidney disease, heart attacks, strokes, blindness, and limb amputations.
Elevated BMI values are also associated with an increased likelihood of developing other health issues, such as:
- Heart diseases
- Fatty liver disease
- Osteoarthritis
- Depression
- Certain types of cancer, including breast, bowel, and bladder cancer.
A BMI in the normal range generally correlates with a lower risk of these diseases by reducing the strain on your body’s metabolic processes, supporting better health and wellbeing. While a mid-low BMI is generally regarded as healthier, an underweight classification can have its own set of implications, such as compromised immune function and osteoporosis.
Understanding your BMI and making lifestyle changes, if necessary, can play a significant role in preventing health issues associated with a BMI of 25 or more, as well as those in the underweight zone of less than 18.5.
Who should not use BMI?
While BMI is a useful screening tool, it should not be the sole measurement for assessing health. BMI does not distinguish between muscle and fat, which can misclassify muscular individuals as overweight or obese, and it doesn't account for fat distribution, which is a critical health risk factor.
Additionally, BMI does not consider other important factors like age, sex, ethnicity, and body composition.
These BMI limitations can lead to inaccurate health assessments for those with considerations that differ significantly from the general population, such as:
- Athletes
- Bodybuilders
- Individuals with high bone density
- Older adults
- Pregnant women
- Babies
- Children and teenagers aged 2-19
- People with certain health conditions, such as those affecting fluid balance
- Ethnicities of Asian, Māori, or Pasifika
For these groups, alternative methods should be utilised, such as measuring body fat percentage and waist-to-hip ratio, plus other comprehensive health evaluations, which might offer a more accurate reflection of their health status.
Other health factors and indicators to consider
When determining your health status, it's important to look beyond your BMI. Waist circumference is a helpful measurement that assesses abdominal fat - a significant risk indicator for heart disease and diabetes. A high waist circumference indicates a greater risk of metabolic conditions, even if your BMI falls within the healthy range.
Once again, this tool has limitations for:
- pregnant women
- babies, children, and teenagers
- those who suffer health conditions that create a swollen abdomen
- Māori, Pasifika, and Asian populations.
Other health determiners might include analysing your body fat percentage, which provides a clearer picture of your overall body composition, and testing your blood pressure, cholesterol, and blood sugar levels, which offers insights into your cardiovascular and metabolic health. Considering these factors alongside your BMI provides a more comprehensive picture of your health and potential risks.
How to maintain a good BMI
Maintaining a mid-range BMI is important for general health and longevity. Here are some effective strategies to help you achieve a healthy BMI:
- Balanced diet: Adopt a balanced diet that includes a variety of fruits, vegetables, lean proteins, and whole grains. Eat fewer processed foods, sugar-filled beverages, and high-fat snacks.
- Physical activity: Maintaining your general health and managing your weight can be supported by regular physical activity. Aim for 75 minutes of intense activity or at least 150 minutes of moderate aerobic activity per week. However, if you have a health condition, consult your doctor about the amount of exercise or type of physical activity you can do.
- Hydration: Make sure you drink enough water each day. Water promotes metabolism, controls hunger, and facilitates digestion. Avoid excessive consumption of sugary beverages and alcohol, which can contribute to weight gain.
- Monitor portion sizes: When eating meals and snacks, be mindful of portion sizes. Avoid eating directly from large containers, as this can lead you to consume more.
- Regular health check-ups: Schedule regular check-ups with your healthcare provider to monitor your BMI and overall health. They can provide personalised recommendations based on your medical history and current health status.
- Manage stress: Chronic stress can affect your eating habits and weight management. Practice stress-relieving techniques, such as deep breathing, meditation, and yoga, and pursue hobbies that bring you joy and help you relax.
- Good sleep: Try to get between seven and nine hours of good sleep every night. Poor sleep can disrupt appetite-regulating hormones and increase cravings for unhealthy foods.
- Supportive environment: Surround yourself with a positive environment that promotes healthy choices. Seek encouragement from friends, family, or support groups who share your health goals.
By incorporating these strategies into your daily routine, you can maintain a healthy BMI and support your wellbeing. Remember, small, consistent changes over time can significantly improve your health and quality of life.
BMI and your health insurance
Understanding how your body mass index affects your insurance can provide valuable insights into your cover and premiums. A higher BMI may indicate increased health risks, particularly if you have a history of heart disease or high blood pressure. This can potentially lead to higher premiums or the need for additional medical assessments before your insurance is approved. Conversely, maintaining a healthy BMI can lower the cost of your insurance premiums, as it reflects lower health risks and a healthier lifestyle.
New Zealand’s best health insurance and life insurance companies assess BMI (as well as other factors) when determining policy terms and premiums. This underscores the importance of maintaining a balanced weight and adopting healthy habits to potentially lower your insurance costs on top of improving your health outcomes. Policyholders are encouraged to disclose accurate BMI information during the application process to ensure their cover aligns with their health status.
Let Policywise help you protect your health
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Disclaimer: This article is for general information only. Nothing in this blog or on this website is intended as medical, dietary, or financial advice. Although we aim to update our content regularly, you are advised to consult a Policywise adviser, health professional, or an appropriate specialist before acting on any information herein. They can factor in your personal circumstances or preferences and help guide your decision-making process.