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Is BMI a Good Indicator of Health?

Updated: May 16, 2022

Do you know your BMI? Increasingly, people know theirs, just as they know their cholesterol. BMI is a calculation of your size that takes into account your height and weight. Although the origin of the BMI is over 200 years old, it is fairly new as a measure of health. BMI was devised in the 1830s by Lambert Adolphe Jacques Quetelet (1796-1874), a Belgian mathematician, sociologist, statistician and astronomer.

You are of normal weight if your BMI is between 18.5 and 25, overweight if it is between 25 and 30. Anybody with a BMI of 30 or more has obesity. People with a BMI of 30 or more, i.e. individuals with obesity, have a significantly higher risk of eventually becoming diabetic, developing cancer, cardiovascular diseases, osteoarthritis, and liver and gallbladder diseases.

BMI alone frequently misclassifies metabolic health, which is linked to how much fat a person has and how it is distributed. A particular problem with BMI as an index of obesity is that it does not differentiate between body lean mass and body fat mass; that is, a person can have a high BMI but still have a very low fat mass and vice versa. BMI may be particularly unreliable during pregnancy, for athletes, and the elderly. Muscle weighs more than fat (it is denser, a cubic inch of muscle weighs more than a cubic inch of fat). Therefore, BMI will inevitably class muscly, athletic people as fatter than they really are.

Why isn’t BMI always the best measure of health?

Generally speaking, the more body fat you’re carrying, the higher your health risk. However, BMI cannot differentiate between body fat and muscle mass. This means there are some exceptions to the BMI guidelines:

  • Muscles – body builders and people who have a lot of muscle bulk will have a high BMI, but are not overweight.

  • Physical disabilities – people who have a physical disability and are unable to walk may have muscle wasting. Their BMI may be slightly lower, but this does not necessarily mean they are underweight. In these instances, it is important to consult a dietitian who will provide helpful advice.

  • Height – BMI is not totally independent of height and it tends to overestimate obesity among shorter people and underestimate it among taller people. Therefore, BMI should not be used as a guide for adults who are very short (less than 150 cm) or very tall (more than 190 cm).

  • People of different ethnic groups – Asians and Indians, for example, have more body fat at any given BMI compared to people of European descent. Therefore, the cut-offs for overweight and obesity may need to be lower for these populations. This is because an increased risk of diabetes and cardiovascular disease begins at a BMI as low as 23kg/m2 in Asian populations. Some populations have equivalent risks at a higher BMI, such as people of Torres Strait Islander and Maori origin.

Accurate Health Indicators to Pay Attention To

A better indicator of overall health is your body fat percentage which includes:

  • Waist-to-height ratio

  • Body fat ratio

  • Muscle percentage

  • Stress levels

  • Blood pressure

  • Cholesterol levels

  • Glucose levels (blood sugar)

Vo2 max and resting metabolic rate are also great indicators of overall health, but they are costly and not readily available. Vo2 max can measure your ability to exercise, including how you intake oxygen and your endurance level.

At the bottom of the list? Body weight. Weight is important, but being an ideal weight doesn’t guarantee health.

Waist-to-height ratio better than BMI

It is normal for your body to store energy as fat. However, too much or too little body fat can increase your risk of illness and disease, depending on where your body stores it. Waist measurements (such as waist circumference and waist-to-hip ratio) can estimate abdominal body fat – but they can be difficult to undertake and less accurate in people with a BMI higher than 35. Tools that break down body composition – such as bioelectrical impedance analysis and dual-energy X-ray absorptiometry – work better. A much cheaper alternative is to estimate your total amount of body fat by calculating your body mass index (BMI).

BMI is a useful indicator of health at the population level. At the population level, BMI is used to indicate level of risk for morbidity (disease risk) and mortality (death rates). However, the distribution of fat on your body is more important that the amount, when assessing your disease risk. For this reason, your waist circumference is thought to be a better predictor of health risk than your BMI. Increased abdominal obesity is related to a higher risk of cardiovascular disease, type 2 diabetes and cancer. Abdominal obesity is measured using waist circumference.

Having fat around the abdomen or a ‘pot belly’, regardless of your body size, means you are more likely to develop certain obesity-related health conditions. Fat predominantly deposited around the hips and buttocks doesn’t appear to have the same health risk. Men, in particular, often deposit weight in the waist region and therefore have an increased risk of obesity-related disease.

Keeping your waist circumference to less than half your height can help increase life expectancy for every person in the world. BMI does not take into account the distribution of fat around the body. Abdominal fat affects organs like the kidney, liver and heart more severely than fat around the bottom or hips. Waist circumference gives an indication of abdominal fat levels.

A healthy waist to height ratio is 0.4 to 0.49, indicating no increased health risks.

A ratio of 0.5 to 0.59 puts people at increased risk of health issues, while 0.6 or more puts them at the highest risk of health problems.

Ways to Measure Body Fat at Home

  • Bio impedance monitors

Body impedance monitors or smart scales are popular amongst those who want an easy way to monitor their body composition regularly at home. Unlike traditional scales that only measure body weight, body fat scales combine weight scales with something called a foot-to-foot impedance meter (FFI). The FFI estimates body fat and muscle mass by sending electrical currents to the body and measuring the response. Muscle and fat respond differently to electrical currents, and the scale uses these differences to determine body fat.

  • Waist circumference

This is a measurement of your waist to check if you are carrying too much fat around your abdomen (belly). You can have a healthy BMI and still have excess abdominal fat, meaning you are still at risk of heart disease, type 2 diabetes and stroke. All you need is a tape measure. It’s a good way to measure fat round your abdomen.

When measured properly, its accuracy is typically within 5 per cent of the body fat value measured using underwater weighing, which is one of the most accurate ways of measuring body composition.

Muscle Mass

Muscle mass is difficult to measure. It also depends on many factors, including height, ethnicity, and fitness level. One way to determine muscle mass is using a body fat scale.

A body fat scale uses bioelectrical impedance to estimate your amount of body fat. It sends an electrical current through your body. Since fat conducts less electricity than muscle, the current can measure how much body fat you have. You’ll also need to enter your height, weight, gender, and age. The scale uses this data, along with the electrical current, to estimate your body fat percentage and muscle mass percentage.

The only source with reliable information is a 2000 study in the Journal of Applied Physiology. The following data will give you an idea of muscle mass percentages for different age groups.

The American Council on Exercise (ACE) has a body fat chart that’s more like the adult BMI chart because it doesn’t factor in age and breaks it up in the following categories:

Body Fat Mass

In general, men have a lower body fat to lean tissue ratio than women, which explains the differences in the ranges. Reproduction plays a role in the higher body fat percentages for women. With that in mind, the ACE chart gives the following ranges for men:

Ideal body fat percentage for men

Ideal body fat percentage for women

Bottom Line

Body mass index (BMI) is a highly controversial health assessment tool designed to estimate a person’s body fat and risk of poor health. BMI and body fat measurements are two methods you can use to assess your body weight and composition. A better indicator of overall health is your body fat percentage which includes Waist-to-height ratio. The waist-to-height ratio is a better indicator of overall health, with 0.4-0.49 indicating no increased health risks.

Eating nourishing foods, staying hydrated, supplementation, exercising, and caring for your mental health all play a critical role in shaping your journey to better health.

About the authors

Madur & Anitha Jagannath are certified Nutrition Consultants, in addition to their professions in technology and human resources. When Madur started feeling lethargic and slowing down, he started exercising regularly, became conscious of healthy eating habits and nutrition. He is an avid runner and does half-marathons often. At Voyage to Wellness, they attribute our reputation to the lasting customer relationships they have developed throughout the years. They believe in health & wellness and being fit, at all stages of people's lives.

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