BMI result: Below 18.5

Those who fall into this category are defined as underweight.

Being underweight could be a sign you're not eating enough or may indicate an underlying medical condition. If you're underweight, contact your doctor for further evaluation.
 

BMI result: Between 18.5 and 24.9

The medical community recommends keeping your weight within this range.
 

BMI result: between 25 and 29.9

People in this category may be at risk of developing obesity. 

There may also be a risk of developing other health problems or current health problems worsening over time. Based on European and American clinical guidelines for obesity management in adults, the following are the most likely recommendations based on BMI ranges.

BMI result between 25 and 26.9
People who do not have weight-related health problems (for example, high blood pressure or high cholesterol) are encouraged to eat healthy and increase their physical activity to prevent further weight gain.

BMI result between 27 and 29.9
People in this range who also have weight-related health problems will likely be recommended to lose weight by combining lifestyle interventions and consider pharmacotherapy.

Committing to health interventions can lead to weight loss, improved health, and experiencing a higher quality of life.
 

Obesity is a chronic disease which requires medical attention. For most populations, being overweight or obese (BMI greater than or equal to 25) is associated with an increased risk of mortality and increased risk of comorbidities.

Obesity screenings can take BMI threshold levels into account. Obesity can also be an indicator of potential future health issues that may require medical advice.

In general, the higher your BMI in the range to be considered obese or living with obesity, the greater the chance of developing other chronic obesity-related diseases including:

• Type II diabetes
• Cardiovascular disease
• Stroke
• High blood pressure
• Infertility
• Depression and anxiety
• Coronary heart disease
• Dyslipidemia
• Nonalcoholic fatty liver disease  (NAFLD)/Nonalcoholic steatohepatitis (NASH)
• Gastroesophageal reflux disease (GERD)
• Metabolic syndrome (MetS)
• Urinary incontinence
• Obstructive sleep apnea and breathing problems
• Chronic kidney disease
• Various types of cancer: including but not limited to - breast, colon, endometrial, oesophageal, kidney, ovarian, and pancreatic cancer
• Knee osteoarthritis
• Gallstone disease
• Thrombosis
• Gout
• Increased risk of mortality compared to those with a healthy BMI

If you are concerned about any of these diseases and how they relate to your BMI, consult your doctor for further information and evaluation.
 

Evidence suggests that fat distribution and body composition differ across certain ethnic groups.

People with certain ethnic backgrounds may have higher or lower health risks compared to those from another ethnic background with the same BMI.

This means some groups may have a greater predisposition for developing obesity-related diseases such as type 2 diabetes or heart disease, for example. Therefore, based on your genetics, you may incur greater health risks associated with excess weight.

This has led to proposals for specific BMI thresholds based on ethnic backgrounds.

For instance, lower BMI cut-off values have been suggested for certain Asian populations. For example, lowering the cut-off values by 3 units for Indonesian, Singaporean, and Hong Kong Chinese populations.

This is because Asian populations tend to have a higher amount of body fat at a lower BMI. As a result, there is an increased risk of associated health complications, compared to other populations.

In the section below, research has pointed to links between BMI and different ethnic backgrounds. These factors may be a consideration when determining if taking action is right for you. 
 

In a study comparing Singaporean Indian, Malay, Chinese, and Caucasian populations, Indians had the highest body fat percentage at equivalent BMIs. Higher body fat percentages have been linked with greater cardiovascular risk factors.

Indian populations were shown to have the same amount of body fat at a BMI of 26, as Caucasians with a BMI of 30, the threshold to be considered obese.

When compared to Caucasian, Chinese, and Aboriginal ethnic groups, a study found that South Asian populations had a higher body fat to lean mass ratio. This indicates that South Asian populations have an increased risk of diabetes.

Populations of South Asian descent living in the UK experienced higher incidences of coronary heart disease and stroke than Caucasians. Both coronary heart disease and stroke are associated with body fat and body fat distribution.
 

A study of East Asian populations found that those with a BMI of 25 or above had a higher risk of mortality from cardiovascular disease, coronary heart disease, and stroke when compared to the reference range typically associated with a given BMI.

In the study of Taiwanese populations, significantly increased mortality risks were experienced at BMI greater than or equal to 25. These findings support the need to define obesity in East Asian populations differently, lowering the BMI cut-off point by 5 units from 30 to 25.

Similarly, data suggested that for Japanese populations obesity should be categorized as a BMI greater than or equal to 25.

Studies have shown that Asian populations had a higher body fat percentage compared to Caucasians for a given BMI. Asian populations also have elevated risk of comorbidities such as type 2 diabetes, hypertension, and hyperlipidemia.
 

In a study of the Thai population, waist circumference was shown to be a better predictor of diabetes than BMI. This may be because most studies evaluating the association of BMI with mortality risks have been conducted on populations of European descent (Caucasians).

According to a multi-ethnic study in Singapore, Malay populations had a higher body fat percentage than Caucasians at an equivalent BMI. Data suggested that average amount of body fat in obese Caucasians (BMI 30), could be found in Malays with a BMI of 27.

Studies of Southeast Asian populations in California found that Filipino- and Vietnamese-Americans were significantly more likely to suffer from type 2 diabetes compared to Caucasians. Therefore, such populations should take into account that being overweight/obese can increase risk factors for type 2 diabetes.
 

Certain Pacific Islander populations have lower body fat percentages compared to Caucasians at the same BMI, though this is not the case for all populations considered to be ‘Pacific Islander’.

A study showed that Pacific Islanders suffering from overweight or obesity had a significantly higher likelihood of having hypertension, compared to Caucasian populations.

Native Hawaiians have been shown to be 3 times more likely to have diabetes compared to Caucasian populations, across all BMI categories.
 

A study found that for populations of the same BMI, Mexicans had a greater total body fat and less skeletal muscle compared to Caucasians.

A separate study found that Mexican-Americans had a higher prevalence of obesity compared to Caucasians, but a lower prevalence of associated hypertension.

Similarly, research on Latino populations in the USA found them to be at least twice as likely to suffer from diabetes when compared with Caucasians, regardless of BMI category.

Various studies of Hispanic/Latino populations have suggested that BMI and waist circumference threshold levels for predicting the likelihood of chronic diseases should be unique to ethnic populations.
 

In the USA, differences in BMI between populations account for almost 30% of the difference in Black and White mortality rates amongst females aged 40-79.

When comparing Caucasians with a BMI of 25, the equivalent type 2 diabetes risk in Black populations was seen at lower BMIs (between 21-23). For a BMI of 30 in Caucasian populations, the equivalent diabetes risk in black populations is at BMI values 0.1–4 units lower (26–29.9).
 

A study conducted in Saudi Arabia highlighted the limitation of using the current BMI cut-off (≥30) in diagnosing obesity among the Saudi and possibly the Arab population. The study suggested lowering the BMI threshold for obesity to 27 in order to accurately reflect the obesity-related health risks in these populations.

In a study conducted in Sweden, the diabetes risk of obese Caucasians (BMI of 30) was equal to that of Iraqi men with a BMI of 28.5, and Iraqi women with BMI of 27.5.

This is one of the main determinants of type 2 diabetes, implying a greater risk for Iraqi populations than Caucasians at the same level of BMI.

When observing the population in Jeddah, Saudi Arabia, researchers reported that women with obesity had a higher risk of prediabetes, diabetes, and dyslipidemia. Men in the same population with obesity had greater chances of having high blood pressure.
 

Studied White/Caucasian populations were shown to have a greater risk of mortality associated with a higher BMI, compared to Black populations at equivalent BMI levels.

The researchers noted greater risk associated with obesity for coronary heart disease, stroke and heart disease among White/Caucasian populations.
 

BMI can be misleading in certain cases. Research has shown that BMI can less accurately predict the disease risks for some groups of people:

• Elderly
• Athletes
• People of tall or short stature
• Body types with more muscle mass

For instance, in certain populations such as elite athletes or bodybuilders an elevated BMI does not directly correlate with their health status. Their increased muscle mass and therefore weight also increases their BMI.

The table below shows how the average body fat percentages differ according to specific groups and categories:

At present, there is no individual BMI calculation for women and men. However, whilst gender is not factored into BMI calculations, the physiological differences between genders may imply a difference in the degree of risk at a given BMI.

Men:
In terms of weight distribution, it has been reported that men tend to accumulate body fat in the upper body, including the abdomen.

Abdominal obesity and higher concentrations of visceral fat in men lead to a higher risk of heart disease and type 2 diabetes.

Women:
Whilst women tend to have a higher percentage of body fat than men, fat deposits in females tend to be distributed in the hips and buttocks.

Due to differences in fat deposition, women may be at lower risk of the comorbidities associated with obesity compared to men at the same or similar BMI.
 

Adult BMI calculations do not take age into account. However, research suggests that whilst obesity increases mortality risk at any age, this correlation is much stronger in people below the age of 50.

Accelerated weight gain as a child has been shown to imply further weight gain during adolescence and adulthood. Weight gain as a child is therefore a strong indicator of obesity in adulthood. A study shows that 40% of children with obesity will become obese adults.

Whilst BMI is interpreted differently for children and adolescents compared to adults, growing evidence suggests that BMI guidelines should be age-specific for adult populations as well.
 

BMI interpretation in children and adolescents is both age- and gender-specific. This is because girls and boys develop at different rates, with body fat varying during developmental periods such as puberty.

Obesity in childhood has been shown to be a strong predictor of various obesity-related diseases such as type 2 diabetes, dyslipidemia, and sleep apnea. Obese children are also more likely to suffer from psychological distress. This can include low self-esteem, anxiety disorders, and depressive symptoms.

If you are a parent concerned about the health of your child with relation to their weight, consult your doctor for guidance on weight management and possible treatment options.
 

The composition of our bodies naturally changes with age. An increase in body fat is statistically likely to occur over adulthood, whilst total muscle mass also decreases with age.

Muscle mass and strength are considered important for the maintenance of physical activity.

Studies have shown that when using standard BMI calculations, being slightly overweight is associated with a reduced risk of mortality compared to the ‘normal’ weight range in older populations.

The standard BMI calculation can also underestimate or overestimate the amount of excess fat carried by elderly persons. Assessments such as waist circumference have therefore been recommended as better options when measuring body fat in the elderly.
 

Diagnosing obesity should not be limited to measuring BMI alone. However, BMI can help identify people who would experience health improvements from obesity management.

Diagnostic testing is often ordered during initial obesity assessments, with the aim of discovering metabolic problems and personalizing treatment options. Screening will typically involve various types of laboratory testing:

• HbA1C
• Electrolytes renal function tests (creatinine, eGFR)
• Total cholesterol, HDL- and LDL-cholesterol, triglycerides
• Alanine aminotransferase (ALT)
• Age appropriate cancer screening

In addition to these tests, healthcare providers may take a comprehensive diagnostic approach to understand the underlying causes of obesity. A comprehensive approach aims to discover potential contributing factors to a person’s obesity, and therefore provide an individualized treatment program.

Consult your doctor if you would like to learn more about comprehensive diagnoses for obesity.
 

To gain a better understanding of health, other diagnostics and measurements may be taken alongside BMI (for example, waist circumference). 

Waist circumference is an indirect measure of abdominal fat, whereas BMI is a representation of total body fat. Waist circumference has therefore been cited as a more accurate measure of obesity-related health risk, such as comorbidity and mortality.

Researchers have recommended that waist circumference be used together with BMI to more accurately evaluate an individual’s health risk factors.

Regardless of BMI, you should consult your doctor if you have concerns about your health.

Weight management programs may be relevant if your waist measurements are or exceed:

• Men: 94cm (37in) or more
• Women: 80cm (31.5in) or more

Higher waist circumferences are associated with greater health risk. You may want to consider obesity treatment programs if your waist measurements are as follows:

• Men: 102cm (40in) or more
• Women: 88cm (34.5in) or more
   

Typically, people suffering from obesity present a variety of health conditions collectively known as metabolic syndrome.

Screening for metabolic syndrome is recommended for the majority of people with higher BMIs.

This involves looking for the metabolic risk factors associated with obesity, including the following:

• Waist circumference
• High triglyceride levels
• ‘good’ HDL cholesterol levels
• ‘bad’ LDL cholesterol levels
• High blood pressure
• High blood sugar

At least three metabolic risk factors must be present to be diagnosed with metabolic syndrome. As such, metabolic syndrome is defined as a cluster of conditions, and can raise the risk of heart disease, type 2 diabetes, and stroke.
 

The link between obesity and obesity-related complications is strong but not absolute.

Some people with obesity do not present with metabolic syndrome and are reported to have limited health risks at higher BMIs. This group is defined as metabolically healthy obese individuals.

These individuals have lower risk of developing diabetes and heart disease compared to other people with obesity who suffer from metabolic syndrome.

However, clinical guidelines specify that metabolically-healthy people living with obesity cannot be considered ‘medically healthy’. They are at greater risk of mortality, as well as other non-metabolic conditions such as depression, back pain, and sleep apnea.

Despite the absence of metabolic risk factors, a study found that metabolically-healthy people living with obesity were likely to develop metabolic abnormalities within 10 years. This means they are still at risk of progressing to an unhealthy metabolic state.

If you do not present with chronic disease symptoms associated with obesity, you may consider consulting your doctor to evaluate your metabolic risk factors.

Adopting a healthier lifestyle can help this risk group to prevent medical complications and avoid further weight gain.
 

The BMI was conceived by the Belgian mathematician, Lambert Adolphe Jacques Quetelet, in the mid-19th century.

Despite not being a doctor, Quetelet introduced the concept of social averages. He noted the relationship between weight and height in what was first known as the “Quetelet Index.”

Keys et al later popularised the measurement, describing it as the Body Mass Index and using it as a classification in population-based studies.

The BMI has been adopted into modern medical practices, especially in Western societies with rising obesity rates.
 

BMI is a simple and objective measurement, which can be easily conducted by a doctor or anyone concerned about their health.

However, beyond the previously discussed limitations, you may also consider that BMI measurements do not take account of the following:

• Hereditary risk factors associated with obesity-related diseases such as metabolic syndrome.
• Environmental and lifestyle factors other than obesity that can contribute to chronic disease risk.
• Individual body fat distribution.

It is also important to remember that obesity is not a definitive indicator of ill-health, just as being at a ‘normal’ weight does not mean you are healthy.

Your BMI does not define you, but knowing and understanding your BMI can be a powerful tool for taking charge of your own health.

Consult with your doctor in order to discuss your weight and health status and evaluate what actions may be needed.
 

There is an important relationship between the amount of body fat a person has and the impacts on our health. Studies have demonstrated health risks associated with both extremes of the BMI spectrum.

Various factors independent of weight can put you at risk of developing chronic diseases (such as ethnicity and genetics). It is important to be aware of these factors, and how they might contribute to your risk if you do suffer from obesity.

BMI levels greater than or equal to 30 are associated with increased mortality and risk of health complications. Obesity screenings should take such BMI thresholds into account.

There are ‘metabolically healthy’ people that sustain limited health issues at higher BMIs. However, obesity can still increase other health risks for such individuals compared to those at lower BMIs.

For the majority of people with obesity, screening for metabolic syndrome is recommended.

Understanding your BMI can help you find a healthy weight range and identify the best way to reach or maintain it together with your healthcare team. For most populations, having a BMI over 25 increases health risk factors.

Your BMI should be used as a guideline and first step towards understanding your weight and height. Adhering to a healthy diet and lifestyle is recommended by healthcare professionals – regardless of your current BMI.

For BMIs equal to or above 25, other actions might be needed in addition to diet and physical exercise. Consulting your doctor is the best way to define the right solutions for you.

Seek medical advice if you have any concerns regarding your weight.