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Obesity: Classification, healthy BMI number and treatment

Obesity: Classification, healthy BMI number and treatment

Obesity can be a risk factor for many medical conditions including diabetes, heart disease, hypertension and certain cancers
Representational image | Shutterstock

The World Health Organization defines obesity as having an abnormal or excessive amount of body fat that presents a health risk. To classify whether a person is overweight or obese, however, it is necessary to consider one’s body mass index (BMI).  

For those who are not in good physical form, BMI, a calculation based on your height and weight, is a useful indicator of obesity. A person having a BMI score of above 30 is considered obese. 

However, BMI is not the only accurate measure of obesity: It can give an inaccurate figure for an athlete who is both tall and high in muscle mass – classifying them as obese even when they are fit. Similarly, what is considered a “healthy” BMI number can vary based on your ethnicity. 

Obesity isn’t just the superficial change in the body, it’s also a prominent factor predisposing an individual to several other medical conditions such as heart disease, hypertension, diabetes, kidney disease and certain types of cancers. 

While excess fat accumulation plays a role in these obesity-associated health conditions, it is understood that distribution of this fat around the abdominal area (apple-shaped figure) carries more risk than an individual with fat distributed around their thighs and hips (pear-shaped figure). 

Reducing even a modest amount of weight or body fat, keeping a check on caloric intake, doing some physical activity, changing behaviour and engaging in aerobic activities can reduce the risk of developing obesity-associated medical conditions. 


We usually gain weight gradually and while most of us are aware when we do so, some easy ways to keep track of this include: 

  • The tightening of clothes requiring someone to size up 
  • Visible weight gain compared to previous measurements 
  • Developing a layer of fat in the abdominal area (apple-shaped) 
  • An increase in body mass index (BMI) 

Obese individuals may also experience breathlessness, increased sweating, snoring, joint pains, fatigue with even a little physical activity, and low self-esteem and confidence. 

Factors that can cause obesity 

Obesity usually occurs when a person consumes a higher number of calories through food and drink than they can burn. The leftover calories are stored in the body as fat which gets accumulated over time. Several factors cause this calorie imbalance, including: 

  • Excessive calorie intake: On average, a physically active male requires 2,500 calories a day, while a woman needs 2,000 calories to maintain a healthy weight. Obesity can be caused when a person’s intake is more than the required number of calories, or if they’re physically inactive 
  • Poor diet: Eating an excessive amount of fast foods, oversized food portions, excessive consumption of alcohol and sugary beverages, eating between meals and a diet lacking fruits and vegetables can contribute to obesity 
  • Family history and genetic influence: Some people might have genes that they inherit, either from their parents or on their own, that cause dysregulation in burning calories and can lead to excessive storage and distribution of fat in the body 
  • Diseases: Suffering from medical conditions such as Prader-Willi syndrome, Cushing’s syndrome, thyroid disorder and PCOS can be a cause for an inability to lose weight. Conditions like arthritis limit physical activity, resulting in weight gain 
  • Medication: Usage of drugs such as steroids, anti-seizure drugs, anti-depressants and anti-diabetics can increase a person’s risk of putting on a lot of weight 
  • Socio-economic and emotional issues: Growing up in a household with bad eating and cooking habits and the lack of access to healthy foods can increase the risk of obesity. Individuals can also end up eating excessively if they are sad, stressed or angry 
  • Others: Factors such as age, pregnancy, smoking, lack of sleep, stress and gut dysbiosis can also contribute to weight gain 


A doctor can perform physical and lab examinations to diagnose obesity. Some of them are: 

  • BMI sets a baseline of what an individual’s weight should be with respect to their height. It is calculated by dividing the body weight (in kilograms) by the square of their height (in metres) and can indicate whether an individual is within the normal weight range, obese or at risk of becoming obese. However, BMI has its limitations, especially in the case of bodybuilders or athletes whose BMI may put them in the overweight or obese categories due to their higher mass of muscles rather than fat. 

Classification of BMI for adults aged 20 and above 

BMI (kg/m2)  Classification   
18.5 – 24.9  Normal or healthy weight   
25 – 29.9  Overweight   
30 – 39.9  Obesity   
>40  Severe obesity   

Sources: https://www.niddk.nih.gov/health-information/health-statistics/overweight-obesity
In Asians, the cut-off for being overweight is below 23 kg/m2 and above 25 kg/m2 for obesity, which is lower than the mentioned criteria due to known risk factors and comorbidities. 

  • Waist circumference and waist-hip ratio (WHR) is another method to assess whether a person is overweight or obese. A waist size of more than 102cm in men and 88cm in women, and a WHR of greater than 1 in men and 0.85 in women indicates the presence of abdominal fat accumulation and is associated with an increased risk of developing medical conditions 
  • A doctor can also perform lab tests such as lipid profile, liver function, thyroid function, fasting glucose and HbA1c to diagnose for any of the comorbidities associated with obesity 


Treating obesity requires significant modifications to one’s lifestyle and fixing any underlying medical conditions that they may be suffering from. Use of medication and surgery might be required if there’s an excessive deterioration of health due to obesity. 

Developing healthy eating habits, gradually losing weight through dieting, increasing the amount of physical activity, limiting intake of high-calorie foods, having fat-free dairy products, cutting back on portion sizes and eating foods with a higher water content are some of the lifestyle changes one can make to tackle obesity. 

Other interventions that may be required can include: 

  • Taking anti-obesity drugs such as orlistat and liraglutide (with a prescription from a doctor) when lifestyle modifications do not help in losing weight. 
  • Bariatric surgery for weight loss can be opted for in case a person is severely obese with co-morbidities that do not allow them to exercise and change their diets. 


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