We are back with the continuation of our weight loss and obesity series. So how do you decide whether you are obese or not and do you need to loose weight or not. Well there is actually a scientific and very precise way of answering those questions and that is BMI
So let’s get started

Body mass index (BMI) is one of the most commonly used tools for assessing whether an individual has a healthy body weight. It provides a simple method for classifying people into categories such as underweight, normal weight, overweight, and obesity.

Although BMI does not directly measure body fat, it is widely used by healthcare professionals and organizations such as the World Health Organization (WHO), the Centers for Disease Control and Prevention (CDC), and the American Heart Association (AHA) as a screening tool for obesity and associated health risks.

Understanding your BMI can help identify potential health problems and guide lifestyle modifications aimed at improving overall health.

What Is BMI?

Body mass index (BMI) is a numerical value calculated using a person’s weight and height.

It is used to estimate whether an individual’s body weight is appropriate for their height.

BMI is primarily a screening tool and should be interpreted alongside other clinical parameters such as waist circumference, body composition, and metabolic health.

How Is BMI Calculated?

The formula for BMI is:

BMI = Weight (kg) ÷ Height² (m²)

Example

Suppose an individual weighs 90 kg and has a height of 1.8 meters.

BMI = 90 ÷ (1.8 × 1.8)

BMI = 27.77 kg/m²

This value falls within the overweight category.

BMI Categories in Adults

According to the World Health Organization (WHO), adults are classified as follows:

BMI (kg/m²) Weight Category
Less than 18.5 Underweight
18.5–24.9 Normal weight
25.0–29.9 Overweight
30.0–34.9 Obesity Class I
35.0–39.9 Obesity Class II
40 or above Obesity Class III (Severe obesity)

Underweight
BMI <18.5 kg/m²

Being underweight may result from:

Malnutrition
Eating disorders
Chronic illnesses
Hyperthyroidism
Malabsorption disorders
Potential Complications
Nutritional deficiencies
Osteoporosis
Anemia
Reduced immunity
Infertility

Normal Weight
BMI 18.5–24.9 kg/m²

Individuals within this range generally have the lowest risk of obesity-related complications.

Maintaining a healthy diet and regular physical activity is important for preserving long-term health.

Overweight
BMI 25–29.9 kg/m²

People in the overweight category have an increased risk of developing:

Hypertension
Type 2 diabetes mellitus
Dyslipidemia
Coronary artery disease

Lifestyle modification at this stage can help prevent progression to obesity.

Obesity
BMI ≥30 kg/m²

Obesity is a chronic disease associated with excessive accumulation of body fat and increased risk of numerous medical conditions.

Obesity Class I
BMI 30–34.9 kg/m²

Health risks begin to increase substantially.

Obesity Class II
BMI 35–39.9 kg/m²

The likelihood of obesity-related complications becomes considerably higher.

Obesity Class III (Severe Obesity)
BMI ≥40 kg/m²

Severe obesity is associated with increased morbidity and mortality and may require pharmacological treatment or bariatric surgery.

Why Is BMI Important?

BMI helps healthcare professionals:

Screen for obesity.
Assess disease risk.
Monitor weight changes.
Identify patients who may benefit from lifestyle interventions.
Determine eligibility for weight-loss medications or bariatric surgery.

Diseases Associated With High BMI

Individuals with elevated BMI have an increased risk of:

Type 2 Diabetes Mellitus

Excess body fat contributes to insulin resistance and hyperglycemia.

Hypertension

Obesity increases sympathetic activity and sodium retention, resulting in elevated blood pressure.

Cardiovascular Disease

High BMI is associated with:

Coronary artery disease
Stroke
Heart failure
Dyslipidemia

Common lipid abnormalities include:

Elevated triglycerides
Increased LDL cholesterol
Reduced HDL cholesterol

Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD)

Obesity is one of the leading causes of fatty liver disease.

Obstructive Sleep Apnea

Excess tissue around the upper airway increases the risk of sleep-disordered breathing.

Osteoarthritis

Weight-bearing joints are subjected to greater mechanical stress, especially the knees and hips.

Certain Cancers

Obesity is associated with the increased risk of:

Breast cancer
Colorectal cancer
Endometrial cancer
Pancreatic cancer
Kidney cancer

BMI in Asian and South Asian Populations

Research suggests that South Asians develop diabetes and cardiovascular disease at lower BMI values compared with Western populations.

For many Asian populations:

BMI (kg/m²) Classification
18.5–22.9 Normal
23–24.9 Overweight
≥25 Obesity

Therefore, healthcare professionals should consider ethnicity when assessing obesity-related risk

Limitations of BMI

BMI has several limitations.

It does not distinguish between:

Fat and muscle mass.
Visceral and subcutaneous fat.
Body composition differences.
Athletic individuals with high muscle mass.

For example, a bodybuilder may have a high BMI despite having very little body fat.

Waist Circumference: An Important Additional Measure

Waist circumference provides information about abdominal obesity and cardiometabolic risk.

Increased Risk Thresholds
Men
Greater than 102 cm (40 inches)
Women
Greater than 88 cm (35 inches)

Abdominal obesity is strongly associated with:

Diabetes mellitus
Hypertension
Cardiovascular disease
Metabolic syndrome

BMI in Children and Adolescents

BMI interpretation in children differs from adults and is based on age- and sex-specific percentiles.

According to CDC growth charts:

Underweight: <5th percentile
Healthy weight: 5th–84th percentile
Overweight: 85th–94th percentile
Obesity: ≥95th percentile

Pediatric BMI should always be interpreted using growth charts.

Can BMI Predict Overall Health?

BMI is a useful screening tool, but health cannot be determined by BMI alone.

Healthcare professionals should also consider:

Waist circumference
Blood pressure
Blood glucose levels
Lipid profile
Physical activity
Diet quality
Family history
Smoking status

How Can You Improve Your BMI?

Adopt a Healthy Diet

Emphasize:

Fruits
Vegetables
Whole grains
Lean proteins
Healthy fats

Limit:

Sugary beverages
Processed foods
Excess calories
Exercise Regularly

Current guidelines recommend:

At least 150 minutes of moderate-intensity aerobic activity weekly.
Muscle-strengthening exercises two to three times per week.
Sleep Adequately

Aim for 7–9 hours of quality sleep per night.

Manage Stress

Chronic stress can contribute to overeating and weight gain.

Seek Medical Advice

Individuals with obesity or obesity-related diseases may benefit from:

Lifestyle intervention programs
Weight-loss medications
Bariatric surgery

So this is the end of this blog, but the weight loss and obesity series continues. The purpose of this blog was to educate you on how to asses your weight according to your height and if you are over weight or not. Knowing your BMI is the key to assessing your fitness. Hope you find this blog useful. Goodbye Weight Loss and Obesity: Causes, Risks, Diagnosis, Treatment, Diet, Exercise, Medications, and Prevention ( an overview ) Beginning of a series.