Obesity Classes 1 Through 3: Each Category Explained
Medically reviewed by Karina Tolentino, RD
Photo composite by Amelia Manley for Verywell Health; Getty Images
Overweight and obesity means weighing more than what is thought to be healthy for a person of that height. Body mass index (BMI), which estimates your level of body fat based on your height and weight, is often used to determine if a person has overweight or obesity.
A BMI of 30 to 34.9 is considered obesity class 1, 35 to 39.9 is obesity class 2, and over 40 is obesity class 3.
Having obesity is considered a risk factor for a number of health conditions, such as heart disease and type 2 diabetes. The risk for health conditions goes up on a continuum as BMI goes up.
On an individual basis, BMI may be used as a screening tool but cannot be used to determine the health of that individual. A healthcare provider needs to perform appropriate health assessments to evaluate an individual person's health and risks.
BMI is calculated differently for children than adults. The growth of children age 2 to 19 years is monitored using additional factors, such as outlined on the growth charts by the Centers for Disease Control and Prevention (CDC).
This article will discuss the obesity classes, health risks associated with obesity, influencing factors beyond BMI, and treatment to go down an obesity class.
What Are the Obesity Classes?
BMI exists on a continuum, but for clinical and research purposes, BMI measures are divided into categories indicating underweight, healthy weight, overweight, and obesity. Obesity is further divided into the following three classes:
Some clinicians and researchers further divide Class 3 into two more categories:
Super obesity: BMI of 50 to 59
Super-super obesity: BMI of 60 or more
Obesity classes do not assess an individual's health but look at overall risks generally associated with those ranges. As a general trend, as BMI increases, so does the likelihood of health problems. These classes may also be used for purposes such as population research and as part of eligibility criteria for treatments such as bariatric surgery.
Risks Associated With Obesity
Compared to people within the BMI category labeled as healthy, people with obesity have an increased risk of developing health conditions such as:
High blood pressure (hypertension)
Type 2 diabetes
High levels of low-density lipoprotein (LDL) cholesterol ("bad cholesterol"), low levels of high-density lipoprotein (HDL) cholesterol ("good cholesterol"), or high levels of triglycerides (a type of fat in the blood)
Coronary heart disease (reduced blood flow to the heart muscle)
Heart attack
Stroke (a blockage of blood flow or bleeding in the brain)
Sleep apnea (breathing stops and restarts repeatedly during sleep)
Mental health conditions, such as depression and anxiety
Bone and joint problems, such as pain, stiffness, and osteoarthritis (wear-and-tear arthritis)
Liver problems
Kidney problems
Obesity is one risk factor for these conditions. The more risk factors a person has, the more likely the person is to develop the health problem.
For example, your risk of developing heart disease increases if you have obesity and other risk factors such as:
High blood pressure
High blood sugar (hyperglycemia)
High blood cholesterol
A family member under age 50 with heart disease
A sedentary lifestyle
Tobacco use
How to Calculate Your BMI
BMI is calculated by dividing weight in kilograms (kg) by the square of height in meters (m).
Consulting a BMI index chart or using a BMI calculating tool can make this easier.
The CDC offers a BMI calculator for people 20 years old and older and a BMI calculator for people age 2 through 19.
Beyond Obesity Classes: Other Influencing Factors
BMI has limitations for its accuracy as a tool to determine a "healthy" weight. For example:
It doesn't take body composition (muscle, fat, bone density) into account.
It is racially biased (measures and associated risks are heavily based on people who are White). BMI ranges can vary between different ethnicities. For example, people who have Chinese, African Caribbean, Black African, and South Asian backgrounds may experience a higher risk of health problems at a lower BMI than people with other ethnic backgrounds.
It isn't a suitable measure for certain groups of people, such as people under age 20, pregnant people, and athletes.
For many people, achieving a BMI that is deemed in the healthy range may not be realistic and may not be the ideal weight for them.
It does not diagnose body fatness or health.
Other tools may also be used to estimate the potential risk for health conditions. These may include:
Waist circumference: Higher abdominal fat increases the risk of developing some conditions, such as type 2 diabetes and coronary artery disease. Waist circumference (measuring around the waist) can be used as a screening tool, but not to make a diagnosis of body fatness or individual health.
Skinfold thickness measurements: This is measured with calipers at various points of the body
Other tools: These include underwater weighing, bioelectrical impedance, dual-energy X-ray absorptiometry (DEXA), and isotope dilution.
Many factors influence both the development of obesity and the risk of developing health conditions associated with obesity. These may include:
Sex and gender
Income and socioeconomic status
Race and ethnicity
Living environment and geography
Access to services
Family and medical history
Trauma
Lifestyle patterns, such as the foods eaten and physical activity levels
Sleep practices
Medications (such as steroids)
Illness and other health conditions (such as hypothyroidism—low thyroid hormones)
Genetics
What Is Considered Underweight?
A BMI of less than 18.5 is considered in the underweight range.
A BMI of 18.5 to 24.9 is considered in the healthy weight range.
A BMI of 25.0 to 29.9 is considered in the overweight range.
A BMI of 30.0 or higher is considered in the obesity range.
Treatment to Go Down an Obesity Class
Achieving the weight or BMI that is optimal for you and involves fostering an overall health-promoting lifestyle.
Assess Where You Are
Keep a journal of what you eat and drink, your activities, your sleep patterns, emotions, and stressors, to help you identify where you can start making adjustments. Look for things in your lifestyle that could pose challenges for your weight loss.
Ask for Help
Talk to a healthcare provider about connecting with support and resources, such as a registered dietitian or community programs.
Set Realistic Goals
Start with a goal of losing 5% to 10% of your current weight. While this may seem small, it can significantly reduce the risk of developing obesity-related health conditions.
Aim for gradual, steady weight loss of about 1 to 2 pounds per week. This increases the chances of keeping the weight off compared to those who lose weight quickly.
Make long-term goals (such as losing a certain amount of weight), and short-term goals (such as taking a walk, or adding a serving of vegetables to your meal). Focus on two or three goals at a time.
Ensure goals are:
Specific
Realistic
Forgiving (you don't have to strive for perfection)
Foster a Support System
Gather around people who will support you in your health goals, including friends, family members, coworkers, and others with similar goals.
Monitor Your Progress
Evaluate your progress in terms of your goals, and make adjustments as needed. Reward your successes with nonfood rewards to help keep you motivated.
Establish and Follow a Nutritious Eating Plan
Focus on adopting healthful eating practices that you can stick to long term, rather than short-term dieting. Talk to your healthcare provider about the amount of calories to take in to make sure you are meeting your body's needs while you lose weight. Your healthcare provider may refer you to a nutrition or weight loss specialist, or a weight loss program.
Engage in Regular Physical Activity
Being physically active burns calories and has health benefits such as strengthening bones and muscles, reducing the risk of disease (such as heart disease and diabetes), improving brain health, and improving your ability to do everyday activities.
Moderate-intensity physical activities increase breathing and heart rate, but you can still carry on a conversation. Examples may include:
A brisk walk
Biking at a casual pace
Light snow shoveling or yard work
Vigorous activities substantially increase heart rate and typically make you breathe too hard and fast to have a conversation. Examples may include:
Running or jogging
Competitive sports like football, basketball, or soccer
Swimming laps
Jumping rope
Cross-country skiing
Other Lifestyle Habits
Look at your sleeping habits and stress levels. Making sure you get enough good quality sleep, and practicing stress management, are important steps to supporting your health goals.
More Intensive Weight Loss Treatments
In some cases, particularly for those who fall under the classification of class 3 obesity, weight loss can be difficult to achieve and maintain with lifestyle changes alone.
Your healthcare provider may suggest treatments such as:
Weight loss medications: Some medications may help with weight loss. They should always be taken as directed, under the guidance of a healthcare provider.
Weight loss surgery: Several types of operations, including bariatric surgery, can help with losing weight and sustaining it long term. Such procedures may be recommended for people who have a BMI of 35 or higher and/or those who have a serious health problem related to obesity.
Weight loss devices: Such as a gastric band or gastric balloon system. These have only been recently approved by the Food and Drug Administration (FDA), and the long-term risks and benefits are not known
Summary
A BMI of 30 or over is considered having obesity. Obesity is divided into three classes, with increasing BMIs. Risk of health conditions increases as BMI goes up. Obesity can increase the risk of developing health conditions such as type 2 diabetes, heart disease, and stroke.
BMI alone cannot measure a person's body composition or health status. Further evaluations performed by a qualified health professional are necessary to make this determination, which is much more complex than a BMI value.
If you have obesity, losing even 5% to 10% of your body weight can reduce the risk of obesity-related health conditions.
If you feel weight loss might be beneficial to you, talk to a healthcare provider. They can help you make a plan that emphasizes healthy ways to achieve and sustain a body weight that is right for you and adopting lifestyle habits that promote health, such as nutritious eating and physical activity.
Read the original article on Verywell Health.
