Body Mass Index Increased

Body Mass Index (BMI) is a simple measure that uses your height and weight to estimate body fat, but it’s important to understand what it means for your health and how to interpret it alongside other factors.

Table of contents

• What is Body Mass Index?
• How BMI is Calculated
• BMI Categories and Their Meaning
• Why BMI Matters for Your Health
• Limitations of BMI as a Health Measure
• Factors That Can Affect Your Weight
• Health Risks Associated with High BMI
• How Healthcare Providers Evaluate BMI
• Managing Your BMI

What is Body Mass Index?

Body Mass Index (BMI) is a calculated measure of a person’s body weight in kilograms divided by the square of their height in meters^[1]. Healthcare providers use BMI to estimate the amount of body fat by using your height and weight measurements^[4].

Although BMI does not directly measure body fat, it is moderately to strongly associated with other measures that capture the amount, location, and distribution of body fat^[1]. BMI is a quick, safe, and reliable screening measure to assess a person’s weight relative to their height^[1].

Compared to direct measures of body fat like dual-energy X-ray absorptiometry (DEXA) scans, BMI is quick and simple to calculate, inexpensive, noninvasive, and easily collected during routine health care visits^[1].

How BMI is Calculated

You can calculate BMI yourself using the following formula: BMI equals weight in pounds multiplied by 703, divided by height in inches, then divided by height in inches again^[4].

For example, a person who weighs 180 pounds and is 5 feet 5 inches tall (65 inches total) would calculate: 180 x 703 = 126,540; then 126,540 ÷ 65 = 1,946.769; then 1,946.769 ÷ 65 = 29.95. Their BMI would be 29.9^[4].

Many online BMI calculators are available that make this calculation easier, including those provided by the Centers for Disease Control and Prevention (CDC)^[1].

BMI Categories and Their Meaning

For adults aged 20 years and older, BMI ranges classify different weight types. A BMI less than 18.5 is considered underweight. The optimum range is 18.5 to 24.9, which indicates healthy weight. A BMI of 25 to 29.9 is considered overweight^[4].

When BMI reaches 30 or higher, it is classified as obesity. Within obesity, there are further classifications: Class I obesity is a BMI of 30 to 34.9, Class II obesity is 35 to 39.9, and Class III obesity (sometimes called severe obesity) is a BMI of 40 or higher^[4].

For children and teens aged 2 through 19 years, BMI is calculated differently and uses age- and sex-specific growth charts. A child’s weight status is determined by comparing their BMI with other same-age and same-sex children^[3].

Why BMI Matters for Your Health

Healthcare providers use BMI to help diagnose weight types and as a screening tool for certain health conditions. Some BMI categories are associated with health problems. For example, a BMI in the obesity category often indicates excess weight for height, and too much weight can increase risk for high blood pressure, high cholesterol, and other chronic conditions^[1].

BMI is also a valuable population health measure used worldwide. It has been used for decades to assess trends and make comparisons across time, geographic areas, and groups of people. BMI data help states, localities, and public health entities make decisions to improve the health of populations^[1].

More than 2 in 5 U.S. adults have obesity. The prevalence of obesity among U.S. adults 20 and over was 41.9% during 2017–March 2020^[6]. Worldwide, adult obesity has more than doubled since 1990^[2].

Limitations of BMI as a Health Measure

BMI does have important limitations. It does not distinguish between fat, muscle, and bone mass, all of which influence a person’s weight. BMI does not indicate what types of fat people have or where in the body people carry fat^[1].

The number does not capture a person’s muscle mass, where on their body fat is stored, or how their race, ethnicity, and gender affect the complex relationship between their body composition and health risks^[5]. A powerlifter with large muscles may have a BMI putting them in the obese category despite low levels of abdominal fat^[5].

Women, compared with men, tend to store more fat in their hips and thighs rather than their abdominal region, yet BMI is not adjusted for gender. Ethnicity also plays a role in body composition and disease risk. For instance, people of Polynesian descent with high BMI levels tend to have less fat on their bodies than Europeans with the same BMI. People of Japanese ancestry have higher rates of metabolic disease at lower BMIs than other ethnic groups^[5].

Research suggests that BMI alone frequently misclassifies metabolic health, which is linked to how much fat a person has and how it is distributed. BMI may be particularly unreliable during pregnancy, for athletes, and the elderly^[5].

Factors That Can Affect Your Weight

Many factors can affect your weight and BMI. These include your genes, age, sex, lifestyle, family habits, culture, sleep, and even where you live and work^[20].

On the most basic level, weight gain happens when you consume more calories than your body can use. However, many things may play a role in why you may eat more food than your body needs^[13].

Certain medications you take to treat other conditions may contribute to weight gain. Examples include antidepressants, steroids, anti-seizure medications, diabetes medications, and beta-blockers^[13].

Eating habits such as consuming more calories than your body needs, eating ultra-processed food, high-sugar foods and drinks, and foods with high amounts of saturated fat may cause overweight. Lack of physical activity, lack of sleep, and stress can also contribute to weight gain^[13].

Research shows people with obesity carry specific genes called obesity-susceptibility genes that affect appetite. Underlying health issues like metabolic syndrome and polycystic ovary syndrome can cause side effects like weight gain. Mental health issues like anxiety and depression can lead to eating high-calorie foods that activate the pleasure centers in your brain^[13].

Health Risks Associated with High BMI

In general, the higher your BMI, the higher your risk of developing a range of conditions linked with excess weight^[4]. Obesity can lead to increased risk of type 2 diabetes and heart disease. It can affect bone health and reproduction, and it increases the risk of certain cancers. Obesity influences quality of living, such as sleeping or moving^[2].

If you have a BMI of 30 or higher, you may be at higher risk for developing diabetes, arthritis, liver disease, several types of cancer (such as those of the breast, colon, and prostate), high blood pressure, high cholesterol, and sleep apnea^[4].

Many adults with obesity have other serious chronic diseases. For example, 58% of U.S. adults with obesity have high blood pressure, a risk factor for heart disease. Also, approximately 23% of U.S. adults with obesity have diabetes^[6].

A higher BMI generally is associated with worsening of medical conditions linked to being overweight. Those include high blood pressure (hypertension), high cholesterol (hyperlipidemia), type II diabetes, coronary artery disease, sleep apnea, degenerative joint disease, blood clots, certain types of cancer, and early mortality^[7].

Obesity is also expensive for patients and the health care system. In 2019 dollars, annual medical costs for adults with obesity were $1,861 higher per person than adults with healthy weight. For adults with severe obesity, the excess costs were $3,097 per person. This accounts for nearly $173 billion in medical expenditures in 2019 dollars^[6].

How Healthcare Providers Evaluate BMI

To diagnose obesity, your healthcare professional may perform a physical exam and recommend some tests. These exams and tests often include taking your health history, where your healthcare team may review your weight history, weight-loss efforts, physical activity and exercise habits^[9].

A general physical exam includes measuring your height and checking vital signs such as heart rate, blood pressure, and temperature. Your healthcare professional checks your BMI and may calculate it at least once a year. This can help pinpoint your overall health risks and what treatments may be right for you^[9].

Measuring your waist size is also important. The distance around your waist is known as the circumference. Fat stored around the waist, sometimes called visceral fat or abdominal fat, may further increase the risk of heart disease and diabetes. Women with a waist that measures more than 35 inches and men with a waist that’s more than 40 inches around may have more health risks than do people with smaller waist measurements^[9].

BMI is one measure that an individual and their healthcare provider can use to help determine chronic disease risk. For a more complete picture of an individual’s health, healthcare providers consider BMI with other factors such as medical history (existing health conditions and family history), health behaviors (diet, physical activity, and sleep), physical exam findings (blood pressure and muscle mass), and laboratory findings (glucose and cholesterol levels)^[1].

Managing Your BMI

If you need to lose weight, work with a healthcare professional to set a weight-loss goal and time frame that will work best for you. For example, losing 5% of your body weight over a period of 6 months may be a good initial goal. If you weigh 200 pounds, this would mean losing 10 pounds. Losing excess weight may help lower your chances of developing health problems related to overweight and obesity^[10].

Healthcare professionals often treat overweight and obesity by recommending lifestyle changes, such as adopting a healthy eating plan and increasing your physical activity, to help you lose weight safely^[10].

Achieving healthy growth and weight includes healthy eating, physical activity, optimal sleep, and stress reduction. Several other factors may also affect weight gain^[17].

Healthy eating means incorporating a variety of healthy foods into your eating pattern. Limiting added sugars can improve health. Getting enough water every day is important for your health^[17].

Regular moderate or vigorous physical activity provides immediate and long-term health benefits. Walking is often a good way to add more physical activity to your lifestyle^[17].

In some cases, your healthcare professional may refer you to a healthcare specialist or a healthcare team trained in weight management. Safe and successful weight-loss programs typically include 14 or more weight-loss counseling sessions conducted over 6 months, an eating plan based on the calories and nutrients your body needs, at least 150 minutes per week of moderate-intensity aerobic physical activity, and regular feedback and support from specialists^[10].

When combined with healthy eating and physical activity, weight-loss medicines or weight-loss surgery can be helpful in some cases^[10].