What is BMI?Body Mass Index (BMI) is a number calculated from a person's weight and height. BMI is a fairly reliable indicator of body fatness for most people. BMI does not measure body fat directly, but research has shown that BMI corre-lates to direct measures of body fat, such as underwater weighing and dual energy x-ray absorptiometry (DXA).1, 2 BMI can be considered an alternative for direct measures of body fat. Additionally, BMI is an inexpensive and easy-to-perform method of screening for weight categories that may lead to health problems.

Why does CDC use BMI to measure overweight and obesity?Calculating BMI is one of the best methods for population assessment of overweight and obesity. Because calculation requires only height and weight, it is inexpensive and easy to use for clinicians and for the general public. The use of BMI allows people to compare their own weight status to that of the general population.

What are some of the other ways to measure obesity? Why doesn't CDC use those to determine overweight and obesity among the general public?Other methods to measure body fatness include skinfold thickness measure-ments (with calipers), underwater weighing, bioelectrical impedance, dual-en-ergy x-ray absorptiometry (DXA), and isotope dilution. However, these meth-ods are not always readily available, and they are either expensive or need highly trained personnel. Furthermore, many of these methods can be difficult to standardize across observers or machines, complicating comparisons across studies and time periods.

back to topHow is BMI calculated and interpreted?Calculation of BMI

BMI is calculated the same way for both adults and children. The calculation is based on the following formulas:

Measure-ment Units

Formula and Calculation

Kilograms and meters (or centime-ters)

Formula: weight (kg) / [height (m)]2

With the metric system, the formula for BMI is weight in kilograms divided by height in meters squared. Since height is commonly measured in

centimeters, divide height in centimeters by 100 to obtain height in meters.

Example: Weight = 68 kg, Height = 165 cm (1.65 m)

Calculation: 68 ÷ (1.65)2 = 24.98

Pounds and inches

Formula: weight (lb) / [height (in)]2 x 703Calculate BMI by dividing weight in pounds (lbs) by height in inches (in) squared and multiplying by a

conversion factor of 703.Example: Weight = 150 lbs, Height = 5'5" (65")

Calculation: [150 ÷ (65)2] x 703 = 24.96

Interpretation of BMI for adults

For adults 20 years old and older, BMI is interpreted using standard weight status categories that are the same for all ages and for both men and women. For children and teens, on the other hand, the interpretation of BMI is both age- and sex-specific.

For more information about interpretation for children and teens, visit Child and Teen BMI Calculator.

The standard weight status categories associated with BMI ranges for adults are shown in the following table.

BMI Weight Status

Below 18.5 Underweight

18.5 – 24.9 Normal

25.0 – 29.9 Overweight

30.0 and Above Obese

For example, here are the weight ranges, the corresponding BMI ranges, and the weight status categories for a sample height.

Height Weight Range BMI Weight Status

5' 9" 124 lbs or less Below 18.5 Underweight

125 lbs to 168 lbs

18.5 to 24.9 Normal

169 lbs to 202 lbs

25.0 to 29.9 Overweight

203 lbs or more 30 or higher Obese

back to topHow reliable is BMI as an indicator of body fatness?The correlation between the BMI number and body fatness is fairly strong; however the correlation varies by sex, race, and age. These variations in-clude the following examples: 3, 4

• At the same BMI, women tend to have more body fat than men.

• At the same BMI, older people, on average, tend to have more body fat than younger adults.

• Highly trained athletes may have a high BMI because of increased mus-cularity rather than increased body fatness.

Waist CircumferenceAnother way to assess your weight is to measure your waist size. Your waist-line may be telling you that you have a higher risk of developing obesity-re-lated conditions if you are:

• A man whose waist circumference is more than 40 inches

• A non-pregnant woman whose waist circumference is more than 35 inches

Excessive abdominal fat is serious because it places you at greater risk for developing obesity-related conditions, such as Type 2 Diabetes, high blood cholesterol, high triglycerides, high blood pressure, and coronary artery dis-ease. Individuals who have excessive abdominal fat should consult with their physicians or other health care providers to develop a plan for losing weight.

2. a What are the health consequences of overweight and obesity for adults?The BMI ranges are based on the relationship between body weight and dis-ease and death.5 Overweight and obese individuals are at increased risk for many diseases and health conditions, including the following: 6

• Hypertension

• Dyslipidemia (for example, high LDL cholesterol, low HDL cholesterol, or high levels of triglycerides)

• Type 2 diabetes

• Coronary heart disease

• Stroke

• Gallbladder disease

• Osteoarthritis

• Sleep apnea and respiratory problems

• Some cancers (endometrial, breast, and colon)

What Are the Health Risks of Overweight and Obesity?

Being overweight or obese isn't a cosmetic problem. It greatly raises the risk in adults for many diseases and conditions.

Overweight and Obesity-Related Health Problems in Adults

Coronary Heart DiseaseCoronary heart disease (CHD) is a condition in which a substance called plaque (plak) builds up inside the coronary arteries. These arteries supply oxygen-rich blood to your heart. Plaque is made up of fat, cholesterol, cal-cium, and other substances found in the blood.

Plaque can narrow or block the coronary arteries and reduce blood flow to the heart muscle. This can cause angina (an-JI-nuh or AN-juh-nuh) or a heart at-tack. (Angina is chest pain or discomfort.)

As your body mass index (BMI) increases, so does your risk of having CHD and a heart attack. Obesity also can lead to heart failure. This is a serious condition in which your heart can't pump enough blood to meet your body's needs.

High Blood PressureBlood pressure is the force of blood pushing against the walls of the arteries as the heart pumps out blood. If this pressure rises and stays high over time, it can damage the body in many ways. Your chances of having high blood pressure are greater if you're overweight or obese.

StrokeBeing overweight or obese can lead to a buildup of plaque in your arteries. Eventually, an area of plaque can rupture, causing a blood clot to form at the site. If the clot is close to your brain, it can block the flow of blood and oxygen to your brain and cause a stroke. The risk of having a stroke rises as BMI in-creases.

Type 2 DiabetesDiabetes is a disease in which the body's blood glucose, or blood sugar, level is too high. Normally, the body breaks down food into glucose and then car-ries it to cells throughout the body. The cells use a hormone called insulin to turn the glucose into energy.

In type 2 diabetes, the body's cells don't use insulin properly. At first, the body reacts by making more insulin. Over time, however, the body can't make enough insulin to control its blood sugar level.

Diabetes is a leading cause of early death, CHD, stroke, kidney disease, and blindness. Most people who have type 2 diabetes are overweight.

Abnormal Blood FatsIf you're overweight or obese, you're at increased risk of having abnormal lev-els of blood fats. These include high levels of triglycerides and LDL ("bad") cholesterol and low levels of HDL ("good") cholesterol.

Abnormal levels of these blood fats are a risk factor for CHD. For more infor-mation about triglycerides and LDL and HDL cholesterol, go to the Health Topics High Blood Cholesterol article.

Metabolic SyndromeMetabolic syndrome is the name for a group of risk factors linked to over-weight and obesity. These risk factors increase your risk of CHD and other health problems, such as diabetes and stroke.

You can develop any one of these risk factors by itself, but they tend to occur together. A diagnosis of metabolic syndrome is made if you have at least three of the following risk factors:

• A large waistline. This also is called abdominal obesity or "having an ap-ple shape." Having extra fat in the waist area is a greater risk factor for

CHD than having extra fat in other parts of the body, such as on the hips.

• A higher than normal triglyceride level (or you're on medicine to treat high triglycerides).

• A lower than normal HDL cholesterol level (or you're on medicine to treat low HDL cholesterol).

• Higher than normal blood pressure (or you're on medicine to treat high blood pressure).

• Higher than normal fasting blood sugar (or you're on medicine to treat di-abetes).

CancerBeing overweight or obese raises the risk of colon, breast, endometrial, and gallbladder cancers.

(bisa buat no. 2.b)OsteoarthritisOsteoarthritis is a common joint problem of the knees, hips, and lower back. The condition occurs if the tissue that protects the joints wears away. Extra weight can put more pressure and wear on joints, causing pain.

Sleep ApneaSleep apnea is a common disorder in which you have one or more pauses in breathing or shallow breaths while you sleep.

A person who has sleep apnea may have more fat stored around the neck. This can narrow the airway, making it hard to breathe.

Reproductive ProblemsObesity can cause menstrual irregularity and infertility in women.

GallstonesGallstones are hard pieces of stone-like material that form in the gallbladder. They're mostly made of cholesterol. Gallstones can cause abdominal or back pain.

People who are overweight or obese are at increased risk of having gall-stones. Also, being overweight may result in an enlarged gallbladder that doesn't work right.

Obesity

What Is Obesity?

Obesity is an excess proportion of total body fat. A person is considered obese when his or her weight is 20% or more above normal weight. The most common measure of obesity is the body mass index or BMI. A person is con-sidered overweight if his or her BMI is between 25 and 29.9; a person is con-sidered obese if his or her BMI is over 30.

"Morbid obesity" means that a person is either 50%-100% over normal weight, more than 100 pounds over normal weight, has a BMI of 40 or higher, or is sufficiently overweight to severely interfere with health or normal func-tion.

2. b Obesity is linked to many health problems -- osteoarthritis is just one of them. Overweight and obesity directly affects weightbearing joints, especially the knees. Studies have shown that knee osteoarthritis is 4 to 5 times more com-mon in overweight people compared with people who are of normal body weight.

The force of 3 to 6 times a person's body weight is exerted across the knee while walking. In other words, being 10 pounds overweight increases the force on the knee by 30 to 60 pounds with each step taken while walking. The force across the hip is estimated to be 3 times body weight. Interestingly, a high BMI has also been linked to hand osteoarthritis.

Joint Replacement More Problematic For Obese Patients

It used to be that joint replacement was not even an option for obese patients, especially very obese patients. Studies have shown that joint replacement surgery is feasible for obese patients but the complication rate is higher.

Obese patients require significantly longer time on the operating room table and longer hospital stays. Obese patients also require care at a rehabilitation or skilled nursing facility more often than non-obese patients. Because of the additional potential for complications and prolonged recovery -- it is recom-mended that obesity be addressed prior to surgery -- if possible.

3.What Causes Obesity?

Obesity occurs when a person consumes more calories than he or she burns. For many people this boils down to eating too much and exercising too little. But there are other factors that also play a role in obesity. These may include:

• Age. As you get older, your body's ability to metabolize food slows down and you do not require as many calories to maintain your weight. This is why people note that they eat the same and do the same activities as they did when they were 20 years old, but at age 40, gain weight.

• Gender. Women tend to be more overweight than men. Men have a higher resting metabolic rate (meaning they burn more energy at rest) than women, so men require more calories to maintain their body weight. Additionally, when women become postmenopausal, their meta-bolic rate decreases. That is partly why many women gain weight after menopause.

• Genetics. Obesity (and thinness) tends to run in families. In a study of adults who were adopted as children, researchers found that participat-ing adult weights were closer to their biological parents' weights than their adoptive parents'. The environment provided by the adoptive fam-ily apparently had less influence on the development of obesity than the person's genetic makeup. In fact, if your biological mother is heavy as an adult, there is approximately a 75% chance that you will be heavy. If your biological mother is thin, there is also a 75% chance that you will be thin. Nevertheless, people who feel that their genes have doomed them to a lifetime of obesity should take heart. Many people genetically predisposed to obesity do not become obese or are able to lose weight and keep it off.

• Environmental factors. Although genes are an important factor in many cases of obesity, a person's environment also plays a significant role. Environmental factors include lifestyle behaviors such as what a person eats and how active he or she is.

• Physical activity. Active individuals require more calories than less ac-tive ones to maintain their weight. Additionally, physical activity tends to decrease appetite in obese individuals while increasing the body's abil-ity to preferentially metabolize fat as an energy source. Much of the in-crease in obesity in the last 20 years is thought to have resulted from the decreased level of daily physical activity.

• Psychological factors. Psychological factors also influence eating habits and obesity. Many people eat in response to negative emotions such as boredom, sadness, or anger. People who have difficulty with weight management may be facing more emotional and psychological issues; about 30% of people who seek treatment for serious weight problems have difficulties with binge eating. During a binge-eating episode, people eat large amounts of food while feeling they can't con-trol how much they are eating.

• Illness. Although not as common as many believe, there are some ill-nesses that can cause obesity. These include hormone problems such as hypothyroidism (poorly acting thyroid slows metabolism), depression, and some rare diseases of the brain that can lead to overeating.

• Medication. Certain drugs, such as steroids and some antidepressants, may cause excessive weight gain.

What is the cause of being overweight or obese?In some respects, the cause sounds quite simple. Your weight de-pends on how much energy you take in (the calories in food and drink) and how much energy your body uses (burns) up:

• If the amount of calories that you eat equals the amount of en-ergy that your body uses up, then your weight remains stable.

• If you eat more calories than you burn up, you put on weight. The excess energy is converted into fat and stored in your body.

• If you eat fewer calories than you burn up, you lose weight. Your body has to tap into its fat stores to get the extra energy it needs.

4.AMD

Obesity’s direct effect on eye health was not well recognized until recently. In 2003, Dr. Seddon found links between increased BMI (a person’s total weight in kilograms divided by the square of height in meters), waist circumference, waist-hip ratio and AMD progres-sion.

In a study published in Archives of Ophthalmology, 261 middle-age and elderly pa-tients were found to have a correlation between high levels of body fat and AMD progres-sion.

“Patients with a BMI between 25 to 30 kg/m2 or greater were more than twice as likely to experience AMD progression compared to patients with a BMI less than 25 kg/m2,” Dr. Seddon said.

A larger waist circumference was associated with a two-fold risk of disease progression, having a more significant risk the greater the waist circumference (P = .02). Patients with a higher waist-hip ratio also increased their risk of disease progression (P = .02).

“To my knowledge this is the first time that anyone has shown a relationship between ab-dominal obesity and overall obesity to AMD progression,” Dr. Seddon said.

Researchers found that increased physical activity in the cohort studied led to a decrease in progression to AMD. Considering these factors, Dr. Seddon discussed a possible asso-ciation between cardiovascular disease and AMD.

“This evidence points to the growing knowledge of the similarities between heart disease and AMD,” Dr. Seddon said. She speculated that cardiovascular factors are somehow re-lated to the neovascularization process that occurs in AMD. “It points to some vascular eti-ology,” she said.

Cataract

A study in Ophthalmic Epidemiology also found an association between cardiovascular disease and eye disease.

Christine Younan, MD, of the University of Sydney, and researchers at the Save Sight In-stitute in Sydney found a link between cardiovascular disorders and cataract in the Blue Mountain Eye Study.

In the study, 2,300 patients over age 48 were followed for 5 years. Patients answered vas-cular history questionnaires and were measured for height, weight and blood pressure. Complete ophthalmic examinations were also performed. Photographs of the lens were taken at initial visits and then again 5 years later to grade for presence of cortical, nuclear, posterior or subcapsular cataract.

Outcomes showed that obesity was significantly associated with the incidence of cortical and posterior subcapsular cataract. Patients over age 65 who were treated for hyperten-sion had a higher incidence of posterior subcapsular cataract at baseline than patients with normal blood pressure. A higher incidence of cataract surgery was found in patients with a history of angina and heart-related problems.

“These longitudinal data provide some evidence supporting a relationship between cardio-vascular disease, vascular risk factors and incident cataract and cataract surgery,” the au-thors said in the study abstract.

Retinopathy

Evidence has also been found to link retinopathy to vascular disorders and type 2 dia-betes, a disease often triggered by obesity.

In a study in Diabetes Care in 2002, Hendrik A. van Leiden, MD, and researchers at the University Medical Center in Amsterdam, Netherlands, found the incidence of retinopathy to be positively associated with increased BMI, among other factors.

“Retinopathy is a multi-factorial microvascular complication, which, apart from hyper-glycemia, is associated with blood pressure, lipid concentrations and BMI,” the authors said in the study abstract.

As part of the Hoorn Study, a population-based study of more than 2,484 50- to 70-year-old white subjects, a subset of 626 diabetic and non-diabetic patients was selected for in-vestigation.

Patients underwent ophthalmic and fundus examinations to assess the incidence of retinopathy.

Retinopathy was positively associated with elevated blood pressure, BMI, cholesterol and triglyceride serum levels. Researchers noted that elevated blood pressure, plasma totals and high cholesterol levels were associated with the presence of retinal hard exudates.

The risk of retinopathy was also linked to an increased waist-hip ratio in another part of the Hoorn Study carried out by Dr. van Leiden. The study, published in Archives of Ophthal-mology in February 2003, followed 233 patients for 9.5 years to investigate the effect of sex, age, glycosylated hemoglobin, hypertension, BMI, waist-hip ratio, serum lipid levels and smoking on the incidence of retinopathy in persons with normal and abnormal glucose metabolism.

Abdominal obesity (waist-hip ratio), glycemia and hypertension were strong determinants for retinopathy development. No significant associations between retinopathy and the re-maining risk factors were found in this study.

Elevated IOP, glaucoma

Elevated IOP and glaucoma are also associated with obesity and vascular disease. Two studies from Asia have established a correlation between increased BMI and elevated IOP.

In a study led by Keiko Mori, PhD, at the University of Nagoya, Japan, researchers con-ducted a cross-sectional analysis on 25,296 Japanese men and women. The study ap-peared in the International Journal of Epidemiology in 2000.

Patients were measured multiple times during a 10-year period for IOP, blood pressure and weight. Mean IOP measurements at baseline were 11.6 mm Hg. After controlling for age, sex and blood pressure, researchers found a significant association between longitu-dinal change in IOP and change in weight.

“These findings suggest that obesity is an independent risk factor for increase in IOP,” the study authors concluded.

An article in the Korean Journal of Ophthalmology found a similar link between obesity and elevated IOP in a large Asian population.

Jong-Soo Lee, MD, PhD, and researchers at the College of Medicine at Pusan National University in Korea, compared the incidence of elevated IOP in patients who were systolic or diastolic hypertensive and obese (group 1) and patients who were systolic or diastolic hypotensive and lean (group 2).

“IOP increased significantly with increasing systolic blood pressure, diastolic blood pres-sure and obesity index (P < .05),” the study authors said.

The mean IOP of group 1 was higher than that of group 2. The difference in IOP was sta-tistically significant (P < .05).

Researchers said that this data could aid investigations on the epidemological and etiologi-cal influences related to risk factors of glaucoma, specifically in Asian populations.

Obesity and vision

Studies show that excess body weight predisposes a person to various systemic diseases that can cause vision loss -- particu-larly cardiovascular disease and diabetes.

Some eye diseases are among a large number of medical con-ditions that can be associated with obesity. For example, since diabetic retinopathy and macular degeneration are directly re-lated to the vascular system and excess weight is known to create pulmonary problems, the blood vessels in the eye are affected and vision can deteriorate.

Other eye conditions that can be caused by high blood pres-sure and high cholesterol because of obesity are hypertensive retinopathy and retinal vein occlusion.