The definition of obesity varies depending on what one reads. In general, overweight and obesity indicate a weight greater than what is healthy. Obesity is a chronic condition defined by an excess amount of body fat. A certain amount of body fat is necessary for storing energy, heat insulation, shock absorption, and other functions.
Body mass index (BMI) is the best parameter for defining obesity, determined by a person’s height and weight. BMI equals a person’s weight in kilograms (kg) divided by their height in meters (m) squared (more information will be found later in the article).
Since BMI describes body weight relative to height, there is a strong correlation with total body fat content in adults:
Normal: BMI of 18.5-24.9
Overweight: BMI of 25-29.9
Obese: BMI over 30
Morbidly obese: BMI over 40
How common is obesity?
Obesity has reached epidemic proportions in the United States. Over two-thirds of adults are overweight or obese, and one in three Americans is obese. The prevalence of obesity in children has increased markedly. Obesity has also been increasing rapidly throughout the world, and the incidence of obesity nearly doubled from 1991 to 1998. In 2015, nearly 40% of adults were obese in the U.S.
What is body mass index (BMI)?
The body mass index (BMI) is now the measurement of choice for many physicians and researchers studying obesity.
The BMI uses a mathematical formula that accounts for a person’s weight and height.
The BMI measurement, however, poses some of the same problems as the weight-for-height tables. Not everyone agrees on the cutoff points for “healthy” versus “unhealthy” BMI ranges. BMI also does not provide information on a person’s percentage of body fat. However, like the weight-for-height table, BMI is a useful general guideline and a good estimator of body fat for most adults ages 19-70. Besides, it may not accurately measure body fat for bodybuilders, certain athletes, and pregnant women.
The BMI equals a person’s weight in kilograms divided by height in meters squared (BMI = kg/m2). To calculate the BMI using pounds, divide the weight in pounds by the height in inches squared and multiply the result by 703.
It is important to understand what “healthy weight” means. Healthy weight is defined as a body mass index (BMI) equal to or greater than 19 and less than 25 among all people 20 years of age or over. Generally, obesity is defined as a body mass index (BMI) equal to or greater than 30, which approximates 30 pounds of excess weight.
The World Health Organization uses a classification system using the BMI to define overweight and obesity.
A BMI of 25 to 29.9 is defined as a “pre-obese.”
A BMI of 30 to 34.99 is defined as “obese class I.”
A BMI of 35 to 39.99 is defined as “obese class II.”
A BMI of or greater than 40.00 is defined as “obese class III.”
The table below has already done the math and metric conversions. To use the table, find the appropriate height in the left-hand column. Move across the row to the given weight. The number at the top of the column is the BMI for that height and weight.
What are the most common causes of obesity?
The balance between calorie intake and energy expenditure determines a person’s weight. If a person eats more calories than he or she burns (metabolizes), the person gains weight since the body will store the excess energy as fat. If a person eats fewer calories than he or she metabolizes, he or she will lose weight. Therefore, the most common causes of obesity are overeating and physical inactivity.
Ultimately, body weight is the result of genetics, metabolism, environment, behavior, and culture:
Genetics: A person is more likely to develop obesity if one or both parents are obese. Genetics also affect hormones involved in fat regulation. For example, one genetic cause of obesity is leptin deficiency. Leptin is a hormone produced in fat cells and the placenta. Leptin controls weight by signaling the brain to eat less when body fat stores are too high. If, for some reason, the body cannot produce enough leptin or leptin cannot signal the brain to eat less, this control is lost, and obesity occurs. The role of leptin replacement as a treatment for obesity is under exploration.
Physical inactivity: Sedentary people burn fewer calories than active people. The National Health and Nutrition Examination Survey (NHANES) shows strong correlations between physical inactivity and weight gain in both sexes.
A diet high in simple carbohydrates: The role of carbohydrates in weight gain is not clear. Carbohydrates increase blood glucose levels, which in turn stimulate insulin release by the pancreas, and insulin promotes the growth of fat tissue and can cause weight gain. Some scientists believe that simple carbohydrates (sugars, fructose, desserts, soft drinks, beer, wine, etc.) contribute to weight gain because they are more rapidly absorbed into the bloodstream than complex carbohydrates (pasta, brown rice, grains, vegetables, raw fruits, etc.) and thus cause a more pronounced insulin release after meals than complex carbohydrates. This higher insulin release, some scientists believe, contributes to weight gain.
Overeating: Overeating leads to weight gain, especially if the diet is high in fat. Foods high in fat or sugar (for example, fast food, fried food, and sweets) have high energy density (a lot of calories in a small amount of food). Epidemiologic studies have shown that diets high in fat contribute to weight gain.
Frequency of eating: The relationship between frequency of eating (how often you eat) and weight is somewhat controversial. There are many reports of overweight people eating less often than people with normal weight. Scientists have observed that people who eat small meals four or five times daily have lower cholesterol levels and lower and/or more stable blood sugar levels than people who eat less frequently (two or three large meals daily). One possible explanation is that small frequent meals produce stable insulin levels, whereas large meals cause large spikes of insulin after meals.
Medications: Medications associated with weight gain include certain antidepressants (medications used in treating depression), anticonvulsants (medications used in controlling seizures such as carbamazepine [Tegretol, Tegretol XR, Equetro, Carbatrol] and valproate [Depacon, Depakene]), some diabetes medications (medications used in lowering blood sugar such as insulin, sulfonylureas, and thiazolidinediones), certain hormones such as oral contraceptives, and most corticosteroids such as prednisone. Some high blood pressure medications and antihistamines cause weight gain. The reason for the weight gain with the medications differs for each medication. If this is a concern for you, you should discuss your medications with your physician rather than discontinuing the medication, as this could have serious effects.
Psychological factors: For some people, emotions influence eating habits. Many people eat excessively in response to emotions such as boredom, sadness, stress, or anger. While most overweight people have no more psychological disturbances than normal-weight people, about 30% of the people who seek treatment for serious weight problems have difficulties with binge eating.
Diseases: Diseases such as hypothyroidism, insulin resistance, polycystic ovary syndrome, and Cushing’s syndrome are also contributors to obesity. Some diseases, such as Prader-Willi syndrome, can lead to obesity.
Social issues: There is a link between social issues and obesity. Lack of money to purchase healthy foods or a lack of safe places to walk or exercise can increase the risk of obesity.
What are other factors associated with obesity?
Other factors associated with obesity include:
Ethnicity. Ethnicity may influence the age of onset and the rapidity of weight gain. African-American women and Hispanic women tend to experience weight gain earlier in life than Caucasians and Asians, and age-adjusted obesity rates are higher in these groups. Non-Hispanic black men and Hispanic men have a higher obesity rate than non-Hispanic white men, but the difference in prevalence is significantly less than in women.
Childhood weight. A person’s weight during childhood, teenage years, and early adulthood may also influence the development of adult obesity. Therefore, decreasing the prevalence of childhood obesity is one of the areas to focus on in the fight against obesity.
For example:
Being mildly overweight in the early 20s was linked to a substantial incidence of obesity by age 35.
Being overweight during older childhood is highly predictive of adult obesity, especially if a parent is also obese.
Being overweight during the teenage years is an even greater predictor of adult obesity.
Hormones. Women tend to gain weight, especially during certain events such as pregnancy, menopause, and in some cases, with the use of oral contraceptives. However, with the availability of lower-dose estrogen pills, weight gain has not been as great a risk.
How is body fat measured?
BMI is a calculated value that approximates the body’s fat percentage. Measuring a person’s body fat percentage is not easy and is often inaccurate without careful monitoring of the methods. The following methods require special equipment, and trained personnel, can be costly, and some are only available in certain research facilities.
Underwater weighing (hydrostatic weighing): This method weighs a person underwater and then calculates lean body mass (muscle) and body fat. This method is one of the most accurate ones; however, the equipment is costly.
BOD POD: The BOD POD is a computerized, egg-shaped chamber. Using the same whole-body measurement principle as hydrostatic weighing, the BOD POD measures a subject’s mass and volume, from which their whole-body density is determined. Using this data, body fat and lean muscle mass can then be calculated.
DEXA: Dual-energy X-ray absorptiometry (DEXA) measures bone density. It uses X-rays to determine not only the percentage of body fat but also where and how much fat is located in the body.
The following methods are simple:
Skin calipers: This method measures the skinfold thickness of the layer of fat just under the skin in several parts of the body with calipers (a metal tool similar to forceps); the results are then used to calculate the percentage of body fat.
Bioelectric impedance analysis (BIA): There are two methods of the BIA. One involves standing on a special scale with footpads. A harmless amount of electrical current is sent through the body, and then the percentage of body fat is calculated. The other type of BIA involves electrodes that are typically placed on a wrist and an ankle on the back of the right hand and the top of the foot. The change in voltage between the electrodes is measured. The person’s body fat percentage is then calculated from the results of the BIA. Early on, this method showed variable results. Newer equipment and methods of analysis seem to have improved this method.
Are weight-for-height tables useful to determine obesity?
Measuring a person’s body fat percentage can be difficult, so other methods are often relied upon to diagnose obesity. Two widely used methods are weight-for-height tables and body mass index (BMI). While both measurements have their limitations, they are reasonable indicators that someone may have a weight problem. The calculations are easy, and no special equipment is required.
Most people are familiar with weight-for-height tables. Although such tables have existed for a long time, in 1943, the Metropolitan Life Insurance Company introduced their table based on policyholders’ data to relate weight to disease and mortality. Doctors and nurses (and many others) have used these tables for decades to determine if someone is overweight. The tables usually have a range of acceptable weights for a person of a given height.
One problem with using weight-for-height tables is that doctors disagree over which is the best table to use. Several versions are available. Many have different weight ranges, and some tables account for a person’s frame size, age, and sex, while other tables do not.
A significant limitation of all weight-for-height tables is that they do not distinguish between excess fat and muscle. A very muscular person may be classified as obese, according to the tables, when he or she is not.
Does it matter where body fat is located? (Is it worse to be an “apple” or a”pear”?)
The concern is directed not only at how much fat a person has but also where that fat is located in the body. The pattern of body fat distribution tends to differ in men and women.
In general, women collect fat in their hips and buttocks, giving their figures a “pear” shape. Men, on the other hand, usually collect fat around the belly, giving them more of an “apple” shape. (This is not a hard and fast rule; some men are pear-shaped and some women become apple-shaped, particularly after menopause.)
Apple-shaped people whose fat is concentrated mostly in the abdomen are more likely to develop many of the health problems associated with obesity. They are at increased health risk because of their fat distribution. While obesity of any kind is a health risk, it is better to be a pear than an apple.
To sort the types of body fat storage, doctors have developed a simple way to determine whether someone is an apple or a pear. The measurement is called the waist-to-hip ratio.
To find out a person’s waist-to-hip ratio:
Measure the waist at its narrowest point, and then measure the hips at the widest point;
Divide the waist measurement by the hip measurement. For example, a woman with a 35-inch waist and 46-inch hips would have a waist-to-hip ratio of 0.76 (35 divided by 46 = 0.76).
Women with waist-to-hip ratios of more than 0.8 and men with waist-to-hip ratios of more than 1.0 are “apples.”
Another rough way of estimating the amount of a person’s abdominal fat is by measuring the waist circumference. Men with a waist circumference of 40 inches or greater and women with a waist circumference of 35 inches or greater are considered to have increased health risks related to obesity.
What can be done about obesity?
All too often, obesity prompts people to follow a strenuous diet in the hopes of reaching the “ideal body weight.” Some amount of weight loss may be accomplished, but the weight usually quickly returns. Most people who lose weight regain their weight within five years. A more effective, long-lasting treatment for obesity must be found.
We need to learn more about the causes of obesity, and then we need to change the ways we treat it. When obesity is accepted as a chronic disease, it will be treated like other chronic diseases such as diabetes and high blood pressure. The treatment of obesity cannot be a short-term “fix” but has to be an ongoing lifelong process.
Obesity treatment must acknowledge that even modest weight loss can be beneficial. For example, a modest weight loss of 5%-10% of the initial weight, and long-term maintenance of that weight loss can bring significant health gains, including:
Lowered blood pressure
Reduced blood levels of cholesterol
Reduced risk of type 2 (adult-onset) diabetes (In the Nurses Health Study, women who lost 5 kilograms [11 pounds] of weight reduced their risk of diabetes by 50% or more.)
Decreased chance of stroke
Decreased complications of heart disease
Decreased overall mortality
It is not necessary to achieve an “ideal weight” to derive health benefits from obesity treatment. Instead, the goal of treatment should be to reach and maintain a “healthier weight.” The emphasis of treatment should be to commit to the process of lifelong healthy living, including eating more wisely and increasing physical activity.
What is the role of physical activity and exercise in obesity?
The National Health and Examination Survey (NHANES I) shows that people who engage in limited recreational activity are more likely to gain weight than more active people. Other studies have shown that people who engage in regular strenuous activity gain less weight than sedentary people.
Physical activity and exercise help burn calories. The amount of calories burned depends on the type, duration, and intensity of the activity. It also depends on the weight of the person. A 200-pound person will burn more calories running 1 mile than a 120-pound person because the work of carrying those extra 80 pounds must be factored in.
However, exercise as a treatment for obesity is most effective when combined with a diet and weight-loss program. Exercise alone without dietary changes will have a limited effect on weight because one has to exercise a lot to simply lose 1 pound. However regular exercise is an important part of a healthy lifestyle to maintain a healthy weight for the long term. Another advantage of regular exercise as part of a weight-loss program is a greater loss of body fat versus lean muscle compared to those who diet alone.
Other benefits of exercise
Improved blood sugar control and increased insulin sensitivity (decreased insulin resistance)
Reduced triglyceride levels and increased “good” HDL cholesterol levels
Lowered blood pressure
A reduction in abdominal fat
Reduced risk of heart disease
Release of endorphins that make people feel good
Remember, these health benefits can occur independently (with or without) achieving weight loss. Before starting an exercise program, talk to a doctor about the type and intensity of the exercise program.
General exercise recommendations
Perform 20-30 minutes of moderate exercise five to seven days a week, preferably daily. Types of exercise include stationary bicycling, walking or jogging on a treadmill, stair climbing machines, jogging, and swimming.
Exercise can be broken up into smaller 10-minute sessions.
Start slowly and progress gradually to avoid injury, excessive soreness, or fatigue. Over time, build up to 30-60 minutes of moderate to vigorous exercise every day.
People are never too old to start exercising. Even frail, elderly individuals (70-90 years of age) can improve their strength and balance.
Exercise precautions
