Introduction

Stable weight depends on an even balance between energy intake from food and energy expenditure. Energy expenditure occurs during the day in three ways:

As energy expended during rest (basal metabolism). This accounts for about two-thirds of expended energy, which is generally used to maintain body functions, such as maintaining body temperature and muscle contractions in the heart and intestine.
As energy used to metabolize food (thermogenesis), accounting for about 10% of expended energy.
As energy expended during physical activity.

When a person's caloric intake exceeds his or her energy expenditure, the body stores the extra calories in the fat cells present in adipose tissue. These adipose cells function as energy reservoirs, and they enlarge or contract depending on how people use this energy. If people do not balance energy input and output by adopting healthy eating habits and regular exercise, then fat builds up, and they may become overweight.

When energy input is equal to energy output, there is no expansion of fat cells (lipocytes) to accomodate excess. It is only when more calories are taken in than used that the extra fat is stored in the lipocytes and the person begins to accumulate fat.

Measurement of Obesity

Obesity is determined by measurement of body fat, not merely body weight. People might be over the weight limit for normal standards, but if they are very muscular with low body fat, they are not obese. Others might be normal or underweight, but still have excessive body fat. Different measurements and factors are used to determine whether or not a person is overweight to the degree that it threatens health:

Body mass index (BMI) (a measure of body fat).
Waist circumference.
Waist-hip ratio.
Anthropometry.
The presence or absence of other disease risk factors (e.g., smoking, high blood pressure, unhealthy cholesterol levels, diabetes, relatives with heart disease) in addition to obesity. (Such risk factors plus BMI may be the most important components in determining health risks with weight.)

The Body Mass Index (BMI). The current standard measurement for obesity is the body mass index (BMI). In general, a BMI of 25 to 29.9 indicates being overweight. Obesity is a BMI of 30 and above. Obesity is then classified into three categories:

class 1: BMI of 30 to 34.9
class II: BMI 35 to 39.9
class III: BMI of 40 and greater

These guidelines are very important for people at risk for diabetes, heart disease, or certain cancers. It is also used to determine treatment approaches, such when surgery may be appropriate. The higher the BMI the greater the risk for significant health problems.

Calculating Body Mass Index (BMI)

One’s body mass index (BMI) is derived by multiplying a person's weight in pounds by 703 and then dividing by the height in inches, then dividing that number by the height in inches. The steps are as follows:

Multiply one's weight in pounds by 703.
Divide that answer by height in inches.
Divide that answer again by height in inches.

For example, a woman who weighs 150 pounds and is five feet eight inches (or 68 inches) tall has a BMI of 22.8.

Waist Circumference and Waist-Hip Ratio. The extent of abdominal fat can also be used in assessing risk of disease. Some studies suggest the following:

Women whose waistlines are over 31.5 inches and men whose waists measure over 37 inches should watch their weight.
A circumference of greater than 35 inches in women and 40 inches in men has been associated with a higher risk for heart disease, diabetes, and impaired functioning.

Evidence strongly suggests that an unequal distribution of body fat around the abdomen and compared to the hips (the apple-shape) is a more consistent predictor of heart problems and health risks than BMI.

The distribution of fat can be evaluated by dividing waist size by hip size. For example, a woman with a 30-inch waist and 40-inch hip circumference would have a ratio of .75; one with a 41-inch waist and 39-inch hips would have a ratio of 1.05. The lower the ratio the better. The risk of heart disease rises sharply for women with ratios above 0.8 and for men with ratios above 1.0.

Click the icon to see a depiction of the waist-to-hip ratio.

Anthropometry. Anthropometry is the measurement of skin fold thickness in different areas, particularly around the triceps, shoulder blades, and hips. This measurement is useful in determining how much weight is due to muscle or fat.

Biologic and Medical Causes

Obesity results when the body consumes more calories than it uses. Research points to several different factors that may influence weight gain. About 90% of people who diet gain every pound back that they lose regardless of their weight-loss method. Some evidence suggests that every person has an inherited weight range that varies by only about 10% either up or down from some set point. (For instance, a man whose "genetically-determined" weight is 200 pounds would tend to swing from 180 to 220 pounds, but would be unlikely to lose or gain more than this.) Genetic factors that influence fat metabolism and regulate certain hormones and proteins that affect appetite may play some part in 70% to 80% of obesity cases.

The Biologic Pathway to Appetite

Appetite, and, thereby weight, is determined by processes that occur in both the brain and gastrointestinal tract. Eating patterns are regulated by feeding and satiety centers located in the hypothalamus and pituitary glands of the brain that respond to signals indicating high fat stores and hunger. A number of molecules are produced that further control this process by stimulating or suppressing appetite. In some cases, genetic factors may produce imbalances in these chemicals:

Insulin. Insulin is a hormone that is critical in the conversion of blood sugar (glucose) into energy. The process of digestion breaks down carbohydrates from our diet into sugar molecules (of which glucose is one) and proteins from our diet into their smaller components, amino acids. Right after a meal, the amount of glucose in the blood rises and signals the release of insulin, which then pours into the bloodstream. Insulin enables the glucose and amino acids to enter cells in the body, importantly, those in the muscles. Here, insulin and other hormones direct whether these nutrients will be burned for energy or stored for future use. The inability to use insulin efficiently (insulin resistance) has been associated with both obesity and diabetes.
Leptin. Leptin is a hormone that is released by fat cells and also possibly by cells in the stomach. It appears to play an important role in insulin resistance and fat storage in the body, but its role in obesity is unclear. The most likely scenario is that in most people, leptin levels rise as more fat is stored in the cells and signal the hypothalamus in the brain to suppress appetite. Falling levels then signal the brain to stimulate appetite. In people who are genetically deficient in leptin, however, the brain may be tricked into thinking that it is always starving because there is no leptin to suppress appetite. Such people, then, would tend to gain weight.
Resistin. Resistin is another hormone produced by fat cells and produces resistance to the activity of insulin. Some experts believe it may help explain the role of obesity in diabetes type 2.
Intestinal Chemicals. Specific chemicals in the intestinal tract pass signals to the brain when a person is hungry or full. Ghrelin is produced in the stomach and appears to be important in triggering the desire to eat. Peptide YY3–36 (PYY) is a peptide secreted in the intestine after a meal in proportion to the number of calories a person eats. It signals fullness to the brain, and deficiencies may contribute to some cases of obesity. Researchers are hoping that blocking ghrelin or infusing PYY may be possible therapies for obesity.
Other Chemicals. Many brain chemicals are being studied for their role in appetite stimulation and weight gain. Among them are neuropeptide Y, melanocortins, agouti-related protein, and melanocyte stimulating hormone. Chemicals known as endorphins may be critical in reducing appetite and regulating energy. Cholecystokinin, a hormone released in the upper intestine that stimulates digestive juices, may work to control meal size.

Insulin is a hormone produced by the pancreas that is necessary for cells to be able to use blood sugar.

Specific Genetic Factors

Genetics may contribute directly to many cases of severe obesity in people with family histories of obesity. Genetic factors may also play indirect roles in susceptibility to being overweight in many people (such those who have slower metabolism than others). There are at least seven known genetic mutations that have been associated with specific and uncommon cases of severe obesity. A few are as follows:

HOB1 (human obesity 1) is a recently identified gene that may contribute directly to obesity. The gene is significantly linked to high BMI in women.
A number of variants of the leptin gene, including those that cause leptin deficiencies and obesity, have been identified.
A gene called melanocortin-4 receptor that plays a key role in shutting off the urge to eat is defective in some families with a history of obesity.
Researchers have also identified a mutation in a gene for a protein called proopiomelanocortin, which results in a syndrome of obesity, red hair, and deficiencies in stress hormones.
About 5% of severely obese people have mutations that over-respond to agouti-related protein.

Genetics also determine the number of fat cells a person has, and some people are simply born with more. It should be noted that even when genetic factors are present, environmental and dietary intake are still important and controllable in the great majority of obesity cases.

The Thrifty Gene. Although genetic abnormalities may make it harder or easier to lose weight, the prevalence of obesity has dramatically increased over the past two decades, and genes cannot have changed within that short amount of time. Human metabolism evolved over centuries so that it could conserve energy and store fat during times of famine. Most cases of obesity occur now in people with normal physiology who live in industrialized nations where food is overly plentiful, and it is easy to avoid expending enough energy to burn the excess calories. One theory that combines genetic and environmental factors suggests that type 2 diabetes and the obesity that usually accompanies this disorder are derived from genetic actions that were once important for survival.

Some experts postulate the existence of a so-called "thrifty" gene, which regulates hormonal fluctuations to accommodate seasonal changes. Theoretically, it works in the following manner:

In certain nomadic populations, hormones are released during seasons when food supplies have traditionally been low, which results in resistance to insulin and efficiently increased fat storage.
The process is reversed in seasons when food is readily available.
Because modern industrialization has made high-carbohydrate and fatty foods available all year long, the gene no longer serves a useful function and is now harmful because fat, originally stored for famine situations, is not used up.

Such a theory could explain the high incidence of type 2 diabetes and obesity found in Pima tribes and other Native American tribes with nomadic histories and Western dietary habits. The traditional low-fat high-fiber foods (corn, lima beans, white and yellow teparies, mesquite, and acorns) of the Pima people may have protected this genetically susceptible population in the past from the high incidence of obesity and type 2 diabetes they are experiencing now.

Medical or Physical Causes of Obesity

A number of medical conditions may contribute to being overweight, although rarely are they a primary cause of obesity.

Some overweight people may believe their weight problem is due to hypothyroidism; patients with an underactive thyroid, however, generally show only a moderate weight increase of five to 10 pounds, mainly due to accumulation of fluid.
Very rare genetic disorders, including Froehlich's syndrome in boys, Laurence-Moon-Biedl, and the Prader-Willi syndromes, cause obesity.
Abnormalities or injury to the hypothalamus region in the brain can cause a condition called hypothalamic obesity.
Cushing's disease is a rare condition caused by high levels of steroid hormones, which results in obesity, a moon-shaped face, and muscle wasting.
Obesity is also linked with polycystic ovarian syndrome, a common hormonal disorder in women.

Click the icon to see an image of polycystic ovaries.

Effects of Certain Medications

Some prescription medications contribute to weight gain, usually by increasing appetite. Such drugs include the following:

Corticosteroids.
Some female hormone treatments, including some oral contraceptives (usually temporary) and certain progestins (such as Megestrol) used to treat cancer.
Antidepressants, and other psychoactive drugs, including certain antipsychotics, lithium, and antiseizure agents (such as valproate).
In a particularly unfortunate conflict of interest for obese individuals with type 2 diabetes, the use of insulin and insulin-stimulating drugs used to treat the condition often leads to weight gain.
Certain anti-seizure agents used in epilepsy and bipolar disorder can cause significant weight gain.
Certain antipsychotics.
Although drugs are not usually the primary cause of obesity or of being overweight, some people may be mistakenly tempted to stop taking their medications without their doctors' knowledge.

Cultural and Emotional Causes

Enough food is produced in the US to supply 3,800 calories every day to each man, woman, and child, far more than any single person needs to sustain life. In a 2002 study, subjects carefully recorded everything they ate and drank and all activities and psychologic factors surrounding the eating events. The people who gained weight ate more and their portions were larger than those who did not. This may be an obvious conclusion, but the public press often plays up biologic factors involved with obesity and overlooks the simple notion: Americans eat too much and exercise too little.

Obesity is dramatically increasing not only in American children and adults, but also in every country that has adopted similar cultural habits. The World Health Organization now considers obesity to be a global epidemic and a public health problem as more nations become "Westernized." In spite of the proven health risks of obesity, the government, insurance companies, and the medical profession spend very little money to counteract the commercial and cultural pressures that are producing millions of overweight people.

Television and Sedentary Habits

Perhaps the primary reason for the dramatic rise in obesity is the sedentary lives led by most Americans, including children and young people. In a 2003 study comparing modern life to the past, labor saving devices had reduced a person's energy expenditure by 111 calories a day--adding up to an extra 11 pounds a year. Half the difference in energy expenditure was due to less walking.

Regular television watching has been singled as the most hazardous pastime. According to a major 2003 study, for every two hours a person spends in front of the TV each day, the risk for obesity increases by 23% and for type 2 diabetes by 14%. In the study, TV watching produced the lowest metabolic rates compared to sewing, playing board games, reading, writing, and driving a car. Just the act of watching TV encourages unhealthy snacks and eating patterns and the advertising on the television compounds the problem by promoting fast foods, cereal, and snack products that are high in salt, fats, and carbohydrates. Even worse, much of these advertisements are directed at children--the most vulnerable group.

Fast Foods and Restaurant Eating

People are not only eating more than they did 20 years ago, but they are replacing home cooking with fast food, dining out, and packaged foods. This behavior, according to studies, place people at higher risk for obesity. Fast foods may be more harmful than restaurant cooking. These foods tend to be served in larger portions and generally contain more calories and unhealthy fats and less ingredients of nutritional value than homemade or restaurant meals. Snack foods and sweet beverages, including juice and soft drinks, are specific culprits in the increasing prevalence of obesity. (Of note: frequent small healthy meals--as opposed to two or three large daily meals--are associated with lower weights.)

Stress

People react differently to chronic stress. Some overeat and gain weight and others stop eating and lose weight. Night-eating has particularly been associated with stress. People who gain weight in response to stress often overeat foods high in sugar, fats, and salt. A 2003 study on rats, in fact, suggested that stress hormones increase the pleasure from eating such so-called "comfort foods". Furthermore, it supported previous research indicating that stress-related eating was associated with the unhealthy accumulation of abdominal fat.

Risk Factors

Just living in the United States is a risk factor for obesity. The prevalence of obesity and being overweight in America has risen dramatically over the past few years and continues to increase. According to a 2002 analysis of government data, 30.5% of American adults are obese (BMI over 30)--up from about 23% in the early 1990s. The prevalence of being overweight also increased during that time from about 56% to a current rate of 64.5%. Even worse, 2% of the population is severely obese (more than 100 pounds overweight)--a rate that has quadrupled over the past 25 years. Obesity has increased in every state, in both men and women, across all age groups, and in every ethnic group, although some groups may face slightly higher risks than others.

Fat tends to settle in certain regions, depending on gender. Women gain fat predominantly in the stomach, hips and thighs, while men tend to gain fat in the belly and waist.

Risk by Age. People of any age are at risk for obesity. More children and adolescents are overweight in America than ever before. Gaining some weight is inevitable with age and adding about 10 pounds to a normal base weight over time is not harmful. The current weight gain in American adults over 50, however, is significant. By age 55, the average American has added nearly 40 pounds of fat during the course of adulthood. This condition is made worse by the fact that muscle and bone mass decrease with age.

Risk by Gender. In men, BMI tends to increase until age 50 and then it levels off. In women, weight tends to increase until age 70 before it plateaus. A 2000 study has found that there are three high-risk periods for weight gain in women.

The first is at the onset of menstruation, particularly if it is early. (Obesity in childhood may actually be a contributor to early puberty, which in turn increases the risk for more weight gain.)
The second is after pregnancy, with higher risk for women who are already overweight.
Finally, many women gain weight after menopause.

These findings are significant because they may allow women to target high-risk times, and consequently prevent unnecessary weight gain.

Risk by Economic Group. Obesity is more prevalent in lower economic groups. One 2002 study reported that women who reported that they did not have enough food were more likely to be overweight than those who said they had sufficient food. Researchers discovered that the low-income women tended to have fewer fruits and vegetables but were actually taking in more calories a day than higher-income women. In any case, obesity it is increasing in young adults with college education along with everyone else.

Ethnic Groups. Among ethnic groups in general, African American women are more overweight than Caucasian women but African American men are less obese than Caucasian men. (Currently, 80% of African American women are overweight.) Hispanic men and women tend to weigh more than Caucasians.

US Regions. Regionally, the prevalence of obesity is lowest in the Western states and highest in the South.

Dietary Habits That Increase Risk

A number of dietary habits put people at risk for becoming overweight:

Night-Eating Syndrome. Night-eating syndrome is defined as having no appetite in the morning, insomnia, and consuming more than half of daily food intake after 6:00 PM. It is associated with obesity and is difficult to treat. Stress reduction and relaxation techniques may be helpful.
Binge Eating and Eating Disorders. About 30% of people who are obese are binge eaters who typically consume 5,000 to 15,000 calories in one sitting. To be diagnosed as a binge eater, a person has to binge at least twice a week for six months. Many experts believe that binge-eating carbohydrates causes an increase in a natural opiate leading to dependence on carbohydrates, and, therefore, the condition should be treated as an addiction. Other eating disorders are bulimia and anorexia. Bulimia is binge eating followed by purging in order to lose weight. Anorexia nervosa is a mental illness in which the person refuses to maintain weight at the normal level because of a terrible fear of getting fat and an abnormal perception of what his or her body looks like. Both conditions pose risks for serious medical problems, and anorexia nervosa can be life threatening. A combined approach using behavioral therapy and antidepressants may help these individuals. [For more information, seeWell-Connected Report # 49, Eating Disorders.]
Restrained Eating. Some people, mostly middle-aged women who have normal weight, have a pattern referred to as restrained eating. This pattern requires a high level of conscious control and usually maintains a lower weight. However, such restraint places these individuals at higher risk for loss of control and subsequent overeating.
Infrequent Eating. There is some evidence to suggest that eating small frequent meals uses more calories than infrequent large meals. It should be strongly noted, however, that packaged snack foods add calories and some do not produce a feeling of being full, so that people simply eat more than they should.

Specific Groups at Risk

Anyone with Sedentary Lifestyles. Office workers, drivers, and anyone whose lifestyle involves sitting for long periods are at higher risk for obesity.

Ex-Smokers. The trend toward weight increase has followed the trend for quitting smoking. Nicotine increases the metabolic rate, and quitting, even without eating more, can cause weight gain, which may be considerable. It is important to note that weight control is not a valid reason to smoke. People in previous centuries did not smoke cigarettes, nor were they usually obese.

Shift-Workers. A recent study found that individuals who work late shifts (between 4PM and 8AM) tend to eat more and take longer naps than day workers and are more likely to gain excess weight.

People with Disabilities. Obesity rates are higher than average in people with physical or mental disabilities. Those with disabilities in the lower part of the body, such as the legs, are at highest risk.

Obesity in Children: Special Considerations

Obesity in children and adolescents is rising at an alarming rate. Currently over 15% of young people over six years old are obese, and obesity is also increasing children five and younger. According to a 2002 government analysis, 10% of American Caucasian and 18.5% of African American children under two years old are overweight.

Definition of Obesity in Children

Children are considered to be overweight if the BMI is over 85% of the weight group in their age and sex categories. If it is 95% and over, they are considered to be obese. Adolescents are generally judged according to adult criteria for obesity, although there are other considerations in this population. Ethnic variations, timing of growth spurts, and higher normal fat levels around puberty can cause disparities in these measurements.

Causes and Risk Factors for Obesity in Children

Lifestyle Factors. Without educational or parental guidance, children are extremely vulnerable to the intense cultural pressures that are largely responsible for the obesity epidemic. The following are some specific problems created by the culture:

Excessive television watching plays a critical role in obesity in children. Not only is it a sedentary activity, but television also offers innumerable temptations with its advertisements for fast foods, sugar cereals, and unhealthy snacks. In one study obesity rates were lowest in children who watched television one hour or less a day and highest in those who watched four or more hours.
Sugar, particularly from soda, other sweetened beverages, and fruit juice, may be major contributors to childhood obesity. One study reported that drinking soda regularly increases a child’s risk for obesity by 60%. And the average American adolescent consumes 15 to 20 extra teaspoons a day just from soda and sugary drinks. (Juice, while better than soda, is still filled with sugar.)
Less physical exercise and greater sedentary activities play another significant role in obesity in children. A high level of physical activity--not just using up energy--is important for weight control in young people. Unfortunately, according to one study, the annual distance walked by children has fallen by nearly 30% since 1972, partially because more parents are driving their children to school out of fear of abduction, molestation, and traffic accidents. Schools are also offering fewer opportunities for daily physical activities than in the past.

Click the icon to see an image about TV watching.

Neither the media nor the educational system has strong well-financed programs that encourage healthy alternatives, including exercise and healthy foods.

Family History. Parental obesity more than doubles the risk that a young child, whether thin or overweight, will become obese as an adult. In older children and teenagers, obesity in parents starts to count less as a predictor for body weight than their own weight. The risk for may be due to environmental or genetic factors, or both.

Ethnic and Socioeconomic Factors. As in adult populations, children from lower socioeconomic groups and minority populations are at higher risk for obesity. For example, among young Mexican Americans and African Americans, there has been an increase in overweight prevalence of about 13% to over 23%.

Factors Surrounding Birth. The following factors surrounding birth are associated with a child's weight:

Low birth weight is a risk factor for later obesity and diabetes. One theory is that humans have a "thrifty gene" that produces metabolic changes in infants with low birth weight. Such changes affect insulin and fat accumulation in order to produce a "catch-up" weight in these young children as quickly as possible. This rapid weight gain in infancy increases the gain risk for obesity in children and also in young adulthood.
In a study of African American children, having an overweight pregnant mother increased the risk for later weight gain, but low birth weight did not.

Although some small studies have reported protection against obesity from breastfeeding, evidence is weak. In a 2003 study, for example, children who were breast fed for three to five months had a lower risk for obesity, but prolonged breastfeeding had no effect. Nevertheless, given the healthful effects of breast feeding and the possibility that it may have even a slight impact on childhood obesity, it is highly recommended.

Biologic Effect of Childhood Obesity on Adult Weight

Achieving a healthy weight becomes more difficult as children get older. The odds of obesity persisting into adulthood ranges from 20% in four-year olds to 80% in teenagers. One reason for the persistence is biologic; fat cells change in number or mass depending on a person's age:

Fat cells themselves multiply during two growth periods: early childhood and adolescence. Overeating during those times, then, increases the number of fat cells. (Some people are also just born with more fat cells.)
After adolescence, fat cells tend to increase in mass rather than quantity, so that adults who overeat and gain weight tend to have larger fat cells, not more of them. This growth in mass may be responsible for the greater risk for persistent obesity among teenagers than in small children who are overweight. Losing weight in after adolescence, then, reduces the size of the fat cells but not their number, so weight loss becomes much more difficult.

Health Consequences of Childhood Obesity

Children and adolescents who are obese have poorer health than other children. Studies are reporting unhealthy cholesterol levels and high blood pressure in obese children and adolescents. Of great concern is the dramatic increase in type 2 diabetes in young people, which is most certainly largely due to the increase in obesity. Obesity in children is also linked to asthma, gallbladder problems, sleep apnea, and liver abnormalities. Childhood obesity may be partly responsible for the declining age for onset of puberty in girls, with subsequent risks for breast cancer.

It is not clear yet how many of these childhood problems persist in people who achieve normal weight as adults. Staying overweight into adulthood certainly confers health risks.

Managing Overweight and Obese Children

Childhood obesity is best treated by a non-drug, multidisciplinary approach including diet, behavior modification, and exercise. Some evidence suggests that reducing calories by only 200 to 260 per day would prevent weight gain in most overweight children. Here some tips for children who are overweight:

Limit or avoid if possible take out, fast foods, high-sugar snacks, commercial packaged snacks, soda and sugar sweetened beverages (including too much juice).
Let children snack but make sure the snacks are healthy. Eating small frequent healthy meals (instead of two or three large ones) has been associated with being thinner and having a better cholesterol profile.
Let children choose their own food portions. One study indicated that children naturally ate 25% less then they chose their own portion size. When they were given larger portions their bite sizes were larger and they ate more.
Don't criticize a child for being overweight. It does not help and such attitudes could put children at risk for eating disorders, which are equal or even greater dangers to health.
Limit television, video games, and computer use to a few hours a week. This can contribute significantly to weight control, regardless of diet and physical activity.
For young children, try the traffic-light diet. Food is designated with stoplight colors depending on their high caloric content: Green for go (low calories); yellow for "eat with caution" (medium calories); red for "stop" (high calories).
Try a low-glycemic index diet. This may be as beneficial and possibly more than a standard reduced-fat diet in obese children. Such a diet focuses on carbohydrates, such as dried beans and soy, that raise blood sugar more slowly than others. This diet is sometimes used in diabetes and as a dietary approach in overweight adults. [For more information, seeWell-Connected Report #42, Diabetes Diet.]

Click the icon to see an image of childhood obesity.

Complications

General Adverse Effects of Obesity. Obesity, defined as a body mass index (BMI) of 30 or over, accounts for nearly 300,000 deaths in the US each year. It is associated with more chronic health problems than smoking, heavy drinking, or being poor. Furthermore, given the current increase in obesity, it will surpass smoking as the most important preventable cause of death in America.

Some studies indicate that the following health risks by body mass:

The lowest risks for heart disease, diabetes, and some cancers are in people with body mass index (BMI) values of 21 to 25.
The risks increase slightly when BMI values are between 25 and 27.
They are significant in BMIs between 27 and 30.
They are dramatic over 30.

Anyone with chronic health problems (e.g., heart or lung disease, stroke, or arthritis) or risk factors for them must be concerned about extra weight. In general, obesity may contribute to disease in several ways:

Metabolic Changes. As fat stores increase, the fat cells themselves enlarge and produce a number of chemicals that increase the risk for a number of diseases. Such diseases may include diabetes, high blood pressure, gallbladder disease, and some cancers.
Increased Mass. The increased body weight itself causes structural problems that cause injury and diseases, including osteoarthritis and sleep apnea.
Harmful Fat Cell Types. Weight concentrated around the abdomen and in the upper part of the body (the so-called apple shape) poses a higher health risk than fat that settles around the hips and flank (the pear shape). Fat cells in the upper part of the body appear to have different qualities from those found in the lower parts. In fact, studies suggest a higher risk for diabetes in people with the "apple shape" and lower risk in those who are "pear shaped".

Weight gain in the area of and above the waist (apple type) is more dangerous than weight gained around the hips and flank area (pear type). Fat cells in the upper body have different qualities than those found in hips and thighs.

General Adverse Effects of Being Overweight (but not obese). It is still not clear if being overweight (a BMI of 25 to 29.9) hurts healthy people with no risk factors for serious illnesses.

According to one 2001 study, just being overweight increases the risk for developing diabetes, gallstones, hypertension, heart disease, stroke, and colon cancer. The risk rose proportionally with the degree to which the individuals were overweight. In any case, adults who are overweight in middle age face a poor quality of life as they age, with the quality declining the greater the weight. (One study suggested, however, that being over 65 and overweight but not obese is not associated with any higher mortality rates).

Some experts argue, in fact, that in anyone who is not severely obese, it is the unhealthy diet and sedentary lifestyle that causes harm--not weight per se. In support of this argument, a British study found that overweight fit individuals had half the death rate of unfit trim individuals.

Being somewhat overweight may also have some benefits under specific circumstances:

In older women, some excess fat may produce extra estrogen that helps slow down bone loss and insulates bones from fall-related injuries. (It should be strongly noted, however, that when older overweight women lose weight they report improved vitality, physical function, and less pain.) The same positive effect of overweight does not appear to hold in older men.
Conditioned athletes may have high BMIs because of very dense muscle tissue. Being fit in general may protect many overweight people.
Some evidence suggests that Caucasians have the lowest mortality with BMIs of 24.3 to 24.7 while African Americans are better off in the range of 26.8 to 27.1.
Children may have higher normal fat levels during growth spurts and around puberty.

It should be stressed, however, that obesity itself is never healthful in anyone.

Heart Disease and Stroke

Individuals with a BMI of at least 30 have a 50% to 100% increased risk for death compared with individuals at a BMI of 20 to 25. Mortality rates from many causes are higher in obese people, but heart disease is the primary cause of death. People who are obese have almost three times the risk for heart disease as people with normal weights. Being physically unfit adds to the risk.

Weight concentrated around the abdomen and in the upper part of the body (apple-shaped) is particularly associated with insulin resistance and diabetes, heart disease, high blood pressure, stroke, and unhealthy cholesterol levels. Fat that settles in a "pear-shape" around the hips and flank appears to have a lower association with these conditions.

Obesity poses many dangers to the heart and circulatory system.

Damage in the Blood Vessels. Changes in body fat as people age, particularly increasing abdominal fat, have specifically been associated with stiffness in the aorta, the major artery leading from the heart. Studies are finding higher levels of a factor called C-reactive protein (CRP) in people with obesity and abdominal fat. CRP is now considered to be a marker for inflammation and damage in the arteries. (Losing weight reduces CRP levels.)

High Blood Pressure. Hypertension is the health problem most commonly associated with obesity, and the greater the weight, the greater the risk. Hypertension carries serious risks for stroke, heart attack, and heart failure. The link between obesity and high blood pressure is complex and may reflect interactions of genetic, demographic, and biologic factors. Many studies have reported that modest weight loss is beneficial for reducing existing blood pressure. [For more information, seeWell-Connected Report #14, High Blood Pressure.]

Heart Failure. An important 2002 study reported that obesity might account for 11% of heart failure cases in men and 14% in women. This link existed independently of other risk factors, such as high blood pressure, sleep apnea, and diabetes, which are also associated with obesity. The biologic mechanisms involved in obesity that lead specifically to heart failure are not clear. [For more information, seeWell-Connected Report #13, Heart Failure.]

Unhealthy Cholesterol Levels and Lipid Levels. The effect of obesity on cholesterol levels is complex. Although obesity does not appear to be strongly associated with overall cholesterol levels, among obese individuals triglyceride levels are usually high while HDL (the so-called "good" cholesterol) levels tend to be low, both risk factors for heart disease. [For more information, seeWell-Connected Report #23, Cholesterol, Other Lipids, and Lipoproteins.]

Click the icon to see an image of coronary artery disease.

Stroke. Obesity is also associated with a higher risk for stroke. [For more information, seeWell-Connected Report #45, Stroke.]

Insulin Resistance, Type 2 Diabetes, and Syndrome X (Metabolic Syndrome)

Type 2 Diabetes and Insulin Resistance. Most people with type 2 diabetes are obese and, in fact, studies strongly suggest that weight loss may be the key in controlling the current epidemic in diabetes type 2. The connection between obesity and diabetes is not entirely clear, since most obese people are not diabetic.

The common factor appears to be insulin resistance. Insulin is a critical hormone in the metabolism of sugar. In type 2 diabetes, different factors cause the body to become insulin resistant--that is, it can no longer use it. This has the effect of increasing blood glucose (sugar in the blood), the hallmark of diabetes. Both obesity and insulin resistance at different phases are marked by elevated levels of certain chemicals (e.g., free fatty acids and the hormones resistin and leptin). It is not known yet if the higher levels are simply a product of obesity or play some causal role in diabetes.

Insulin resistance is also associated with high blood pressure and abnormalities in blood clotting. Some research indicates that obesity, in fact, is the one common element linking insulin resistance, diabetes type 2, and high blood pressure. [For more information, see the Well-Connected Report #60, Diabetes Type 2.]

Metabolic Syndrome. Metabolic syndrome (also called syndrome X) is a pre-diabetic condition that is significantly associated with heart disease and higher mortality rates from all causes. The syndrome consists of obesity marked by abdominal fat, unhealthy cholesterol levels, high blood pressure, and insulin resistance. A 2002 study estimated that nearly a quarter of the U.S. population now has this condition. Even worse, according to a 2003 study, nearly a million American teenagers have this syndrome. A combination of weight loss and exercise is an effective treatment for this syndrome.

Cancer

Obesity has been associated with a higher risk for cancer in general and specific cancers in particular. Studies have also suggested that restricting calories reduces the risk for cancer. Some experts believe that effective weight control for children and adults could reduce cancer rates by 30% to 40%. One way obesity may increase the risk for cancer is its association with high levels of hormones called growth factors, which can trigger rapid cell proliferation leading to cancer.

Uterine Cancers. Women who are obese appear to have two to three times the risk for uterine cancer as thinner women.

Prostate Cancer. A 2001 study reported that obesity was associated with a modest increase in prostate cancer mortality, although not with the risk for prostate cancer itself. Some evidence suggests that it is a high-calorie intake rather than obesity or fat intake increases the risk for prostate cancer.

Click the icon to see an image of prostate cancer.

Breast Cancer. Studies have reported mixed effects on the association between obesity and breast cancer. A number of studies have linked obesity to breast cancer in postmenopausal women, particularly in women who begin to gain weight after age 18. One study, in fact, suggested that being heavier as a child conferred a lower risk for breast cancer after menopause.

Click the icon to see an illustrated series detailing a breast cancer surgery.

Gallbladder Cancer. Obese women are at higher risk for gallbladder cancer.

Gastrointestinal Cancers. A number of cancers in the gastrointestinal tract have been associated with obesity:

Cancer of the esophagus. The increased risk may be due to a higher incidence of gastroesophageal reflux disorder (heartburn) in people who are overweight.
Colon cancer. There is a demonstrated link between increased body mass and colon cancer risk for both men and women.
Pancreatic cancer. There has been a weak association between obesity and pancreatic cancer, with one study reporting a lower risk in overweight people who are physically active.

Click the icon to see an illustrated series detailing a colon cancer surgery.

(Obesity does not appear to be related to a higher risk for stomach cancer.)

Muscles and Bones

Obesity places stress on bones and muscles, and overweight people are at higher risk for hernias, low back pain, and aggravation of gout and other arthritic

Weight Control and Diet

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