WHAT IS OBESITY?

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.

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 (eg, 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.)

BMI. The current best single gauge for body fat is a measurement called body mass index (BMI). [ See Box Calculating Body Mass Index (BMI).] In general a BMI of 25 to 29.9 indicated being overweight and obesity is a BMI of 30 and above. Higher BMIs are associated with significant health problems. Experts argue, however, that being overweight may not harmful under various circumstances:

• In the elderly, studies do not report any higher health risk for BMIs of 25 to 27. In older women, some extra weight may even be healthful, including protecting against osteoporosis. (Obesity, itself, however, is never healthful in anyone.)
  
  
• 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.

Calculating Body Mass Index (BMI) Ones 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. The result is graded on a scale to indicate levels of body fat. Federal guidelines define the following: Being overweight is a BMI of 25 to 29.9, and Obesity as a BMI of 30 or greater. These guidelines are very important for people at risk for diabetes, heart disease, or certain cancers.

Waist Circumference and Waist-Hip Ratio. The extent of abdominal fat is also 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 an increased risk for heart disease, diabetes, and impaired functioning. (In one 2000 study, a high triglyceride level along with a waist measurement of over 36 inches was a particularly strong predictor of heart problems in men.)

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 health risks than BMI or waist circumference alone.

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.

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.

WHAT ARE THE BIOLOGIC AND MEDICAL CAUSES OF OBESITY?

Obesity results when the body consumes more energy 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. When researchers first observed that genetically fat mice were deficient in leptin and that injecting them with leptin caused them to become thin, they believed that leptin offered a solution for obesity. The specific role that leptin plays in obesity, if any, however, is still unclear and may be complex. People who are overweight but lack a genetic susceptibility to obesity tend to have normal or high levels of leptin. When such people diet, leptin levels drop in direct association with reductions in weight. The most likely scenario is that in people without genetic deficiencies, leptin levels rise as more fat is stored in the cells and signal the hypothalamus to suppress appetite. Falling levels then signal the brain to stimulate appetite. In overweight people who are genetically deficient in leptin, however, the brain is tricked into thinking that it is always starving because there is no leptin to suppress appetite. Some researchers hope that although leptin is not a weight-loss agent for non-genetically obese people it may help people maintain normal weight after losing it. Leptin may also affect the body's resistance to the effects of insulin, a hormone that is critical for metabolizing blood sugar.
  
  
• Agouti-Related Protein (AGRP). AGRP is a newly discovered protein that is controlled by leptin and regulates how many calories are consumed.
  
  
• Wnt-10b. A protein called Wnt-10b apparently acts as a "fat switch" by turning off two molecules that regulate genes controlling fat cell formation.
  
  
• Resistin. Resistin, a newly discovered hormone, is 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. More research is warranted.
  
  
• Other Chemicals. Certain hormones (particularly neuropeptide Y, pro-opiomelanocortin, and melanocyte stimulating hormone) and brain chemicals known as endorphins and enkephalins may play a critical role in appetite regulation. Cholecystokinin, a hormone released in the upper intestine that stimulates digestive juices, may work with leptin to stimulate or suppress appetite. A family of proteins known as uncoupling proteins (UCPs) may be critical in converting energy into heat rather than having it stored as fat.

Specific Genetic Factors

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:

• 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.

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. The 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.

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.

WHAT ARE THE CULTURAL AND EMOTIONAL CAUSES OF OBESITY?

The Western Lifestyle

The Western lifestyle plays a major role in obesity. The effect of Western culture can be demonstrated by the fact that adolescent obesity increases dramatically among second- and third-generation immigrants to the US as they adopt the American diet and lifestyle. A number of factors are involved:

• 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. Such food has to be marketed and sold. In spite of the proven health risks of obesity, the government, insurance companies, and the medical profession spend very little money to oppose the billions of dollars that the food industry spends to promote food products.
  
  
• The Western diet typically supplies more than 30% of its calories from fat. Sugar is also a problem.
  
  
• Both leisure and working time are increasingly sedentary as people move from one seated position to another in their use of the automobile, the television, video games, and the computer.
  
  
• As more couples work and income levels rise, many people choose the convenience of fast food, dining out, and packaged foods in place of preparing a meal. In one study, men who ate outside the home were heavier than those who ate at home. Greater weight in women was associated with eating fast foods but not restaurant cooking. These foods tend to be served in larger portions and generally contain more calories and fat and less ingredients of nutritional value than homemade meals.

Stress and Mood Disorders

Stress. An interesting 2000 study has linked stress to the accumulation of abdominal fat. According to the study, both thin and overweight women who were vulnerable to stress and reportedly had more stress in their daily lives had waist-hip ratios indicative of fat storage at the waist. The study was limited to Caucasian Americans and warrants further investigation.

Seasonal Affective Disorder. Seasonal affective disorder (SAD) is depression that occurs during winter months. Patients with SAD also tend to gain weight during the winter. (Both conditions may be treated effectively with light therapy.)

WHO BECOMES OBESE OR OVERWEIGHT?

The World Health Organization now considers obesity to be a global epidemic and a public health problem as more nations become "Westernized." Globally, an estimated 250 million adults are now obese, and many more are overweight.

Obesity in American Adults

The prevalence of obesity (defined as a BMI of over 30) in the United States has risen dramatically over the past few years. It is now estimated that 61% of Americans are now overweight, up from 43% in the early 1940s. And according to a 2001 study, nearly 20% of American adults are obese (BMI over 30). Regionally, the prevalence of obesity is lowest in the Western states (13.8% in Colorado) and highest in the South (24% in Mississippi).

Gaining some weight is inevitable with age and adding about 10 pounds to a normal base weight over time is not harmful. The weight gain in American adults over 50, however, is significant, with 64% of women and 73% of men being seriously overweight. This condition is made worse by the fact that muscle and bone mass decrease with age, so the fat increase is actually about one and a half pounds. Some studies suggest that by age 55, the average American has added over 37 pounds of fat during the course of adulthood.

Obesity by Ethnic, Social, and Income Groups

Obesity is more prevalent in lower economic groups but it appears to be increasing in young adults with some college education. Obesity, in fact, has increased in every state, in both men and women, across all age groups, and in every ethnic group. Among ethnic groups, African American women are more overweight than Caucasian women but African American men are less obese than Caucasian men. Hispanic men and women tend to weigh more than Caucasians.

Weight Gain 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. (It should also be noted, that 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 tend to gain weight after menopause.

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

Obesity in Children

More children and adolescents are overweight in America than ever before. According to a 2001 report based on a study of 8,000 children, the rate of overweight children among African-American and Hispanics increased by more than 120% and among Caucasian children by 50% between 1986 and 1998. In the study, 22% of African-American and Hispanic children were overweight, while about 12% of Caucasian children were overweight. Other studies have estimated that about 35% of children were either at risk for being overweight or are overweight. And the problem is becoming global. [ See Box Obesity in Children: Special Considerations .]

Dietary Habits

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

• Night-Eating. Consuming between 25% and 50% of daily calories between the evening meal and the next morning is referred to as night-eating syndrome and is associated with obesity.
  
  
• 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. Dangerous consequences of binge eating are its antitheses, the eating disorders 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. [For more information, see the 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 restrain 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.

Specific Groups at Risk

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 a 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.

OBESITY IN CHILDREN: SPECIAL CONSIDERATIONS Identifying Obesity in Children The same BMI standards used for adults along with anthropometry (measurement of fat by skin fold thickness) may be used to identify overweight adolescents, 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 Factors Surrounding Birth. The following are some studies reporting certain factors surrounding birth that are associated in a child's weight: Some studies report an association between low birth weight and a risk for later obesity and diabetes. A 2000 UK study proposed that some infants who have a low birth weight due to conditions that restrain growth in the womb (such as having thin mothers who smoke) may undergo a natural catch-up growth between infancy and two years old. This rapid growth, in turn, may increase the risk for later obesity. 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. Some studies have found that prolonged and exclusive breast-feeding may offer some protection against childhood obesity. Socioeconomic and Cultural Factors. Children are particularly vulnerable to the temptations proffered by the media-minded culture, such as food advertisements and sedentary video games. And, neither the media nor even the educational system has strong well-financed programs that encourage healthy alternatives including exercise and healthy foods. The following are some specific problems created by the culture: Sugar is a significant problem. (The role of high fat diets on obesity in children is less clear.) Soda, other sweetened beverages, and fruit juice in fact may be singled out as major contributors to childhood obesity. One 2001 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 is playing a significant role in obesity in children. One study has found that 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. Excessive television watching plays a critical role in obesity in children, particularly in girls and minority children. In one 2001 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. Studies report that children in low-income families and little mental stimulation have an elevated risk for developing obesity. Parental Effects. Obesity in parents is a strong risk factor. It is not known if the risk is primarily genetic or environmental. When a parent of a child under three is obese, the child, even if thin, has a 30% chance of becoming obese later on. Similarly, parental obesity more than doubles the risk that the young child, whether thin or overweight, will become obese as an adult. In older children and teenagers, however, obesity in their parents starts to count less as a predictor for body weight than their own weight. Biologic Effect of Childhood Obesity on Adult Weight 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. Losing weight in adulthood, then, reduces the size of the fat cells but not their number, so weight loss becomes much more difficult for adults who become overweight when fat cells were replicating in childhood. (Such fat-cell growth in adolescence poses a greater risk for being obese in adulthood than in toddlerhood.) Long-Term Consequences of Childhood Obesity In one study among overweight children, 77% remained obese into a adulthood, although another study suggested that the risk for persistently high weight was significant only in obese children age 13 and over. It is not exactly clear if being overweight as a child confers health risks later on if the child achieves normal weight in adulthood. A 2001 study reported that obesity in childhood was not related to any excess health risk. Nevertheless some experts believe that a sudden increase in heart attacks and the rise in type 1 diabetes among young people may be associated with the parallel dramatic increase in obesity. It may also explain the decreasing age for puberty in girls. Staying overweight or becoming obese in adulthood, in any case, certainly confers health risks. (Of interest was a 2001 study that reported the greatest health risks in obese adults who were very thin children.) Managing Overweight and Obese Children Childhood obesity is best treated by a non-drug, multidisciplinary approach including diet, behavior modification, and exercise. Here some tips for children who are overweight: Nearly all children snack, which is not itself unhealthy. In fact, if the snacks are healthy eating small frequent meals (instead of two or three large ones) has been associated with being thinner and having a better cholesterol profile. Parents should limit take out, high-sugar snacks, commercial packaged snacks, soda and sugar sweetened beverages (including too much juice), and fast foods in general. Parents should not criticize their children for being overweight. Such attitudes could put children at risk for eating disorders, which are equal or even greater dangers to health. Simply limiting television, video games, and computer use to a few hours a week 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). One 2000 study found that a low-glycemic index diet may be as beneficial and possibly more than a standard reduced-fat diet in obese children. Such a diet focuses on carbohydrates that raise blood sugar more slowly than others. This dietary approach is sometimes used in diabetes. [For more information see Report #42, Diabetes Diet .]

HOW SERIOUS IS OBESITY AND BEING OVERWEIGHT?

General Adverse Effects of Obesity

Over 300,000 lives could be saved each year if all Americans maintained a healthy weight. Obesity is associated with more chronic health problems than smoking, heavy drinking, or being poor. And next to smoking, obesity is the most common preventable cause of death in the US. According to one 2001 study, even being overweight increased the risk for diseases. In this 10-year study, the risks for developing diabetes, gallstones, hypertension, heart disease, stroke, and colon cancer rose proportionally with the degree to which the individuals were overweight.

Some studies indicate that the following:

• 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. [For calculating the BMI, see box Calculating Body Mass Index (BMI)]

Anyone with chronic health problems (eg, 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. One can argue that this increased mass is associated with psychological disorders, particularly depression, which is now a known health risk.
  
  
• Harmful Fat Cell Types. Weight concentrated around the abdomen and in the upper part of the body poses a higher health risk than fat that settles in a pear-shape around the hips and flank. Fat cells in the upper part of the body appear to have different qualities from those found in the lower parts.

Experts are still debating, however, about the degree to which being overweight hurts healthy people with no risk factors for serious illnesses. Some argue, in fact, that in anyone who is not severely obese (BMI over 30), it is an 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. In any case, actual obesity is known to be harmful, and eating healthy foods and exercising are essential in any case and usually lead to weight loss.

Weight in the Older Adult Age plays an important role in helping to define the risk from obesity. The mortality rates due to being overweight decline with age. One study suggested, for example, that being over 65 and overweight but not obese (a BMI between 25 and 27) is not associated with any higher mortality rates. A BMI over 28, however, is dangerous in people at any age and is associated with an increased risk for death among people over 65. In older women, being slightly overweight or even moderately obese may not be harmful and may offer some protection. Some excess fat in older women may produce some extra estrogen, nutritional reserve, and insulate 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. Being severely underweight is also dangerous in both older women and men, possibly because of the relationship underweight older adults are likely to be smokers, which causes major health problems.

Cardiovascular Disease

 

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.

Damage in the Blood Vessels. Studies are reporting higher levels of a factor called C-reactive protein, which is a marker for inflammation and damage in the arteries from an over-active immune response. 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 heard.

High Blood Pressure. Hypertension is the health problem most commonly associated with obesity, and the greater the weight, the greater the risk. While hypertension carries its own serious risks for stroke and heart attack, overweight people with high blood pressure are also at increased danger for enlargement of the left heart chamber, a major risk factor for 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 and the risk for heart failure. [For more information, see the Report #14 , High Blood Pressure .]

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 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.

Stroke. Obesity is also associated with a higher risk for stroke.

Insulin Resistance and Type 2 Diabetes

Most people with type 2 diabetes are obese and, in fact, losing weight can help prevent its development. It should be noted that only a minority of obese people is diabetic. Nevertheless, researchers have blamed obesity and sedentary living for the dramatic increase in type 2 diabetes over the past years.

People with type 2 diabetes have abnormalities that produce an inability to use insulin, a critical hormone in the metabolism of sugar. This condition, called insulin resistance , and has effect of increasing blood glucose (sugar in the blood), the hallmark of diabetes. (Insulin resistance is also associated with high blood pressure and abnormalities in blood clotting.)

Although the exact mechanisms of the relationship between obesity and diabetes type 2 is still not entirely clear, fat cells may release certain chemicals that inhibit the body's sensitivity to insulin. [For more information, see the Report #60 , Diabetes Type 2 .]

Cancer

Obesity has been associated with certain cancers, and some experts believe that effective weight control for children and adults could reduce cancer rates by 30% to 40%.

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

Prostate Cancer. A Western lifestyle is associated with prostate cancer, although direct causal role for either obesity or dietary fats has not been established. A 2001 study did find obesity to be associated with a modest increase in prostate cancer mortality, although not with the risk for prostate cancer itself. In a previous study of Chinese men, however, it was not obesity itself but an unhealthy fat distribution that was associated with a higher risk. High risk individuals in the study were those whose fat was more centered in the abdomen, the so-called apple-shape. Either one or both of the hormones that are associated with both obesity and diabetes, , leptin and insulin, could theoretically stimulate prostate cancer growth.

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.

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. One study has linked obesity to pancreatic cancer, but also found that overweight patients who are physically active have a lower risk.

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

Muscles and Bones

Effects of Weight on 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 conditions. Studies report that the incidence of osteoarthritis is significantly increased in people who were overweight. People who are obese are also at higher risk for carpal tunnel syndrome and other problems involving nerves in their wrists and hands. It should be noted that some weight may be protective against osteoporosis (loss of bone density).

Osteoporosis. Some extra weight is beneficial for maintaining bone density in women after menopause. Before menopause, however, overweight women who lose weight and who also increase their intake of dietary calcium are not at risk for bone loss.

Eyes and Mouth Disorders

Obesity increases the risk for the following mouth and eye disorders:

• Gum disease.
  
  
• Cataracts. A study of 17,150 men concluded that there is a higher association between cataracts and greater body mass, height, and carrying fat around the abdomen.
  
  
• Maculopathy. Maculopathy is an eye disease related to aging. Obesity also appears to be related to this disease.

Reproductive and Hormonal Problems

Infertility. Abnormal amounts of body fat, either 10% to 15% too high or too low, can contribute to infertility in women. Obesity is specially related to certain problems related to infertility, such as uterine fibroids or menstrual irregularities. In men, obesity can contribute to reduced testosterone levels.

Effect on Pregnancy. The dangerous effects of obesity on pregnancy are multifold. They include high blood pressure, gestational diabetes (diabetes, usually temporary, that occurs during pregnancy), urinary tract infections, blood clots, prolonged labor, a higher fetal mortality rate in late stages of pregnancy, and cesarean delivery. Infants of women who are obese are also at higher risk for neural tube birth defects, which affect the brain or spine. Folic acid supplements, ordinarily effective in preventing these conditions, may not be as protective in overweight women.

Effects on the Lungs

Obesity is thought to be a risk factor for adult-onset asthma, although there is some evidence that although obesity causes wheezing and shortness of breath it does not appear to be strongly associated with the disease mechanisms in the lungs that cause true asthma.

Obesity also puts people at risk for hypoxia, in which oxygen is insufficient to meet the body's needs. Obese people need to work harder to breathe and tend to have inefficient respiratory muscles and diminished lung capacity. The Pickwickian syndrome, named for an overweight character in a Dickens novel, occurs in severe obesity when lack of oxygen produces profound and chronic sleepiness and, eventually, heart failure.

Effect on the Liver

Hepatitis. People with obesity and diabetes type 2 are at higher risk for a condition called nonalcoholic steatohepatitis (NASH), liver damage that is similar to liver injury seen in alcoholism. In some cases it can be very serious and require liver transplantation.

Gallstones. The incidence of gallstones is significantly higher in obese women and men. The risk for stone formation is also high if a person loses weight too quickly. In people on ultra-low calorie diets, gallstones may be prevented by taking ursodeoxycholic acid (Actigall).

Sleep Disorders

People who are obese and nap tend to fall asleep faster and sleep longer during the day. At night, however, it takes them longer to fall asleep and they sleep less than people with normal weights. In an apparent vicious circle, studies have suggested that not only can obesity interfere with sleep, but that sleep problems may actually contribute to obesity.

Sleep Apnea. Obesity, particularly the apple-shape, is particularly associated with sleep apnea, which occurs when the upper throat relaxes and collapses at intervals during sleep, thereby temporarily blocking the passage of air. It is increasingly being viewed as a potentially serious health problem, including heart disease and stroke. Some studies in fact suggest that among overweight people, those who have sleep apneas have a greater heart risk than those without them. Obesity may contribute to sleep apnea simply by fatty cells infiltrating the throat tissue, which could narrow the airways. In one study, the more obese a person with sleep apnea was, the higher the pressure on the airway and therefore the greater the obstruction of the airway. (Obstructive sleep apnea may also cause obesity itself, however, as sleepy people tend to be sedentary.) Some studies are even indicating that treating sleep apnea may even help people lose abdominal fat.

Narcolepsy. A small European study found a link between narcolepsy (a sleep disorder characterized by excessive daytime sleepiness with frequent daily sleep attacks) and high BMI.

Emotional and Social Problems

A study that followed obese adolescents for seven years found that, compared to thinner peers, overweight girls completed fewer years of school, were 20% less likely to be married, and had 10% higher rates of household poverty. A 2000 study of third graders found a direct relationship between depressive symptoms and body mass index in girls, but not boys. Women and girls tend to blame themselves for being heavy while males tend to attribute being overweight to outside factors. Studies consistently show that overweight males (both boys and men) are not as severely emotionally affected as females of any age. Nevertheless, in the first study mentioned above, 11% of obese men were less likely to be married than non-obese men and their incomes were lower.

No evidence exists, however, that obese people suffer from emotional disorders, such as major depression or anxiety, to any greater degree than thinner people. Generally, depression and anxiety are caused by the weight problem and are usually resolved by weight loss.

WHAT ARE THE GENERAL GUIDELINES FOR WEIGHT TREATMENTS?

General Approach to Weight Loss and Maintenance

Life long changes in eating habits, physical activity, and attitudes about food and weight are essential to weight management. [ See Table Key Components to Lifestyle Change Program.] The following offer some general suggestions for dieters:

• Start with realistic goals. Diet failure is extremely common and the odds of significant weight loss are poor, particularly in people with the highest weights. People embarking on a weight loss program should keep in mind that only a 5% to 10% reduction in weight, even in people who are obese, can improve health significantly. Certainly, the current unwholesome and distorted image of a super-thin female shape is a cultural idea that almost no one can or should achieve. (Anorexia, obesity's alter ego, is less common but is the other side of this dysfunctional aspect of our culture.) Obesity, however, still poses a threat to life, health, and well being, and the struggle against it is worthwhile. And obesity in children is never acceptable, unless there is a proven medical reason.
  
  
• The simplest (but still difficult) approach to weight loss is reducing calories and exercising at least 150 minutes a week. One study suggested that only about 20% of people who try to lose weight use these effective methods. (It should be noted that many physicians have limited time as well as training in nutrition and weight management and some may be tempted to prescribe diet pills, particularly when urged by the patient, even though a diet and exercise have not been tried.)
  
  
• Hunger pangs should not be taken as cues to eat. A stomach that has been stretched by large meals will continue to signal hunger for large amounts of food until its size reduces over time with smaller meals.
  
  
• Once a person has lost weight, maintenance is required. To maintain a healthy weight in our culture, everyone must make daily, even hourly, decisions about what is consumed and what is expended through activity. Such thinking, in many cases, can become automatic and not painful.
  
  
• Even repeated weight loss failure is no reason to give up. Most studies indicate that yo-yo dieting or weight cycling has no adverse psychological or physical effects. (Of some concern was a 2000 study reporting lower HDL levels, the so-called good cholesterol, in women whose weight cycled from frequent dieting. No other heart risks were evident, however.) Repeated dieting also does not impair the body's ability to burn calories efficiently.
  
  
• Weight loss, in any case, should not be the only or even the primary goal for people concerned about their health. The success of weight reduction efforts should be evaluated according to improvements in chronic disease risk factors or symptoms and by the adoption of healthy lifestyle habits, not by just the number of pounds lost.

Key Components of a Lifestyle Change Program
Lifestyle	Reduce rate of eating. Keep food records. Eliminate environmental triggers to eating. Identify high-risk situations for overeating. Uncouple eating from other activities.
Exercise	Confront psychological barriers to exercise. Understand mechanisms linking exercise to weight control. Establish reasonable exercise goals. Develop a plan for regular activity. Integrate increased activity into daily lifestyle.
Attitudes	Develop reasonable weight-loss goals. Avoid "all or none" thinking. Focus attention away from the scale and toward behavior. Uncouple weight from self-esteem. Recover from lapses with constructive action (relapse prevention).
Relationships	Understand the key role of social support to health. Identify supportive others. Match personal style to support-seeking activities. Be specific in making support requests. Be assertive but reinforcing in drawing help from others.
Nutrition	Resist the lure of popular fad diets. Develop pro-health rather than restriction mentality about eating. Eat with moderation in mind. Maximize fiber. Develop a tailored plan.

From Brownell KD. The LEARN Program for Weight Control. 7th ed. Dallas, Tex: American Health Publishing Company; 1998.

WHAT ARE THE DIETS AND LIFESTYLE METHODS FOR MANAGING WEIGHT?

A 1999 analysis of 2,800 individuals who had lost at least 30 pounds and maintained the weight loss for more than a year reported the following results:

• About 55% had been involved in a formal weight loss program.
  
  
• 20% succeeded with liquid meal replacements.
  
  
• Only 4.3% used medications.
  
  
• 1.3% had surgery.
  
  
• 81% reported that they exercised more often and more vigorously than with previous attempts.

Calorie Restriction

Calorie restriction has been the cornerstone of obesity treatment. The standard dietary recommendations for losing weight are the following:

• As a rough rule of thumb, one pound of fat equals about 3,500 calories, so one could lose a pound a week by reducing daily caloric intake by about 500 calories a day. Naturally, the more severe the daily calorie restriction, the faster the weight loss. Very-low calorie diets have also been associated with better success, but extreme diets can have some serious health consequences. [See Box Warning on Extreme Diets.]
  
  
• To determine the daily calories requirements for specific individuals, multiply the number of pounds of ideal weight by 12 to 15 calories. The number of calories per pound depends on gender, age, and activity levels. For instance a 50-year old woman who wants to maintain a weight of 135 pounds and is mildly active might require only 12 calories per pound (1,620 calories a day). A 25-year old female athlete who wants to maintain the same weight might require 25 calories per pound 2,025 (calories a day).
  
  
• Fat intake should be no more than 30% of total calories. Most fats should be in the form of monounsaturated fats (such as olive oil) and saturated fats (found in animal products) should be avoided.

Warning on Extreme Diets Extreme diets of less than 1,100 calories carry health risks and are often followed by bingeing or overeating and a return to the obese state. Such diets often have insufficient vitamins and minerals, which must then be taken as supplements. Most of the initial weight loss is in fluids. Later, fat is lost, but so is muscle, which can account for more than 30% of the weight loss. No one should be on severe diets longer than 16 weeks or fast for more than two or three days. Severe dieting has unpleasant side effects, including fatigue, intolerance to cold, hair loss, gallstone formation, and menstrual irregularities. There have been rare reports of death from heart arrhythmias when liquid formulas did not have sufficient nutrients. Of note, those whose diets include a high intake of fluids and much reduced protein and sodium are at risk for hyponatremia, which can cause fatigue, confusion, dizziness, and in extreme cases, coma.

Low-Fat and High-Fiber Diets

 

Some studies suggest that replacing foods high in fats with low-fat complex carbohydrates (fruits, vegetables, and whole grains) may be more effective than calorie counting, particularly in maintaining weight loss. This dietary approach requires counting only grams of fat with goal of achieving 30% or fewer calories from fat. (One gram of fat contains nine calories while one gram of carbohydrates or protein has only four calories, and dietary fat converts more readily to fat in the body than carbohydrates or proteins.) Simply switching to low-fat or skimmed diary products may be sufficient for some people.

There are possible drawbacks to this approach, however:

• Some people who reduce their fat intake may not consume enough of the basic nutrients, including vitamins A and E, folic acid, calcium, iron, and zinc. People on low-fat diets should consume a wide variety of foods and take a multivitamin if appropriate.
  
  
• Many people over-increase their intake of carbohydrates, believing that they are not adding calories. No one should use a low-fat diet as an excuse for over-consuming carbohydrates, particularly starchy foods and sugar. A high calorie diet from any source will add pounds.
  
  
• Replacing fatty foods, such as cakes, cookies, and chips, with their commercial "low-fat" counterparts does not constitute a low-fat diet. These foods generally contain more sugar and hence calories, not to mention other ingredients which have virtually no nutritional value. In fact, a 2002 study suggested that increasing sugar may overtime reduce levels of HDL cholesterol, the so-called good cholesterol.
  
  
• Very low-fat diets may increase the risk for stroke from hemorrhage in the brain.
  
  
• Very low fat diets may reduce calcium absorption, which may be particularly harmful in women at risk for osteoporosis.

Some fat in a diet is essential. It should be derived from plant oils and fish, however, and not from saturated fat from animal products or trans-fatty acids from hydrogenated (hardened) oils.

Fat Substitutes. Fat substitutes added to commercial foods or used in baking deliver some of the desirable qualities of fat, but do not add as many calories. It should be noted, however, that one study suggested that people who consume foods that contain fat substitutes do not learn to dislike fatty foods, while people who learn to cook using foods naturally lacking or low in fat eventually lose their taste for high fat diets. They include the following:

• Plant substances known as sterols have long been known to reduce cholesterol by impairing its absorption in the intestinal tract. Sterols are now being isolated as sterol derivatives or as stanols (which are saturated sterols) to produce margarines (Benecol, Take Control). Benecol is derived from pine bark and Take Control from soybeans. Studies on such margarines are reporting that either two servings a day as part of a low-fat diet can lower LDL and total cholesterol. It should be noted, however, that these margarines may be hydrogenated and include some trans-fatty acids. Of further concern is the possibility that stanol may block absorption of important fat-soluble nutrients, including vitamins A, E, and D and carotenoids (compounds, such best carotene, that convert to vitamin A). One study suggested that it had no effect on the vitamins but did impair absorption of beta carotene. In people already on a low-fat diet, the addition of these margarines may not produce much additional benefit.
  
  
• Olestra (Olean) passes through the body without leaving behind any calories from fat. (It should be noted, however,