OBESITY

 

Obesity and overweight now affect more than 50 percent of adult Americans. Diabetes mellitus, hypertension, heart disease, gallbladder disease, and some forms of cancer result from obesity. Whether these diseases are yet present or not, the obese individual should be encouraged to lose weight by appropriate methods to reduce the future likelihood that they will develop. Methods of weight loss include diet, nutritional education, self-help groups, and behavioral change. Under some circumstances drugs or surgery may be considered.

Definition and Measurement of Obesity

Obesity and overweight are best defined using the body mass index (BMI). This index is determined by dividing body weight in kilograms by the square of the height in meters: BMI = W/H2. The normal rate for BMI is 18.5 to 25. A BMI between 25 and 30 kg/m2 is defined as overweight and a BMI above 30 kg/m2 is defined as obesity (Table 1). Visceral fat can be used as an index of central adiposity. An increase in visceral fat reflects central obesity and increases health risks. The waist circumference is used to assess the amount of visceral obesity. A waist circumference in men of 40 inches (102 cm) or more, and in women, of 35 inches (88 cm) or more, is the threshold for defining central obesity (Table 1).

Prevalence of Overweight

More females than males are overweight at any age. The frequency of overweight increases with age to reach a peak at forty-five to fifty-four years in men and at age fifty-five to sixty-four in women. The National Health and Nutrition Examination Survey (NHANES) conducted by the U.S. government (published in 1993) found a BMI of 25 or more in 59.4 percent of men age twenty years or older and in 50.7 percent of women over the age of twenty years. The prevalence of obesity (BMI 30 or more) was 19.5 percent in men and 25.0 percent in women. The incidence of obesity continues to increase dramatically in the United States and elsewhere. A number of factors including age, sex, and physical inactivity influence the amount of body fat.

At birth, the human infant contains about 12 percent body fat. During the first years of life, body fat rises rapidly to reach a peak of about 25 percent by six months of age and then declines to 18 percent over the next ten years. At puberty, there is a significant increase in the percentage of body fat in females and a decrease in males. By age eighteen, males have approximately 15 to 18 percent body fat, and females have 25 to 28 percent. Between ages twenty and fifty, the fat content of males approximately doubles and that of females increases by about 50 percent. Total body weight, however, rises by only 10 to 15 percent: fat now accounts for a larger part of the body weight and lean body mass decreases.

Risks Related to Obesity

As the BMI increases, there is a curvilinear rise in excess mortality. This excess mortality rises more rapidly when the BMI is above 30 kg/m2. A BMI over 40 kg/m2 is associated with a further increase in overall risk and for the risk of sudden death. The principal causes of the excess mortality associated with overweight include hypertension, stroke, and other cardiovascular diseases, diabetes mellitus, certain cancers, reproductive disorders, gallbladder disease, and sudden death.

The insulin-resistant state or metabolic syndrome is strongly associated with visceral fat. It may include consequences such as glucose intolerance or type 2 diabetes mellitus, hypertension, polycystic ovarian syndrome, dyslipidemia (the state of abnormal—either higher or lower—values for blood fats), and other disorders. These are often responsive to weight loss, especially when this is achieved early and the loss is maintained.

Development of Obesity

Several mechanisms lead to obesity, including neuroendocrine imbalances, particular drugs, diet, reduced energy expenditure, and genetic factors that lead to certain syndromes and predisposition to obesity. Obesity can follow damage to the hypothalamus in the brain, but this is rare. Cushing’s disease is somewhat more common and can result in obesity. Treatment should be directed at the cause of the increased formation of adrenal corticosteroids.

Treatment of diabetics with insulin, sulfonylureas, or thiazolidinediones (but not metformin) can increase hunger and food intake, resulting in weight gain. Treatment with some antidepressants, anti-epileptics, and neuroleptics can also increase body weight, as can cyproheptadine (a serotonin antagonist that produces weight gain), probably through effects on the monoamines (including norepinephrine, epinephrine, dopamine, histamine, and serotonin) in the central nervous system.

Eating a high-fat diet and excessive consumption of sugar-sweetened beverages and the prevalence of abundant varieties of food in cafeterias or supermarkets are dietary factors in the development of obesity. Reduced energy expenditure relative to energy intake is another major component. Energy expenditure can be divided into four parts.

An inactive individual at rest burns between 800 and 900 kilocalories during a twenty-four hour period. This rate is lower in females than in males, and declines with age, and could account for much of the increase in fat stores if food intake does not decline similarly. The effect of physical exercise on metabolism is variable but on average is responsible for about one-third of the daily energy expenditure. From a therapeutic point of view this component of energy expenditure is most easily manipulated. Dietary thermogenesis is the energy expenditure that follows the ingestion of a meal. Heat produced by eating may dissipate up to 10 percent of the ingested calories. These thermic effects of food are one type of metabolic “inefficiency” in the body, that is, where dietary calories are not available for “useful” work. In the obese, the thermic effects of food are reduced particularly in individuals with impaired glucose tolerance or diabetes. Acute over- or underfeeding will produce corresponding shifts in overall metabolism, which can be as large as 15 to 20 percent.

Genetic factors can produce some types of obesity that are easily recognized. Among these types of obesity are: (1) the Bardet-Biel syndrome, characterized by retinal degeneration, mental retardation, obesity, polydactyly, and hypogonadism; (2) the Alstrom syndrome, characterized by pigmentary retinopathy, nerve deafness, obesity, and diabetes mellitus; (3) Carpenter syndrome, characterized by acrocephaly (abnormalities in the facial and head bones), mental retardation, hypogonadism, obesity, and preaxial syndactyly (extra fingers or toes on one hand or foot); (4) the Cohen syndrome, characterized by mental retardation, obesity, hypotonia (reduced tone of the muscles, resulting in a “floppy” muscle mass), and characteristic facies (an appearance of the face that is typical of specific genetic diseases); (5) the Prader-Willi syndrome, characterized by hypotonia, mental retardation, hypogonadism, and obesity; and (6) the pro-opiomelanocortin (POMC) syndrome, characterized by defective production of POMC that is recognized as a red-headed fat child with a low plasma cortisol (a value that is below the normal range).

If both parents are obese, about 80 percent of their offspring will be obese. If only one parent is obese, the likelihood of obesity in the offspring falls to less than 10 percent. Studies with identical twins suggest that inheritance accounts for about 70 percent and environmental factors (diet, physical inactivity, or both) account for 30 percent of the variation in body weight. Deficiency of the gene leptin and deficiency of the leptin receptor are rare, but are associated with massive human obesity. Absence of convertase I has also been associated with obesity in one family. The most common defects associated with massive obesity are abnormalities in the melanocortin receptor system—up to 4 percent of massively obese people may have this type of defect.

Evaluation of the Obese Patient

A medical evaluation should include the expected medical history, family history, personal and social history, and review of the systems of the body with a particular focus on the medications that can cause weight gain. A physical examination should include an assessment of the patient’s height, weight, waist circumference, blood pressure, and level of health risk due to obesity. Laboratory tests should include a lipid panel, glucose level, chemistry panel for hepatic (liver) function and uric acid, thyroid function testing, and, if indicated a cortisol level.

Evaluating Risk Using the Body Mass Index (BMI)

Individuals with a normal BMI (20–25 kg/m2) have little or no risk from obesity. Any individual in this weight range who wishes to lose weight for cosmetic reasons should do so only with conservative methods. Individuals with a BMI of greater than 25 to 29.9 kg/m2 are in the low-risk group for developing heart disease, hypertension, gallbladder disease, and diabetes mellitus associated with obesity. They too should be encouraged to use low-risk treatments, such as caloric restriction and exercise. Individuals with a BMI of 27 to 30 kg/m2 or more who have diseases related to obesity may use adjunctive pharmacotherapy for weight loss.

Individuals with a BMI of 30 to 40 kg/m2, have moderate risk for developing diseases associated with obesity. Diet, drugs, and exercise would all appear to be appropriate forms of treatment. Individuals with significant degrees of excess weight often find exercise difficult. However, exercise is very important in helping to maintain weight loss. The use of weight loss medications, as an adjunct to treatment, may also be useful in this group. Individuals who have a BMI above 40 kg/m2 have a high risk of developing diseases associated with their obesity. Moderate to severe restriction of calories is the first line of treatment, but for some of these patients surgery may be advisable.

Treatment of Obesity

Any diet must reduce an individual’s caloric intake below daily caloric expenditure if it is to be successful. This requires an assessment of caloric requirements, by estimating caloric expenditure from desirable weight tables; for men, multiply desirable weight by 30 to 35 kilocalories/kilogram, (14–16 kilocalories/lb.); for women, multiply desirable weight by 25 to 30 kilocalories/kilogram (12–14 kilocalories/lb.). After assessing caloric requirements, a reasonable calorie deficit can be prescribed. A caloric deficit of 500 kilocalories/day (3,500 kilocalories/week) will produce the loss of approximately one lb. (0.45 kilograms) of fat tissue each week. Table 2 gives a list of diets divided into different levels of energy.

The very low calorie diet (below 800 kilocalories) was developed to facilitate the rate of weight loss since lower energy intake should lead to greater energy deficit. In free living people, however, diets with 400 kilocalories/day have not produced greater weight loss than those with 800 kilocalories/day, suggesting either that they are harder to adhere to or that there is an adaptation in energy expenditure. In either case, these diets should only be used under appropriate medical supervision.

Types of diets. There are several types of diets with more than 800 kilocalories/day that usually have more than 1,200 kilocalories/day. They can be divided into several categories. These categories are based on the relative proportion of macronutrients included in the diet and whether they use special foods. For all diets it must be true that they reduce the calorie intake to produce a negative energy balance. Low-carbohydrate diets are touted because they produce ketosis (a state of increased ketones associated with diabetes and fasting) and allow you to eat all of the protein and fat you want. This ends up reducing total calorie intake to about 1,500 kilocalories/day. Since these diets generally have carbohydrate levels below 50 g./day they are ketogenic and can be monitored clinically by the appearance of ketones in the urine. They vary in the level of fiber that is employed. The Atkins diet has low fiber levels, the Sugar Busters diet higher fiber levels.

Low-fat diets recommend fat intake in the range of 10 to 20 percent of calories. The higher carbohydrate increases fiber intake. These diets were developed in a setting designed to reverse the atherosclerotic plaques associated with risks for heart disease, but because of the high fiber content they were often associated with weight loss. Moderate fat levels with higher carbohydrates are characteristic of many widely recommended “healthy diets.” For weight loss, the New York Health Department recommends the Prudent Diet, which has stood the test of time.

The portion-controlled diet makes use of prepared foods that have a narrow range of calories. This includes liquid or powdered drinks as well as frozen or canned entrees that have about 300 kilocalories/meal. These can be combined conveniently and thus removes the problem of counting calories from the individual. A number of popular diets focus on a single food, and although nutritionally unbalanced, they are simple to follow and the monotony of single items tends to limit food intake.

Food Guide Pyramid. The Food Guide Pyramid provides an approach to evaluating the quality of your diet. At the bottom of the pyramid are the grains, beans, and starchy vegetables that provide vitamins, minerals, fiber, and energy; six or more servings are recommended. On the next level are the vegetables (3–5 servings) and the fruits (3–4 servings). On the third level are the meats, fish, poultry, and nuts (2–3 servings) along with the milk and yogurt (2–3 servings). At the top are the fats, sweets, and alcohol. Reducing the number of servings proportionally will provide you with a calorie-reduced diet. Most important for the dieter, however, is to sharply reduce the fats and sugar at the top of the pyramid and to reduce or eliminate alcoholic beverages. Not only do alcoholic beverages have calories, their consumption tends to reduce the individual’s control in selecting the quality and quantity of foods to eat.

Changing behavioral patterns of eating. The basic principles of behavioral approaches for obesity can be summarized under the ABCs of eating.

• The A stands for antecedent. If one looks at eating as the response to events in the environment, then the antecedent events are those that trigger eating.

• The B stands for the behavior of eating. This includes among other things the place, the rate, and the frequency with which an individual eats. If the act of eating can be focused at one place with one plate and place setting it can help to provide control over eating.

• The C is the consequence of the eating. The feelings an individual has about eating can be altered, and rewards for changing eating patterns can be instituted.

Exercise and physical activity. The only part of energy expenditure that is amenable to significant manipulation is physical activity. During sleep, the lowest level of activity, approximately 0.8 kilocalories/minute is consumed. Thus, if an individual sleeps for an entire 24 hours, approximately 1,150 calories will be expended. Reclining increases this level to approximately 1.0-1.4 kilocalories/minute. Obese and diabetic patients should be encouraged to increase their physical activity for two reasons: First, it consumes calories, but second, and more important, exercise increases glucose utilization and may improve insulin sensitivity.

Drug treatment of obesity. Only a few drugs have been approved by the Food and Drug Administration for treatment of obesity. Studies following individuals who have used these drugs for two years have been published for sibutramine (Meridia) and orlistat (Xenical). Weight-loss drugs should be reserved for patients with moderate- or high-risk obesity (BMI
30 kg/m2) or a BMI above 27 if they have other significant diseases related to obesity. They should be considered for the patient who has failed to lose weight with other methods. Herbal products containing ephedra and an herbal source of caffeine can also produce weight loss when used in accordance with the package instructions.

Surgery. Gastric operations reduce the size of or bypass the stomach, but should be reserved for people with a BMI above 40 or when recommended by a physician.

The Obese Child

Estimates of the prevalence of obesity in children range from 3 to 15 percent. This figure has been rising more rapidly than in the rest of the population. The appearance of obesity in childhood and particularly adolescence is important because it most often persists into adult life. It may be a precursor to the appearance of type 2 diabetes in adolescents. The possibility of treatment should be considered for children who are above the seventy-fifth percentile of weight for height, and might be encouraged for those who are above the ninety-fifth percentile of weight for height. The treatment of prepubertal children should probably involve both parents and child since at this age the principal control of food availability is in the hands of the parents. For adolescents, however, it may be better to separate patient and parents, since the interaction between these groups may be part of the problem. Where growth has not reached its fullest extent, dietary restriction should attempt to reduce further weight gain. Severe caloric restriction and the use of appetite-suppressing drugs may slow height growth. For both children and adolescents, involvement in a regular exercise program is probably the first line of treatment.

Writen by George Bray in "Encyclopedia of Food and Culture", vol.3, Scribner Library of Daily Life, Salomon H. Katz, editor in chief, Thomson/Gale, USA, 2003, excerpts pp. 1-5.Digitized, adapted and illustrated to be posted by Leopoldo Costa.