Ординатура / Офтальмология / Английские материалы / Handbook of Nutrition and Ophthalmology_Semba_2007

Elliot Joslin (1869–1962), a physician, noted that a large proportion of patients with diabetes were overweight (3). The prevalence of diabetes decreased in countries that experienced food shortages during World War I, as observed by Harold Himsworth (1905– 1993), former secretary of the Medical Research Council in England (4). The Metropolitan Life Insurance Company developed actuarial tables based on the relationship of weight and mortality in adults. These “desirable weight” tables were based on height, weight, and type of frame, for men and women aged 25 yr and over (5).

3. Patterns of the Nutrition Transition

The emergence of obesity as a prominent public health problem relates to long-term demographic changes and diet shifts that have been termed the nutrition transition (6). There are five broad patterns of the nutrition transition in human history, and these patterns do not necessarily represent a temporal sequence, as in some locations in the world different patterns may still coexist. In Pattern 1, Collection of Food, the diet was high in carbohydrates and fiber and low in fat. In this hunter-gatherer society, wild animal meat was consumed. In Pattern 2, Famine, agriculture was evolving and the diet was less varied and subject to variation and episodic famines. In Pattern 3, Receding Famine, societies made some progress in reducing famines, and the consumption of fruits and vegetables and animal proteins increased, and starchy staples were less important in the diet. In Pattern 4, Degenerative Disease, a diet high in total fat, cholesterol, sugar and carbohydrate and low in polyunsaturated fats and fiber predominates, and this diet is often accompanied by an increase in sedentary lifestyle, higher obesity, and increased degenerative diseases (6). Pattern 5, Behavioral Change, reflects concern about modifying the diet in order to reduce risk of disease and prolong life. There is an increased intake of fruits and vegetables and carbohydrates, and a reduced intake of processed foods, meat, and dairy products.

4. DEFINITIONS

The World Health Organization (WHO) classifies obesity in adults based on BMI (weight/height2) in metric units (kg/m2). The cut-offs and ranges for the categories of underweight, normal, overweight, pre-obese, and obese are considered to represent the risk of comorbidities (7) (Table 1). In 1997, WHO held an expert consultation on obesity, which indicated a new shift in emphasis by this organization, which had usually focused on issues of breastfeeding and malnutrition. The upper limit of the normal range of a BMI of 24.9 was considered as a compromise to the United States, where higher levels of BMI were considered “normal” (7). Scientists from Asian countries have proposed an alternative classification system for obesity, because comorbidities such as diabetes and hypertension were considered higher among Asians than others in the WHO classification. Under this alternative classification, normal range is 18.5 to 22.9; overweight is ≥23; atrisk is 23 to 24.9; Obese I is 25 to 29.9; and Obese II is ≥30 kg/m2 (7).

There is no clear definition of obesity in children, but many studies have used a BMI between the 85th and 95th percentile of the National Health and Nutrition Examination Survey (NHANES) to define overweight, and BMI greater than the 95th percentile to define obese (8). The International Obesity Task Force (IOTF) recently has proposed a new classification system for overweight and obese in children (9). The IOTF analyzed

Fig. 1. Historic, current, and projected obesity prevalence rates for the United States, England, and Wales, Mauritius, Australia, and Brazil, 1960–2025. (Reprinted from ref. 11, with permission of Macmillan Publishers Ltd.)

international reference median (13). The countries with the highest prevalence of overweight children are located mainly in the Middle East, North Africa, and Latin America. Of countries with trend data, overweight increased in 16 of 38 countries (13). The global disparities in nutrition and health are apparent when undernutrition is compared with overweight worldwide, as undernutrition still remains a major problem in Africa and Asia, while overweight is more prevalent in other regions (13) (Fig. 2). It is estimated that about 22 million children under 5 yr of age are overweight worldwide (14).

5.3. Regions of the World

5.3.1. UNITED STATES AND CANADA

Currently more than half of the population in the United States is overweight and 20% are obese (10). There has been a large increase in obesity between the first US NHANES in 1960–1961 and the US NHANES III in 1988–1994 (15). In NHANES III, among individuals aged 20–74 yr, 59.3% of men and 49.6% of women were overweight (BMI ≥ 25 kg/m2), and 19.9% of men and 24.9% of women were obese (BMI ≥ 30 kg/m2) (15). A large increase in overweight and obesity has also been observed in Canada (16). The prevalence of overweight increased from 48% to 57% among men and 30% to 35% among women from 1981 to 1996 (16). In the same interval, the prevalence of obesity increased from 9% to 14% among men and 8% to 12% among women (16). The estimated number of deaths per year attributable to obesity among adults in the United States is 280,000 based on hazard ratios from all subjects and 325,000 based on hazard ratios from only nonsmokers and never-smokers (17). In Canada, about 57,000 deaths have been attributed to overweight and obesity from 1985 to 2000 (18).

Childhood obesity is considered the most serious and prevalent nutritional disorder in the United States (19), as 22% of children are overweight and 11% are obese, with girls

being more affected than boys (8,20). In a 20-yr period between NHANES I and NHANES II, the prevalence of overweight and obesity increased more than twofold for young girls, but for young boys it increased about 25%. But in children older than 6 yr of age, there has been a doubling of obesity prevalence among boys as well as girls (21). In the Bogalusa Heart Study, the trends in relative weight and obesity were examined among 5- to 24-yr- olds between 1973 and 1994. The prevalence of overweight increased by about twofold between 1973 and 1994, with the largest increases seen in 19to 24-yr-olds (22). In the United States, the highest prevalence of overweight among boys and girls is among Mexican American children, intermediate among non-Hispanic black children, and lowest in non-Hispanic white children (14). The obesity rates among American Indian children and adolescents are higher than in all other racial groups in the United States (23).

5.3.2. EUROPE

Among adults in Europe, the prevalence of obesity (BMI ≥ 30 kg/m2) is about 10–20% among men and 15–25% among women (10), which is less than in the United States. However, the prevalence of overweight (BMI 25–29.9 kg/m2) is more than 50% in Germany, Finland, and Great Britain. The prevalence of obesity is higher in southern and eastern Europe, especially among women, with higher prevalence of obesity associated with low education, low income, marital status, high parity, cessation of smoking, and low physical activity (24). From 1980 to 1997 in England and Wales, there has been an increase in obesity in adult men from 6% to 17% and in adult women from 8% to 20% (25). In contrast, there have been limited increases in the prevalence of obesity in France. From 1980 to 1991, in two cross-sectional studies involving random sample of households, there were slight increases in the prevalence of obesity and overweight among women but no change among men (26). From 1985 to 1997 in southwestern France, prevalence rates for obesity among men increased from 10% to 13% and in women remained stable at 11% (27). Among adolescents, the prevalence of overweight in 1997–1998 was highest among those in Ireland, Greece, and Portugal, but the prevalence of overweight among adolescents in Europe was less than in the United States (28).

5.3.3. AFRICA

Northern African and sub-Saharan Africa represent different phases of the nutrition transition. Although sub-Saharan Africa has the lowest prevalence of obesity and overweight of any large region in the world, this area has not been spared the general trend toward obesity. The prevalence of obesity and type 2 diabetes mellitus is slowly increasing in some areas of sub-Saharan Africa, and urban areas are more affected than rural areas (29,30). Studies from Mali, Nigeria, and Tanzania show that increases in BMI are accompanied by an increase in the prevalence of diabetes (30). In the Demographic and Health Survey in South Africa in 1998, 29.2% of men and 56.6% of women were overweight (BMI ≥ 25 kg/m2) (31). Among preschool children in Africa, undernutrition remains the dominant problem compared with overweight; however, in countries undergoing transition, such as Algeria, South Africa, and Egypt, both wasting and overweight have high prevalence (13).

5.3.4. LATIN AMERICA

Latin America is undergoing rapid demographic change and nutritional transition, with a decline in deaths from infectious diseases and an increase in deaths from noncom-

municable chronic disease (32,33). Obesity has increased from 1974 to 1997 in Brazil (34,35), and in a situation of nutrition transition in Brazil, higher income was a risk factor for obesity, whereas education was protective (35). The prevalence of obesity has approximately doubled in Brazil from 1975 to 1997 (33), and whereas in 1975 the ratio of obesity to underweight was 1:2, the ratio was 2:1 by 1997 (36). In Chile, the prevalence of obesity in large urban populations appears to have increased from 6% to over 15% in men and from 14% to about 23% in women from 1988 to 1997 (33). Obesity and overweight are highly prevalent, especially among women, in Mexico, Costa Rica, and many Caribbean countries (32). In data from 13 countries in Latin America, the prevalence of overweight among children aged 1–5 yr ranged from 6% in Haiti to 24% in Peru (32). The highest prevalence of overweight in children and obesity in women were found in urban areas and households with higher socioeconomic status (32).

5.3.5. RUSSIA AND THE FORMER RUSSIAN STATES

In the Russian Federation, the Russian Longitudinal Monitoring Survey from 1992 to 2000 shows that among men and women aged 19 to 55 yr, the prevalence of overweight (BMI ≥ 25 kg/m2) has remained relatively stable at 50% but the prevalence of obesity (BMI ≥ 30 kg/m2) increased from 13.3% to 16.0% (37). In Kazakhstan, a survey of over 25,000 individuals over 15 yr of age showed that obesity occurred in 23.7% (38).

5.3.6. SOUTH ASIA AND SOUTHEAST ASIA

The prevalence of central obesity was high in a random sample of adults aged 25–64 yr from a city in Kerala, India (39). A survey conducted in an urban slum area in northern India showed that 15.6% of women and 13.3% of men had BMI ≥ 25 kg/m2 (40). In the National Health Survey of Pakistan, 1990–1994, the proportion of adults aged 25–44 yr who had BMI ≥ 25 kg/m2 was 9% for men and 14% for women in rural areas and 22% for men and 37% for women in urban areas (41). Increasing urbanization, higher energy dense diets, and reduce physical activity are contributing to the rise of obesity in Pakistan and other parts of south Asia (41). The trend towards obesity has been associated with a rise in the prevalence of diabetes in India. India now has the largest number of people with diabetes of any given country (42). In 1995, there were an estimated 19.4 individuals with diabetes in India, and the number is expected to rise to 57.2 million by 2025 (42).

5.3.7. EAST ASIA AND PACIFIC

In Japan, the National Nutrition Surveys show that the prevalence of overweight and obesity has increased in the 20-yr period from 1976 to 1995 among adults aged 20 yr and older (43). Among men, the prevalence of overweight (BMI 25–29.9 kg/m2) increased from 14.5% to 20.5%, and the prevalence of obesity (BMI ≥ 30 kg/m2) increased from 0.8% to 2.0%. Among women, the prevalence of overweight and obesity decreased slightly during this same period (43). From 1976 to 2000, there was a trend of increased BMI and obesity among boys and girls in Japan (44). In a large study from Kagoshima City, increases in obesity occurred among elementary school children from 1989 to 2001–2002 (45). In China in 1992, the prevalence of overweight (BMI 25–29.9 kg/m2) and obesity (BMI ≥ 30 kg/m2) were 10.7% and 1.6% among men, respectively, and 15.4% and 1.6% among women, respectively (46). Using the same definitions, in South Korea in 1995, the prevalence of overweight and obesity among men was 18.0% and 0.8%, respectively, and among women was 19.9% and 2.2% (48). The prevalence of obesity in some Pacific

Island populations is among the highest reported in the world. The age-standardized prevalence of obesity in Nauru was 64.8% among men and 70.3% among women, and in Western Samoa, 47.7% of men and 70.4% of women were obese (48). Where longitudinal data are available, there have been dramatic increases in obesity over time in the Pacific region (48).

5.3.8. AUSTRALIA AND NEW ZEALAND

In the Australian Diabetes, Obesity and Lifestyle (AusDiab) Study, a cross-sectional study of 11,247 adults aged ≥25 yr from 42 randomly selected districts throughout Australia, the prevalence of overweight and obesity among men was 48.2% and 19.3%, respectively, and the prevalence of overweight and obesity among women was 29.9% and 22.6%, respectively (49). The prevalence of obesity increased 2.5-fold compared to data from 1980 (49). Low education level, higher television viewing time, and lower physical activity were each strongly associated with obesity (49). In the 1995 National Nutrition Survey in Australia, 45% of men and 29% of women were overweight, and 18% of men and women were obese (50). There are more than 350,000 individuals who are reported to have diabetes in Australia (51). In the 1997 National Nutrition Survey in New Zealand, 40.4% of males and 30.1% of females were overweight, and a further 14.7% of males and 19.2% of females were obese (52). There has been an increase in overweight and obesity from the 1989 National Nutrition Survey, when 32% were overweight and 11% were obese (52).

6. PATHOGENESIS

6.1. High Fat Intake

High dietary fat intake increases the risk of obesity, as demonstrated by randomized clinical trials and experimental animal studies (53). The energy density of high dietary fat may be a factor in its role in obesity (54). Dietary fat appears to have a weak effect on both satiation and satiety, which may also explain why high fat foods can lead to overconsumption (55).

6.3. Television

The number of hours watching television is a strong predictor of adolescent obesity. Among 4063 children, aged 8–16 yr, in NHANES III, 1988–1994, 26% of the children watched four or more hours of television per day, and 67% watched at least 2 h per day (56). Forty-two percent of black children watched four or more hours of television per day, which was the highest rate of any group. Boys and girls who watched television four or more hours per day had significantly greater body fat and BMI than those who watched television less than 2 h per day. Less vigorous activity was reported for girls and especially non-Hispanic black girls. Children who watched more television were less likely to participate in vigorous activity and tended to have higher BMI (56). A strong dose– response type of relationship was found between hours of television watching and both the prevalence and incidence of overweight (defined as BMI > 85th percentile for age and gender) in a nationally representative cohort of 746 youths aged 10–15 yr (57) (Fig. 3A,B). Television watching may be linked to obesity because of the passiveness of television viewing and the excess of poor nutritional products being advertised (58) (Fig. 4). More

Fig. 3. Estimated prevalence (A) and incidence (B) of overweight children by amount television viewed per day in 1990. All estimated are weighted, and incidence rates are per 4-yr follow-up. (Adapted from ref. 57.)

than half of all youth in the United States have a television set in the room where they sleep (59). The average high school graduate will likely have spent 15,000 to 18,000 h watching television but only 12,000 h in school (58).

6.4. Low Physical Activity

Sedentary lifestyles are associated with a positive energy balance and weight gain. Physical activity accounts for about 15–30% of total energy expenditure (60). Data from studies conducted around the world suggest that if the physical activity level (energy expenditure/basal metabolic rate) is <1.8, there is about a sevenfold increase of being overweight (61). These figures can be translated into practical terms using some estimates. For example, an adult male aged 30–60 yr who weighs 70 kg and is fairly sedentary (employed in a low-energy occupation such as office work) would have a physical

Fig. 4. Walt Handelsman cartoon: “Bobby darling, did you see this?” Copyright Times Picayune. (Reprinted with permission of ©Knight-Ridder Tribune Media Services. All rights reserved.)

activity level of 1.58, placing him at high risk of overweight and obesity (61). To achieve a physical activity level of at least 1.7, this individual would need to expend at least 300 calories per day, which would require 20 min of rapid jogging at a speed of 12 km/h or 1 h of walking at a speed of 4 km/h. If the person has time constraints and is too busy during the week, it would be challenging to transfer this exercise to the weekend, as the same objective of an average activity level of 1.7 would require jogging for 2.5 h or walking 7 h (61). Such considerations suggest that major lifestyle changes may be needed for many individuals in order to reduce the risk of obesity. Despite the increasing prevalence of obesity, evidence suggests that most physicians and health care professionals in the United States do not advise their overweight and obese patients about strategies to lose weight (62).

There has been a steady decline in physical activity among children and adolescents in the United States (63). The 1995 Nationwide Personal Transportation Survey showed that less than one-third of children who lived within a mile of school actually walked to school (59). In the United States in 1991, 42% of high school students were enrolled in daily physical education classes, but by 1997, this rate had fallen to 27% (59).

6.5. Poor Community Design

Urban sprawl, lack of sidewalks, and the propensity to drive instead of walk has an impact on overweight and obesity. In the Behavioral Risk Factor Surveillance System, pooled data from 1998, 1999, and 2000 were used to examine the relationship between obesity and urban sprawl in 206,992 adults (64). The country sprawl index was significantly associated with minutes walked, obesity, BMI, and hypertension, and residents of sprawling counties were less likely to walk during leisure time and more likely to weigh more and to have hypertension compared with those from more compact counties (64). In a travel survey of 10,878 participants in the Atlanta, Georgia region, land-use mix was significantly associated with obesity, with each quartile increase in land-use mix being