Childhood Obesity: Contemporary Issues
http://www.100md.com
《新英格兰医药杂志》
There's nobody better than the Brits at breaking scientific bad news in plain, blunt language. Consider this dispiriting assessment of medical and public health professionals' track record to date on helping overweight children: "Regrettably, most dietary (and physical activity) prescriptions for the treatment and prevention of childhood obesity have had spectacularly unsuccessful results." That verdict, by M.B.E. Livingstone of the University of Ulster and K.L. Rennie of MRC Human Nutrition Research in Cambridge, England, comes at the end of a chapter on what determines children's food intake, and it typifies medical science's alarming ignorance about how best to respond to an epidemic that menaces the future health of children in the United States and many other countries. Childhood Obesity is a collection of reviews of the latest research evidence on childhood obesity; it is written for the most part by British researchers, and clearly conveys both the seriousness of the international public health threat and the inadequacy of current knowledge about what should be done.
(Figure)
"The Fat Boy," by Harold Copping.
An illustration (color lithograph) for Character Sketches from Dickens, compiled by B.W. Matz, 1924.
From The Bridgeman Art Library.
Although the United States, Canada, and Mexico have had some of the steepest rises in the prevalence of pediatric obesity, it is not just a North American problem. A similar trend is also occurring in many European countries and in Australia. In adult populations, obesity rates are rising faster in developing countries with growing incomes than in rich countries, and international evidence suggests that obesity begins to affect the health of poorer citizens disproportionately once a country's gross national product rises higher than about $1,700 per capita. Overweight children and adolescents, in addition to being liable to remain overweight as adults, are more vulnerable than lean children and adolescents to the development of diabetes, unhealthy levels of blood lipids and other cardiovascular risk factors, asthma, orthopedic complications, fatty liver, gallstones, and various other disorders. Many also have depression and damage to their self-esteem, especially if they are teased or ostracized by their peers.
The epidemic of childhood obesity is clearly driven by aspects of the modern environment, but it is not known which factors are most responsible. As compared with children of 30 years ago, today's children eat more food prepared outside the home, snack more often, drink more sugared drinks, are served larger portions, and are the target of more intensive food marketing. Against this background, public health interventions aimed at shifting children toward more healthful diets have had no measurable effect on obesity rates, but some studies have found that combining simple, clear messages with increased access to healthful foods (such as fresh fruit) can positively change eating behavior.
Modern children are also more physically inactive than children of previous generations. School-based interventions to increase physical activity have benefited children's cardiovascular fitness and even their classroom performance, but with few exceptions, they have not reduced the prevalence of obesity. Yet patterns of physical activity appear to be easier to change than diet, and regular exercise (besides burning calories) may increase a person's ability to sense satiety, so additional interventions to boost children's levels of physical activity are currently being evaluated. So far, according to John J. Reilly of the University of Glasgow in his chapter in this book, the most promising strategy for lowering obesity rates is to focus on reducing inactivity — specifically, to get children to watch less television. At least two randomized, controlled trials have found that reducing television viewing time led to a lower prevalence of obesity, and larger studies with longer follow-up periods are currently under way.
The key to obesity prevention may lie in factors that operate during infancy or even before birth. Fetal growth restriction and rapid "catch-up" growth after birth are risk factors for the later development of obesity and insulin resistance; infants with very high birth weights and those whose mothers had gestational diabetes are also more likely to become obese, whereas breast-fed infants appear to be modestly protected. There is mounting evidence that appetite regulation, food preferences, and patterns of physical activity are influenced both by genetics and by environmental factors operating during pregnancy and infancy. Although early-life interventions clearly deserve to be studied, the authors emphasize that in the meantime, simple and effective strategies for reducing obesity rates in today's children are urgently needed. Since such interventions do not exist at present, pediatrician Robert C. Whitaker of Mathematica Policy Research in Princeton, N.J., has suggested that physicians can at least seek to modify behavior in ways that do no harm, are likely to have additional health benefits, and have shown evidence of linkage with obesity ("Obesity prevention in primary care: four behaviours to target," Archives of Pediatric and Adolescent Medicine 2003;151:725-7). Targets that meet this test include reducing television viewing, encouraging outdoor play, promoting breast-feeding, and limiting children's consumption of sugar-sweetened drinks.
Susan Okie, M.D.((Society for the Study of)
(Figure)
"The Fat Boy," by Harold Copping.
An illustration (color lithograph) for Character Sketches from Dickens, compiled by B.W. Matz, 1924.
From The Bridgeman Art Library.
Although the United States, Canada, and Mexico have had some of the steepest rises in the prevalence of pediatric obesity, it is not just a North American problem. A similar trend is also occurring in many European countries and in Australia. In adult populations, obesity rates are rising faster in developing countries with growing incomes than in rich countries, and international evidence suggests that obesity begins to affect the health of poorer citizens disproportionately once a country's gross national product rises higher than about $1,700 per capita. Overweight children and adolescents, in addition to being liable to remain overweight as adults, are more vulnerable than lean children and adolescents to the development of diabetes, unhealthy levels of blood lipids and other cardiovascular risk factors, asthma, orthopedic complications, fatty liver, gallstones, and various other disorders. Many also have depression and damage to their self-esteem, especially if they are teased or ostracized by their peers.
The epidemic of childhood obesity is clearly driven by aspects of the modern environment, but it is not known which factors are most responsible. As compared with children of 30 years ago, today's children eat more food prepared outside the home, snack more often, drink more sugared drinks, are served larger portions, and are the target of more intensive food marketing. Against this background, public health interventions aimed at shifting children toward more healthful diets have had no measurable effect on obesity rates, but some studies have found that combining simple, clear messages with increased access to healthful foods (such as fresh fruit) can positively change eating behavior.
Modern children are also more physically inactive than children of previous generations. School-based interventions to increase physical activity have benefited children's cardiovascular fitness and even their classroom performance, but with few exceptions, they have not reduced the prevalence of obesity. Yet patterns of physical activity appear to be easier to change than diet, and regular exercise (besides burning calories) may increase a person's ability to sense satiety, so additional interventions to boost children's levels of physical activity are currently being evaluated. So far, according to John J. Reilly of the University of Glasgow in his chapter in this book, the most promising strategy for lowering obesity rates is to focus on reducing inactivity — specifically, to get children to watch less television. At least two randomized, controlled trials have found that reducing television viewing time led to a lower prevalence of obesity, and larger studies with longer follow-up periods are currently under way.
The key to obesity prevention may lie in factors that operate during infancy or even before birth. Fetal growth restriction and rapid "catch-up" growth after birth are risk factors for the later development of obesity and insulin resistance; infants with very high birth weights and those whose mothers had gestational diabetes are also more likely to become obese, whereas breast-fed infants appear to be modestly protected. There is mounting evidence that appetite regulation, food preferences, and patterns of physical activity are influenced both by genetics and by environmental factors operating during pregnancy and infancy. Although early-life interventions clearly deserve to be studied, the authors emphasize that in the meantime, simple and effective strategies for reducing obesity rates in today's children are urgently needed. Since such interventions do not exist at present, pediatrician Robert C. Whitaker of Mathematica Policy Research in Princeton, N.J., has suggested that physicians can at least seek to modify behavior in ways that do no harm, are likely to have additional health benefits, and have shown evidence of linkage with obesity ("Obesity prevention in primary care: four behaviours to target," Archives of Pediatric and Adolescent Medicine 2003;151:725-7). Targets that meet this test include reducing television viewing, encouraging outdoor play, promoting breast-feeding, and limiting children's consumption of sugar-sweetened drinks.
Susan Okie, M.D.((Society for the Study of)