Prognosis in obesity
http://www.100md.com
《英国医生杂志》
We all need to move a little more, eat a little less
Obesity has a colossal impact on physical, mental, and social ill health in many parts of the world. Without effective action, expanding waists in ageing populations and the associated health problems will present enormous financial burdens for future generations. The prevalence of obesity is already above the critical threshold of 15% set by the World Health Organization for epidemics needing intervention.1 We cannot withdraw medical support for obese individuals, but we urgently need politically driven public health measures to curb this epidemic.
In this week's BMJ, Reilly et al, who have previously documented rising rates of childhood obesity, stimulating public and political concern, examine risk factors for obesity in a cohort of 7 year olds in Bristol, England (p 1357).2 The authors do not claim causality but did find potentially relevant independent associations, including environmental contributions to high birth weight, early adiposity or "rebound" as body mass index rises in early life catch-up growth between birth and 2 years, and high rates of weight gain in the first 12 months. They found no robust protective effect of breast feeding, a major focus for American policies against obesity.3 However, obesity was associated with certain behaviour among the children in the first three years of life, including watching television more than four hours a day and having only short periods of sleep, and with maternal smoking. This study did not look at all potential causal risks and examined diet only through a form of cluster analysis, producing weak evidence for exposure to "junk food" as a factor. Other dietary factors related to childhood obesity, such as the consumption of sugary drinks, have been documented elsewhere.4
"Diagnosing" obesity is difficult in young children, but in the United Kingdom standard growth charts are now used, based on data on body mass index from birth to 20 years for children in 1990.w1 Viner and Cole, in another paper this week, report an analysis of data on obesity among children in the British birth cohort of 1970 (p 1354).5 At the age of 10 (in 1980), only 4.3% of this cohort were defined as obese. At the age of 30, 16.3% had become obese—that is, with body mass index greater than 30 kg/m2. In adulthood, the women who were obese experienced adverse educational, social, psychological, and economic outcomes, but obese men did not. Indeed, some evidence showed that obese men were more successful socially. These findings were irrespective of any history of obesity in childhood. Only about half of the obese children went on to become obese adults, although this figure is probably higher nowadays. Obese children who were not obese as adults had no problems.
In a third paper this week, Whitmer et al (p 1360) find that obesity in middle age is associated with future risk of dementia.6 They found an increased incidence of dementia among overweight as well as obese people, with body mass index greater than 25 kg/m2 used to define being overweight. Again, problems associated with obesity were more marked in women. The most likely explanation is that vascular dementia is accelerated among heavier adults with the phenotype for the metabolic syndrome. The authors point out that waist circumference might have been a better predictor of vascular risk than body mass index.w2
Although the mass media have highlighted the issue of increasingly overweight children, most of the medical and social burdens and most of the costs of obesity arise in adulthood. Overweight children do have problems during childhood including low self esteem, which may perpetuate patterns of inactivity, overeating, and obesity into adulthood.7 Public health measures against obesity cannot ignore the increasing prevalence of obesity in childhood, but must focus on the much more sinister increase in body fat across the whole population. The 2004 white paper Choosing Healthw3 and the subsequent action plan Choosing a better dietw4 have set tough targets to reduce childhood obesity, but no specific targets to focus the broader effort against obesity related ill health in adults.
New economic analyses help dispel the myth of people getting fatter but eating less. The first 20 years of our adult obesity epidemic, from the 1970s to 1990s, was explained mainly by declining physical activity: Americans believe they have less time to do things but in reality are spending more time watching television and being inactive.8 Subsequently, the obesity epidemic appears to have been fuelled largely by increasing food consumption.9 A paradoxical increase and deregulation of appetite during inactivity10 11 has been matched by an increasing supply of food at lower real cost.12 Consumption of "supersize" food portions will accelerate this process, reflecting a failure of the free market that demands government intervention.w5
Both sides of the energy balance equation must be tackled, such that people can "move a little more, eat a little less," as the non-profit campaigning organisation America on the Move says.w6 The necessary changes are small: 90% of obesity in the United States could be abolished by walking an extra 2000 steps a day (equivalent to using up 0.418MJ) and reducing intake by 0.418MJ per day. These changes are well within the range of day to day variability in activity and diet and are potentially achievable and sustainable by large numbers.w6 People will need better education about activity and diet, but a sustainable reduction in obesity will also require the food and exercise industries to work with consumers towards small changes in the environment.
M E J Lean, professor
Division of Developmental Medicine, Human Nutrition, University of Glasgow, Glasgow G31 2ER
(lean@clinmed.gla.ac.uk)
Additional references are on bmj.com
Papers pp 1354, 1357, 1360
Competing interests: None declared.
References
World Health Organization, Food and Agriculture Organisation. Report of the joint WHO/FAO expert consultation on diet, nutrition and the prevention of chronic diseases. Geneva: WHO Tech Report 916, 2003.
Reilly JJ, Armstrong J, Dorosty AR, Emmett PM, Ness A, Rogers I, et al. Early life risk factors for obesity in childhood: cohort study. BMJ 2005;330: 1354-7.
US Department of Health and Human Services. The surgeon general's call to action to prevent and decrease overweight and obesity. Rockville, MD: US Department of Health and Human Services, Public Health Service, Office of the Surgeon General, Washington 2001. www.surgeongeneral.gov/topics/obesity/ (accessed 1 Jun 2005)
Ludwig DS, Peterson KE, Gortmaker SL. Relation between consumption of sweetened drinks and childhood obesity: a prospective observational analysis. Lancet 2001;357: 505-508.
Viner RM, Cole TJ. Adult socioeconomic, educational, social, and psychological outcomes of childhood obesity: a national birth cohort study. BMJ 2005;330: 1354-7.
Whitmer RA, Gunderson EP, Barrett-Connor E, Quesenberry CP, Yaffe K. Obesity in middle age and future risk of dementia: a 27 year longitudinal population based study. BMJ 2005;330: 1360-2.
Sweeting H, Wright C, Minnis H. Psychosocial correlates of adolescent obesity, "slimming down" and "becoming obese." J Adoles Health 2005 (in press).
Sturm R. The economics of physical activity: societal trends and rationales for interventions. Am J Prevent Med 2004;27(3S): 126-35.
Putnam J, Allshouse J, Kantor LS. US per capita food supply trends: more calories, refined carbohydrates and fats. Food Rev 2002;25: 2-15.
Mayer J, Thomas DW. Regulation of food intake and obesity. Science 1967;156: 328-37.
Tsofliou F, Pitsiladis YP, Malkova D, Wallace AM, Lean MEJ. Moderate physical activity permits acute coupling between serum leptin and appetite-satiety measures in obese women. Int J Obes Relat Metab Disord 2003;27: 1332-9.
Drewnowski A. Obesity and the food environment: dietary energy density and diet costs. Am J Prevent Med 2004;27(3S): 154-62.
Obesity has a colossal impact on physical, mental, and social ill health in many parts of the world. Without effective action, expanding waists in ageing populations and the associated health problems will present enormous financial burdens for future generations. The prevalence of obesity is already above the critical threshold of 15% set by the World Health Organization for epidemics needing intervention.1 We cannot withdraw medical support for obese individuals, but we urgently need politically driven public health measures to curb this epidemic.
In this week's BMJ, Reilly et al, who have previously documented rising rates of childhood obesity, stimulating public and political concern, examine risk factors for obesity in a cohort of 7 year olds in Bristol, England (p 1357).2 The authors do not claim causality but did find potentially relevant independent associations, including environmental contributions to high birth weight, early adiposity or "rebound" as body mass index rises in early life catch-up growth between birth and 2 years, and high rates of weight gain in the first 12 months. They found no robust protective effect of breast feeding, a major focus for American policies against obesity.3 However, obesity was associated with certain behaviour among the children in the first three years of life, including watching television more than four hours a day and having only short periods of sleep, and with maternal smoking. This study did not look at all potential causal risks and examined diet only through a form of cluster analysis, producing weak evidence for exposure to "junk food" as a factor. Other dietary factors related to childhood obesity, such as the consumption of sugary drinks, have been documented elsewhere.4
"Diagnosing" obesity is difficult in young children, but in the United Kingdom standard growth charts are now used, based on data on body mass index from birth to 20 years for children in 1990.w1 Viner and Cole, in another paper this week, report an analysis of data on obesity among children in the British birth cohort of 1970 (p 1354).5 At the age of 10 (in 1980), only 4.3% of this cohort were defined as obese. At the age of 30, 16.3% had become obese—that is, with body mass index greater than 30 kg/m2. In adulthood, the women who were obese experienced adverse educational, social, psychological, and economic outcomes, but obese men did not. Indeed, some evidence showed that obese men were more successful socially. These findings were irrespective of any history of obesity in childhood. Only about half of the obese children went on to become obese adults, although this figure is probably higher nowadays. Obese children who were not obese as adults had no problems.
In a third paper this week, Whitmer et al (p 1360) find that obesity in middle age is associated with future risk of dementia.6 They found an increased incidence of dementia among overweight as well as obese people, with body mass index greater than 25 kg/m2 used to define being overweight. Again, problems associated with obesity were more marked in women. The most likely explanation is that vascular dementia is accelerated among heavier adults with the phenotype for the metabolic syndrome. The authors point out that waist circumference might have been a better predictor of vascular risk than body mass index.w2
Although the mass media have highlighted the issue of increasingly overweight children, most of the medical and social burdens and most of the costs of obesity arise in adulthood. Overweight children do have problems during childhood including low self esteem, which may perpetuate patterns of inactivity, overeating, and obesity into adulthood.7 Public health measures against obesity cannot ignore the increasing prevalence of obesity in childhood, but must focus on the much more sinister increase in body fat across the whole population. The 2004 white paper Choosing Healthw3 and the subsequent action plan Choosing a better dietw4 have set tough targets to reduce childhood obesity, but no specific targets to focus the broader effort against obesity related ill health in adults.
New economic analyses help dispel the myth of people getting fatter but eating less. The first 20 years of our adult obesity epidemic, from the 1970s to 1990s, was explained mainly by declining physical activity: Americans believe they have less time to do things but in reality are spending more time watching television and being inactive.8 Subsequently, the obesity epidemic appears to have been fuelled largely by increasing food consumption.9 A paradoxical increase and deregulation of appetite during inactivity10 11 has been matched by an increasing supply of food at lower real cost.12 Consumption of "supersize" food portions will accelerate this process, reflecting a failure of the free market that demands government intervention.w5
Both sides of the energy balance equation must be tackled, such that people can "move a little more, eat a little less," as the non-profit campaigning organisation America on the Move says.w6 The necessary changes are small: 90% of obesity in the United States could be abolished by walking an extra 2000 steps a day (equivalent to using up 0.418MJ) and reducing intake by 0.418MJ per day. These changes are well within the range of day to day variability in activity and diet and are potentially achievable and sustainable by large numbers.w6 People will need better education about activity and diet, but a sustainable reduction in obesity will also require the food and exercise industries to work with consumers towards small changes in the environment.
M E J Lean, professor
Division of Developmental Medicine, Human Nutrition, University of Glasgow, Glasgow G31 2ER
(lean@clinmed.gla.ac.uk)
Additional references are on bmj.com
Papers pp 1354, 1357, 1360
Competing interests: None declared.
References
World Health Organization, Food and Agriculture Organisation. Report of the joint WHO/FAO expert consultation on diet, nutrition and the prevention of chronic diseases. Geneva: WHO Tech Report 916, 2003.
Reilly JJ, Armstrong J, Dorosty AR, Emmett PM, Ness A, Rogers I, et al. Early life risk factors for obesity in childhood: cohort study. BMJ 2005;330: 1354-7.
US Department of Health and Human Services. The surgeon general's call to action to prevent and decrease overweight and obesity. Rockville, MD: US Department of Health and Human Services, Public Health Service, Office of the Surgeon General, Washington 2001. www.surgeongeneral.gov/topics/obesity/ (accessed 1 Jun 2005)
Ludwig DS, Peterson KE, Gortmaker SL. Relation between consumption of sweetened drinks and childhood obesity: a prospective observational analysis. Lancet 2001;357: 505-508.
Viner RM, Cole TJ. Adult socioeconomic, educational, social, and psychological outcomes of childhood obesity: a national birth cohort study. BMJ 2005;330: 1354-7.
Whitmer RA, Gunderson EP, Barrett-Connor E, Quesenberry CP, Yaffe K. Obesity in middle age and future risk of dementia: a 27 year longitudinal population based study. BMJ 2005;330: 1360-2.
Sweeting H, Wright C, Minnis H. Psychosocial correlates of adolescent obesity, "slimming down" and "becoming obese." J Adoles Health 2005 (in press).
Sturm R. The economics of physical activity: societal trends and rationales for interventions. Am J Prevent Med 2004;27(3S): 126-35.
Putnam J, Allshouse J, Kantor LS. US per capita food supply trends: more calories, refined carbohydrates and fats. Food Rev 2002;25: 2-15.
Mayer J, Thomas DW. Regulation of food intake and obesity. Science 1967;156: 328-37.
Tsofliou F, Pitsiladis YP, Malkova D, Wallace AM, Lean MEJ. Moderate physical activity permits acute coupling between serum leptin and appetite-satiety measures in obese women. Int J Obes Relat Metab Disord 2003;27: 1332-9.
Drewnowski A. Obesity and the food environment: dietary energy density and diet costs. Am J Prevent Med 2004;27(3S): 154-62.