Throughout much of the history of man kind, the overt manifestations of body weight gain in children and adults have been considered as signs of personal health and family wealth and an indicator of the economic prosperity of societies. Until recently, in most developing societies being thin has been equated with poor health and thinness in babies is associated with increased risk of illness. Increase in body weight and girth have often been perceived as being attractive and weight gain after marriage and the presence of plump children in some communities reflects positively on the man's ability to be a good provider and on the woman as a good mother and cook. These additional perceptions are changing as developing societies embrace the more dominating western economic culture and social mores. As developing societies industrialize and urbanize, and as standards of living continue to rise, weight gain and obesity are now beginning to pose a growing threat to the health of the citizens. Obesity is now widely prevalent in several developing countries, particularly those in rapid transition, and is affecting both children and adults. It is now vying with other traditional public health concerns such as under nutrition and infectious diseases as a significant contributor to the ill health of people in developing countries. Obesity is a key determinant and an important risk factor for other non-communicable diseases (NCDs) such as non-insulin dependant diabetes mellitus (NIDDM), cardiovascular disease (CVD) including hypertension, and certain cancers. The increasing prevalence of obesity in a population is an early indicator of an emerging health burden due to the in- creasing mortality and morbidity from NCDs in developing societies(1).

How do we diagnose obesity and what information do we have on the trends in the prevalence of obesity in children and adults ? With only a recent agreement that a Body Mass Index (BMI) of>30.0 be used as a cut- off for obesity in adults(2), and the lack of good nationally representative data from countries in the developing world, it is difficult at the moment to compare prevalences or to track secular trends in obesity in adults in developing countries. The most comprehensive data world-wide on the prevalence of obesity using a cut-off BMI >30.0 is the WHO MONICA project(3). And although the population samples are not necessarily representative of the countries, China is the only country in the developing world with valid data suggesting that the prevalence. of obesity in adults is >5% for men and> 1 0% for women. In most developing countries, obesity among adults co-exists with undernutrition and remains relatively uncommon in Asia and Africa. It is however, more prevalent in urban than in rural areas and in the more economically advanced regions and the more affluent sub-groups within the population, the prevalence rates of obesity may be as high as that seen in industrialized countries in the West(2).

The current lack of consistency between studies over the classification of obesity in children limits our ability to look at either the comparative prevalence or the secular trends in childhood obesity both in developed and developing societies. Suffice to say that irrespective of the method of classification used almost all studies generally report an increasing prevalence of obesity in childhood and adolescence. In the USA, the prevalence of overweight (i.e., >85th percentile of weight- for-height) in this age group in the Bogalusa Heart study increased twofold between 1973 and 1994 with more dramatic increases on an annual basis in the last 10 years(4). Over a similar period (1974-1993) in Japan, the prevalence of obesity (as indicated by a > 120% of standard body weight) in children aged 6 to 14 years increased from 5% to 10%(5). Increases in the prevalence of child- hood obesity are also seen in developing countries. In Thailand, obesity in 6-12 year aids (defined by weight-for-height > 120% of the Bangkok reference) increased from 12.2% to 15.6% in two years between 1991 and 1993(6) while a similar prevalence (15.8%) was observed in a recent study of 6 to 18 year aids in Saudi Arabia(7). Figures on the global prevalence of childhood obesity have been compiled by the WHO using the NCHS median weight-for-height plus 2 standard deviations (or Z scores) as the cut- off point(8). Several countries in the developing world show a prevalence rate of over 2% which include Nicaragua, Brazil, Antigua, Zambia, Venezuela and Peru; others such as Barbados, Honduras, Lesotho, Bolivia, Trinidad and Tobago, Iran, and Mauritius have a >4% prevalence; while Jamaica and Chile top the list with a 10% or greater prevalence rate of obesity in the pre" school child (0-4.99 years). According to this global database, India has a pre-school child obesity prevalence of about 1 %. It is important to remind oneself that the use of this commonly used indicator of pre-school childhood malnutrition (Wt for Ht) may exaggerate the problem of obesity among the stunted children in these population groups(9).

One of the major issues in assessing the magnitude of the problem and for observing changes or trends in childhood obesity, be it globally, regionally or nationally, is the need to use a uniform criteria for the definition of the problem. Although, attempts to delineate objective measures for the. assessment of undernutrition in children and in adults have been available for some time, it is only recently that a general agreement has been reached on criteria for obesity in adults(2,10). In the case of children and adolescents however, there has been little agreement over either the criteria or the classification of overweight and obesity. The WHO recommends the use of appropriate weight- for-height in children based on the NCHS growth standard and considers >+2 Z scores as a cut-off for overweight in children(10). This anthropometric indicator is recommended for screening overweight children in population samples while changes in weight- for-height or weight-for-age as well as absolute weight loss over a period of time may b~ used for the clinical monitoring of over:- weight children. In the case of adolescents" the WHO Expert Committee( 10) recommends the use of both BMI-for-age and skinfolds-for-age. A cut-off of >85th percentile of BMI-for-age is considered to be indicative of the risk of overweight while a >85th percentile of BMI-for-age plus a >90th percentile triceps skinfold-for-age and a >90th percentile sub-scapular skinfold-for-age would be diagnostic of adolescent obesity. Despite these recent recommendations by a!1 expert committee of the WHO, it is important to recognize that there is a pressing need for a simple and universally applicable definition of obesity in children and adolescents.

Does obesity in childhood matter? Obesity in adults is a well recognized risk factor for several NCDs such as NIDDM, CVD, hypertension and some cancers (like endometrial, breast, ovarian in women and prostate in men) as well as for premature death. It is also associated with increased risk of dyslipidemias, gall-bladder disease and osteoarthritis. The most significant long-term consequence of obesity in childhood is that it predisposes to later obesity and thus in- creases the risk of NCDs and premature death in adulthood(11, 12). In addition, dyslipidemias, elevated' blood pressure/ hypertension and abnormal glucose metabolism/insulin resistance are frequently manifest in obese children(13,14). Other health consequences of obesity in children include sleep apnea and orthopedic complications while adolescents are likely to suffer considerable psychological effects as well as social stigma and discrimination which are largely the result of culture-bound values which view, grossly obese individuals as 'ugly' and 'unhealthy'.

Why is obesity becoming an increasing problem in children in developing countries? Stated in very simple terms, obesity is the result of an energy imbalance due to energy intake having exceeded energy expenditure over a period of time. In modern times powerful societal and environmental influences have tended to overwhelm and upset the physiological regulatory mechanisms that balance intake with expenditure to maintain stable body weights. Both dietary intakes and physical activity patterns have changed considerably in recent times and in particular the high fat/energy dense diets and the sedentary lifestyles of modern societies have thus predisposed to increasing obesity in population Life style changes resulting in physical inactivity and sedentary behavior seem to t more important in contributing to the problem of obesity in children. This is exemplified by more time in a day spent by children in physically passive behaviors such as T viewing, working or playing games on
computer, talking on the telephone, etc.(15). Children in the USA spend more time watching TV than attending school(16). These passive behaviors are often accompanied t other adverse practices such as snacking or consuming high fat or high sugar food Life styIe changes further reflect parent anxieties regarding children and their future which results in children being ferried and fetched from school in cars and being discouraged from active play in the streets for fear of accidents and encouraged to sit and study; all of which contributes further to reduced physical activity levels when dietary intakes are not constrained in a growing child.

How can we prevent or reverse the increasing problem of obesity in children Three effective approaches can be used deal with this problem and they include (i) family-based, (ii) school based, and (iii) primary care based interventions. Children often eat what their parents eat and parental eating behavior has a strong influence on children. Targeting families is hence important and should include not merely dietary approaches but also attempt to deal with sedentary behavior practices. In the management of an obese child, family-based intervention have not always been successful although more recent report indicates that use of t parent as the exclusive agent of change c be successful (17). Children spend a fair pr portion of time in schools and hence school based interventions are important. These include encouraging schools to devote more time for physical education, promoting safe walking or cycling to school where possible, encouraging a positive attitude to activity and imparting skills to continue to be active in leisure sports after leaving school, and promoting an active school 'concept' by opening up its sports and recreational facilities for use of the community, School based programmes where regular exercise was integrated into the school curricula have been shown to be effective in improving weight and health status of children in Australia(18) and Singapore(19). Primary care based interventions when targeted properIy can prevent the onset of obesity in children from a very young age, Providing mothers with appropriate advice about breast feeding, weaning and diet for toddlers in primary care settings can not only prevent obesity in children but can also help manage the problem among mothers(20), Program strategies that enable health professionals to have contacts from an early age at primary care levels have been shown to be effective both in the prevention and management of childhood obesity(21), This is clearly a useful strategy in countries like India where contact with health professionals occurs at an early age in order to cater to the requirements of immunization of the young infant.

Obesity, its attendant health consequences and the consequent health burden is expected to reach epidemic proportions in developing countries like India, particularly in some sections of the population, Over- weight and obesity in children and adolescents can no 'longer be considered as reflecting the economic development and the attainment of food adequacy in developing countries, Childhood obesity is the prelude to public health disaster that we will have to deal with in the new millenium. There is an urgent need to address the problem and the time to act is now, As the old dictum goes, 'prevention is better than cure'!
 

P .S. Shetty,
Professor of Human Nutrition,
Head, Public Health Nutrition Unit,
 Department of Epidemiology and
Population Health,
London School of Hygiene and
Tropical Medicine,
49-51 Bedford Square,
London WC1B 3DP, UK.