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Monday, December 5, 2011

The epidemic of obesity ~ as fat as it gets

The epidemic of obesity ~ as fat as it gets

John Minnoch (1941-1983) lived in Seattle and is credited in the Guinness Book of Records as being the heaviest male in history. At 6 feet 1 inch tall, he weighed 442kg, equivalent to a BMI of 128. That equates to the biomass of just 4.5 Irish adult males! Now when we talk about the epidemic of obesity, there is a possibility that some people might think that a significant fraction of the population would reach the weight of John Minnoch. That is not how it works. Several years ago Steve O’Rahilly, Professor of Medicine at Addenbrooke’s Hospital Cambridge and a world authority on the genetics of obesity, raised the possibility that the epidemic of obesity was beginning to level off in the UK. Thus, faced with an obesogenic environment, the population variation in genetic predisposition to obesity is such that those who can cope with this environment will remain within the normal weight range while those susceptible to an obesogenic environment will attain a level of over weight or obesity up to their genetic potential. Two recent papers now put flesh on O’Rahilly’s speculation.

The first of these papers gathered data on time trends in obesity over the period 1999 to 2010.  The authors of the paper[1], from the Institute of Preventative Medicine at Copenhagen, set out a total of 7 criteria, which had to be met if a published study was to be included in their analysis. For example, the sample size had to be greater than 5,000 and data on weight and height had to be measured directly and not self reported. Thus out of 52 studies, only 44 met the 7 inclusion criteria. They also graded the studies into very high, high, medium or low quality. Of the 6 studies graded very high quality data, 5 showed that obesity rates were stable during the period 1999 to 2010. These 5 were from France, Sweden, England, Greece and Australia and only in China did a very high quality study show an in crease in obesity. Among children and adolescents, there was a clear trend toward a stabilization of obesity across continents and while the pattern among adults was less clear-cut, nonetheless, stabilization was generally evident.

The second study comes from Australia, actually from a rather distinguished WHO Collaborating Centre for Obesity Prevention, and it looked at obesity trends in preschool children over the period 1999 to 2007[2]. They studied two cohorts, one aged 2 years old in 1999 (130,000) and the other 3.5 years old in 1999 (96,000), each of which was followed annually to the year 2007. Weight, height (and length for younger age groups) were measured annually. Whereas in 1999, some 2.5 % of 2 year olds were obese, in 2007, this fell to 1.7%. For three year olds in 1999, the comparable figures were 4.5% and 2.9%. Similar trends were seen when obese children were combined with over weight children (from 13.5% to 12.4% in the 2 year old cohort and from 18.5% to 15.4% in the 3.5 year old group over the period 1999-2007). Although the overall rate of obesity and overweight was higher in the lower socioeconomic groups, the rate of decline in fatness was highest in these groups.

The first study would suggest that, as expected, the variation in the genetic potential to develop obesity would ultimately be met and that the prevalence rate would stabilize. It doesn’t mean the problem has gone away since obesity will continue to be a major drain on the economics of our health care systems. What it will do is to increase the focus on the management of the physiological disadvantages of obesity and overweight and in that regard, a greater emphasis on the promotion of physical must emerge, since nothing compares with physical activity as an antidote to the adverse effects of obesity. In the case of the Australian study of preschool children, the data suggests that there is a greater awareness of the problem of obesity among parents, particularly those who are socially disadvantaged. Preschool children do not make their own food choices so this reflects a mind change of mums and dads. Whether this all translates into fewer obese adolescents remains to be seen.

[1] Rokholm R et al Obesity Reviews (2010) 11, 835
[2] Nichols MS (2011) International Journal of Obesity 35, 916-024

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