The epidemiology of obesity: the size of the problem.

The epidemic of obesity took off from about 1980 and in almost all countries has been rising inexorably ever since. Only in 1997 did WHO accept that this was a major public health problem and, even then, there was no accepted method for monitoring the problem in children. It was soon evident, however, that the optimum population body mass index is about 21 and this is particularly true in Asia and Latin America where the populations are very prone to developing abdominal obesity, type 2 diabetes and hypertension. These features are now being increasingly linked to epigenetic programming of gene expression and body composition in utero and early childhood, both in terms of fat/lean tissue ratios and also in terms of organ size and metabolic pathway regulation. New Indian evidence suggests that insulin resistance at birth seems linked to low birth weight and a higher proportion of body fat with selective B12 deficiency and abnormalities of one carbon pool metabolism potentially responsible and affecting 75% of Indians and many populations in the developing world. Biologically there are also adaptive biological mechanisms which limit weight loss after weight gain and thereby in part account for the continuing epidemic despite the widespread desire to slim. Logically, the burden of disease induced by inappropriate diets and widespread physical inactivity can be addressed by increasing physical activity (PA), but simply advocating more leisure time activity is unrealistic. Substantial changes in urban planning and diet are needed to counter the removal of any every day need for PA and the decades of misdirected food policies which with free market forces have induced our current 'toxic environment'. Counteracting this requires unusual policy initiatives.