Developing countries should act now to head off their own "obesity epidemic", says a global policy group.The Organisation for Economic Co-operation and Development (OECD) says obesity levels are rising fast.In a report in the Lancet medical journal, it says low-income countries cannot cope with the health consequences of wide scale obesity.Rates in Brazil and South Africa already outstrip the OECD average.Increasing obesity in industrialised countries such as the UK and US has brought with it rises in heart disease, cancer and diabetes.However, increasing prosperity in some developing countries has led to a rise in "Western" lifestyles.Now the OECD warns that they are catching up fast in terms of obesity rates.Across all the countries represented in the OECD, 50% of adults are overweight or obese.Childhood obesityRates in the Russian Federation are only just below this, and while fewer than 20% of Indians are classed this way, and fewer than 30% of Chinese people, the body says things are worsening fast.