<p>This paper investigates time series persistence in obesity and severe obesity rates in a group of 38 OECD countries by using techniques based on fractional integration. The idea is to determine if there are trends in the time series and if the impact of health policy exposure might have permanent or transitory effects. The results based on aggregated and disaggregated data by sex indicate high levels of persistence in all cases, with orders of integration of magnitude higher than three. Trends in these rates are also of high magnitudes, particularly in Australia, New Zealand and United Kingdom. An implication of the findings is that long-term measures are required to tame obesity rates and severe obesity rates in OECD countries. The paper finally highlights the long-term measures needed to reduce the alarmingly high obesity rates in the developed countries.</p>