Objectives The paper tests the thrifty phenotype hypothesis, according to which nonharmonious growth trajectories are costly for adult health. Methods The American surge in the prevalence of type 2 diabetes is concentrated in the South, a region characterized by a long history of poverty followed by rapid economic growth beginning in the 1960s. Civil rights legislation further accelerated income growth for African‐Americans in the region. The paper investigates the hypothesis by using per capita income at the state level as a proxy for net nutritional conditions. Results Regressions at the state level explain 56% of the variation in the prevalence rate of type 2 diabetes in 2009 using two explanatory variables: the ratio of per capita income in 1980 to that in 1950 and the share of the population that was African‐American. The paper discusses ways that rapid economic growth may have translated into weight gain and type 2 diabetes. Conclusions If the thrifty phenotype hypothesis is correct, future rates in the prevalence of type 2 diabetes are predictable based on income history. The forecast for rapidly developing countries such as India and China are ominous. Am. J. Hum. Biol. 25:508–515, 2013. © 2013 Wiley Periodicals, Inc.