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Last sum­mer a team of researchers from the Massa­chusetts Institute of Technology set out to better understand the effects of yogurt on obesity. They were following up on the results of a long-term study from the Harvard School of Public Health that had suggested yogurt, more than any other food, helped to prevent age-related weight gain. The M.I.T. team, led by cancer biologist Susan Erdman and evolutionary geneticist Eric Alm, wanted to replicate the work in mice. The researchers took a group of 40 males and 40 females and either fed the animals a high-fat,...