Some have quit in frustration. The leading nutrition scientist at the N.I.H., Kevin Hall, recently resigned, saying he was being censored. Jim Jones, the chief of the F.D.A.’s food division, quit last month, saying “indiscriminate” layoffs would make it “fruitless” for him to continue.

In some studies, synthetic food dyes used in the United States have been associated with hyperactivity and behavioral effects in children.