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In the early 1960s, when the federal government first physically measured a representative sample of American adults, about 13% had obesity. The number barely moved through the 1970s — then, between the 1976–80 and 1988–94 surveys, it jumped from 15% to 23%, the steepest single-cycle rise in the whole series. It kept climbing to a measured peak of 42.4% in 2017–18, and sits at 40.3% in the latest survey. Adult obesity has, by this measure, roughly tripled.
The child and adolescent curve is younger — the comparable ages-2–19 series starts in 1971–74 at about 5% — and it is still rising, reaching 21.1% in 2021–23 even as the adult curve flattened. Severe obesity, the most consequential band, rose even faster proportionally: from under 1% of adults in the 1960s to 9.7% today. The strength of the evidence comes from consistency — NHANES has measured, not asked, using the same method for six decades.
Source: CDC/NCHS NHANES. Adult series (age-adjusted, 20+) begins 1960–62; the comparable child series (ages 2–19) begins 1971–74. Both plotted to the latest survey, August 2021–August 2023.