Why is the US result 1.10 but pooled 1.21, and what causes the gap?

Research question: Why does the US highest-versus-lowest quartile estimate (HR 1.10) differ from the pooled meta-analysis estimate (HR 1.21), and how much of that gap is explained by exposure definitions, comparison contrasts, or pooling choices across the primary studies?

The verified facts do not directly explain the gap between the 1.10 and 1.21 estimates, and they do not quantify how much of it comes from exposure definitions, comparison contrasts, or pooling choices. The 1.10 figure appears in the records as a hazard ratio per 10% increment in ultra-processed food consumption for all-cause mortality ⁶, not as a US highest-versus-lowest quartile estimate, and the only highest-versus-lowest hazard ratio reported for a related outcome is 1.15 for incident hypertension ³. The pooled estimate also varies across sources, with one meta-analysis reporting 1.29 for highest versus lowest all-cause mortality ² and another reporting 1.22 with substantial heterogeneity (I² = 78.5%) ⁵. On exposure definitions, the highest-quartile group ate about three times as much ultra-processed food per day as the lowest group, a wide contrast that bears on how the top-versus-bottom estimate was framed ¹, and the authors identify the lack of standardized UPF categorization as a key limitation ⁴. The newest fact is dated 2025 ⁵, so it is over a year old as of October 2026.

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