Does exclusion of extreme reporters of energy intake (the "Goldberg cutoffs") reliably reduce or eliminate bias in nutrition studies? Analysis with illustrative associations of energy intake with health outcomes

Abstract

Background: The Goldberg cutoffs are used to decrease bias in self-reported estimates of energy intake (EI$_{\textrm{SR}}$). Whether the cutoffs reduce and eliminate bias when used in regressions of health outcomes has not been assessed. Objective We examined whether applying the Goldberg cutoffs to data used in nutrition studies could reliably reduce or eliminate bias. Methods We used data from the Comprehensive Assessment of Long-Term Effects of Reducing Intake of Energy (CALERIE), the Interactive Diet and Activity Tracking in American Association of Retired Persons (IDATA) study, and the National Diet and Nutrition Survey (NDNS). Each data set included EI$_{\textrm{SR}}$, energy intake estimated from doubly labeled water (EI$_{\textrm{DLW}}$) as a reference method, and health outcomes including baseline anthropometric, biomarker, and behavioral measures and fitness test results. We conducted 3 linear regression analyses using EI$_{\textrm{SR}}$, a plausible EI$_{\textrm{SR}}$ based on the Goldberg cutoffs (EI$_{\textrm{G}}$), and EI$_{\textrm{DLW}}$ as an explanatory variable for each analysis. Regression coefficients were denoted $\hat{\beta_{\textrm{SR}}}$, $\hat{\beta_{\textrm{G}}}$, and $\hat{\beta_{\textrm{DLW}}}$ ⁠, respectively. Using the jackknife method, bias from $\hat{\beta_{\textrm{SR}}}$ compared with $\hat{\beta_{\textrm{DLW}}}$ and remaining bias from $\hat{\beta_{\textrm{G}}}$ compared with $\hat{\beta_{\textrm{DLW}}}$ were estimated. Analyses were repeated using Pearson correlation coefficients. Results The analyses from CALERIE, IDATA, and NDNS included 218, 349, and 317 individuals, respectively. Using EIG significantly decreased the bias only for a subset of those variables with significant bias: weight (56.1%; 95% CI: 28.5%, 83.7%) and waist circumference (WC) (59.8%; 95% CI: 33.2%, 86.5%) with CALERIE, weight (20.8%; 95% CI: −6.4%, 48.1%) and WC (17.3%; 95% CI: −20.8%, 55.4%) with IDATA, and WC (−9.5%; 95% CI: −72.2%, 53.1%) with NDNS. Furthermore, bias significantly remained even after excluding implausible data for various outcomes. Results obtained with Pearson correlation coefficient analyses were qualitatively consistent. Conclusions Some associations between EI$_{\textrm{G}}$ and outcomes remained biased compared with associations between EI$_{\textrm{DLW}}$ and outcomes. Use of the Goldberg cutoffs was not a reliable method for eliminating bias.