In observational studies of dietary exposures, the energy adjustment strategy has a critical impact on the effect being estimated. Adjusting for total energy intake or expressing the exposure as a percentage of total energy, leads to a substitution effect being estimated. This impacts the interpretation of primary studies and meta-analyses. Unless energy adjustment strategies are considered, meta-analyses may end up pooling estimates for incomparable effects. This meta-scientific review aimed to investigate the extent to which meta-analyses of dietary exposures may be pooling incomparable effects by reviewing the energy adjustment strategies. We identified all meta-analyses examining the relationship between saturated fat and fish and cardiovascular disease. The two most recent and two most cited reviews for each exposure were examined, along with all primary studies. Information on the study aims, targeted effects, and interpretations were summarized. The eight meta-analyses summarised results from 82 primary studies including 144 unique models. Only one meta-analysis explicitly considered the energy adjustment strategy of the primary studies to determine eligibility for a substitution subgroup analysis. None of the meta-analyses acknowledged that they were pooling estimates for different effects. 82% of the models from the primary studies were implicitly estimating substitution effects but this was not explicitly stated in most study aims, interpretation or conclusions. Our meta-scientific review found little evidence that the energy adjustment strategies of the primary studies were being considered in the synthesis or interpretation of evidence. Consequently, the pooled estimates reflect ill-defined quantities with unclear interpretations. We offer recommendations to improve the conduct of future meta-analyses and the quality of evidence that informs nutritional recommendations.

翻译：在膳食暴露的观察性研究中，能量调整策略对所估计的效应具有关键影响。通过调整总能量摄入或将暴露量表达为总能量的百分比，所估计的是一种替代效应。这影响了对原始研究和荟萃分析结果的解读。若不考虑能量调整策略，荟萃分析可能最终汇集了不可比效应的估计值。本元科学综述旨在通过审视能量调整策略，探讨膳食暴露荟萃分析在多大程度上可能汇集了不可比效应。我们识别了所有检验饱和脂肪及鱼类摄入与心血管疾病关系的荟萃分析。针对每种暴露，我们审查了最近的两篇综述和被引次数最高的两篇综述，以及所有原始研究。我们汇总了关于研究目的、目标效应和解读的信息。这八项荟萃分析共汇总了82项原始研究中的144个独立模型。仅有一项荟萃分析明确考虑了原始研究的能量调整策略，以确定其是否适合纳入替代效应亚组分析。没有一项荟萃分析承认它们汇集了不同效应的估计值。原始研究中82%的模型隐含地估计了替代效应，但这在大多数研究的目的、解读或结论中并未明确说明。我们的元科学综述发现，在证据综合或解读过程中，原始研究的能量调整策略很少被考虑。因此，汇总的估计值反映的是定义不清、解读不明的量。我们提出建议，以改进未来荟萃分析的实施，并提升为营养建议提供依据的证据质量。