Evaluation of dietary management and monitoring practices in pharmaceutical clinical trials for inborn errors of metabolism.

BACKGROUND

Inborn errors of metabolism (IEMs) are rare genetic conditions that often require strict dietary management to prevent serious health complications. With the rise of pharmaceutical therapies for IEMs, clinical trials now use diet-sensitive biomarkers to assess drug efficacy. However, uncontrolled dietary variation can confound biomarker outcomes. This review evaluates how diet is managed and monitored in pharmaceutical clinical trials for IEMs and compares those practices against FDA guidance and validated nutrition assessment standards.

METHODS

An analytic narrative review was conducted from November 2023 to March 2024 using Cochrane Library searches. Seventeen clinical trials met inclusion criteria, involving phenylketonuria (PKU), fatty-acid oxidation disorders, and methylmalonic/propionic acidemia. Each trial was evaluated against 14 dietary study design elements based on the 2023 FDA guidance document and principles of precision, reproducibility, and validity from nutrition science literature.

RESULTS

Dietary methodologies varied widely across trials. Fatty-acid oxidation disorder and methylmalonic/propionic acidemia studies used more structured dietary controls and multiple biomarkers/clinical assessments. In contrast, PKU trials relied heavily on blood phenylalanine levels, with limited assessment of dietary variability or adherence. Only a few of the included studies used validated dietary assessment methods, defined the range of acceptable dietary intake, or statistically assessed adherence to the dietary plan. Most failed to use objective tools to confirm compliance and instead relied on self-reported diet records. Newer trials showed improved adherence to FDA recommendations, but no study met all 14 elements.

CONCLUSIONS

Dietary assessments remain inconsistently addressed in IEM clinical trials, particularly in PKU. Failure to account for dietary variability reduces confidence in biomarker interpretation. Adopting validated dietary assessment methods and statistical modeling of intake variation can improve reproducibility and reduce confounding. Future trials should quantify acceptable dietary fluctuations and incorporate validated tools to ensure dietary rigor in biomarker-based drug efficacy studies.