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OBJECTIVES: To evaluate the influence of bias from methodological characteristics on intervention effect estimates in nutrition randomized controlled trials (RCTs) using the Cochrane Risk Of Bias 2 (RoB2) tool. METHODS: , and prediction intervals were calculated. RESULTS: = 0.01; PI 0.97-1.72). We confirmed these findings in subgroup and meta-regression analyses. CONCLUSION: Most methodological characteristics in nutrition RCTs, as assessed by RoB2, did not overestimate or underestimate intervention effect estimates. However, the unexpected finding that biases arising from deviations from intended interventions may lead to an underestimation of effects, rather than an overestimation, requires further research. PLAIN LANGUAGE SUMMARY: RCTs are considered the most reliable method for determining whether an intervention is effective. However, weaknesses in study design or conduct can distort the results, a problem known as bias. The RoB2 tool helps researchers check in a structured way whether bias is present and how much it might affect the results. In this study, we looked at 82 RCTs on dietary interventions published up to 2020. We assessed 120 outcome-specific RoB assessments and identified whether they had a low, some concerns, or high RoB. We then compared the results of trials with a higher RoB to those with a low RoB to see whether bias influenced the reported treatment effects. The reviewed trials showed variable levels of RoB and had little overall impact on the trial results. The main exception was how well participants followed the assigned diet and whether the researchers used the best available analysis methods. Problems in this area may have made the intervention's true effect seem smaller than it really was. Our findings suggest that studies on nutrition interventions are mostly free from major bias and their results can be considered reliable. However, how well participants followed the assigned intervention and how good the analysis methods were seemed to play an important role. More research is needed to understand how study quality influences the results of nutrition trials.
Bantle et al. (Sat,) studied this question.