Saturated fat and human health: a protocol for a methodologically innovative systematic review and meta-analysis to inform public health nutrition guidelines

Abstract

Background The health effects of dietary fats are a controversial issue on which experts and authoritative organizations have often disagreed. Care providers, guideline developers, policy-makers, and researchers use systematic reviews to advise patients and members of the public on optimal dietary habits, and to formulate public health recommendations and policies. Existing reviews, however, have serious limitations that impede optimal dietary fat recommendations, such as a lack of focus on outcomes important to people, substantial risk of bias (RoB) issues, ignoring absolute estimates of effects together with comprehensive assessments of the certainty of the estimates for all outcomes. Objective We therefore propose a methodologically innovative systematic review using direct and indirect evidence on diet and food-based fats (i.e., reduction or replacement of saturated fat with monounsaturated or polyunsaturated fat, or carbohydrates or protein) and the risk of important health outcomes. Methods We will collaborate with an experienced research librarian to search MEDLINE, EMBASE, CINAHL, and the Cochrane Database of Systematic Reviews (CDSR) for randomized clinical trials (RCTs) addressing saturated fat and our health outcomes of interest. In duplicate, we will screen, extract results from primary studies, assess their RoB, conduct de novo meta-analyses and/or network meta-analysis, assess the impact of missing outcome data on meta-analyses, present absolute effect estimates, and assess the certainty of evidence for each outcome using the GRADE contextualized approach. Our work will inform recommendations on saturated fat based on international standards for reporting systematic reviews and guidelines. Conclusion Our systematic review and meta-analysis will provide the most comprehensive and rigorous summary of the evidence addressing the relationship between saturated fat modification for people-important health outcomes. The evidence from this review will be used to inform public health nutrition guidelines. Trial registration PROSPERO Registration: CRD42023387377.

Walking speed and the risk of type 2 diabetes: a systematic review and meta-analysis

“…The magnitude of the absolute risk reduction in the analysis of brisk/striding walking was also larger than the threshold set by the GRADE working group as the minimally important difference for non-fatal outcomes (2 fewer cases per 100 patients),46 suggesting that brisk/striding walking can result in an important reduction in the risk of type 2 diabetes. However, it is unclear whether walking speed is an indicator of health status or a causal factor.…”

“…The certainty of the evidence was rated moderate for brisk/striding walking due to a double downgrade for a very serious risk of bias and an upgrade for the dose–response gradient. Of note, the magnitude of the absolute effect for brisk/striding walking surpassed the threshold set as the minimally important difference (20 fewer cases per 1000 patients),46 suggesting that brisk/striding walking can exert an important reduction in the risk of type 2 diabetes.…”

“…A detailed description of the GRADE domains is provided in online supplemental eText 1. We considered a 2% absolute risk reduction (20 fewer per 1000 patients), proposed by the GRADE working group for non-fatal outcomes,46 as the threshold for minimally important difference. We adapted a recently published GRADE minimally contextualised approach to rate imprecision based on minimally important difference 47 48.…”