Table 1.

Recommendations for authors, reviewers, and editors of nutritional investigations.

Domain	Commonplace practice	Limitation	Recommendation
Design	Unrefined, grain-based “chows” are commonly utilized as “control” comparators for purified diets	“Chows” and “purified” diets differ substantially in their composition and present an immeasurably confounded design	The use of chows as comparators for purified diets should be limited to pilot investigations and eliminated as the sole source of data for final publication comparisons
	Various “control” and “experimental” purified diet formulations are purchased and utilized across separate experiments that are ultimately juxtaposed in a manuscript	Diet formulations, including those differing in a dietary component of interest, can differ broadly in their overall composition and introduce unquantifiable confounding	Work with commercial diet vendors and trained animal nutritionists before undertaking diet investigations to ensure the proposed study diets are feasible and the appropriate control diets are procured
	An experimental and a control diet are intended to be fed with the aim of targeting a specific metabolic pathway and making causal inferences about an individual ingredient/nutrient in order to inform therapeutic approaches	Diets differ in at least 2 variables, limiting attribution to a single component. Effects may be due to any one variable modified, or the substitution, and such effects may be modified by interacting variables in the background diet. Food components exhibit significant pleiotropy, targeting multiple downstream mechanisms, and rarely exhibit linear dose-response relationships	Employ multi-level ingredient/nutrient substitution matrix designs where possible that consider substitution effects, assess dose-response relationships, as well as effect modification by background diet composition
			Harmonize diet design with other elements of the experimental design (e.g. genetic, pharmacological manipulations) that can isolate the contributions of potential relevant mechanisms at play. Employ unbiased, high-throughput approaches (e.g. metabolomics) to characterize the metabolic context in which relevant diet-induced mechanisms occur
	Experimental diet manipulations are undertaken with limited feasibility or pilot testing and unclear rigor	Experimental diet manipulations frequently have unintended consequences that compromise the ability to test the intended hypothesis. Confounded attempts may go unpublished and resources wasted, or published and the confounding impacts of the unintended consequences go unrecognized, minimized, or unreported	Undertake pilot studies to confirm expected phenotypes (e.g. weight gain or maintenance), to assess for unintended consequences of dietary manipulations (e.g. food aversion and weight loss, apparent pathology) and to facilitate a priori power analyses
Analysis and reporting		Deviations from protocols or in-tandem decisions can introduce biases and compromise rigor; practices may include selective reporting of assessed outcomes, unjustified and/or nontransparent removal of outliers and other protocol modifications, and reporting of spurious findings as significant	Open pre-registration of studies should become commonplace, including the intended diet formulations, age at diet manipulation, sex of animal, power calculations, all outcomes to be assessed and their method of assessment, and statistical analysis plan
	Diet composition is assumed based on the label compositional analysis	Diet manufacturing and processing, shipment and/or storage conditions can influence diet composition in unintended manners, resulting in alterations to the concentration of compounds of interest being fed. Diet contains numerous unquantified factors that may be relevant effect modifiers for the outcomes studied	Pursue an independent laboratory analysis of commercially purchased diet to ensure expected concentrations of relevant food derived components, especially when conducting long-term studies with >1 lot number. It is advisable that researchers store a frozen aliquot of investigational diets for future analysis and comparison
	Diet information used throughout the study is not specified (e.g. “chow”) and/or listed throughout the text. Referenced diets may or may not be open source. Bedding type and consumable enrichment is rarely reported	Without brand and catalog number information, diet composition is challenging to assess. Custom purified diets do not have full diet composition data available through vendor websites, requiring contact with vendors to retrieve such information. Bedding and enrichment can modify metabolism-related phenotypes and cannot be accounted for without reporting	Transparently list the name, formulation, and known composition of all feeds used in the investigation in a main or supplementary table. Bedding type and identifier information should be reported as well as consumable enrichment use
	Total number of rodents is reported per diet group	Rodents are group-housed and diet is delivered at the level of the cage, introducing non-independence of the individual animals. Failing to utilize a cluster analysis of such data results in artificially lower estimates of variance and lower P values	Clearly report the unit of randomization within a study (cage or individual rodent) and related relevant parameters (e.g. animals per cluster). Choose the appropriate statistical approach and explicitly justify this in manuscripts
	Investigations modifying diet composition do not report longitudinal changes in food intake and body weight. Conclusions about a diet’s effects on food intake are made regardless of the statistical power to detect an effect. Diet composition and/or feeding protocols may change the pattern of intake (i.e. duration of fasting between feeding intervals, relation of intake to the circadian cycle)	The impact of diet composition changes on outcomes may be mediated through alterations in energy balance and body composition rather than through independent effects of the diet component. Many studies are underpowered to detect food intake changes that may underlie phenotypes. Few studies assess whether changes in diet composition or feeding protocol imparts their effects through altering the pattern of intake	Report the impact of diet composition modification on longitudinal measures of food intake, body weight, and body composition regardless of whether such variables are the primary outcome of the investigation. Limit conclusions about the impact of diet on components of energy balance when not explicitly powered to do so. Design experiments to manipulate food access to control for alterations in fasting duration and circadian alignment
	A single diet component is highlighted throughout the manuscript	Diets lack a placebo, introducing an inherent relative effect of investigational diets in relation to their selected control. Investigations rarely employ multiple comparators across a dose-response relationship to confidently attribute causal effects to one diet component	Titles, abstracts, and in-text descriptions should transparently report effects of the investigational diet relative to comparator diets, highlight relevant substitution effects, and make evident the degree of confidence in the dose-response relationships. Named diets and their compositions should be clearly detailed in the main manuscript leaving readers with a clear appreciation for variables differing between diets