Proposed guidelines to evaluate scientific validity and evidence for genotype-based dietary advice

Genes & Nutrition

Table 2 Framework for stepwise assessment of the evidence relating to gene × diet interactions

Scientific validity assessment criteria
Study quality rating (A, B, C, D): * Interventional or observational design * Prospective and retrospective approach * Randomised, placebo controlled and blinded * Study power (high subject number with ‘effect’ allele) * Effect magnitude * P values, false discover rate (FDR) and multiple testing * Replication study in different populations and meta-analysis Type of gene × diet Interaction: * Direct phenotype * Intermediate phenotype * Indirect phenotype Nature of the genetic variant * Causal * In LD with functional variant * Associated but unknown function Biological plausibility * Rated as high/medium/low/unknown Scientific validity score for gene × diet interaction * Convincing * Probable * Possible * Not demonstrated

*P values must be at least .05 to be significant. The P value must remain within .05 after correcting for multiple testing, e.g. Bonferroni
^aThe ‘effect magnitude’ required depends on the type of study. For example, the effect of folate on high homocysteine in carriers of the effect allele in MTHFR should be a return to normal within a few weeks of starting the intervention. The magnitude of reduction of blood pressure would be acceptable for as little as 1 mmHg, and any risk reduction, however small, for cardiovascular disease would be adequate

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