We use the PICO(TS) format to do this:

Population: Which population are we searching for answers for?

Intervention: Which intervention or what type or classes of intervention are we looking for?

Comparator: Are we trying to see if the intervention is better than placebo only or another intervention?

Outcomes: Which specific part of health are we trying to find evidence of improvement by this intervention?

Timeline: What timeline are we looking for the results or intervention for?

Setting: What clinical setting are we focusing on, if any?

We start our searches looking for the highest quality evidence first, at the top of something known as the 'hierarchy of evidence' and working our way down. An initial search for weight loss might focus on systematic reviews in one database:

Weight Loss (MeSH term) AND ((((systematic review[ti] OR systematic literature review[ti] OR systematic scoping review[ti] OR systematic narrative review[ti] OR systematic qualitative review[ti] OR systematic evidence review[ti] OR systematic quantitative review[ti] OR systematic meta-review[ti] OR systematic critical review[ti] OR systematic mixed studies review[ti] OR systematic mapping review[ti] OR systematic cochrane review[ti] OR systematic search and review[ti] OR systematic integrative review[ti]) NOT comment[pt] NOT (protocol[ti] OR protocols[ti])) NOT MEDLINE [subset]) OR (Cochrane Database Syst Rev[ta] AND review[pt]) OR systematic review[pt])

We would then follow up this search with a systematic search of weight loss interventions not covered by the most recent systematic reviews, such as:

Weight Loss (MeSH term) AND ((randomized controlled trial[Publication Type] OR (randomized[Title/Abstract] AND controlled[Title/Abstract] AND trial[Title/Abstract]))) or Weight Loss (MeSH term) AND (((clinical[Title/Abstract] AND trial[Title/Abstract]) OR clinical trials as topic[MeSH Terms] OR clinical trial[Publication Type] OR random*[Title/Abstract] OR random allocation[MeSH Terms] OR therapeutic use[MeSH Subheading]))

Finally, we would search for existing published guidelines, patient resources, commercially available technologies & their associated publications.

Depending on the type of study we retrieve, we use checklists to critique it and decide what to do next. The types of checklists we use include:

Legend: SRMA - Systematic Review & Meta Analysis

• SRMA of interventions: PRIMSA 2009 + AMSTAR2 + Longevity School Checklist
• SRMA of diagnostic or prognostic test accuracy studies: PRISMA-DTA 2018 + Longevity School Checklist
• SRMA of harms: PRISMA-Harms + Longevity School Checklist
• SRMA of multi-component clinical prediction models: CHARMS 2018 + Longevity School Checklist
• Randomised controlled trials: RoB-2 2019 /CONSORT + Longevity School Checklist
• All other intervention studies (e.g. any non-randomised study): ROBINS-I + Longevity School Checklist
• Observational studies: (e.g. cohort, case-control, cross-sectional): STROBE 2007 + Longevity School Checklist
• Diagnostic test accuracy studies: QUADAS2 + JAMA EBM Diagnostic Test Guide + Longevity School Checklist
• Harm studies: JAMA EBM Harm Users Guide + Longevity School Checklist
• Screening Guidelines or Recommendations: JAMA EBM Screening Guide + Longevity School Checklist
• Multiple-component clinical prediction tools: TRIPOD 2018 + Longevity School Checklist

To do this we systematically assess

1. Barriers to starting a behaviour, using our custom "Behavioural Barriers Checklist" 
2. Barriers to maintaining a behaviour, using our "Automaticity Formation Equation".

Additionally, to more formally assess the quality of our content and what is included in the latest draft we use:

• AGREE-II
• Modified Delphi Method
• JAMA EBM Users Guides on "How to Use a Clinical Practice Guideline"

We draw on methods such as The Cochrane Living Systematic Reviews Guidance and the 2016 Garner Updating Systematic Reviews BMJ Study to update and iterate our evidence base.