Evidence Grade B
Well-designed single studies with strong methodology
What Grade B Means
Grade B represents good confidence in a research finding. These claims are supported by well-designed single studies or consistent observational data that hasn't yet been independently replicated to Grade A standards.
- At least one high-quality study supports this finding
- The methodology is sound and bias is minimized
- Results are plausible and align with related research
- Independent replication is pending or limited
Grade B findings are reliable enough to inform health decisions, but carry more uncertainty than Grade A.
Criteria for Grade B Classification
A finding receives Grade B status when it meets most of the following:
1. Single Well-Designed Study
The finding comes from a randomized controlled trial (any size), a large prospective cohort study, or a well-controlled intervention study.
2. Strong Methodology
The study demonstrates appropriate sample size, proper control groups, clear outcome definitions, and minimal obvious bias.
3. Plausible Mechanism
The finding fits within established physiological understanding, even if the specific claim is new.
4. Consistent with Related Evidence
While not directly replicated, the finding aligns with patterns seen in related research.
5. Peer-Reviewed Publication
The study has undergone peer review in a recognized journal.
The Gap Between Grade A and B
The primary difference between Grade A and B is replication.
| Aspect | Grade A | Grade B |
|---|---|---|
| Number of studies | 2+ confirmatory | 1 primary |
| Independent verification | Yes | Pending |
| Scientific consensus | Established | Emerging |
| Confidence level | High | Good |
A Grade B finding may be promoted to Grade A when additional studies confirm the results. Conversely, it may be downgraded if replication attempts fail.
Why Replication Matters
The reproducibility crisis in science reveals why we distinguish between single studies and replicated findings:
- • Begley & Ellis (2012): Only 21% of landmark cancer studies replicated
- • Open Science Collaboration (2015): Only 36% of psychology studies replicated
This doesn't mean Grade B evidence is unreliable — it means appropriate caution is warranted. Many Grade B findings will ultimately prove correct. Some won't.
Examples of Grade B Evidence on Metabolicum
TG/HDL Ratio in Japanese Populations
TG/HDL ratio correlates with LDL particle size in healthy Japanese adults.
Source: Maruyama et al., 2003 (J Atheroscler Thromb)
Why Grade B: Single study in a specific population. The finding aligns with Grade A evidence in Western populations but requires independent confirmation in Asian populations specifically.
TG/HDL Predicts Both Heart Disease and Diabetes
TG/HDL ratio predicts heart disease mortality and type 2 diabetes incidence independently.
Source: Vega et al., 2014 (J Investig Med) — Cooper Center Longitudinal Study, 29,526 men
Why Grade B: Large, well-designed study but male-only population. Requires replication including women and diverse ethnicities.
HOMA-IR Cutoffs Vary by Age and Gender
Optimal HOMA-IR cutoff values differ between age groups and between men and women.
Source: Gayoso-Diz et al., 2013 (BMC Endocr Disord)
Why Grade B: Single study examining demographic variation. Important finding that needs independent confirmation before adjusting universal thresholds.
WHtR Predicts Visceral Fat
WHtR strongly predicts visceral adipose tissue (the metabolically harmful type of fat).
Source: Swainson et al., 2017 (PLoS One)
Why Grade B: Single study using DXA validation. Consistent with the broader Grade A evidence on WHtR but specific visceral fat correlation needs replication.
How We Use Grade B Evidence
On Metabolicum, Grade B evidence informs:
Supporting context
Additional information that enriches understanding
Population-specific guidance
When Grade A data exists for general populations but Grade B addresses specific groups
Emerging thresholds
Alternative cutoffs under investigation
Mechanistic explanations
How and why markers relate to health
We clearly label Grade B evidence and avoid presenting it with the same certainty as Grade A findings.
When Grade B Evidence is Particularly Valuable
Addressing Understudied Populations
Grade A evidence often comes from Western, predominantly white populations. Grade B studies in Asian, African, or Hispanic populations may be the best available data.
Examining Subgroups
Studies on women, elderly, or athletic populations may only exist at Grade B level even when Grade A exists for general populations.
Investigating New Markers
Emerging biomarkers may only have Grade B evidence until research catches up.
Providing Practical Guidance
When Grade A evidence establishes a principle but Grade B provides specific implementation details.
The Path from B to A
Grade B findings can be upgraded to Grade A when:
- Independent research teams replicate the finding
- Results remain consistent across different populations
- The scientific community reaches consensus
- No significant contradictory evidence emerges
We regularly review our evidence grades and update when new research warrants reclassification.
Grade B Citations on Metabolicum (8)
Maruyama C, Imamura K, Teramoto T (2003)
Assessment of LDL particle size by triglyceride/HDL-cholesterol ratio in non-diabetic, healthy subjects without prominent hyperlipidemia
Journal of Atherosclerosis and Thrombosis
Key finding: TG/HDL ratio correlated with LDL particle size in healthy adults
Vega GL, Barlow CE, Grundy SM, Leonard D, DeFina LF (2014)
Triglyceride-to-high-density-lipoprotein-cholesterol ratio is an index of heart disease mortality and of incidence of type 2 diabetes mellitus in men
Journal of Investigative Medicine
Key finding: TG/HDL predicted both heart disease mortality and diabetes incidence
Salazar MR, Carbajal HA, Espeche WG, Aizpurúa M, Leiva Sisnieguez CE, et al. (2013)
Comparison of the abilities of the plasma triglyceride/high-density lipoprotein cholesterol ratio and the metabolic syndrome to identify insulin resistance
Diabetes & Vascular Disease Research
Key finding: TG/HDL ratio was better than metabolic syndrome criteria for identifying insulin resistance
Stern SE, Williams K, Ferrannini E, DeFronzo RA, Bogardus C, Stern MP (2005)
Identification of individuals with insulin resistance using routine clinical measurements
Diabetes
Key finding: HOMA-IR ≥2.6 identified insulin resistance with 84% sensitivity
Gayoso-Diz P, Otero-González A, Rodriguez-Alvarez MX, Gude F, García F, et al. (2013)
Insulin resistance (HOMA-IR) cut-off values and the metabolic syndrome in a general adult population: effect of gender and age
BMC Endocrine Disorders
Key finding: Optimal HOMA-IR cutoffs vary by age and gender
Walton CM, Perry K, Hart RH, Berry SL, Bikman BT (2019)
Improvement in glycemic and lipid profiles in type 2 diabetics with a 90-day ketogenic diet
Journal of Diabetes Research
Key finding: TG/HDL improved from 4.7 to 1.9, HbA1c improved from 8.9% to 5.6%
St-Onge MP, Janssen I, Heymsfield SB (2004)
Metabolic syndrome in normal-weight Americans: new definition of the metabolically obese, normal-weight individual
Diabetes Care
Key finding: ~25% of normal-weight individuals have metabolic syndrome criteria
Swainson MG, Batterham AM, Tsakirides C, Rutherford ZH, Hind K (2017)
Prediction of whole-body fat percentage and visceral adipose tissue mass from five anthropometric variables
PLoS One
Key finding: WHtR strongly predicts visceral fat (the metabolically harmful type)
See also
Evidence grades are informational and do not replace medical advice.