Black 1994

Methods	RCT, parallel, (low fat diet vs usual diet), 24 months Summary risk of bias: moderate or high
Participants	People with non‐melanoma skin cancer N: 66 intervention, 67 control (analysed, 57 intervention, 58 control) Level of risk for CVD: low Male: 54% intervention, 67% control Mean age in years (SD): 50.6 (9.7) intervention, 52.3 (13.2) control Age range: not reported Smokers: not reported Hypertension: not reported Medications taken by at least 50% of those in the control group: not reported Medications taken by 20%‐49% of those in the control group: not reported Medications taken by some, but less than 20% of the control group: not reported Location: USA Ethenicity: white 100% (excluded from study if of Asian, Black, Hispanic or American Indian ancestry)
Interventions	Type: dietary advice Comparison: reduced fat (lower omega‐6 + total PUFA) vs usual diet (CHO + protein) Intervention: aims total fat 20% E, protein 15% E, CHO 65% E; methods 8 × weekly classes plus monthly follow up sessions, with behavioural techniques being taught following individual approach (not clear if in a group or individual). At 4‐month intervals, clinic examination by dermatologist. Intervention delivered face‐to‐face by a dietitian Control: aims usual diet; methods no dietary change, clinic examination by dermatologist at 4‐month intervals Dose aim: reduce total fat to 20% E, including omega‐6 and total PUFA (no aim provided) Baseline n‐6: unclear, but baseline PUFA 8% E Compliance by biomarkers: unclear, no serum total cholesterol reported, no tissue fatty acids Compliance by dietary intake: all assessed "during study", months 4‐24, using 7‐day food records verified by a dietitian Energy intake: control 2196 kcal/d (SD 615), intervention 1995 kcal/d (SD 564) Total fat intake: control 37.8% E (SD 4.1), intervention 20.7% E (SD 5.5) (MD −17.10%, 95% CI −18.88 to −15.32) significant reduction Saturated fat intake: control 12.8% E (SD 2.0), intervention 6.6% E (SD 1.8), (MD −6.20%, 95% CI −6.90 to −5.50) significant reduction PUFA intake: control 7.8% E (SD 1.4), intervention 4.5% E (SD 1.3), (MD −3.30%, 95% CI −3.79 to −2.81) significant reduction PUFA n‐3 intake: not reported PUFA n‐6 intake: LA, control 16.9 g (SD 5.6), intervention 8.5 (SD 3.3) Trans fat intake: not reported MUFA intake: control 14.4% E (SD 1.7), intervention 7.6% E (SD 2.2), (MD −6.80%, 95% CI −7.52 to −6.08) significant reduction CHO intake: control 44.6% E (SD 6.9), intervention 60.3% E (SD 6.3), (MD 15.70%, 95% CI 13.29 to 18.11) significant increase Sugars intake: not reported Protein intake: control 15.7% E (SD 2.4), intervention 17.7% E (SD 2.2), (MD 2.00%, 95% CI 1.16 to 2.84) significant increase Alcohol intake: control 3.2% E (SD 3.9), intervention 3.2% E (SD 3.4) Duration of intervention: 24 months (mean 1.9 years in trial)
Outcomes	Main study outcome: incidence of actinic keratosis and non‐melanoma skin cancer Dropouts: unclear intervention, unclear control Available outcomes: deaths, CVD deaths, cancer deaths (none), (weight data provided but without variance)
Notes	Study funding: National Cancer Institute Response to contact: Prof Black provided data on mortality NOTE: for this trial the higher PUFA arm is the control, and lower PUFA arm is the intervention
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "list of randomly generated numbers"
Allocation concealment (selection bias)	Unclear risk	Randomisation method not clearly described
Blinding of participants and personnel (performance bias) All outcomes	High risk	Dietary advice provided, so participants not blinded
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quote: "examined .... by dermatologists unaware of their treatment assignments". Deaths (all‐cause and CVD) not considered relevant to the intervention
Incomplete outcome data (attrition bias) All outcomes	Low risk	For mortality. Unclear for other outcomes
Selective reporting (reporting bias)	Unclear risk	No protocol or trials registry entry found
Attention Bias	High risk	Weekly classes and monthly follow‐up in intervention group, 4‐monthly check‐ups only in control
Compliance	Low risk	Dietary intake data suggest omega‐6 and total PUFA were significantly reduced in the intervention arm
Other bias	Low risk	None noted