Methods	RCT
Participants	Overweight or obese adults (USA) CVD risk: low Intervention reduced fat: 202 randomised, 202 analysed Intervention modified fat: 201 randomised, 201 analysed Mean years in trial: reduced fat 1.78, modified fat 1.84 % male: reduced fat 33%, modified fat 36% Age, years: reduced fat 50 (SD 10), modified fat 51 (9)
Interventions	Reduced fat vs Modified fat diet Reduced fat aims: total fat 20%E, SFA ≤8%E, MUFA 6%, PUFA 6%, dietary chol 150mg/1000kcal, CHO 55%, protein 25%E, dietary fibre 20g/d Modified fat aims: total fat 40%E, SFA ≤8%E, MUFA 22%E, PUFA 10%E, dietary chol 150mg/1000kcal, CHO 35%E, protein 25%E, dietary fibre 20g/d Reduced fat methods: 18 group sessions in first 6 months, then 2 group sessions per month to 2 years, plus individual sessions every 8 weeks for 2 years. All sessions included behavioural counselling, daily meal plans provided, food diary and web-based self-monitoring tool provided, 90 mins/week of moderate exercise encouraged Modified fat methods: 18 group sessions in first 6 months, then 2 group sessions per month to 2 years, plus individual sessions every 8 weeks for 2 years. All sessions included behavioural counselling, daily meal plans provided, food diary and web-based self-monitoring tool provided, 90 mins/week of moderate exercise encouraged Total fat intake (at 2 years): low fat 28.4 (sd 8.1)%E, mod fat 35.1 (sd 7.0)%E Saturated fat intake (at 2 years): low fat 8.9 (sd 3.8)%E, mod fat 10.5 (sd 2.7)%E Style: diet advice Setting: community
Outcomes	Stated trial outcomes: weight Data available on total mortality? yes (no events) Cardiovascular mortality? yes (no events) Events available for combined cardiovascular events: unclear Secondary outcomes: cancer deaths (no events) and cancer diagnoses Tertiary outcomes: weight; total, LDL and HDL cholesterol; TGs; systolic and diastolic blood pressure, QoL (QoL outcomes not reported)
Notes	This was a factorial trial, so there were also 2 arms with lower protein intake (see Sacks low protein 2009)
Risk of bias
Bias	Authors’ judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	‘Randomization assignments to one of 4 diet groups were generated by the data manager at the coordinating center… after confirming, by computer program, that all screening activities had occurred… Diet group assignments were stratified by site with varying block sizes to ensure a balance at each site.’
Allocation concealment (selection bias)	Low risk	As above
Blinding (performance bias and detection bias) All outcomes	Low risk	‘Blinding was established by naming each diet with colors, and using the same foods for each diet. Blinding and equipoise were strictly maintained by emphasizing to intervention staff and participants that each diet adheres to healthy principles, and each is advocated by certain experts to be superior for long-term weight-loss. Except for interventionists … investigators and staff were kept blind to diet assignment of the participants. The trial adhered to established procedures to maintain separation between staff that take outcome measurements and staff that deliver the intervention. Staff members who obtained outcome measurements were not informed of the diet group assignment…. All investigators, staff and participants were kept masked to outcome measurements and trial results.’
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Unclear for cardiovascular events. Yes for tertiary outcomes -intention to treat analysis, imputing zero change from baseline for missing data (except for weight which was more complex, assuming weight regain for missing data following weight loss, and zero change for those who had previously gained weight)
Selective reporting (reporting bias)	Low risk	ClinicalTrials.gov number NCT00072995. Protocol secondary outcomes (hepatic and skeletal muscle, visceral fat, and quality of life) not yet reported in full
Other bias	Low risk
Free of systematic difference in care?	Low risk	Identical follow up for all groups
Free of dietary differences other than fat?	Low risk	Clear dietary goal similarities across saturated fat, fibre, cholesterol etc