The diets weren’t just about eating less fat — they also banned butter, added lots of vegetable oil, and cut out eggs, so we don’t know which part actually mattered.
Scientific Claim
The dietary interventions in the trials often included multiple changes beyond fat reduction — such as banning animal fats, increasing vegetable oils, and restricting eggs — making it unclear which component affected outcomes.
Original Statement
“A number of studies impaired assessment of one intervention (administering oils) by adding other dietary restrictions. ... The LA Veterans study ... restricted animal fats and quantified egg consumption.”
Evidence Quality Assessment
Claim Status
appropriately stated
Study Design Support
Design supports claim
Appropriate Language Strength
definitive
Can make definitive causal claims
Assessment Explanation
The claim is directly supported by the authors’ critique of trial design in the discussion. It accurately describes the complexity of interventions without overinterpreting.
Evidence from Studies
Supporting (1)
Evidence from randomised controlled trials did not support the introduction of dietary fat guidelines in 1977 and 1983: a systematic review and meta-analysis
The study found that the old diet rules changed many things at once — like swapping butter for oil and cutting eggs — but no one knew which change actually helped, and in the end, it didn’t even lower heart disease deaths.