Sigma Nutrition Radio #481: Why Saturated Fat Really Does Impact Heart Disease Risk
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May 9, 2023 Why do some studies find no link between saturated fat and heart disease? A deep dive into how diet studies measure intake, what people eat instead, and why blood cholesterol matters. The discussion also revisits the Seven Countries Study and weighs evidence from population research and dietary interventions.
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Overadjustment Hides Saturated Fat Effect
- Many cohort studies showing null links between saturated fat and heart disease overadjusted for blood lipids, masking the causal pathway.
- In the Siri-Tarino meta-analysis ~42% of events came from studies that adjusted for cholesterol, biasing results toward the null.
Circulating SFAs Don't Equal Dietary Intake
- Circulating saturated fatty acids are poor biomarkers of dietary saturated fat because many even-chain SFAs are endogenously synthesized.
- Choudhury's null finding partly reflects mixing weak biomarkers with robust dairy-fat markers that behave differently.
Replacement Nutrient Determines Risk Signal
- Meta-analyses that combine heterogeneous cohorts without substitution modelling obscure effects because replacement nutrient matters.
- De Souza used risk estimates from Siri-Tarino; removing those studies shifted risk to a 26% higher CHD mortality.