Interaction of dietary fat saturation and cholesterol level on cholesterol synthesis measured using deuterium incorporation.
Level 2 - randomized trial
Individual controlled dietary intervention trial
What was done
Moderately hypercholesterolemic human subjects were fed solid-food diets containing 30% fat (80 mg cholesterol/1000 kcal) for 5-week periods. Two-thirds of the dietary fat was provided as either corn oil or beef tallow, tested with and without additional dietary cholesterol (120 mg/1000 kcal). At the end of each diet period, oral deuterium oxide was administered to measure 24-hour de novo fractional synthesis rates (FSR) and absolute synthetic rates (ASR) of cholesterol into the rapid exchangeable pool, along with serum lipoprotein profiles.
What was found
Plasma total and LDL cholesterol were significantly elevated (P < 0.01) with both beef tallow feeding and cholesterol addition. Triglycerides were higher with beef tallow (P < 0.02) but unaffected by cholesterol level. HDL was higher when cholesterol was added to corn oil versus beef tallow (P < 0.02). Both FSR (P < 0.02) and ASR (P < 0.02) were increased by corn oil compared to beef tallow feeding, but neither was influenced by dietary cholesterol level. Calculated cholesterol pool sizes did not differ. No absolute values, baseline numbers, or effect sizes were reported in the abstract.
Why it matters
It demonstrates that polyunsaturated fat (corn oil) lowers circulating LDL cholesterol without suppressing endogenous cholesterol synthesis (in fact, synthesis increases), and that moderate dietary cholesterol does not exert feedback inhibition on whole-body cholesterogenesis.
Limits
The abstract does not state the sample size (n), participant demographics (age, sex), or quantitative baseline/outcome values. The exact trial allocation design (randomized crossover vs. parallel) is unstated in the abstract, and findings are restricted to moderately hypercholesterolemic adults on 5-week dietary interventions.
Cited by
- contradicts Saturated fat intake increases endogenous cholesterol production.