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Dr. Axe Wire · Study decoded · gut
Stearic and Oleic Acid Diets Shift Bile Acids in 17 Postmenopausal Women
A crossover trial on three fats found stearic and oleic acid diets changed bile acid and cholesterol pathways differently than palmitic acid.
A randomized crossover trial published October 6, 2026 in The American Journal of Clinical Nutrition found that diets enriched in stearic acid or oleic acid shifted bile acid and cholesterol metabolism differently than a palmitic acid diet in 17 mildly hypercholesterolemic postmenopausal women.
17postmenopausal women
5-weekdiet phases
22-24%lower synthesis ratio
3-4xhigher gene expression
Seventeen mildly hypercholesterolemic postmenopausal women completed a randomized crossover trial, eating isocaloric diets enriched in stearic acid, palmitic acid, or oleic acid for 5 weeks each, separated by 2-week washout periods. Both the stearic acid and oleic acid diets lowered fasting primary bile acids compared with the palmitic acid diet, by an average of 159.1 and 200.2 units respectively, and raised certain non-fasting bile acids 2.4 to 2.7-fold. Stearic acid also lowered stool secondary bile acids by 15.2 units compared with oleic acid, and raised certain bound bile acids 1.4-fold compared with palmitic acid. Two liver genes regulating bile acids, farnesoid X receptor and small heterodimer partner, were expressed 3- to 4-fold higher after both stearic and oleic acid diets versus palmitic acid. The ratio of cholesterol production to absorption markers was 22% to 24% lower after both diets. Gut microbial diversity stayed stable across all three diets, with only modest species-level differences.
The authors concluded stearic acid and oleic acid lower cholesterol compared with palmitic acid through shared liver regulation of bile acid and cholesterol pathways, while stearic acid uniquely altered specific gut bacteria and bile acids, suggesting changed recycling of bile acids between gut and liver. Bile acids are made from cholesterol in the liver, sent to the gut to digest fat, then mostly reabsorbed; shifting that recycling changes how much new cholesterol the liver makes.
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Cholesterol Synthesis-to-Absorption Ratio: Percent Lower vs Palmitic Acid Diet
This was a small crossover study of 17 women with mildly elevated cholesterol, so results may not generalize to men, younger women or people with higher cholesterol. The study measured metabolic markers, not heart disease outcomes.
Dr. Axe’s Take
Saturated fat is not one thing, and this data backs that up. Stearic acid behaves nothing like palmitic acid when it comes to cholesterol metabolism, even though both are classified as saturated fats. A 22% to 24% drop in the cholesterol synthesis-to-absorption ratio with both stearic and oleic acid tells me the liver backs off unnecessary cholesterol production when the right fats are on the plate. This week, I would favor whole-food fat sources rich in oleic acid, like olive oil and avocado, over processed foods high in palmitic acid, and add fiber-rich vegetables to support healthy bile flow.
— Dr. AxeTake the Metabolic Health Quiz →
Study summary
- Who
- 17 mildly hypercholesterolemic postmenopausal women
- Design
- Randomized controlled crossover trial, secondary analysis
- Dose
- Isocaloric diets enriched in stearic, palmitic, or oleic acid, 5 weeks each, 2-week washouts
- Primary result
- Cholesterol synthesis:absorption ratio 22-24% lower after stearic and oleic acid diets vs palmitic acid
- Secondary
- Fasting primary bile acids lower by 159.1 (stearic) and 200.2 (oleic) units vs palmitic; FXR/SHP gene expression 3-4x higher; fecal microbiome diversity stable across diets
- Funding / conflicts
- Funders listed in the journal record: National Institute of Food and Agriculture; US Department of Agriculture. Conflict statement in the PubMed record: The authors report no conflicts of interest.
- Date
- Oct 6, 2026