Elucidating the Effect of Dietary Stearic Acid on the Regional Heterogeneity of the Gut Microbiome and Metabolome: Focus on Bile Acid Metabolism (SAMPill Study)

Elucidating the Effect of Dietary Stearic Acid on the Regional Heterogeneity of the Gut Microbiome and Metabolome: Focus on Bile Acid Metabolism

Stearic acid and palmitic acid are two common consumed saturated fatty acids found in foods. Palmitic acid is associated with increases in blood cholesterol, whereas stearic acid is generally considered neutral with respect to blood cholesterol. However, the mechanisms underlying these different effects are not fully understood. The goal of this clinical trial is to determine how replacing dietary palmitic acid with stearic acid affects microorganisms living in the gastrointestinal tract (gut microbiome) and the metabolites they produce, including secondary bile acids, and whether these changes influence heart and metabolic health in postmenopausal women. The main question it aims to answer is whether the cholesterol lowering effect of dietary stearic acid, compared to dietary palmitic acid is due to changes in the composition and function of the gut microbiome and bile acid metabolism. Participants will consume a controlled diet high in palmitic acid for a 10-day run-in period, followed by a controlled diet high in stearic acid for 28 days. During the study, participants will provide biological samples, including blood samples collected in both fasting and non-fasting states, for assessment of cardiometabolic outcomes. Participants will also swallow mini-pills designed to collect samples from different regions of the gastrointestinal tract to assess the gut microbiome and related metabolites. Results will contribute to understanding the relationship between stearic acid mediated microbiota effects on cardiometabolic heath.

Inclusion Criteria:

1. Postmenopausal women (defined as complete natural cessation of menses for >12 months or a bilateral oophorectomy), who are not currently using hormone replacement therapy (HRT) or gender-affirming hormone treatments
2. Age >50 years
3. BMI >20 to <35 kg/m2, inclusive
4. Non-smoker or former smoker who quit > 6 months
5. Normotensive with or without medication
6. Normal gastrointestinal function with regular bowel movements at least once every other day
7. Willingness to swallow the mini-pills
8. Willingness to collect and return multiple stool samples
9. Adequate refrigerator and freezer space to store study meals
10. Intent to remain in the greater Boston area during the intervention periods

Exclusion Criteria:

1. Allergy/intolerance/religious reasons to avoid study meals or food ingredients
2. Regular use of dietary supplements, pre/probiotics, laxatives or fiber supplements (except multivitamins) within the past 3 months
3. Use of steroids (excluding topical) within the past 3 months
4. Regular use of aspirin (except baby aspirin), NSAIDS, or anti diarrheal medication
5. Current smokers or former smokers who quit < 6 months ago, and use of nicotine replacement products within the last 6 months
6. Chronic constipation
7. Use of oral antibiotics within the past 3 months.
8. Use of dental prophylaxis within the past 3 months
9. Regular use of stomach acid lowering and weight loss medications such as GLP-1 agonists
10. Planned colonoscopy 3 months prior to or during the study period
11. Swallowing disorder or inability or difficulty taking pills
12. Malabsorptive and inflammatory bowel disease, diverticulosis, and history of diverticulitis, gastric esophageal/intestinal surgery, including lap banding or bariatric surgery.
13. History of bowel obstruction, gallstones, gastroparesis, pancreas and liver/gallbaldder disorders.
14. Any form of active substance abuse or dependence (including drug or alcohol abuse).
15. Established major chronic diseases such as CVD, diabetes, active cancer within the last 5 years, or any significant medical condition at the study MD's discretion
16. A clinical condition that, in the judgment of the study MD or PI, could potentially pose a health risk to the subject while involved in the study.
17. Unwillingness to adhere to study protocol
18. Intent to increase or decrease body weight during the study period
19. No Social Security number (for payment and IRS forms).
20. Individuals who directly report to any member of the research team.