The Study
Walnut Consumption Alters the Gastrointestinal Microbiota, Microbially Derived Secondary Bile Acids, and Health Markers in Healthy Adults: A Randomized Controlled Trial
This study showed that when people ate walnuts for a few weeks, their gut bacteria and cholesterol levels changed in a way that might be good for them. But it didn't prove walnuts cause better health—it just showed a link in a small group of people.
Analysis score
Maximum 90 for a randomized controlled trial.
Where the score came from
Eating a small handful of walnuts every day for 3 weeks changed the good bacteria in your gut and lowered some harmful substances linked to inflammation and heart disease.
Where does this study sit?
Reviews of RCTs (Meta-analyses)
Max 100Randomized Trials
Max 90Reviews of Cohort Studies
Max 85Cohort Studies
Max 72Reviews of Case-Control Studies
Max 63Case-Control Studies
Max 58Cross-Sectional & Case Series
Max 50Expert Opinion
Max 560 / 100
Quality score
Participants are randomly assigned to treatment or control groups, minimizing bias. The gold standard for testing whether an intervention causes an effect.
Key takeaways
Summary
Based on the study abstract and findings.
- 1These changes suggest walnuts may help protect your gut and heart, but they didn't improve overall cholesterol or inflammation in just 3 weeks.
- 2Walnuts increased good bacteria (Faecalibacterium, Roseburia) by up to 160%, lowered two harmful bile acids by 25% and 45%, and reduced LDL ('bad') cholesterol by 7%.
Score breakdown, methodology, conflicts of interest, evidence analysis & raw study data
Publication
Journal
The Journal of Nutrition
Year
2018
Authors
H. Holscher, Heather M. Guetterman, K. Swanson, R. An, N. Matthan, A. Lichtenstein, J. Novotny, D. Baer
Related Content
Claims (7)
People who eat walnuts have a lower rate of death from any cause compared to those who do not.
People who eat different types of nuts have different levels of mortality risk, and walnuts are linked to a greater reduction in mortality risk compared to other nuts.
Eating 42 grams of walnuts every day for three weeks lowers LDL cholesterol by 7% and campesterol by 6% in healthy adults.
Eating 42 grams of walnuts every day for three weeks lowers levels of two bile acids in the stool—deoxycholic acid by 25% and lithocholic acid by 45%—in healthy adults.
Eating 42 grams of walnuts every day for three weeks changes the gut bacteria in healthy adults aged 35–68 by increasing certain bacteria and decreasing others.
Eating 42 grams of walnuts every day for three weeks does not change levels of total cholesterol, HDL cholesterol, triglycerides, glucose, or key inflammatory markers in healthy adults. The effect is limited to LDL cholesterol and gut microbiota.
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.