Scientists from Pennsylvania State University and Juniata College performed the study with 42 participants between the ages of 30 and 65 years of age who met the criteria for being overweight or obese, according to results published in the Journal of Nutrition.
Prior to the study, participants ate a standard Western diet for two weeks that was higher in saturated fat than the subsequent study diets. After the two-week period, study participants were randomized into one of three groups. All three groups ate a diet in which walnuts or vegetable oils replaced saturated fat for six weeks, according to the study.
The team then collected and analyzed fecal samples from participants 72 hours prior to both the end of the two-week standard Western diet period and the study diet period. They discovered that samples of participants in the group that consumed walnuts were enriched with beneficial gut bacteria including Roseburia, Eubacteria eligens, and Lachnospiraceae, researchers determined.
Roseburia produces butyrate, a compound intestinal cells use as fuel and which also helps protect gut lining. Greater levels of Eubacterium eligens were associated with improved blood pressure values. And higher levels of Lachnospiraceae were associated with reductions in blood pressure, non-HDL cholesterol, and total cholesterol, according to study results.
The team notes that previous research has shown that eating a diet that is low in saturated fats and contains walnuts benefits heart health by lowering blood pressure and cholesterol levels. Results of the new study suggest changes in the gut microbiome may explain the heart health benefits derived from eating walnuts.
Improvements in heart disease risk factors were not seen with either of the two study group diets where saturated fat was replaced with vegetable oils.
What makes walnuts so special? Researchers note that they are rich in fatty acids, bioactive compounds, and fiber that serve as food for beneficial gut bugs. Beneficial gut bacteria manufacture beneficial compounds for our bodies.
Participants in the walnut study diet group consumed approximately 2 to 3.5 ounces of walnuts daily. One ounce of walnuts is about 12 to 14 halves or approximately one-quarter cup or one handful.
MedicineNet author Benjamin Wedro, MD, FACEP, FAAEM, notes that walnuts and other types of nuts may be helpful in lowering cholesterol levels. "However, nuts are high in calories and should be eaten in moderation," he said.
Dr. Wedro notes that the American Heart Association and the American College of Cardiology have guidelines that outline how to help decrease their patients' risk of developing heart disease. Weight reduction, exercise, diet, and cholesterol-lowering statins may be prescribed. Dr. Wedro urges people to eat a heart-healthy diet such as the Mediterranean diet, which emphasizes fruits, vegetables, whole grains, fish, seafood, olive oil, nuts, and moderate portions of poultry, dairy, and eggs. The Mediterranean diet limits red meat and sweets and includes daily physical activity.
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