Mice Fed High‐fat Obesigenic Diets with Walnut Plus Other Whole Foods Demonstrate Metabolic Improvement and Changes in Gene Expression and Metabolomic Patterns

We tested the hypothesis that addition of PUFA‐rich walnut to a high‐fat Western diet (HF) would improve metabolism in male C57BL/6J mice. Further, various polyphenol‐rich foods were added to walnut‐containing HF diets to evaluate the potential for additional metabolic improvement. Groups of mice (n=8 each) were provided either a low‐fat diet (LF, 10% kcal fat), high‐fat diet (HF, 45% kcal fat), HF supplemented with walnut (W), or W diet supplemented with blueberry (W+BB), raspberry (W+RB), apple (W+AP), cranberry (W+CB), cherry (W+CH), broccoli (W+BR), olive oil (W+OO), soy protein (W+SP), or green tea (W+GT) for 9 weeks. In week 8, a glucose tolerance test was conducted: W‐fed mice showed improved glucose control vs. HF‐fed mice while W+RB‐ and W+AP‐fed groups showed improvement vs. W‐fed mice. After 9 weeks, LF‐fed mice gained less weight than all other HF‐fed groups. Histological analysis showed hepatic lipid in W‐fed mice was not significantly different from LF‐fed mice, while W+BR‐ and W+GT‐fed mice had lowest lipid levels with the exception of the LF‐fed mice. Patterns of expression of serum cytokines indicate a generalized reduction of inflammatory cytokines in all W‐fed groups vs. HF‐fed mice. Gene expression in LF, HF, W, W+RB, W+CH, and W+GT groups was measured using a focused gene array (Qiagen). Analysis of relative mRNA levels revealed that walnut‐fed mice and walnut plus another whole food had differentially regulated gene expression compared to HF‐fed and W‐fed mice. Significantly regulated mRNAs were associated with functions related to lipid, carbohydrate, and xenobiotic metabolism, antioxidant effect, and inflammation. The analysis indicates each diet produces a unique expression pattern. Finally, a global metabolomic study compared LF‐, HF‐, W‐, W+CH‐, W+RB‐, and W+GT‐fed mice. Changes in metabolite levels related to energetics, inflammation and redox homeostasis were observed. Changes in carbohydrate metabolism were observed in W+CH‐fed mice, with more subtle effects in W+RB‐fed mice; these may reflect changes in increased energy demand. Changes in biomarkers in HF‐ vs. LF‐fed mice pointed to increasing inflammation in HF mice; HF+W mice showed increases in omega‐3 polyunsaturated fatty acids which may negatively regulate inflammation. W‐fed mice supplemented with RB, CH or GT produced signs of declining inflammation. Finally, changes in biomarkers of redox homeostasis in HF+W+CH may suggest declining oxidative stress, which may also impact inflammation in the liver. Further studies assessing feces could identify microbiome‐related changes associated with dietary supplementation. Finally, an assessment of how dietary supplementation might affect obesity‐related disease models (e.g. NASH) may identify new therapeutic opportunities to target disease. We conclude that intake of walnut, a high PUFA‐containing food, on its own or in combination with a polyphenol‐rich food, was demonstrated to have significant effects on physiological parameters related to metabolic syndrome and changes in both hepatic gene expression and metabolite levels consistent with an improved metabolic state. Support or Funding Information California Walnut Commission