Walnut dreg is a high-quality protein resource rich in a variety of bioactive peptides. However, the research on pancreatic lipase inhibitory peptides from walnuts is limited. In this study, different molecular-weight fractions of alkaline protein hydrolysate from walnut dreg were found to exhibit inhibitory activities against pancreatic lipase, with the < 1 kDa fraction exhibiting the most prominent activity, followed by the 1–3, 5–10, and 3–5 kDa fractions, showing IC₅₀ values of 12.22, 13.60, 17.23, and 37.65 mg/mL, respectively. Within the < 1 kDa fraction, 5 peptides (VIAFP, LVAFP, IAFP, LTYP, and LFDP) with the strongest binding ability (−10.03 to −11 kcal/mol) to pancreatic lipase were screened by molecular docking technique. Among them, LFDP (IC₅₀ = 6.931 mmol/L) exhibited the strongest pancreatic lipase inhibitory activity and reversible competitive pancreatic lipase inhibition. LFDP induced fluorescence bursts and structural changes in pancreatic lipase and exhibited strong biological activity even under high temperatures, strong acidic and alkaline conditions, exposure to metal ions, and gastrointestinal digestion conditions. In addition, LFDP significantly inhibited lipid accumulation in 3T3-L1 adipocytes. In conclusion, these results suggest that the peptide LFDP from walnut dregs is a potential pancreatic lipase inhibitor.

Walnut green husk, a byproduct of walnut processing, is rich in polyphenols with potential antidiabetic effects. However, the antidiabetic activity of walnut green husk polyphenols (WGHP) in vivo has not been reported and their mechanism of action is still unclear. This study investigated its impact on type 2 diabetes mellitus (T2DM) in mice induced by a high-fat diet and streptozotocin. We found that WGHP improved glycolipid metabolism, reduced inflammation and oxidative stress, and protected the pancreas and liver. WGHP also reshaped the gut microbiota, lowering the Firmicutes/Bacteroidota ratio and boosting beneficial bacteria. Network pharmacology indicated that WGHP’s effects are mediated by the PI3K/AKT signaling pathway, which was confirmed by increased protein expression of phosphorylated insulin receptor substrate 1 (p-IRS-1), phosphoinositide 3-kinase (PI3K), phosphorylated protein kinase B (p-AKT), and glucose transporter type 4 (GLUT4) in the liver. In conclusion, these results indicate that WGHP ameliorates T2DM by modulating gut microbiota and the IRS/PI3K/AKT pathway, providing a theoretical basis for the in-depth utilization of walnut green husk.