Vegetable-oil preloading modulates postprandial glycemic and insulin responses to a high-glycemic meal in healthy adults

Excessive intake of rapidly digestible starches increases metabolic risks. This randomized crossover trial involved twenty-two healthy adults (age 29 ± 6 years, BMI 21.6 ± 1.8 kg/m 2 ). Participants completed 5–10 sessions with 7-day washouts. The study examined whether preloading leafy vegetables (200 g) ± canola oil (20 g) modulates starch digestion (300 g mashed potatoes) by stimulating GLP-1 and delaying gastric emptying. Based on a ≥ 10-minute preloading interval identified in an exploratory Phase Ι pilot ( n = 10), the powered Phase II trial ( n = 22) demonstrated significant treatment×time interactions for the effect of preloading on postprandial glycemic and insulin responses ( p < 0.001) using linear mixed-effects models. Oil-containing preloads resulted in blunted postprandial blood glucose and insulin responses, delayed gastric emptying ( p < 0.001), and higher GLP-1 ( p < 0.001). Satiety and ad libitum energy intake remained unchanged. Furthermore, despite identical nutrients, co-ingestion underperformed timed preloading. In conclusion, an oil-containing vegetable preload modulates glycemic kinetics, offering a practical “food-first” strategy for post-meal glycemia management.