Effect of eating vegetables before carbohydrates on glucose, insulin and glycemic control - A systematic review and meta-analysis of randomized controlled trials.

BACKGROUND AND AIMS: It is discussed that eating vegetables before carbohydrates may reduce the increase of postprandial glucose and improve insulin secretion. However, findings of studies investigating the effectiveness are inconclusive. Therefore, the aim of this systematic review and meta-analysis was to assess the effects on glycemic control in adults with and without health conditions. METHODS: PubMed and the Cochrane Library were searched until September 2025. Randomized controlled trials (RCTs) examining the effect of a vegetable preload before carbohydrate consumption on postprandial and fasting glucose, insulin and HbA1c levels in adults were selected. RESULTS: In total, we included 18 RCTs. Using risk of bias tool RoB 2 ten trials were rated with moderate risk of bias and eight with a high risk. With very low certainty of evidence the intervention reduced postprandial glucose and insulin concentration after 30 min (MD (95% CI): -1.21 mmol/L [-1.75, -0.68] and -13.14 μU/mL [-18.63, -7.65]) and 60 min (-0.52 mmol/L [-0.67, -0.37]; and -12.03 μU/mL [-18.27, -5.78]) compared to their controls without vegetable preloads. After 120 min, postprandial glucose and insulin values were higher compared to the controls (0.24 mmol/L [0.06, 0.42] and 7.10 μU/mL [1.94, 12.26]). In people with type 2 diabetes, the intervention reduced HbA1c (baseline: 8.3 ± 1.7%, after 24 months: 6.8 ± 0.8%). CONCLUSION: Although this meta-analysis shows short-term improvements in glucose and insulin concentrations and individual studies indicate beneficial effects on HbA1c, the interpretability of these results is severely restricted due to methodological limitations. PROSPERO registration number: CRD42024529101.