Dietary fiber (DF) consumption has been associated with improved glycemic control in epidemiological and long-term interventional studies. However, its acute effects are not yet clear. This systematic review aims to elucidate the postprandial effects of DF in starchy products on glycemia and insulinemia. An electronic search of databases was conducted, and forty-one records met the inclusion criteria and underwent a risk-of-bias assessment. It was shown that soluble DF does not clearly affect glycemia in individuals with normal weight, while resistant starch may be more effective in flattening glycemic responses. Concerning insulinemia, both soluble DF and resistant starch have mixed results, with either favorable or no effects. Data on insoluble DF and glucose metabolism are scarce. The same mixed results for glycemia can be seen in healthy volunteers with overweight/obesity, while resistant starch seems to improve insulinemic responses. Finally, more studies need to examine the acute effects of DF in starchy foods on glucose metabolism and insulin secretion in individuals facing glucose abnormalities. Additionally, more studies are needed to prove whether ingesting high-fiber carbohydrate-containing products per se can result in blunted glycemic and insulinemic responses and which DF type and amount are more effective. Additionally, more studies are needed to prove whether ingesting high-fiber carbohydrate-containing products per se can result in blunted glycemic and insulinemic responses and which DF type and amount are more effective. Keywords: dietary fiber, soluble dietary fiber, insoluble dietary fiber, resistant starch, starchy foods, glycemic responses, insulinemic responses, humans status released display-pdf yes is-olf no is-manuscript no is-preprint no is-journal-matter no is-scanned no is-retracted no Received 2023 Apr 28; Revised 2023 May 11; Accepted 2023 May 17; Collection date 2023 May. 1. A recent systematic review and meta-analysis of twenty-one randomized controlled trials (RCTs) in patients with T2DM reported that, compared to controls, dietary fiber at a median daily dose of 10 g/day for a mean intervention duration of 8 weeks significantly reduced glycated hemoglobin A1c (HbA1c), fasting glucose and insulin, and Homeostatic Model Assessment for Insulin Resistance (HOMA-IR) [ 28 ]. Both soluble fiber products and fiber from natural foods were found to be effective in improving glycemic control and insulin sensitivity in T2DM patients, with the former yielding better effects [ 28 ]. Concerning the type of fiber that is more effective in ameliorating postprandial glycemic and insulinemic responses, the evidence is not consistent. On the one hand, it is believed that diets high in insoluble and only moderately fermentable cereal fiber reduce the risk of developing T2DM [ 29 ], whereas, in some other studies, naturally available high-fiber products, such as oats and barley, containing soluble β-glucan have been connected with improved glycemic control [ 11 , 16 ]. Finally, dietary fiber is thought to reduce the glycemic index (GI) of carbohydrate-containing products [ 30 ]. The results of the searches are represented in Figure 1 (PRISMA flow diagram). Figure 1 PRISMA flow diagram of included studies. 2.2. Eligibility Criteria In this systematic review, studies examining the acute effects of dietary fiber existing in or added to starchy foods, e.g., bread, spaghetti, and biscuits, on glycemic and insulinemic responses were included. The flours that were examined are the following: wholegrain or whole-meal or whole-wheat or whole-kernel or refined wheat, rye, barley, sorghum, or semolina, durum or not, with or without sourdough, and In total, the main issues pertaining to the selected records concerned missing details of the randomization process and, specifically, missing data on the blinding of the participants and/or researchers, as well as on the selection of a prespecified analysis. 3.2. Main Exposures The main outcomes of this systematic review were changes in glycemic and insulinemic responses a few hours, e.g., 120 min (acute), after the consumption of starchy foods e.g., bread or meals containing starchy foods, differing in the amount and/or type of dietary fiber. In conclusion, the acute effects of dietary fiber in starchy foods on the glycemic responses are not well studied in individuals facing metabolic abnormalities. More studies are needed in this field to evaluate the impact of different dietary fiber types a few hours after the ingestion of starchy foods enriched with them. This is extremely important for patients with impaired glucose metabolism. The available data from the analysis cannot lead to solid conclusions. 3.4. In particular, it is crucial to assess whether there is a difference in acute insulinemic responses of individuals with prediabetes or T2DM after the intake of starchy foods high in soluble or insoluble fiber or resistant starch. 4. Discussion This systematic review did not reveal favorable acute effects of dietary fiber incorporated in different starchy products on glycemic and insulinemic responses among healthy individuals and participants with various health conditions. In contrast, it instead confirmed the inconsistency that dominates in the literature. In the majority of meals, dietary fiber is accompanied by other macronutrients. Specifically, the protein and fat contents of foods may impact glycemic and insulinemic responses [ 112 ]. It has been proved that the co-ingestion of large amounts of fat with a carbohydrate meal has glucose-lowering effects even in healthy subjects, without a concomitant reduction in plasma insulin levels [ 113 ]. Additionally, protein intake seems to stimulate insulin secretion, thus resulting in glucose uptake and its reduction in the bloodstream [ 85 , 86 , 114 ]. However, the amount of protein content that is capable of inducing higher insulin responses is not yet established [ 114 ].