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Background: Structure and protein-starch interactions in pasta products may be responsible for lower postprandial glycemic responses compared with other cereal foods. Objective: We tested the effect on postprandial glucose metabolism induced by two pasta products, couscous and bread, through their structural changes during mastication and simulated gastric digestion. Methods: Two randomized controlled trials (n = 30/trial) in healthy normal weight adults (23.9 and 23.0 kg/m2) evaluated postprandial glucose metabolism modulation to 50g of available carbohydrate portions of durum wheat semolina spaghetti, penne, couscous, and bread. A mastication trial involving 26 normal weight adults was conducted to investigate mastication processes and changes in particle size distribution and microstructure (light microscopy) of boluses after mastication and in vitro gastric digestion. Results: Both pasta products resulted in lower areas under the 2h-curve for blood glucose (-40% for spaghetti and -22% for penne vs couscous; -41% for spaghetti and -30% for penne vs bread), compared with the other grain products (P < 0.05). Pasta products required more chews (spaghetti: 34 ± 18; penne: 38 ± 20; bread: 27 ± 13; couscous: 24 ± 17) and longer oral processing (spaghetti: 21 ± 13 s; penne: 23 ± 14 s; bread: 18 ± 9 s; couscous: 14 ± 10 s) than bread or couscous (P < 0.01). Pastas contained more large particles (46-67% of total particle area) compared to bread (0-30%) and couscous (1%) after mastication and in vitro gastric digestion. After in vitro gastric digestion, pasta samples still contained large areas of non-hydrolyzed starch embedded within the protein network, protein in bread and couscous was almost entirely digested, and starch was hydrolyzed. Conclusions: Preservation of the pasta structure during mastication and gastric digestion explains slower starch hydrolysis and, consequently, lower postprandial glycemia compared to bread or couscous prepared from the same durum