t. At present, the use of by-products from plant food production is gaining more interest because these products contain a large amount of valuable nutritional compounds e.g. dietary fibre, proteins, polyphenols, unsaturated fatty acids, vita- mins. The by-products improve both the nutritional profile and the health-promoting properties of bakery products but simulta- neously impair some technological properties, which is strongly related to the structure of the gluten network. FT-IR spectroscopy was used to determine changes in the gluten structure through the addition of by-products from the vegetable industry and cold oil pressing production. The supplements were added to the com- mon wheat dough in the amounts of 3, 6, 9 and 12%. Analysis of the spectra indicates that changes in the gluten structure and the distribution of water populations are connected with the type of technological process from which the supplement originat- ed and hence its chemical composition. Vegetable supplements cause the formation of aggregated structures such as pseudo-β- sheets, whereas gluten samples modified by oil supplements contain mainly basic secondary structures i.e. α-helices, β-turns and antiparallel-β-sheets. With regard to the water populations, oil supplements do not affect them or affect them slightly. Vegetable supplements lead to the formation of a weaker gluten network. This is observed in the form of a decrease in the number of strong hydrogen bonds.