Nutritional Limitations of a Green Protein Shift with Focus on Iron
Abstract: A dietary shift into plant-based diets (PBD) to reduce the climate footprint is advocated. Effects on nutrition and health from a modern PBD, composed of replacement products based on protein extracts are however currently unknown. In Scandinavian countries, where cultivation of soy is not suited to the climate, domestic crops such as fava bean have been suggested as having large potential in replacing animal products. In this thesis, fava bean has therefore been selected as a model crop for investigating the replacement of meat in the context of a green protein shift. Analyzing 15 cultivars of fava bean, only one had an adequate estimated bioavailability of iron, and variation in antinutritional contents (phytate, lectins, trypsin inhibitors, oligosaccharides, saponins, total phenolics) was high. Even greater variations were seen in antinutritional and nutritional contents of 42 meat substitutes on the Swedish market, probably explained by differences in processing methods and the accumulation of phytate by protein extraction. Meat substitutes had a high content of phytate and a very low estimated bioavailability of iron and zinc, except for mycoprotein products and tempeh. Also, a high content of salt, saturated fat and dietary fiber was found in meat substitutes. Low theoretical iron bioavailability of extracted and texturized fava bean protein was confirmed in a clinical study. Non-heme iron absorption from single meals in 27 women of fertile ages measured with radioisotope technique was 4.2% from texturized fava bean meal, 21.7% and 9.2% from beef and cod protein meals respectively. Furthermore, fermentation of a fava bean drink for decreasing phytate content, and therebyimprove iron and zinc bioavailability, was investigated. A Pediococcus pentosaceus strain was able to substantially degrade phytate during co-fermentation with a phytase-producing yeast strain. By itself, P. pentosaceus did not have the ability to degrade phytate, which illustrates the importance of optimal conditions as well as selection of suitable microorganisms during fermentation for improved bioavailability. Overall, results show that nutritional consequences of consuming meat substitutes and fava bean is significantly affected by the product, cultivar and processing method used. Substituting meat with products analyzed in this thesis is estimated to markedly reduce the absorbable iron from the diet.
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