Diets containing a high percentage of Nori or Konbu algae are well-accepted and efficiently utilised by growing rats but induce different degrees of histological changes in the liver and bowel
Introduction
Marine algae are habitually consumed in Asia and occasionally in other parts of the world (Nisizawa et al., 1987). However, Eastern cousine and vegetarian diets have gained popularity in Western countries in recent years and in turn increased the demand for these marine vegetables. Seaweeds are rich in polysaccharides, minerals, and vitamins. Protein content is generally higher in red than brown algae (Mabeau, and Fleurence, 1993, Fleurence, 1999). Although their fat content is low, 1/5–1/2 of the total fatty acid content consists of n-3 fatty acids (Jeong et al., 1993). These marine vegetables are rich in minor compounds such as phytosterols (Ergueta Martı́nez, 2001) and constitute potential sources of dietary fibre that differ chemically and physicochemically from those of land plants, for which reason they may have different physiological effects on man (Jiménez-Escrig, and Sánchez-Muniz, 2000, Lahayen, 1991, Fleury, and Lahayen, 1991). However, although algae are rich in several components, the bioavailability and nutritional properties of those components have scarcely been investigated and the effects of diets containing relatively large amounts of algae have not yet been studied in growing animals. Further, there are indications of adverse effects associated with herbal medications with algae, which include among others liver failure, toxic hepatitis, and death (Ernst, 2003). Organ (mainly liver and spleen) hypertrophy has been considered a signal parameter of possible organ damage (López-Varela et al., 1995). In recognition of the increasing consumption of seaweeds by young persons and because serious adverse effects of unconventional therapies with herbal medications in children and adolescents recently have been published (Ernst, 2003), this study was designed in growing male Wistar rats to determine the effect of these alga-diets on (i) growth and dietary efficiency ratio (DER); (ii) mineral absorption; (iii) the size and histological structure of several organs.
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Materials
A brown seaweed (Phaeophyceae): Nori (Porphyra tenera) and a red seaweed (Rhodophyceae): Konbu (Laminaria digitata) were obtained from a local supplier (Algamar C.B., Redondela, Pontevedra, Spain). These commercial, edible marine seaweeds were freeze-dried and milled using a cyclotic mill (Tecator 1093, Sweden) to a particle size of <1.0 mm before use. The composition of the seaweeds employed in the current study had been previously reported (Rupérez and Saura-Calixto, 2001). Both seaweeds
Food intake
Table 2 shows that food intake did not significantly differ between groups. Diets containing seaweeds are normally well accepted, with experimental diets being consumed at a rate similar to that of the control diet (Ren et al., 1994, Wong et al., 1999). However, average food intakes may differ among studies (Gudiel-Urbano, and Goñi, 2002, Wong et al., 1999). These different results may be related to the caloric density and fibre content of the diets, initial body weight and length of the
Acknowledgments
We are indebted to Drs. Isabel Goñi, Fulgencio Saura, Laura Barrios and Gonzalo Guerrero for their assistance. This work was supported by a grant from the Spanish Comisión Interministerial of Ciencia y Tecnologı́a (Spanish Interministerial Science and Technology Committee), Project ALI 98-830. Thanks are due for the fellowship awarded to Beatriz Blas by the Complutense University of Madrid (Spain).
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