The effects of the addition of 10% of insoluble fibre (cellulose), insoluble high polyphenol content [natural carob fibre (NCF)] and a mixed of NCF and soluble fibre high viscosity (carob gum), in the proportion (9:1) to a semisynthetic diet, with a fat content of 8 and 15%, on food efficiency ratio (FER) and fat (FD) and nitrogen (NF) digestibility coefficients, were studied in male "Wistar" rats. We did not obtain difference with respect to the weight increase of the animals, the intake and fecal weight always is higher in the rats feed NCF. Significant differences were recorded for the (ND) we found lower values in the animals feed NCF, either 8% than 15% of diet fat content (0.85 +/- 0.02 lote Iap-G8, 0.85 +/- 0.01 lote IapV-G8, 0.85 +/- 0.01 lote Iap-G15, 0.84 +/- 0.00 lote IapV-G15) than in the feed cellulose (0.82 +/- 0.02 lote I-G8, 0.93 +/- 0.00 lote I-G15). We did not found any significant difference on the FD.