|Background The transition from exclusive breastfeeding to family foods, referred to as complementary feeding, is a very vulnerable phase that typically covers the period from 6 to 24 months of age of infants and young children. It is the time when growth faltering starts in developing countries. This is due to the traditional complementary foods, which are often inadequate to meet the nutritional requirements of infants because of their low energy density and poor digestibility and bioavailability of nutrients. Dietary quality rather than quantity appears to be the key problem with complementary food diets. There is need to optimize the processing conditions using local technologies like germination and extrusion cooking to produce complementary foods that have good protein quality, are energy dense and have improved micronutrient availability. Objective of the study The main objective of the study was to produce energy dense and good protein quality complementary foods using malting and extrusion processing. Methods Finger millet, field pea and soybean were germinated at 25°C and 30°C for 48hours and 72hour and extrusion in a twin screw 600JR Insta-Pro extruder at extrusion temperatures that ranged from 110 to 160°C, dried and made into flours. The flours were analysed for changes due to germination and extrusion processing for proximate principles, minerals, sugar, starch, amino acids, vitamin A, fatty acids, dietary fiber, antinutritional factors (trypsin inhibitors, lectins, condensed tannins and phytates) and viscosity. Iron and zinc molar ratios were also determined. Blends with cereal-legume ratio of 70:30 respectively, were prepared from ungerminated, germinated and extruded grains and enriched with fish at 5% level. The influence of germination and extrusion on porridges cooled to 45°C and viscosities < 3.0 Pa.s were investigated for their rheological and nutritional properties. Isocaloric 400 kcal 100g-1 and isonitrogenous 10% complementary diets were formulated and fed to weanling rats for 5 days to assess the digestibility and metabolic efficiency of the diets. The growth study was also conducted for 28 days and Casein + 0.3% was used as the control diet. Protein quality was assessed using various biological indices; amino acid scores, protein digestibility corrected amino acid scores (PDCAAS), protein efficiency ratio (PER), weight gain, food transformation ratio (FTI), apparent digestibility coefficient (ADC), true protein digestibility (TPD), nitrogen retention, biological value (BV), net protein utilization (NPU) and net protein ratio (NPR) according to AOAC (2000). Histological investigations on the sytemic organs and light microscopic morphormetric (stereological) evaluation on intestines were studied following the method of Baddeley et al. (1986). Results The optimum germination condition at 30C for 48hours was more effective in reducing viscosity and increasing energy density of the finger millet/soybean diet to 20% solids, compared with extrusion processing (15% solids) of the same diet. The energy densities of finger millet-soybean porridges were sufficient to cover energy required for average breast fed infants aged 6 to 11 months receiving two meals of complementary foods per day. Germination significantly (P<0.05) reduced or eliminated α-galactosides from the legumes while longer germination conditions resulted in increased dry matter loss without appreciable increase in nutrients. The optimum extrusion processing temperature of 138-141ºC favourable (P<0.05) reduced the ANFs, making extruded finger millet/soybean diet free of trypsin inhibitor activity (TIA), lectins and low levels of condensed tannins (CTs) and phytates compared to germination processing. The relative inhibitory effect of the soybean phytates were overcome which simultaneously increased the iron and zinc bioavailability to high and moderate levels respectively. However, the reduction in phytates due to extrusion processing was not enough to compensate for the rather low iron and zinc content of the complementary foods. The amino acid scores for all the complementary diets ranged from 68 to 86%, true protein digestibility from 71 to 92%, protein digestibility corrected amino acid scores from 53 to 0.74 expressed as a proportion of the respective amino acids for infant’s amino acid requirements. The growth trials showed that unprocessed finger millet/field pea and extruded finger millet/soybean diets produced growth performance that were similar (P≥0.05) to the control diets in terms of PER, weight gain, FTI, ADC, BV and NPU. Fish fortification significantly (P<0.05) improved the protein quality of all the diets and it’s inclusion in extruded diet was highly liked and accepted by consumers. Histopathology of the organs showed the presence of pancreatic hypertrophy and hyperplasia among the rats fed all the diets except the control and the fish fortified germinated finger millet/field pea diets. This was confirmed by the significant increases (P<0.05) in the weight of the pancreas. The animals fed the unprocessed and germinated finger millet/soybean diets induced the the least growth rates which was followed by significant (P<0.05) decrease of the organs (kidney, liver and heart) per/body ratio, shortening of villus length and enterocyte heights. These were due to nutrient restriction and absorption and the multiple biologically active components (lectins, TIA, CTs and phytates) in those diets. Conclusion and recommendations Composite complementary foods produced from combinations of finger millet and soybean resulted in nutritionally improved food products which were further improved with fish fortification therefore, supporting the concept of legume/cereal/animal foods complementation and enhancement for feeding infants. Germination was a better method in producing high energy-density complementary foods, free of α-galactosides but with appreciable loss in amino acids. While extrusion processing produced complementary foods with high energy density, improved protein quality that resulted in better growth than that from germination. Extrusion processing therefore is recommended as the method for preparing high energy and nutrient dense infant and young children’s complementary foods.