AIM OF THE STUDY: An allergen-reduced dietary intervention programme with strict dietary requirements was implemented over the first four months of life in an unselected population-based infant cohort and compared to a non-intervention cohort (the ZUFF study). Recommendations for the dietary programme in the intervention cohort were extended, but not strictly implemented, until the end of month six. The intervention was based on breastfeeding, a moderate whey hydrolysate formula (pHF), and delayed introduction of weaning foods with a high allergenicity. This study was a prospective, controlled, and unblinded study, the first to assess the effects of an allergen-reduced, pHF-based early nutritional programme in a broad unselected infant population. Because overall healthy development of the infant is a major objective of any nutritional programme, the study evaluated the effects of the dietary intervention on infant growth and general health status rather than specific allergic manifestations. Part I of this paper gave results for nutritional behaviour only, and Part II gives results for growth and general health status during the intervention period through the sixth month of life. METHODS: Assignment of study infants was to demographically comparable intervention (Z) or control (FF) cohorts according to place of birth. In the intervention cohort (Z=564), the recommended dietary regimen was breastfeeding and--if exclusive breastfeeding was not possible--supplementation with a moderately hydrolysed, allergen-reduced infant formula (pHF). Weaning foods were delayed until four months of age or later in case of weaning foods with high allergenicity. In the control cohort (FF=566), there was no specific intervention. Imbalances between cohorts in confounding (adjuvant) factors that could influence health-related outcomes were integrated as covariates into the logistic regression of the main analyses. Growth parameters included weight, length, head circumference, BMI, and Z scores (SDS). General health status was assessed by clinically significant findings in gastrointestinal, respiratory, or skin symptoms. RESULTS: Growth at 6 weeks and at 3 and 6 months was similar for Z and FF. Significantly fewer Z than FF infants had clinically noteworthy health findings at 3 months (Z=27% versus FF=37%, odds ratio=0.63, CI=0.48-0.82) and 6 months (Z=33% versus FF=49%, odds ratio=0.51, CI= 0.40-0.66). This corresponds to a 30 % reduction in overall health concerns at 6 months for the intervention cohort. At 3 and 6 months, differences between cohorts in most measures of general health status were strongly influenced by a lower incidence of skin symptoms in the Z cohort. Within FF, there were fewer exclusively breastfed (eBF) infants with health problems at 3 months compared with those who were partially (pBF) or non-breastfed (nBF) (eBF=31%, pBF=40%, nBF=39%, p< 0.05). In contrast, in the Z intervention cohort, the number of infants with health concerns was similar for exclusively breastfed infants and for those in whom mother's milk was supplemented or replaced by pHF (eBF=29%, pBF=25%, nBF=26%, ns). In a subanalysis of overall health findings in infants without a family risk of allergies, there were again significantly fewer Z than FF infants with any health or any skin problem. CONCLUSION: An allergen-reduced dietary recommendation that includes a moderate whey hydrolysate infant formula (pHF) has no negative effects on growth parameters up to 6 months of life in an infant population unselected for atopic risk. The dietary intervention produced improvements in general health status when compared with a control cohort that received infant formula with unhydrolysed proteins (IF), and high allergenic weaning foods at an earlier age. The difference between cohorts was principally due to fewer adverse skin findings. (ABSTRACT TRUNCATED)