Dietary levels of yeast grown on n-paraffins (single-cell protein, SCP) were given for 7 months to female CD-COBS rats treated with a single oral dose of 7,12-dimethylbenzanthracene (DMBA) or 3-methylcholanthrene (MC). A control group received the same dietary levels of SCP and a single oral administration of olive oil. The experimental diets did not modify rat growth rate or food consumption in comparison with a group receiving a standard diet. The leukopenia observed after DMBA administration was not changed by the SCP diets. The first tumour appeared in animals in the DMBA experiments at the same time as for standard and SCP-fed animals; in the MC study the SCP diet groups had a tumour-free life of 60 days compared to 30 days for the group given the control diet. The incidence of mammary tumours induced by polycyclic hydrocarbons was not modified by dietary levels of SCP. These results suggest that, under these experimental conditions, dietary SCP do not influence carcinogenesis in rats.
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