Novel and useful compositions derived from rooibos for treating diabetes are provided. The present invention is particularly concerned with the treatment of Type 2 diabetes. The invention provides a new use for aspalathin and rutin and compositions containing them for use in the prevention and treatment of diabetes. The invention provides an anti-diabetic agent, an anti-diabetic composition containing the anti-diabetic agent, a foodstuff or beverage containing the anti-diabetic agent, a method for preventing or treating diabetes or impaired glucose tolerance, and a method of decreasing blood glucose level. The anti-diabetic agent may be an extract from rooibos (Aspalathus spp.), aspalathin as such or in combination with rutin.