The effect of livingstone potato (Plectranthus esculenthus N.E.Br) on serum glucose, glycated hemoglobin (HbA1C), serum triglyceride, total cholesterol, high density lipoprotein (HDL), low density lipoprotein (LDL), very low density lipoprotein (VLDL), hepatic malic enzyme (ME), isocitrate