The aim of this study was to investigate the effect of high and low fat diets on glucose tolerance test on healthy human beings.The study was carried out on 18 volunteers( subjects), their ages between 23-31 years with an average body weight.They were receiving reasonable amount of fat in their normal food ,they were divided into two groups.The first group ate a low fat diet providing less than 30g of fat per day for nine days. After fifteen days period on their usual dietary regimen the volunteers ate a high fat diet for nine days. The second group of volunteers were maintained on a reversed dietary regimen. i.e. high fat before low fat diet. this second group was carefully assessed beforehand to ensure only those whose fat intake was usually less than 130g of fat.