Objective To evaluate the effects of dietary intervention with low glycemic index (LGI) and low glycemic load (LGL) on dietary knowledge and dietary modification of patients with type 2 diabetes mellitus (T2DM).Methods This study was a cluster randomized controlled study.From June to September 2010,105 T2DM patients were randomly sampled from 3 residential areas (n =35 in each) in Jin Pen Ling community,Changsha,Hunan province and divided into three groups with a random number table:whole-day dietary intervention group (group A,n =35),breakfast dietary intervention group (group B,n =35),and control group (group C,n =35).Interventions included 3-month health education and dietary intervention.Dietary knowledge,dietary oils,glycemic index (GI),and glycemic load (GL) of the three groups were compared before and after intervention.Results Before intervention,all the three groups showed a low level of knowledge about GI (57.7 ％),and high levels of average GI value of each meal (69.71 ± 8.55),GL value per day (132.45 ± 16.25),and daily cooking oil intake [(39.95 ± 20.64)g].The average knowledge level about GI increased after intervention in both group A (96.3％ vs.57.1％,P ＜0.05) and group B (94.5％ vs.60.5％,P＜0.05),but not in group C (54.8％ vs.55.3％,P＞0.05).The reduction of daily cooking oilintake in group A was larger than those in group B and group C [(7.81 ± 3.91) g vs.(-5.12 ± 1.37) g,(7.81 ± 3.91) g vs.(-3.45 ± 5.95) g,both P ＜ 0.05];so was the average GI value of each meal [group A,(5.95±2.27);groupB (-0.85±1.87);groupC,(-2.87±1.93);allP＜0.05].The changes of GL values in group A (11.31 ±4.31) was better than in group B (1.23 ±27.82) and group C (-0.43 ± 18.40)(both P ＜0.05).Conclusions The average GI value,GL value,and daily cooking oil intake of T2DM patients were all at a high level before intervention,while the level of knowledge about GI was at a low level.Health education providing GI knowledge may effectively improve the knowledge about GI in T2DM patients,while LGI and LGL dietary intervention may promote diet modification.Whole-day dietary intervention may be more effective than breakfast intervention.