The use of different reference foods in determining the glycemic index of starchy and non-starchy test foods

BACKGROUND Glycemic index (GI) is intended to be a property of food but some reports are suggestive that GI is influenced by participant characteristics when glucose is used as a reference. OBJECTIVE To examine the influence of different reference foods on observed GI. DESIGN The GIs of five varieties of rice and a sugary beverage (LoGiCane™) were tested in 31 European and 32 Chinese participants using glucose or jasmine rice as reference foods. The GIs of two ready-to-eat breakfast cereals (Kellogg's cornflakes and Sustain) were tested in 20 younger and 60 older people using glucose or Sustain as reference foods. RESULTS The GIs of rice tended to be higher in the Chinese compared with the Europeans when glucose was used as a reference (jasmine 80 vs 68, P = 0.033; basmati 67 vs 57, P = 0.170; brown 78 vs 65, P = 0.054; Doongara 67 vs 55, P = 0.045; parboiled 72 vs 57, P = 0.011). There were no between-group differences in GI when jasmine rice was the reference. The GIs of breakfast cereals tended to be lower in younger compared with older groups (cornflakes 64 vs 81, P = 0.008; Sustain 56 vs 66, P = 0.054). There was no between-group difference in the GI of cornflakes when Sustain was the reference (cornflakes 115 vs 120, P = 0.64). There was no ethnic difference in GI when glucose was the reference for another sugary food (LoGiCane™ 60 vs 62; P = 0.69). CONCLUSIONS A starchy reference may be more appropriate than a glucose beverage when attempting to derive universally applicable GI values of starchy foods. TRIAL REGISTRATION The Chinese/European trial is registered with the Australian New Zealand Clinical Trials Registry as ACTRN12612000519853.