Although different carbohydrates do produce differing glycemic responses, to be of benefit clinically, this benefit should translate into long-term improvements in glycemia or lipids. Table 2 summarizes the research comparing high versus low GI diets on glucose and lipid outcomes in studies with a minimum duration of 2 weeks [14-28]. Examining the data reveals no clear trend in outcome benefits. A meta-analysis of GI diets in persons with diabetes reported a reduction in HbA1c by 0.4% units (a 7.4% decrease) from
Table 3. Epidemiologic studies on glycemic index (GI), glycemic load (GL), and fiber and effect on insulin resistance and risk of diabetes
Nurses Health Study 1997 
Health Professional Study
Framingham Offspring Cohort 2004 
GI/GL associated with risk of developing diabetes GI/GL associated with risk
GI/GL associated with prevalence of insulin resistance
Atherosclerosis Risk in Communities Study (ARIC) 2002 
No association GI/GL and risk developing diabetes
No association between GI and fasting insulin No association between GI/GL with insulin-resistant diseases; fiber beneficial association No association between GI/GL and insulin resistance; fiber beneficially associated with insulin resistance No association between GI/GL and insulin sensitivity and adiposity; fiber beneficial association
Inter99 Study 2005 
Resistance and Atherosclerosis Study (IRAS) 2005 
Iowa Women's Study 2000 
Zutphen Elderly Study 2000 
low GI diets compared to high GI diets and a reduction in HbA1c from baseline by 0.35% units . However, included in the meta-analysis are two studies not included in table 2. In the study by Gilbertson et al. , there were no significant differences in the GI of the diets at study end in the study arms. Thus, it is questionable if the lowering of the GI in one study arm can be attributed to differences in GI. In the study by Giacco et al. , 50g of fiber are included in the low GI group. Fiber and GI are not necessarily the same and therefore it is unknown if the effect on glucose response is due to the low GI of the diet or to the fiber content. These two studies account for 47% of the total subjects in the meta-analysis.
Early epidemiological studies suggest that a low GI/GL diet may play a role in the prevention of diabetes [4, 5]. Table 3 summarizes the outcomes from later studies and from countries other than the United States. Whereas, 3 studies report a positive association between low GI/GL diets and the risk of developing diabetes or insulin resistance, 5 do not. Interestingly, in 3 studies fiber was positively associated with insulin sensitivity, whereas GI/GL was not.
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