Mann (1) and Brand-Miller et al. (2) state in this issue of Diabetes Care that study subjects have been on previous nutrition therapies before the implementation of low–versus high–glycemic index diets. Although this may be the case, in reviewing the studies included in the meta-analysis, only two studies state this clearly. The first is the study by Fontvieille et al. (3), in which the low–compared with high–glycemic index diet did not improve HbA1c levels over 5 weeks but did result in a decrease in fructosamine (P < 0.05). The second is the study by Heilbronn et al. (4), wherein subjects participated in 12 weeks of energy restriction. After 4 weeks on a weight loss diet similar in composition to the average Australian diet, the subjects were randomized to a low–versus high–glycemic index diet for 8 weeks. At week 12 there was no statistically significant difference in improving glycemic control or weight loss between the low–and high–glycemic index groups. However, if subjects in the reported trials had been on previous food/meal planning approaches, it supports the position of the American Diabetes Association, which holds that there is not evidence “to recommend use of low–glycemic index diets as a primary strategy in food/meal planning,” (5) but as is suggested in the editorial, “glycemic responses of foods can best be used for fine-tuning glycemic control” (6).
There are three questions that need answering in order to assist clinicians in deciding on an intervention approach. First, have two different approaches been compared and which approach has the better outcome? This is the question that Brand-Miller et al. addressed in their meta-analysis (7). They determined that low–glycemic index diets compared with high–glycemic index diets resulted in a small but significant improvement in glycemia (7.4% reduction in glycated proteins). Although Brand-Miller et al. (2) state in their letter that the change in HbA1c is >0.6%, they also state in their conclusion that “after an average duration of 10 weeks, subjects who were following low–glycemic index diets had HbA1c levels ∼0.4% lower than those ingesting a high–glycemic index diet.” But regardless if it is 0.4 or 0.6%, it is still less than other nutrition intervention outcomes cited in the editorial, which report decreases in HbA1c of ∼1–2% and, therefore, are better choices for primary nutrition therapy interventions (8,9).
The second question is of equal importance. What is the expected outcome from the intervention? Table 1 lists the studies included in the meta-analysis with a duration of 6 weeks or longer, their baseline HbA1c values, and the study-end HbA1c value. The low–glycemic index intervention resulted in decreases from baseline to study end in HbA1c ranging from 0.0 to 0.7%, with an average per subject decrease of 0.35%. Readers can decide the clinical significance of this change for themselves.
The final question is also of importance to clinicians. Can people with diabetes implement the intervention outside of a research center? Although not addressed in these studies, one clue does emerge from the reported research. In the longest study (10), which was 1 year, at the end of the year both groups reported diets with similar glycemic index values, suggesting that it may be difficult in the real world to change the overall glycemic index of an individual’s food intake over the long term.
The bottom line is that dietitians and other health care providers will make the decision on which food/meal-planning approach their patients with diabetes will understand, be able to implement, and benefit from. Some individuals will benefit from simple guidelines as to what to eat and when, others will benefit from carbohydrate counting or exchange lists, moderate weight loss, and yes, some may even benefit from the use of low–glycemic index foods. However, the research suggests that the use of low–glycemic index diets is not as effective as other nutrition interventions. And ultimately, people with diabetes will decide what foods they eat and, by using their glucose monitoring results, determine if their choices have led to their target goals.