Reply to Brighenti F et al.

Dear Editor:

We thank the signatories on behalf of the International Carbohydrate Quality Consortium for their comments on our recently published article (1). The mission of this consortium is “to support, summarize and disseminate the science around dietary carbohydrate and health with a focus on quality and to harmonize the work of scientists from academia, industry and government” (2). In its consensus paper (3), the consortium strongly recommended the inclusion of concepts of glycemic index (GI) and glycemic load (GL) in “dietary guidelines, country-specific GI databases, food composition tables and food labels” (3).

The consortium regularly takes umbrage with conclusions not consistent with their consensus statement, including those of the European Food Safety Authority, which concluded that “evidence is still inconclusive on the role of the glycemic index and glycemic load in maintaining weight and preventing diet-related diseases” (4), Health Canada, which concluded that “inclusion of the GI value on the label of eligible food products would be misleading and would not add value to nutrition labeling and dietary guidelines in assisting consumers to make healthier food choices” (5), and numerous peer-reviewed publications (6–21).

This most recent letter to the editor states that “the results clearly demonstrate that, once understood that the GI is a property of food, it must be calculated following a stable protocol in order to provide meaningful results.” First, we question the statement that the GI value is a property of food alone. We (22) and others (23, 24) have documented that intraindividual variability in response to a test food introduces at least an equivalent amount of variability to the determination of a GI value as interindividual variability among individuals. More recently, we reported a significant contribution of baseline glycated hemoglobin levels and insulin index to the variability in GI value determinations (22). Hence, GI values calculated in response to a food challenge cannot be considered a property solely of the food, but are also mediated by the metabolic response of an individual to the food. In addition, foods and beverages are rarely consumed in isolation. We (25) and others (26, 27) have observed that foods consumed in combination alter the GI value determination of an individual food. These findings were supported by Trico and Natali (28) in response to our publication. In our most recent work (1) we identified an additional factor that alters the GI value of an individual food: foods eaten prior to the determination. This observation is not without precedent (29, 30). Collectively, these data raise questions as to whether using multiple individual GI values established under highly controlled conditions can be used to accurately predict the glycemic response to meals or an entire day's food intake summarized by a single GI or GL value, and whether those data can be used to draw “meaningful” conclusions about the relationship between the GI or GL value and chronic disease risk (1, 25–27, 29–31).

The concept of GI was first introduced in 1981. Since then questions have been raised as to whether it should be used to guide food choices (22–27, 32). Various members of the International Carbohydrate Quality Consortium have challenged almost every study that has expressed opinions contradictory to theirs (6–21). A number of these members have financial conflicts of interest owing to books, testing services and research funding. As stated previously (33), we cannot help but wonder whether some of this activity and allegiance bias to their position has shaped their interpretation of the data.