Effects of dietary carbohydrate on 1,5-anhydroglucitol in a population without diabetes: results from the OmniCarb trial

Aims: To determine the effects of dietary changes in amount and type of carbohydrate on 1,5-anhydroglucitol levels. Methods: We conducted an ancillary study to a completed, randomized clinical trial in overweight and obese adults without diabetes (N=159). Using a crossover design, participants were fed each one of four diets in turn for 5 weeks, with 2-week washout periods inbetween. The four diets were: high glycaemic index (≥65) with high proportion of carbohydrate (58% kcal) (GC); low glycaemic index (GI≤45) with low proportion of carbohydrate (40% kcal) (gc); low glycaemic index with high proportion of carbohydrate (gC); and high glycaemic index with low proportion of carbohydrate (Gc). Plasma 1,5-anhydroglucitol levels were measured at baseline and after each feeding period. Results: At baseline, participants had a mean age of 53 years (53% women, 52% non-Hispanic black, 50% obese). Their mean fasting glucose and 1,5-anhydroglucitol levels were 97 mg/dl (5.4 mmol/l) and 18.6 μg/mL (113.3 μmol/l), respectively. Compared with baseline, each of the four diets reduced 1,5-anhydroglucitol by a range of –2.4 to –3.7 μg/mL (–14.6 to –22.5 μmol/l); all P <0.001). Reducing either glycaemic index or proportion of carbohydrate lowered 1,5-anhydroglucitol levels. These effects were additive, such that reducing both glycaemic index and proportion of carbohydrates decreased 1,5-anhydroglucitol by –1.31 μg/mL [95% CI: –1.63, –0.99; P<0.001 or –8.0 (–9.9, –6.0) μmol/l]. Furthermore, these effects were confirmed in a subgroup of participants with 12-h glucose monitoring and no documented hyperglycaemia (fasting glucose <160 mg/dl or 8.9 mmol/l). Conclusions: Both type and amount of dietary carbohydrate affect 1,5-anhydroglucitol plasma concentrations in adults without diabetes. This finding contradicts the long-standing notion that 1,5-anhydroglucitol remains at constant concentrations in the blood in the absence of hyperglycaemic excursions. (Clinical trials registry number: NCT00051350).