Isomaltulose improves postexercise glycemia by reducing CHO oxidation in T1DM
Journal Title: Med Sci Sports Exerc
Year: 2010
Page numbers:
doi: 10.1249/MSS.0b013e3181eb6147

Summary of Background and Research Design

Background:Individuals with type 1 diabetes (T1DM) are encouraged to consume carbohydrates (CHO) to prevent hypoglycemia (blood glucose [BG] concentration ≤ 3.5 mmol/L) during or after exercise. However, research comparing the effects of specific types of CHO is limited. Carbohydrates with a low glycemic index (LGI) are preferred for individuals with T1DM because they digest at slower rates than CHO with a high glycemic index (HGI). Isomaltulose (ISO) is a disaccharide sucrose-isomer with a 20% to 25% slower hydrolysis rate than that of sucrose. Consumption of ISO has been shown to alter exercising fuel metabolism in non-T1DM individuals.

Hypothesis: The authors hypothesized that consumption of ISO may spare both endogenous and exogenous CHO use and increase fat oxidation in subjects with T1DM, resulting in better preservation of BG during the post-exercise period compared with a HGI CHO such as dextrose (DEX).

Subjects: 8 subjects (7 males, 1 female) with T1DM who exercised regularly, had moderate glycemic control, and had no significant complications participated in the study. Mean age ± standard deviation (SD) was 35 ± 2 years, and mean body mass index (BMI) ± SD was 26 ± 0.3 kg/m2. Subjects were instructed to administer 1.30 ± 0.06 U insulin/10 g CHO.

Experimental design: Randomized, crossover

Treatments and protocol: Subjects initially participated in a continuous incremental treadmill assessment test to determine peak rate of oxygen consumption (VO2peak), peak heart rate (HRpeak), and respiratory exchange ratio (RER). After 2 preliminary tests spaced 7 days apart, study subjects administered 25% of their normal rapid-acting insulin dose and then consumed 75 g DEX (GI 96) or ISO (GI 32) in 750 mL water. Two hours later, a pre-exercise blood sample was taken, after which subjects performed 45 minutes of steady-state treadmill running at a velocity equivalent to 80% ± 1% VO2peak. Heart rate and breath-by-breath data were collected and analyzed for CHO and lipid oxidation. Subjects then remained at rest for a 3-hour post-exercise period, during which additional blood samples were taken at 0, 5, 15, 30, 60, 120, and 180 minutes.

Summary of research findings:
  • Subjects who consumed ISO and DEX had similar resting rates of oxygen consumption and carbon dioxide production (P = .46).
  • Exercise intensity was similar in both groups (ISO 80.8% ± 0.9% VO2peak vs DEX 78.2% ± 0.9% VO2peak; P = .12).
    • However, oxygen use during exercise was higher in the ISO group (P = .05).
  • Mean peak BG was lower in the ISO group (δ+4.5 ± 0.4 mmol/L vs δ+9.1 ± 0.6 mmol/L, P < .01) and occurred 30 minutes later (120 min vs 90 min) compared with the DEX group.
  • During the final 10 minutes of exercise, mean CHO oxidation rates were lower in the ISO group (2.85 ± 0.07 g/min vs 3.18 ± 0.08 g/min; P < .05) and mean lipid oxidation rates were higher in the ISO group (0.33 ± 0.03 g/min vs 0.20 ± 0.03 g/min; P < .05) compared with the DEX group.
  • Post-exercise BG was lower in the ISO group than in the DEX group for the entire 180-minute period (BG area under the curve [21% ± 3% lower] and for mean BG concentration [3.0 ± 0.4 mmol/L lower], P < .05).
  • There were no episodes of hypoglycemia (BG ≤ 3.5 mmol/L) during the 2-hour rest period or during treadmill running with either treatment. In the postexercise period there were 2 episodes for the DEX treatment (5 and 120 min) and 2 for the ISO treatment (30 and 180 min). The hypoglycemia episodes at 120 and 180 min postexercise both occurred in the same subject.

Interpretation of findings/Key practice applications:

ISO ingestion resulted in BG levels that were lower in the pre-exercise period and were closer to the baseline pre-exercise value in the 3-hour post-exercise period compared with DEX. It is noteworthy that these differences were observed via the use of venous and not capillary blood samples. Given the greater sensitivity of capillary blood versus venous blood to detect differences in postprandial glycemia, these differences in BG might have been even more pronounced with capillary blood sampling. In any case, these results most likely reflect the slower rates of hydrolysis and absorption for ISO relative to DEX. Reduced postprandial glucose excursions prevented BG from reaching hyperglycemic concentrations (≥ 12.4 mmol/L) after ISO ingestion. This observation is significant to the management of T1DM because maintaining a condition as close to euglycemia as possible is fundamentally important, especially for individuals with T1DM undertaking physical exercise.
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