Effect of carbohydrate-energy replacement on glycaemic control following high-intensity interval training : does lactose improve glycaemic control in comparison to sucrose? : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science majoring in Nutrition and Dietetics, Massey University, Auckland

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Background. High-intensity interval training (HIIT) is an increasingly popular training method due to its efficient, rigorous nature and proven benefit on glycaemic control and insulin sensitivity. There has been some research into how remaining in a carbohydrate-energy deficit post-exercise influences next-day glycaemic control, however there has been minimal research into how different types of carbohydrates affects glycaemic control. Lactose has a low glycaemic index of 46 which has been associated with both lower and more stable post-prandial blood-glucose concentrations. However, the effect of both lactose and HIIT on glycaemic control remains to be investigated. Aims. The primary aim of the study were to identify the extent to which replenishing the exercise-induced energy deficit with different carbohydrates alters next-day glycaemic control following standard meal ingestion. Specifically, we were interested in evaluating if there was a difference in the glycaemic control in response to ingesting the milk sugar lactose compared to when ingesting ordinary sugar sucrose; two sugars with known different effects on the post-prandial blood-glucose response and liver metabolism. Methods. Eight sedentary, untrained, lactose tolerant participants (n=4 males; n=4 females) with a VO₂max 29 ± 8 ml·kgˉ¹·minˉ¹ aged 20-70 years completed a crossover comprising three, two-day trials involving exercise and continuous glucose monitoring (CGM; Medtronic Guardian Connect, Northridge, CA, USA). Day 1 consisted of a HIIT session at 1700 h, comprising of 10 x 1-min cycle intervals at 80% maximal power, with 1 min recovery at 30% maximal power for 20 min total. A post-exercise carbohydrate beverage was ingested containing either lactose, sucrose, or a non-caloric control. Day 2 consisted of an oral glucose tolerance test (OGTT) at 0700 h, whereby a 75-g glucose drink was ingested after an overnight fast with blood samples collected overtaken ever 0, 30, 60, 90 and 120 min. To control for other glycaemic effects, a standardised controlled diet was consumed across the entire two-day period. Results. There was a large mean increase in post-exercise glycaemic response represented by the 3-h area under the curve (AUC) with lactose (normalised AUC 2828 mmol·Lˉ¹·1hˉ¹, ±90% confidence interval 1741; d=1.62, ±90% confidence interval 1.02) and sucrose (5172 mmol·Lˉ¹·1hˉ¹, ±1877; d=2.03, ±2.19) ingestion compared to control (remaining in a carbohydrate deficit after HIIT), with the lactose-sucrose contrast eliciting a lower moderate response (-1344 mmol·Lˉ¹·1hˉ¹, ±1719; d=-0.65, ±1.00). Overnight glycaemia (22:00 to 07:00 h) post-exercise was moderately greater after the consumption of sucrose (5730 mmol·Lˉ¹·1hˉ¹, ±4685; d=0.61, ±0.57) and lactose (6202 mmol·Lˉ¹·1hˉ¹, ±5329; d=0.66, ±0.64), relative to control, while the lactose-sucrose contrast was inconclusive (472 mmol·Lˉ¹·1hˉ¹, ±4845; d=0.00, ±0.58). The next-day post-prandial glycaemic response to the standard meals revealed largely non-clear differences between carbohydrate types and the carbohydrates and control. Meanwhile, there was a trivial-moderate reduction in overall (7:00 – 24:00 h) mean glycaemia with post-exercise lactose was (-1539, ±2349; d=-0.27, ±0.40), while the sucrose-control contrast was unclear (505, ± 3503; 0.06, ±0.59). Conclusion. In sedentary adults, overnight glycaemic responses provided evidence to suggest improved glycaemic response when consuming lactose compared to when remaining in a carbohydrate deficit after HIIT; an effect that trended lower compared to sucrose. However, the next day OGTT and post-prandial glycaemic responses were inconclusive. While the data is provisional, the results suggest that remaining in a carbohydrate-energy deficit after HIIT provides benefit to overnight glycaemia, and more research is required into the role of lactose.
Figure 1 (=Gillen et al., 2021 Fig 1) was removed for copyright reasons. Figure 2 is reproduced under a Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License.
exercise, glycaemic control, post-prandial, lactose, sucrose, continuous glucose monitoring, carbohydrate-energy deficit