Notbohm et al. Journal of the International Society of Sports Nutrition (2021) 18:38 https://doi.org/10.1186/s12970-021-00439-z RESEARCH ARTICLE Open Access Metabolic, hormonal and performance effects of isomaltulose ingestion before prolonged aerobic exercise: a double-blind, randomised, cross-over trial Hannah L. Notbohm1, Joshua F. Feuerbacher1, Finn Papendorf1, Nils Friese1, Mats W. Jacobs1, Hans-Georg Predel2, Jonas Zacher2, Wilhelm Bloch1 and Moritz Schumann1* Abstract Background: Isomaltulose has been discussed as a low glycaemic carbohydrate but evidence concerning performance benefits and physiological responses has produced varying results. Therefore, we primarily aimed to investigate the effects of isomaltulose ingestion compared to glucose and maltodextrin on fat and carbohydrate oxidation rates, blood glucose levels and serum hormone concentrations of insulin and glucose-dependent insulinotropic polypeptide (GIP). As secondary aims, we assessed running performance and gastrointestinal discomfort. Methods: Twenty-one male recreational endurance runners performed a 70-min constant load trial at 70% maximal running speed (Vmax), followed by a time to exhaustion (TTE) test at 85% Vmax after ingesting either 50 g isomaltulose, maltodextrin or glucose. Fat and carbohydrate oxidation rates were calculated from spiroergometric data. Venous blood samples for measurement of GIP and insulin were drawn before, after the constant load trial and after the TTE. Capillary blood samples for glucose concentrations and subjective feeling of gastrointestinal discomfort were collected every 10 min during the constant load trial. (Continued on next page) * Correspondence: [email protected] 1Department of Molecular and Cellular Sports Medicine, German Sport University Cologne, Am Sportpark Müngersdorf 6, 50933 Cologne, Germany Full list of author information is available at the end of the article © The Author(s). 2021 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Notbohm et al. Journal of the International Society of Sports Nutrition (2021) 18:38 Page 2 of 10 (Continued from previous page) Results: No between-condition differences were observed in the area under the curve analysis of fat (p = 0.576) and carbohydrate oxidation rates (p = 0.887). Isomaltulose ingestion led to lower baseline postprandial concentrations of blood glucose compared to maltodextrin (percent change [95% confidence interval], − 16.7% [− 21.8,-11.6], p < 0.001) and glucose (− 11.5% [− 17.3,-5.7], p = 0.001). Similarly, insulin and GIP concentrations were also lower following isomaltulose ingestion compared to maltodextrin (− 40.3% [− 50.5,-30.0], p = 0.001 and − 69.1% [− 74.3,-63.8], p < 0.001, respectively) and glucose (− 32.6% [− 43.9,-21.2], p = 0.012 and − 55.8% [− 70.7,-40.9], p < 0.001, respectively). Furthermore, glucose fluctuation was lower after isomaltulose ingestion compared to maltodextrin (− 26.0% [− 34.2,-17.8], p < 0.001) and glucose (− 17.4% [− 29.1,-5.6], p < 0.001). However, during and after exercise, no between-condition differences for glucose (p = 0.872), insulin (p = 0.503) and GIP (p = 0.244) were observed. No between-condition differences were found for TTE (p = 0.876) or gastrointestinal discomfort (p = 0.119). Conclusion: Isomaltulose ingestion led to lower baseline postprandial concentrations of glucose, insulin and GIP compared to maltodextrin and glucose. Consequently, blood glucose fluctuations were lower during treadmill running after isomaltulose ingestion, while no between-condition differences were observed for CHO and fat oxidation rates, treadmill running performance and gastrointestinal discomfort. Further research is required to provide specific guidelines on supplementing isomaltulose in performance and health settings. Keywords: Glucose, GIP, Insulin, Fat oxidation, Glycaemic index, Endurance exercise, Carbohydrate oxidation, Running Introduction studied, however in exercise settings, especially in For prolonged endurance exercise, carbohydrates repre- healthy runners, knowledge on these effects is more lim- sent one of the main energy sources [1, 2]. Carbohydrates ited. Oral administration of isomaltulose has previously differ in respect to their glycaemic index (GI), i.e. they are been shown to result in lower postprandial blood glu- classified based on their postprandial glucose responses cose and insulin concentrations in healthy and type 2 [3]. Food sources with a lower GI show lower postprandial diabetes mellitus (T2DM) patients [11, 15–17]. During glucose concentrations, as well as a decreased insulin re- exercise, insulin concentrations were shown to be lower sponse [4]. Furthermore, insulin is known to be a major following isomaltulose ingestion throughout a 150 min suppressor of fat oxidation [5], therefore increased fat oxi- cycling trial [18] or not differ during 60 min of cycling dation rates after low-glycaemic meals before exercise [19] compared to sucrose or maltodextrin respectively. have been observed [6]. Consequently, low GI carbohy- The associations of blood glucose, insulin and GIP se- drate sources have been suggested to be beneficial for en- cretion after isomaltulose ingestion have been studied in durance performance due to the preservation of muscle resting conditions [16, 20], however to the best of our glycogen, sustained carbohydrate availability and mainten- knowledge these kinetics have not yet been investigated ance of euglycaemia [4, 6–8], which have been shown to in exercise settings. A reduced secretion of insulin and prevent central fatigue [9]. GIP during exercise would be beneficial to maintain One of the recently investigated low GI carbohydrate constant blood glucose concentrations and prevent sources is isomaltulose, which is a dissacharide com- hyperinsulinaemia. Consequently, these possible effects posed of α-1,6-linked glucose and fructose. The rate of may also explain differences observed in altered sub- hydrolysis and absorption compared to sucrose is con- strate utilisation and improved performance in pro- siderably reduced (up to 85%) [10] due to the α-1,6- longed endurance exercise when comparing isomaltulose glycosidic bond, however, a full absorption is still achiev- and sucrose energy substrates. able [11]. Results regarding altered substrate utilisation However, also only a few exercise studies have focused during exercise after isomaltulose ingestion remain am- on endurance performance and substrate utilisation after biguous. Some studies reported increased fat oxidation isomaltulose ingestion in both healthy and T1DM indi- and lower carbohydrate oxidation at least at some point viduals. The results have been inconclusive, possibly be- during cycling trials (150 min at 50% Wmax [12]or90 cause the glycaemic index or load has previously been min at 60% VO2peak [13]) while others showed no dif- shown not to affect endurance performance or metabolic ference in a short incremental running trial in persons responses, when conditions were matched for carbohy- with Type I Diabetes (T1DM) [14]. drate and energy [21]. Nevertheless, when matched for Effects of isomaltulose ingestion on resting blood glu- carbohydrate intake, one study has found improved time cose and hormone concentrations have been well trial performance after cycling for 90 min at 70% Notbohm et al. Journal of the International Society of Sports Nutrition (2021) 18:38 Page 3 of 10 VO2max following isomaltulose ingestion [13], while Experimental design others have found no difference in cycling and soccer This double-blind randomized-crossover study consisted specific exercise [14, 19, 22] or even impaired cycling of four separate testing sessions: A preliminary ramp test performance [12]. In addition, due to the slow absorp- to assess peak oxygen uptake (VO2peak) and maximal tion rate in the small intestine, isomaltulose has been treadmill running speed (Vmax), as well as three separate suggested to cause gastrointestinal discomfort when experimental trials. The experimental trials were per- ingested during 2 h cycling at 60% Wmax [12], however formed in a randomised and counterbalanced order and other trials have produced contrasting results, when ≤50 consisted of a 70-min constant workload test followed g were ingested before cycling [19] or soccer specific ex- by a time to exhaustion test (TTE). The trials were per- ercise [22]. These inconsistent findings may be partly ex- formed after ingesting either isomaltulose, maltodextrin plained by differences in the timing and the amount of or glucose (Fig.