Interstitial glucose concentrations and hypoglycemia during 2 days of caloric deficit and sustained exercise: a double-blind, placebo-controlled trial

Abstract

Military personnel and some athlete populations endure short-term energy deficits from reduced energy intake and/or increased energy expenditure (EE) that may degrade physical and cognitive performance due to severe hypoglycemia (<3.1 mmol/l). The extent to which energy deficits alter normoglycemia (3.9-7.8 mmol/l) in healthy individuals is not known, since prior studies measured glucose infrequently, not continuously. The purpose of this study was to characterize the glycemic response to acute, severe energy deficit compared with fully fed control condition, using continuous glucose monitoring (CGM). For 2 days during a double-blind, placebo-controlled, crossover study, 23 volunteers (17 men/6 women; age: 21.3 ± 3.0 yr; body mass index: 25 ± 3 kg/m) increased habitual daily EE [2,300 ± 450 kcal/day [means ± SD)] by 1,647 ± 345 kcal/day through prescribed exercise (~3 h/day; 40-65% peak O consumption), and consumed diets designed to maintain energy balance (FED) or induce 93% energy deficit (DEF). Interstitial glucose concentrations were measured continuously by CGM (Medtronic Minimed). Interstitial glucose concentrations were 1.0 ± 0.9 mmol/l lower during DEF vs. FED (P < 0.0001). The percentage of time spent in mild (3.1-3.8 mmol/l) hypoglycemia was higher during DEF compared with FED [mean difference = 20.5%; 95% confidence interval (CI): 13.1%, 27.9%; P = 0.04], while time spent in severe (<3.1 mmol/l) hypoglycemia was not different between interventions (mean difference = 4.6%; 95% CI: -0.6%, 9.8%; P = 0.10). Three of 23 participants spontaneously reported symptoms (e.g., nausea) potentially related to hypoglycemia during DEF, and an additional participant reported symptoms during both interventions. These findings suggest that severe hypoglycemia rarely occurs in healthy individuals enduring severe, short-term energy deficit secondary to heavy exercise and inadequate energy intake.

A comparison of isomaltulose versus maltodextrin ingestion during soccer-specific exercise

“…Indeed, we observed lower HT insulin concentrations in PSE when compared to MDX (Fig. 2 b) and fewer participants experienced hypoglycaemia (defined as glucose concentrations < 3.8 mmol l −1 ; Balijepalli et al 2017 ; Smith et al 2016 ) at 60 min (18 versus 27%). Moreover, the change in glycaemia from HT was also less in PSE compared to MDX (− 4%; − 0.2 ± 0.75 mmol l −1 versus − 19%; − 1.0 ± 1.31 mmol l −1 ; P = 0.015) at 60 min (Fig.…”

Physiological and psychological determinants of whole-body endurance exercise following short-term sustained operations with partial sleep deprivation

“…Considering that the locomotive muscle aerobic metabolism, as determined by the NIRS measures on the vastus lateralis, was not perturbed by SUSOPS, the greater pulmonary O 2 values were probably attributable to higher metabolic demands of other tissues; for instance, of the metabolic costs associated with the exaggerated exercise hyperpnoea and the hyperkinetic circulation in the SUSOPS trials. It is also plausible that, following SUSOPS, the amount of liver and skeletal muscle glycogen was relatively low, as suggested by the lower RER (i.e., enhanced rate of lipolysis) and capillary [La] (Smith et al 2016 ; Rognum et al 1981 ); a condition that may explain, at least partly (Bahr et al 1991 ), the increase in submaximal values of systemic O 2 , as well as of HR, E and RPE (Lima-Silva et al 2011 ; Carter et al 2004 ; Heigenhauser et al 1983 ).…”

“…Specifically, military-based studies have suggested that a prolonged period of sustained operations (SUSOPS) degrades cognitive and physical performance; thus, aerobic work capacity is typically suppressed (Guezennec et al 1994 ; Nindl et al 2002 ). Physiological and psychological modifications, such as low energy substrate availability (Smith et al 2016 ; Rognum et al 1981 ), muscle-mass loss (Johnson et al 1994 ), hypovolemia and/or hypohydration (Lieberman et al 2005 ; Wittels et al 1996 ), functional peripheral deteriorations (e.g., impaired mitochondrial efficiency; Fernstrom et al 2007 ), and decreased motivation and enhanced effort perception (Lucas et al 2009 ; Lieberman et al 2005 , 2006 ), have been regarded as potential determinants of physical performance in such multi-stressor conditions.…”

The Use of Continuous Glucose Monitors in Sport: Possible Applications and Considerations

“…It is understood that acute reductions in BG occur as a result of imbalances between EI and total energy expenditure and, thus, may be an important early warning sign that LEA is disturbing metabolic homeostasis (Koehler et al, 2016;Loucks, 2006;Loucks & Thuma, 2003). The effect of an acute (2 days), severe energy deficit (EI 270 kcal/day; total daily energy expenditure ∼4,000 kcal/day) on interstitial glucose responses using CGMs has been investigated in 23 healthy military personnel (Smith et al, 2016). Interstitial glucose concentrations were lower (4.1 ± 0.8 mmol•L −1 vs. 5.0 ± 1.2 mmol•L −1 ) and mean percentage of time in hypoglycemia (< 3.9 mmol•L −1 ) higher (38.7% ± 25.0% vs. 13.6% ± 13.7%) during severe energy deficit compared with energy balance, indicating perturbations to interstitial glucose control following a period of restricted EI coupled with increased exercise energy expenditure (Smith et al, 2016).…”