The Effects of Exercise on β-Hydroxybutyrate Concentrations over a 36-h Fast: A Randomized Crossover Study

Abstract

PurposeThis study assessed β-hydroxybutyrate (BHB) concentration during a short-term fast and the degree to which an initial bout of exercise influences the rate of ketogenesis.MethodsTwenty subjects (11 male, 9 female) completed two 36-h fasts, with one protocol requiring the subject to complete a treadmill exercise session at the beginning of the fast. BHB levels were assessed via portable meter every 2 h, along with mood and hunger ratings. Venipuncture was performed every 12 h.ResultsThe mean (SD) areas under the curve for BHB concentration were 19.19 (2.59) mmol·L−1 (nonexercised) and 27.49 (2.59) mmol·L−1 (exercised), yielding a difference of 8.30 mmol·L−1 between conditions (95% posterior probability interval (PPI), 1.94 to 14.82 mmol·L−1; posterior probability (PP) = 0.99). The mean (SD) times to BHB concentration of 0.5 mmol·L−1 were 21.07 (2.95) h (nonexercised) and 17.5 (1.69) h (exercised), a 3.57-h difference (95% PPI, −2.11 to 10.87 h; PP = 0.89). The differences in area under the curve between conditions were 5.07 μU·mL−1 (95% PPI, −21.64 to 36.18 μU·mL−1; PP = 0.67) for insulin, 97.13 pg·mL−1 (95% PPI, 34.08 to 354.21 pg·mL−1; PP = 0.98) for glucagon, and 20.83 (95% PPI, 4.70 to 24.22; PP = 0.99) for the insulin/glucagon ratio.ConclusionsCompleting aerobic exercise at the beginning of a fast accelerates the production of BHB throughout the fast without altering subjective feelings of hunger, thirst, stomach discomfort, or mood. Insulin and the insulin/glucagon ratio experience a marked reduction within the first 12 h of fasting and was not altered with exercise. Thus, exercising at the beginning of a fast may improve the metabolic outcomes of fasting.

The Effects of Exercise on Appetite-Regulating Hormone Concentrations over a 36-h Fast in Healthy Young Adults: A Randomized Crossover Study

“…However, the relationship between hormone concentration and hunger seems to be complicated and the changes that we observed in GLP-1 and ghrelin did not seem to be enough to alter the subjective rating of hunger. These results, coupled with our previously reported findings [20], indicate that starting a fast with exercise accelerates the metabolic substrate switching observed during a fast without negatively impacting the subjective and physiological drives to consume food. These results may educate individuals participating in a variety of approaches to fasting (i.e., intermittent fasting, alternate day fasting, or time-restricted feeding), and potentially improve adherence and sustainability over time.…”

“…We also describe the overall change in hormone concentrations over the course of a 36-h fast. These results represent secondary outcomes to data that has been previously reported [20].…”

“…We previously published the primary outcomes of this study. These results show that initiating a fast with a bout of exercise accelerated some of the metabolic changes that occur during fasting [20]. Specifically, exercise reduced the time to metabolic ketosis from 21.0 h to 17.5 h postprandially.…”

“…Results from our lab recently found that a state of nutritional ketosis could be reached approximately 3.5 h sooner when a fast was initiated with exercise [20]. The metabolic substrate switching associated with fasting can be achieved more quickly with exercise at the beginning of a fast without any negative impact on hormones that drive hunger.…”

Low carbohydrate high fat ketogenic diets on the exercise crossover point and glucose homeostasis

“…The opposite is observed in persons with type-2 diabetes whose fitness levels are very low; whose blood glucose and insulin concentrations are high; in whom insulin action is impaired; and who have low rates of fat oxidation, even during low-intensity exercise when fat oxidation should be maximized ( Ghanassia et al, 2006 ). The availability of FFA is a key determinant of fat oxidation and thus ketogenesis, but only in low-insulin environments in which insulin’s direct roles in attenuating both adipocyte lipolysis, hepatic fat oxidation and ketogenesis, and whole-body lipid oxidation ( Owen et al, 1969 ; Balasse, 1979 ; Moller, 2020 ; Deru et al, 2021 ; Hengist et al, 2022 ) are removed. For example, Hengist et al ( Hengist et al, 2022 ) have recently reported that a single isocaloric and isoprotein LCHF meal increases fat oxidation and blood ketone concentrations and lowered carbohydrate oxidation post-prandially but only when blood insulin concentrations are very low.…”