Many individuals engage in fasting for its purported health benefits but the effects of fasting on immune cell and whole body metabolism are not well understood in humans. Moreover, how exercising during a prolonged fast impacts immunometabolic outcomes is unclear. This study will determine how a 2 day fast - performed with or without daily exercise - impacts immune cell bioenergetics, immune cell function, and whole-body glycemic control in healthy active individuals.
Aged between 19 and 35 years.
Physically active (engaging in ≥150 minutes of weekly moderate to vigorous physical activity).
History of cardiometabolic diseases or inflammatory diseases (e.g., chronic obstructive pulmonary disease (COPD), rheumatoid arthritis, cardiovascular disease).
Individuals currently following a ketogenic diet, low-calorie diet, periodic fasting regimen, or consuming ketogenic supplements (e.g., exogenous ketone drinks).
Cigarette/vaping smoking.
Physical limitation that will impair the ability of the participant to perform exercise.
Crossover
Fasting + Exercise (FAST+EX): fasting + exercise condition
Other interventionParticipants will complete a 48-hour fast. One hour of exercise will be performed on each morning of the fast.
Fasting only (FAST): Non-exercise fasting condition
Other interventionParticipant will complete a 48-hour fast. No structured exercise will be performed during each of the fasting days.
Monocyte mitochondrial respiration
Mitochondrial respiration will be measured in primary human monocytes using high resolution respirometry before and after a 48-hour fast performed with or without exercise.
Alteration in immune cell functions
Immune cell functions will be assessed with the combination of whole blood cultures treated with lipopolysaccharide (with or without interleukin-10) and the subsequent measurement of cytokine secretion, immune cell counts, and phenotyping via flow cytometry, both before and after 48 hours fast (with and without exercise).
Change in glucose tolerance
Investigate whether exercise performed during a 48-hour fast can reduce the temporary glucose intolerance typically seen after fasting, both in controlled and free-living conditions. Glucose tolerance will be evaluated by measuring capillary glucose levels before, and at 30, 60, and 120 minutes after a mixed meal tolerance test.
Blood pressure
Systolic and diastolic blood pressure, as well as heart rate, will be measured using an automatic blood pressure device at baseline (Day 1), 24 hours into the fast (Day 2), and at the end of the 48-hour fast (Day 3) in both conditions (fasting alone and fasting with exercise).
Rate and level of ketosis
Examine whether performing exercise at the beginning and during a fast can influence the ketone levels achieved after 24 and 48 hours of fasting. Capillary beta-hydroxybutyrate (a ketone body) will be measured via finger pricks using the Freestyle Neo ketone test.
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