1.
Flipping the Metabolic Switch: Understanding and Applying the Health Benefits of Fasting.
Anton, SD, Moehl, K, Donahoo, WT, Marosi, K, Lee, SA, Mainous, AG, Leeuwenburgh, C, Mattson, MP
Obesity (Silver Spring, Md.). 2018;(2):254-268
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Abstract
OBJECTIVE Intermittent fasting (IF) is a term used to describe a variety of eating patterns in which no or few calories are consumed for time periods that can range from 12 hours to several days, on a recurring basis. This review is focused on the physiological responses of major organ systems, including the musculoskeletal system, to the onset of the metabolic switch: the point of negative energy balance at which liver glycogen stores are depleted and fatty acids are mobilized (typically beyond 12 hours after cessation of food intake). RESULTS AND CONCLUSIONS Emerging findings suggest that the metabolic switch from glucose to fatty acid-derived ketones represents an evolutionarily conserved trigger point that shifts metabolism from lipid/cholesterol synthesis and fat storage to mobilization of fat through fatty acid oxidation and fatty acid-derived ketones, which serve to preserve muscle mass and function. Thus, IF regimens that induce the metabolic switch have the potential to improve body composition in overweight individuals. Moreover, IF regimens also induce the coordinated activation of signaling pathways that optimize physiological function, enhance performance, and slow aging and disease processes. Future randomized controlled IF trials should use biomarkers of the metabolic switch (e.g., plasma ketone levels) as a measure of compliance and of the magnitude of negative energy balance during the fasting period.
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The effects of fasting on metabolism and performance.
Maughan, RJ, Fallah, J, Coyle, EF
British journal of sports medicine. 2010;(7):490-4
Abstract
An overnight fast of 8-10 h is normal for most people. Fasting is characterised by a coordinated set of metabolic changes designed to spare carbohydrate and increase reliance on fat as a substrate for energy supply. As well as sparing the limited endogenous carbohydrate, and increased rate of gluconeogenesis from amino acids, glycerol and ketone bodies help maintain the supply of carbohydrate. Many individuals undergo periodic fasts for health, religious or cultural reasons. Ramadan fasting, involving 1 month of abstention from food and fluid intake during daylight hours, is practised by a large part of the world population. This period involves a shift in the pattern of intake from daytime to the hours of darkness. There seems to be little effect on overall daily dietary intake and only small metabolic effects, but there may be implications for both physical and cognitive function. The limited evidence suggests that effects of Ramadan-style fasting on exercise performance are generally small. This needs to be balanced, however, against the observation that small differences in performance are critical in determining the outcomes of sporting events. Studies involving challenging sporting events (prolonged sustained or intermittent high-intensity events, hot and humid environments) are needed. Increases in subjective sensations of fatigue may be the result of loss of sleep or disruption of normal sleep patterns. Modifications to the competition timetable may minimise or even eliminate any effect on performance in sport, but there may be negative effects on performance in some events.