Endocrinol Metab.  2021 Aug;36(4):745-756. 10.3803/EnM.2021.405.

Effects of Intermittent Fasting on the Circulating Levels and Circadian Rhythms of Hormones

• Kim BH
• Joo Y
• Kim MS
• Choe HK
• Tong Q
• Kwon O

• KMID: 2519662
• DOI: http://doi.org/10.3803/EnM.2021.405

Abstract

Intermittent fasting has become an increasingly popular strategy in losing weight and associated reduction in obesity-related medical complications. Overwhelming studies support metabolic improvements from intermittent fasting in blood glucose levels, cardiac and brain function, and other health benefits, in addition to weight loss. However, concerns have also been raised on side effects including muscle loss, ketosis, and electrolyte imbalance. Of particular concern, the effect of intermittent fasting on hormonal circadian rhythms has received little attention. Given the known importance of circadian hormonal changes to normal physiology, potential detrimental effects by dysregulation of hormonal changes deserve careful discussions. In this review, we describe the changes in circadian rhythms of hormones caused by intermittent fasting. We covered major hormones commonly pathophysiologically involved in clinical endocrinology, including insulin, thyroid hormones, and glucocorticoids. Given that intermittent fasting could alter both the level and frequency of hormone secretion, decisions on practicing intermittent fasting should take more considerations on potential detrimental consequences versus beneficial effects pertaining to individual health conditions.

Keyword

Intermittent fasting; Circadian rhythm; Insulin; Thyroid hormones; Glucocorticoids

Figure

• 

  Fig. 1 Graphs illustrating the relative levels of hormones during acute fasting in human (dashed line). Fasting started at different time points (an arrow head in each graph): (A) insulin, fasting onset at 6:00 PM [42], (B) triiodothyronine, fasting onset at 11:30 PM [61], (C) cortisol, fasting onset at 8:30 AM [78]. For comparison, the hormonal level during regular feeding (solid line; breakfast at 7:00 AM, lunch at 12:00 PM, and dinner at 6:00 PM) was depicted in accordance with the clock time. X axis means duration from fasting (hours).

• 

  Fig. 2 Estimated changes in hormones after long-term intermittent fasting in human (dashed line). X axis presents daily light cycle: light box means daytime (6:00 AM–6:00 PM) and dark box indicates nighttime (6:00 PM–6:00 AM). Normal circadian rhythms of hormones were presented with solid line. (A) Insulin; postprandial peaks were depicted after breakfast (7:00 AM), lunch (12:00 PM), and dinner (6:00 PM). (B) Triiodothyronine. (C) Cortisol.

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