INTERMITTENT FASTING: HORMONAL IMPACT
INTERMITTENT FASTING: HORMONAL IMPACT
Intermittent fasting (IF) has wide-ranging effects on the body's hormones, touching everything from metabolism to stress and reproduction.
Regarding metabolic hormones, IF reliably lowers insulin levels and improves the body's response to insulin, encouraging a shift from burning glucose to burning fat for energy.
Leptin, the hormone that signals fullness, usually decreases with extended fasting, reflecting lower fat stores and reduced calorie intake.
Ghrelin, often called the "hunger hormone," typically rises while fasting, making you feel hungrier, though this response can mellow out as your body adjusts to the routine.
There’s also evidence that IF increases adiponectin, a hormone tied to better insulin sensitivity and reduced inflammation. Several gut hormones that help control appetite and fullness—like GLP-1, PYY, and CCK—may also be positively influenced by IF, supporting weight management and metabolic health (PLOS ONE; MDPI).
Fasting also interacts with circadian and stress hormones. For example, cortisol—the primary stress hormone—tends to rise during periods of fasting, especially early on or when calories are scarce, but this generally levels out with time.
Melatonin, crucial for sleep, can be affected if fasting disrupts your usual sleep schedule, potentially impacting sleep quality and overall energy (Synapse).
When it comes to reproductive hormones, the impact depends a lot on sex and individual health. In women, IF may lower androgens like testosterone and boost sex hormone-binding globulin (SHBG), which is helpful for conditions such as polycystic ovary syndrome (PCOS).
Still, for women with low body fat or a lot of physical stress, IF can disrupt hormones like estrogen, luteinizing hormone (LH), and follicle-stimulating hormone (FSH), sometimes leading to menstrual irregularities or fertility issues.
For men, the effects are generally milder—testosterone might dip slightly, but there’s usually no significant impact on reproductive function (MDPI; International Medical Journal).
In summary, intermittent fasting sets off hormonal changes that support metabolic health by lowering insulin and leptin, raising insulin sensitivity and adiponectin, and adjusting hunger and fullness signals. It also shapes stress and circadian rhythms, and its effects on reproductive hormones are highly individual. While many of these changes can be beneficial, especially for metabolism, fasting that’s too aggressive or not tailored to the individual can lead to unwanted hormonal imbalances. For more details and specific study data, see reviews in Nutrients (MDPI), Endocrinology and Metabolism (Synapse), and PLOS ONE (PLOS ONE).
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