TLDR
Restricting when people eat can change not only weight and blood sugar, but also the body’s daily hormone patterns. These effects may help some people but could create risks for those with diabetes or thyroid problems.
Summary
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1 Study Aim
The authors review how intermittent fasting (regularly scheduled periods without food) changes hormone levels and circadian rhythms (natural daily body cycles). They focus on insulin, thyroid hormones, glucocorticoids, and several other hormones in humans and rodents. The review asks whether altered hormone timing or secretion could produce benefits or harms. It also considers whether fasting effects differ from ordinary calorie restriction and whether eating time matters. The review examines how limiting food to certain times may change the body’s daily hormone patterns and affect health differently across people.
2 Study Design
The study is a narrative review, meaning it summarizes findings from earlier research rather than conducting a new experiment. The authors examine human and rodent studies of alternate-day fasting, whole-day fasting, Ramadan fasting, and time-restricted feeding (TRF; eating only during a set daily window). They compare acute fasting with longer regimens. Reviewed outcomes include hormone levels, acrophase (the time of a daily hormone peak), rhythm size, and secretion frequency. The review includes studies of healthy participants and limited studies involving prediabetes, diabetes, and thyroid disorders. The authors note that animal results require caution because rodents are active at night, unlike humans. The review combines results from earlier human and animal experiments to compare different fasting schedules and hormone changes.
3 Findings
The review reports that fasting generally lowers insulin and improves insulin sensitivity (the body’s response to insulin), although human daily insulin rhythms were rarely measured. Thyroid hormone T3 (triiodothyronine, an active thyroid hormone) falls during fasting, while thyroid-stimulating hormone often stays unchanged. Glucocorticoids, including cortisol (a hormone involved in stress and energy control), rise more quickly and may peak later or more often. Rodent TRF commonly shifts corticosterone peaks toward feeding time. Growth hormone responses vary between species and fasting duration. Fasting may disrupt reproductive cycles in female rodents, while melatonin timing changes little. The authors recommend separating fasting effects from calorie reduction and studying eating time, activity, and patient conditions. People with diabetes or thyroid disorders should seek medical guidance. Fasting changes several body signals, so its benefits and risks depend on the schedule and the person’s health.