“Feeding the Rhythm”—Effects of Food and Nutrients on Daily Cortisol Secretion: From Molecular Mechanisms to Clinical Impact

Daily rhythms define physical, mental, and behavioral changes that the body experiences over a 24 h cycle. The light–dark cycle plays a crucial role in regulating daily rhythms, but other factors such as food intake, stress, and physical activity also affect them. Cortisol secretion exhibits one of the largest endocrine amplitudes, with an early morning peak and late-evening nadir driven by the suprachiasmatic nucleus and hypothalamus–pituitary–adrenal axis, representing the most robust endocrine output of the circadian system. Beyond photic cues, feeding is a potent non-photic zeitgeber that entrains peripheral oscillators and dynamically shapes cortisol secretion. This narrative review aims to explore the effect of feeding in modulating cortisol secretion. The misalignment of the daily cortisol-secretion rhythm, with blunted cortisol awakening response and elevated evening levels, leads to metabolic syndrome, psychiatric disorders, shift work, and jet lag. In endogenous hypercortisolism, the loss of rhythmicity rather than absolute exposure best predicts risk. Therefore, we discuss practical nutritional tools as opportunities to partially restore rhythmic hypothalamus–pituitary–adrenal axis physiology.