02/19/2026
Studies show that prolonged fasting or long gaps without food can increase cortisol in some people, especially if energy balance is already low. Elevated cortisol over time can influence appetite, blood sugar variability, and fat distribution patterns.
(e.g., studies on fasting and stress response see—Gonzales et al., 2018; Moro et al., 2016).
Intermittent fasting itself isn’t inherently bad — there are multiple clinical trials showing benefits for certain populations:
• IF can improve insulin sensitivity, aid weight management, and support aspects of metabolic flexibility in adults without uncontrolled glycemic issues.
(For example, systematic reviews/meta-analyses by Patterson & Sears, 2017 and Longo & Panda, 2016.)
The key nuance is context and individual physiology:
—For people with stable sleep, low stress, consistent energy intake, and no history of disordered eating, fasting windows can be a helpful tool.
—For people under chronic stress, with unstable blood sugar, high cortisol, poor sleep, or low caloric/protein intake, longer fasts may increase the stress burden rather than reduce it.
A lot of the hormonal effects we talk about — cortisol, insulin, leptin — respond first to energy balance, sleep quality, consistency of eating, and stress load before timing alone.
So in practice:
• IF isn’t inherently harmful — but it isn’t universally optimal either.
• Consistency in meals — especially consistent protein and energy intake — supports hormonal regulation and metabolic stability for many individuals.
• We always need to interpret fasting research in the context of the whole person’s physiology, not just the timing.
The goal in coaching isn’t strict fasting or eating windows —
it’s creating sustainable patterns that reduce physiological stress and support metabolic regulation. 🦋
