Hourglass

Health Information

Last updated: 9 November 2026

Hourglass is a tracking tool for general wellness. It is not a medical device and does not give medical advice, diagnosis or treatment.

Talk to a doctor first

Check with a doctor before you start fasting, and especially before fasts longer than 24 hours, if you:

  • are pregnant or breastfeeding
  • have diabetes or take medication that affects blood sugar or blood pressure
  • have, or have had, an eating disorder
  • are under 18, underweight, or have any ongoing medical condition

Stop fasting and get medical help if you feel faint, confused, have heart palpitations or feel seriously unwell.

About the fasting stages

The stages shown in the timer (ketosis, autophagy, growth hormone and so on) are general estimates based on published research. The timing differs a lot from person to person, depending on diet, activity, body composition and health. Some effects, especially autophagy and immune changes, have mostly been measured in animal studies and are not yet well established in humans. Treat the stages as motivation and education, not as a measurement of what is happening in your body.

Sources

  • de Cabo R, Mattson MP. Effects of intermittent fasting on health, aging, and disease. New England Journal of Medicine. 2019;381:2541–2551.
  • Anton SD, et al. Flipping the metabolic switch: understanding and applying the health benefits of fasting. Obesity. 2018;26(2):254–268.
  • Ho KY, et al. Fasting enhances growth hormone secretion and amplifies the complex rhythms of growth hormone secretion in man. Journal of Clinical Investigation. 1988;81(4):968–975.
  • Alirezaei M, et al. Short-term fasting induces profound neuronal autophagy. Autophagy. 2010;6(6):702–710. (Study in mice.)
  • Cheng CW, et al. Prolonged fasting reduces IGF-1/PKA to promote hematopoietic-stem-cell-based regeneration and reverse immunosuppression. Cell Stem Cell. 2014;14(6):810–823. (Mostly studies in mice.)