Health Information & Sources
Last reviewed July 2026
My Cooking Calendar shows some health and physiology information — mainly on the fasting timeline and in your calorie estimate. This page lists every such claim in plain language, tells you honestly how strong the human evidence is, and links to the original published research so you can read it yourself.
This is educational information, not medical advice
My Cooking Calendar is a meal-planning and cooking app. Its nutrition, fasting, and calorie information is for general education only — it is not medical advice, diagnosis, or treatment, and it is not a substitute for a qualified healthcare professional. Do not start, change, or stop a fast, diet, or calorie goal based on this app alone, especially if you have a health condition, take medication, or are unsure whether it is right for you. If you feel unwell while fasting, stop and seek medical care.
Who should not fast without medical guidance
Intermittent fasting is not appropriate for everyone. Talk to a doctor before fasting if any of these apply to you. This list is not exhaustive — when in doubt, ask a healthcare professional.
- You are pregnant or breastfeeding
- You have diabetes or take medication that affects blood sugar or insulin (including type 1 / insulin-dependent diabetes)
- You have, or have had, an eating disorder or a difficult relationship with food
- You are underweight, malnourished, or prone to low blood sugar (hypoglycemia)
- You are under 18 years old
- You have a chronic medical condition or take prescription medication
The science behind what you see, with sources
Digestion, blood sugar, and the first hours of a fast
Strong human evidenceAfter you eat, your body runs on glucose from that meal and stores the excess. As the hours pass without food, insulin falls and the liver draws on its glycogen stores to keep blood sugar steady. These are well-established basics of human metabolism. Exact timing varies with your last meal, activity, and body composition.
The metabolic switch — fat burning (around 12 hours)
Moderate human evidenceOnce liver glycogen runs low — typically after roughly 12 hours without food — the body increasingly breaks down stored fat for fuel and begins producing ketones. Researchers call this the “metabolic switch.” The 12-hour figure is an approximation, not a fixed threshold, and differs from person to person.
Ketosis (around 14–16 hours)
Moderate human evidenceAs a fast continues, the liver makes more ketones, which circulate as an alternative fuel. This rise in blood ketones is measurable in people, though when it begins and how high it climbs differs between individuals.
Autophagy — cellular “cleanup” (around 16 hours and beyond)
Limited human evidence — largely animal studiesAutophagy is how cells recycle damaged components. Animal and laboratory studies suggest fasting can switch it on. Important caveat: measuring autophagy directly in living humans is difficult, so the direct human evidence — and any specific hour it “starts” — remains limited. Treat this as promising but not proven in people.
Growth hormone rises during longer fasts
Moderate human evidenceIn a classic human study, fasting increased the body’s natural growth hormone secretion, thought to help preserve muscle and mobilise fat. That study was small and used a multi-day fast, so the direction is sound but the exact hour and size of the effect are approximate.
Deeper ketosis and insulin sensitivity (around 24 hours and beyond)
Moderate human evidenceWith longer fasting, ketones supply a growing share of the body’s — and the brain’s — energy, and several human trials link intermittent fasting to improved insulin sensitivity. Note that ketones become a major brain fuel over multiple days of fasting, not fully within 24 hours.
Prolonged fasting, stem cells, and the immune system (48–72 hours)
Limited human evidence — largely animal studiesThis is the most over-hyped area of fasting, so we are deliberately careful. In mice, repeated 2–3 day fasts triggered stem-cell-based renewal of the immune system. In humans, only a small trial has been done: 3-day fasting during chemotherapy was associated with better-preserved white-blood-cell counts. Stem-cell “regeneration” has not been demonstrated in people. Multi-day fasting also carries real risks and should not be attempted without medical supervision.
How we estimate your daily calories
Strong human evidenceYour calorie estimate uses the Mifflin-St Jeor equation, which predicts resting energy needs from your height, weight, age, and sex, then adjusts for activity and your goal. A systematic review by the Academy of Nutrition and Dietetics found it the most reliable of the common equations. It is still an estimate — individual needs vary and it is not a prescription. For personalised targets, work with a registered dietitian or doctor.
- Mifflin MD, St Jeor ST et al. “A new predictive equation for resting energy expenditure in healthy individuals.” American Journal of Clinical Nutrition, 1990 (PubMed)
- Frankenfield D et al. “Comparison of predictive equations for resting metabolic rate…” Journal of the American Dietetic Association, 2005 (PubMed)
Sources last reviewed July 2026. Research evolves — if you spot something out of date, email contact@mycookingcalendar.com. Links open external websites we do not control.