Does alcohol break a fast?
Alcohol breaks a fast. Ethanol supplies 7 calories per gram and is metabolised in preference to everything else. More importantly, drinking on an empty stomach after a fast is specifically dangerous: alcohol suppresses the liver’s ability to make new glucose, and in a glycogen-depleted person that can produce hypoglycaemia and, in prolonged cases, alcoholic ketoacidosis.
| Fasting for | Verdict | Why |
|---|---|---|
| Weight loss | Breaks it | 7 kcal per gram — roughly 100 kcal for a spirit measure, 120 to 200 for a glass of wine or a beer. |
| Autophagy | Breaks it | Energy intake and hepatic metabolic disruption. It ends the fasted state. |
| Blood work | Breaks it | Not permitted, and alcohol distorts liver enzymes and triglycerides for longer than the fast itself. |
| Ketosis | Depends | Dry spirits contain no carbohydrate and ketone production often continues, but ethanol is metabolised first and this is not a case where "still in ketosis" means "no harm done". |
| Gut rest | Breaks it | Directly irritating to the gastric mucosa. |
Why
Ethanol is metabolised in the liver ahead of other substrates, which is the ordinary reason it interrupts fasting metabolism. The reason this entry leads with a warning rather than a calorie count is the interaction with a depleted glycogen store. Ethanol suppresses hepatic gluconeogenesis, and alcohol-induced hypoglycaemia is a documented and long-established clinical entity. Someone who has fasted has already drawn down liver glycogen, so the two hits stack: no stored glucose to release, and the pathway for making more is inhibited. The severe form of this is alcoholic ketoacidosis, which characteristically arises in people who have been drinking while eating little or nothing, and which presents with high anion-gap acidosis and a normal or low blood glucose. That is a medical emergency, not a fasting inconvenience.
7 kcal per gram of ethanol. Roughly 100 kcal per 44 ml spirit measure, 120 to 200 kcal per drink.
The exceptions
This is usually where the real question lives.
- Dry spirits and dry wine are low-carbohydrate, so ketosis may persist. That does not make them fast-compatible.
- Beer contains maltose and carbohydrate and ends ketosis outright.
- Tolerance is markedly lower after a fast. The first drink behaves like a larger one.
- If you are breaking a fast and intend to drink, eat first. This is the one piece of advice on this page that matters more than the verdict.
Sources
- Ethanol-induced hypoglycemia — Adv Metab Disord, 1968PMID 4301254
- Alcoholic ketoacidosis — Emerg Med J, 2006PMID 16714496
- Alcoholic Ketoacidosis: Etiologies, Evaluation, and Management — J Emerg Med, 2021PMID 34711442
No clinician reviews this site. Sources on this entry were verified by the author, who is not a doctor or a dietitian — what that means.
Last updated 2026-08-15.
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