Does cinnamon break a fast?
A sprinkle of cinnamon does not meaningfully break a fast — a quarter-teaspoon is about 1.5 calories. Meta-analyses find cinnamon lowers fasting blood glucose modestly, which is a point in its favour rather than against. The genuine warning here is unrelated to fasting: cassia cinnamon contains coumarin, which is hepatotoxic in quantity, and supplement doses can exceed safe intake.
| Fasting for | Verdict | Why |
|---|---|---|
| Weight loss | Doesn't break it | Approximately 1.5 kcal per quarter-teaspoon. |
| Autophagy | Depends | Trace energy and no protein. The quantity is negligible; the certainty is not, because nobody has studied it in fasting subjects. |
| Blood work | Breaks it | Water only — and cinnamon measurably lowers fasting glucose, which is precisely what the test is reading. |
| Ketosis | Doesn't break it | A quarter-teaspoon of cinnamon contains under 1 g of carbohydrate and will not interrupt ketosis. Pre-mixed cinnamon sugar will. |
| Gut rest | Doesn't break it | Negligible digestive load at a sprinkle. |
Why
At culinary doses cinnamon is a spice, and the calorie arithmetic settles the fasting question immediately. The reason it recurs in fasting discussions is its glycaemic effect, which is better supported than most such claims: a meta-analysis found cinnamon intake lowers fasting blood glucose, an updated systematic review and meta-analysis examined cinnamon use in type 2 diabetes, and a more recent dose-response meta-analysis of randomised controlled trials assessed its effect on glycaemic control. The effects are modest and the trials heterogeneous, but the direction is consistent and it points the harmless way for a faster. The coumarin issue is the part that gets omitted, and it is better established than most things on this page. Coumarin is hepatotoxic in a proportion of people, and a risk assessment of the human data sets a tolerable daily intake on that basis. When 47 retail cinnamon powders were measured, cassia — the ordinary supermarket kind — carried high coumarin levels with enormous variation between samples, enough that a heavy user can exceed that tolerable intake. Ceylon cinnamon contains far less. None of this is a fasting question, and it is the thing most worth knowing about a daily cinnamon habit.
Approximately 1.5 kcal per quarter-teaspoon.
The exceptions
This is usually where the real question lives.
- Cassia cinnamon contains coumarin. Daily high-dose supplementation is a genuine liver risk; a sprinkle in coffee is not.
- Ceylon cinnamon is the low-coumarin species and the better choice for regular use.
- Cinnamon supplements in capsule form are a different dose class from culinary use.
- Pre-mixed cinnamon sugar is sugar. It breaks a fast.
Sources
- Cinnamon use in type 2 diabetes: an updated systematic review and meta-analysis — Ann Fam Med, 2013PMID 24019277
- Cinnamon intake lowers fasting blood glucose: meta-analysis — J Med Food, 2011PMID 21480806
- The effect of cinnamon supplementation on glycemic control in patients with type 2 diabetes mellitus: An updated systematic review and dose-response meta-analysis of randomized controlled trials — Phytother Res, 2024PMID 37818728
- Quantification of flavoring constituents in cinnamon: high variation of coumarin in cassia bark from the German retail market and in authentic samples from indonesia — J Agric Food Chem, 2010PMID 20853872
What it does not show: Measures coumarin in retail cinnamon samples. It shows cassia levels are high and enormously variable — enough that the tolerable daily intake may be exceeded by heavy users — but it measures the spice, not people, and reports no health outcome.
- Toxicology and risk assessment of coumarin: focus on human data — Mol Nutr Food Res, 2010PMID 20024932
What it does not show: A toxicological risk assessment, not a study of cinnamon eaters. It establishes that coumarin is hepatotoxic in susceptible people and what the tolerable intake is; it does not show that anyone has been harmed by cinnamon in food.
- FoodData Central — USDA Agricultural Research Service, 2026
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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