Does bone broth break a fast?
Bone broth breaks a fast. It contains protein — typically 6 to 10 g per cup — and protein is the one macronutrient that ends a fast under every definition, including autophagy. It is often recommended during fasting protocols, but that is a decision to eat a small amount, not evidence that it is fasting-compatible.
| Fasting for | Verdict | Why |
|---|---|---|
| Weight loss | Depends | 30 to 50 kcal per cup. Small enough that it rarely undoes a deficit, but it is food. |
| Autophagy | Breaks it | This is the clearest yes on the site. Broth is an amino-acid solution, and amino acids are the direct off-switch for autophagy. The dose is unreliable, but "a small and variable amount of protein" is still protein. |
| Blood work | Breaks it | Not permitted. It is food in liquid form. |
| Ketosis | Doesn't break it | Almost no carbohydrate, so ketosis usually survives. This is why it appears in keto protocols. |
| Gut rest | Breaks it | Protein requires active digestion. |
What matters here
- Bone broth breaks a fast for autophagy, because it supplies amino acids, which are the direct off-switch for the pathway autophagy fasting is meant to trigger.
- Bone broth is an unreliable source of the collagen it is sold for: when researchers measured prepared broths against the collagen doses used in research, the broths were significantly lower in every key amino acid, and varied enormously between different recipes.
- Bones store lead, and a small analysis found more lead in chicken bone broth than in the water it was made from. That is one small study in a hypothesis-generating journal, not a survey of commercial broths.
- Bouillon and plain stock are mostly salt with little protein, so they are a far more fasting-compatible way to get sodium during a long fast than bone broth is.
Why
Bone broth is water, minerals, gelatin and free amino acids. The minerals are why it is recommended on long fasts — it addresses the sodium loss that makes extended fasting unpleasant, a loss driven by falling insulin and measured directly in fasting subjects. The amino acids are why it breaks one. Amino-acid availability, and leucine in particular, is the principal nutritional regulator of mTORC1 signalling in human skeletal muscle, and mTORC1 activation is the mechanism that suppresses autophagy. A protein pre-load also produces a measurable insulin and incretin response. So the answer splits cleanly by goal: if you are fasting to restrict energy, broth is a rounding error; if you are fasting for autophagy, broth is the specific thing you were avoiding. Two things almost nobody selling bone broth will tell you. First, it is an unreliable source of the thing it is sold for. When researchers measured the amino acid content of prepared broths against the collagen doses used in actual collagen research, the broths were both far lower and highly variable — the protein content depends on the bones, the simmer time and the recipe, so there is no such thing as a standard dose. Second, bones store lead, and a small analysis of broth made from organic chickens found measurably higher lead concentrations in the broth than in the water it was made with. That study is a single small one in a hypothesis-generating journal, it is not a survey of commercial products, and it does not show that any particular broth is unsafe — but it is a real open question and it belongs on the page. The claims made for gut-barrier repair rest largely on cell and animal work rather than human trials, which is stated here rather than repeated as fact.
Approximately 30 to 50 kcal and 6 to 10 g protein per 240 ml cup, though homemade broth varies widely and measured collagen content is inconsistent between batches.
The exceptions
This is usually where the real question lives.
- Collagen and gelatin are the main proteins in broth and are incomplete, but they still supply amino acids and still signal.
- Bouillon cubes and commercial stock are mostly salt with little protein — closer to salted water, and a genuinely different answer. If sodium is what you actually want on a long fast, this is the cheaper and more fasting-compatible way to get it.
- Vegetable broth without added protein is much closer to fasting-compatible than bone broth.
- Broth is a common and reasonable part of a supervised extended fast. Being useful and being fast-compatible are different claims.
- If you are drinking it for collagen, the dose is unreliable. Measured broths contained far less collagen precursor than the supplement doses used in research, and varied enormously between different recipes and preparations — though batches of the same standardised recipe were consistent.
- Homemade and shop-bought broths differ so much in protein and salt that no single calorie or protein figure covers both. Read the label where there is one.
- Lead is stored in bone. One small study found more lead in chicken bone broth than in the water used to make it. It is not established that this matters at normal intakes, and it is worth knowing if broth is a daily habit — particularly during pregnancy or for young children.
Sources
- Incretin, insulinotropic and glucose-lowering effects of whey protein pre-load in type 2 diabetes: a randomised clinical trial — Diabetologia, 2014PMID 25005331
- Nutritional and contractile regulation of human skeletal muscle protein synthesis and mTORC1 signaling — J Appl Physiol (1985), 2009PMID 19150856
- Bone Broth Unlikely to Provide Reliable Concentrations of Collagen Precursors Compared With Supplemental Sources of Collagen Used in Collagen Research — Int J Sport Nutr Exerc Metab, 2019PMID 29893587
What it does not show: Analyses the amino acid content of prepared broths. It shows the dose is variable and low relative to studied collagen supplements; it does not test any health outcome.
- The risk of lead contamination in bone broth diets — Med Hypotheses, 2013PMID 23375414
What it does not show: A single small analysis of broth made from one set of organic chickens, published in a hypothesis-generating journal. It is not a survey of commercial bone broth and it does not establish that any particular broth is unsafe. It is the reason to be aware of the question, not an answer to it.
- Bone Broth Benefits: How Its Nutrients Fortify Gut Barrier in Health and Disease — Dig Dis Sci, 2025PMID 40180691
What it does not show: A narrative review of proposed mechanisms, drawing substantially on cell and animal work. It does not demonstrate a gut-barrier benefit of bone broth in humans, and it is not evidence that broth is compatible with fasting.
- Influence of insulin and glucagon on sodium balance in obese subjects during fasting and refeeding — Int J Obes, 1981PMID 6113218
- FoodData Central — USDA Agricultural Research Service, 2026
Corrections
What this entry used to say, and why it changed. Nothing here is edited silently.
This entry said the collagen content of bone broth "varies enormously between batches". That overstated the source. Re-reading the analysis, broths made to a standardised recipe were consistent between batches; the enormous variation was between different recipes and preparations, with café-made broths highest. The underlying point stands — measured broths were significantly lower in every key amino acid than the collagen doses used in research — but the wording named the wrong kind of variation.
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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