Does Bone Broth Break a Fast? The Answer Depends on Your Goal

Yes, bone broth breaks a strict fast. A cup carries roughly 30 to 80 calories and 5 to 10 grams of protein, and protein prompts an insulin response. Whether that matters depends on why you're fasting: for a calorie-focused eating window it's a small cost; for a zero-calorie fast or gut rest, it ends the fast.

The internet likes to answer this one with a flat yes or a cheerful no. Both skip the useful part, which is the reason you stopped eating in the first place. A mug of broth does very different things to a 16-hour eating window, a three-day water fast and a morning when you're trying to give your digestion a break. So this guide sorts it by goal, with the numbers, and it's honest about the parts nobody has measured yet.

What's in a cup of bone broth?

A typical cup of bone broth has about 30 to 80 calories, 5 to 10 grams of protein, very little carbohydrate or fat, and a few hundred milligrams of sodium. The exact numbers swing with the bones, the simmer and how much water went in.

The USDA figure comes from its reference entry for home-prepared beef stock, scaled to a 240-gram cup [1]. The second row comes from label data for four store-bought bone broths in the USDA's branded foods database, each per 8-ounce serving [2]. As a supporting check only, a small undergraduate lab analysis of 15 store-bought broths found about 5.6 grams per cup (23.2 milligrams of protein per gram of broth) [3]. Researchers who compared broths made several ways found the amino acid content varied widely from recipe to recipe [4], so treat any single number as an estimate unless it's printed on a label.

Most of broth's energy comes from protein, and that's the part that decides whether it "counts." Calories matter to some fasting goals. The protein matters to nearly all of them.

What counts as breaking a fast?

A fast is broken when you take in enough of something to switch off the effect you were fasting for. That line sits in a different place for each type of fast, which is why the same mug of broth gets opposite verdicts online.

• Water fast or strict zero-calorie fast. Anything with calories breaks it, broth included.
• Time-restricted eating (16:8, 18:6 and similar). The goal is a daily window without food. Broth outside the window technically breaks the fast; how much that costs you depends on the goal behind the window.
• Modified fasting. Some protocols include food on purpose. In one randomized trial of a two-day-a-week plan, restricted days allowed about 2,710 kilojoules, roughly 650 calories [5].
• Religious fasts. Ramadan, Lent, Yom Kippur and other traditions set their own rules. Those rules come from the tradition, so ask your faith leader rather than a protein company.

Why does the protein in bone broth matter more than the calories?

Because protein is what your body reads as "food has arrived." Calories from a cup of broth are small. The protein, though, triggers two signals that fasting is trying to keep quiet.

The first is insulin. A review of how people respond to individual macronutrients found that protein stimulates insulin secretion, while fat eaten on its own does not [6]. That's the reason a splash of cream in coffee and a mug of broth aren't equal in fasting terms, even when the calories are close.

The second is nutrient sensing inside your cells. A protein complex called mTORC1 links amino acid supply to cell growth and to autophagy, the cleanup process many people fast for [7]. When amino acids show up, that growth signal switches on.

Researchers who design diets to mimic fasting take this seriously. The fasting-mimicking diet tested in a 100-person randomized trial was built to be low in calories, sugars and protein, and high in unsaturated fats [8]. If protein didn't matter, nobody would bother restricting it.

Does bone broth break a fast by fasting goal?

Here's how a cup of broth plays against the most common reasons people fast.

If you fast for weight or metabolic health

This is the goal where broth costs you the least. In a 12-month trial of 139 adults with obesity, eating only between 8 a.m. and 4 p.m. on a calorie-restricted diet produced about the same weight loss and the same changes in metabolic risk factors as calorie restriction alone [9]. A six-month trial found a two-day-a-week restriction plan and daily restriction equally effective for weight loss [5].

Read together, those trials suggest the fasting window itself isn't magic. What you eat across the week does most of the work. A mug of broth mid-morning is a known, small number. If it helps you wait for a real meal, many people find that a fair trade. If it turns into three mugs and a snack, it's no longer small.

If you fast for autophagy

Autophagy is one of the most talked-about reasons to fast and one of the least measured in humans. The authors of a 2025 study put it plainly. Autophagy is stimulated by nutrient restriction in animal studies, "however, this has never been shown in humans" [10]. Their own six-month trial found a possible difference between an intermittent fasting group and standard care, with no significant increase from baseline inside the fasting group itself [10].

So nobody can tell you the hour autophagy starts in a person, or how much a cup of broth pushes it back. What the cell biology does say is that amino acids activate mTORC1, and mTORC1 activity holds autophagy back [7]. If autophagy is your reason for fasting, protein of any kind, broth included, works against the theory you're fasting for. Save it for when the fast ends.

If you fast to rest your gut

Broth ends that fast. The idea of gut rest is to give digestion nothing to do, and broth gives it protein, fat traces and salt to handle. That's no knock on broth. It just means the question answers itself.

One exception is worth naming. If a clinician has put you on a clear-liquid diet or bowel rest before a procedure, follow their instructions to the letter, including what they say about broth. That's a medical plan with its own rules.

Clean fasting vs dirty fasting: where does bone broth land?

"Clean fasting" usually means water, black coffee and plain tea only. "Dirty fasting" allows a small amount of calories, often a splash of cream, a spoon of butter or a mug of broth. Both are community terms, and neither has an official definition.

You'll see a rule that anything under 50 calories keeps a dirty fast intact. We couldn't find a study that sets that line, so treat it as folklore. The more useful question is what the calories are. Broth's small calorie count is mostly protein, and protein raises insulin; fat on its own doesn't [6]. On the insulin scorecard, a cup of broth is a "dirtier" fast than a tablespoon of cream, which surprises people.

If dirty fasting keeps you consistent and your goal is weight or metabolic health, broth is a reasonable dirty-fast option: warm, salty and very low in calories. If your goal is autophagy or a true fast, it isn't.

What about a bone broth fast?

A "bone broth fast" usually means drinking only broth for one to several days. We couldn't find a controlled trial of broth-only fasting in people, so there's no evidence base for specific results, and we won't quote a number of pounds.

What we can do is the arithmetic. At 5 to 10 grams of protein a cup, six cups a day comes to roughly 30 to 60 grams of protein and a few hundred calories. That's a very low-calorie diet with a modest amount of incomplete protein, since broth's protein is dominated by collagen's signature amino acids (per a small undergraduate lab analysis) [3], and collagen lacks the essential amino acid tryptophan [11].

Two cautions apply to anyone going longer than a day or two:

• Extended low intake has a known risk. A clinical review in the BMJ notes that any patient with negligible food intake for more than five days is at risk of refeeding problems when eating resumes [12]. That's rare in healthy people doing short fasts, and it's the reason multi-day fasts deserve a plan.
• Medications change the math. A review on fasting with diabetes found the evidence base almost non-existent and concluded it can be done safely when a healthcare provider supervises it and glucose is monitored [13]. The same logic applies to blood pressure medications and anything else your doctor doses around meals.

Is bone broth good for breaking a fast?

It's a reasonable first thing to drink, and there's no evidence it's better than a normal meal. Refeeding problems are a concern after days of negligible intake [12], not after a 16-hour eating window, so for a typical intermittent fast a regular meal is fine. Broth earns its reputation as a fast-breaker because it's warm, salty, simple to drink and brings some protein.

What broth can't do is be the whole meal. Its protein is collagen-rich and, in a small undergraduate lab analysis, low in leucine [3], and collagen protein does a poor job of building muscle compared with a complete protein. In a randomized trial in older women, whey raised muscle protein synthesis at rest and after exercise, while collagen raised it only in the exercised leg and to a smaller degree [14]. So if you break a fast with broth, follow it within the hour with a meal built on eggs, meat, fish or another complete protein.

For longer fasts, start smaller and slower, and if you've gone past a few days, involve a clinician [12].

Where does bone broth collagen powder fit?

A collagen powder breaks a fast for the same reason broth does: it's protein. Our Grass-Fed Bone Broth Collagen has 16 grams of protein and 70 calories in an 18-gram scoop, and that protein is bone broth protein with grass-fed beef collagen [15]. That's more protein than most cups of broth, so it's a bigger fast-breaker, not a smaller one.

Where it fits is the moment your fast ends, or anywhere inside your eating window. Stir a scoop into hot water and you've got a warm, broth-style mug with a known amount of collagen instead of a guess. Then eat a real meal with complete protein, because collagen isn't a complete protein [11]. Our guide to whether collagen counts as protein covers why.

One more thing, since fasting and weight loss travel together. Our product warnings say to use it as a food supplement only and not for weight reduction [15]. We mean it. It's collagen in a mug, and it isn't a fasting tool or a diet product. If you want to know how much collagen real broth delivers, read does bone broth have collagen, and if you're choosing between formats, bone broth vs collagen peptides walks through it. Both collagen formats we make sit side by side in our collagen collection.

Frequently asked questions

Does bone broth break an intermittent fast?

Technically yes, because a cup has roughly 30 to 80 calories and 5 to 10 grams of protein. If you fast on a 16:8 schedule for weight or metabolic reasons, trials suggest total daily intake matters more than a strict window, so the cost is small. If you fast for autophagy, save broth for your eating window.

Can you drink bone broth during a 72-hour fast?

You can, but it turns a water fast into a very low-calorie broth fast. That's a different protocol, and it can still be a deliberate choice. For any fast longer than a day or two, especially if you take medication for blood sugar or blood pressure, plan it with your doctor.

How many calories are in a cup of bone broth?

Usually about 30 to 80. USDA data for home-prepared beef stock works out to about 31 calories and 4.7 grams of protein per cup, while store-bought bone broths in USDA's label database run from 36 to 79 calories and 7 to 10 grams of protein per cup. Check the carton you buy.

Does bone broth spike insulin?

It raises insulin to some degree, because protein stimulates insulin secretion. A cup holds only about 5 to 10 grams of protein, far less than a protein-rich meal. Fat eaten on its own doesn't stimulate insulin, which is why broth counts as a "dirtier" fast than a splash of cream.

Does bone broth stop autophagy?

In theory it could, since amino acids activate mTORC1, a growth signal that holds autophagy back. Nobody has measured the effect of broth on autophagy in people, and human autophagy research is still early. If autophagy is your reason for fasting, keep broth for after the fast.

Is bone broth a good way to break a fast?

It's a gentle, warm first drink with some protein and sodium, and there's no evidence it beats a normal meal. Follow it within the hour with a meal built on complete protein, because broth's collagen-rich protein is low in leucine and missing tryptophan.

Does collagen powder break a fast?

Yes. Collagen powder is protein, so it breaks a fast for the same reason broth does. Check the protein grams on the label to see the size of the hit, and use it when your fast ends or inside your eating window rather than during the fast.

Should you drink bone broth while fasting?

Broth isn't fasting-neutral, and it doesn't have to be. Decide what your fast is for, then put the mug where it serves that goal.

When your fast ends, Grass-Fed Bone Broth Collagen gives you a warm mug with 16g of bone broth protein with grass-fed beef collagen, 70 calories and four ingredients, backed by a 60-day money-back guarantee. Pair it with a complete protein like Paleo Protein for the meal that follows.