Vegetable broth is one of the beverages explicitly permitted during fasting in the most widely used clinical and research protocols. An international expert consensus published in 2024 defined “fluid-only fasting” as a regimen allowing water, unsweetened herbal tea, and clear vegetable broth, among other low-calorie liquids, up to a combined limit of 500 calories per day.1Cell Metabolism. Standardizing fasting terminology and definitions: An international Delphi consensus study Whether that answer satisfies you depends on which version of fasting you practice and what you hope to get out of it, because the rules shift depending on the goal.
What Researchers Mean When They Say “Fasting”
One reason the broth question gets confusing is that “fasting” does not have a single agreed-upon definition in everyday use. A person doing a religious fast during Ramadan, someone on a 16:8 intermittent fasting schedule, and a patient undergoing a medically supervised multi-day fast are all using the same word to describe very different practices. Researchers recognized this problem and convened an international panel to standardize the terminology. The resulting Delphi consensus, published in Cell Metabolism, drew clear lines between categories. “Fluid-only fasting” was defined as consuming only beverages for a set period, with clear vegetable broth, vegetable and fruit juices, water, and unsweetened herbal tea all explicitly listed as acceptable options, provided total caloric intake from those fluids stays at or below 500 calories per day. The panel also specified that ultra-processed fluids should be excluded.1Cell Metabolism. Standardizing fasting terminology and definitions: An international Delphi consensus study
This matters because it means vegetable broth is not a loophole or a gray area in clinical fasting research. It is a named, endorsed component. When you see studies reporting results from “fasting” interventions, many of them allowed participants to consume small amounts of broth or juice throughout the fasting window. The science on fasting’s benefits was largely built with these low-calorie liquids in the picture, not in spite of them.
How Many Calories Are in Vegetable Broth
A standard cup of clear vegetable broth, the kind made by simmering vegetables and straining out the solids, typically contains between 10 and 20 calories. Store-bought versions vary, but most commercial vegetable broths land in the range of 10 to 15 calories per cup. That is a tiny fraction of the 500-calorie daily ceiling that clinical fasting protocols use. Even if you drank three or four cups across a fasting day, you would still be well within the limits that researchers consider compatible with fasting.
The calorie count matters less than what those calories are made of. Vegetable broth is almost entirely water, with small amounts of dissolved minerals, trace sugars from the vegetables, and sometimes added salt. It contains negligible protein and virtually no fat. This nutritional profile is what makes it a useful fasting companion: it delivers electrolytes like sodium and potassium without triggering a meaningful metabolic response in the way that solid food or calorie-dense liquids would.
Does Broth Affect Ketosis
One of the main concerns people have is whether drinking broth will knock them out of ketosis, the metabolic state where the body shifts to burning fat for fuel. The short answer is that the small number of calories in clear vegetable broth is unlikely to interfere. A study of patients undergoing medically supervised therapeutic fasting found that even when participants received roughly 40 grams of carbohydrates per day as part of their fasting regimen, their bodies still entered ketosis reliably. Blood levels of beta-hydroxybutyrate, the main ketone body, rose steadily to a mean peak of 3.6 mmol/L, while blood sugar decreased but stayed within normal range.2Nature (European Journal of Clinical Nutrition). Ketosis in patients undergoing medically supervised therapeutic fasting—results from an observational trial
To put that in perspective, 40 grams of carbohydrates is far more than what you would get from vegetable broth. You would have to drink an almost absurd quantity of broth to reach 40 grams of carbs from it alone. If supervised fasting patients achieved robust ketosis with that level of carbohydrate supplementation, a few cups of broth are not going to be the thing that derails the process. The body has a substantial buffer before small caloric inputs override the metabolic shift that fasting triggers.
Intermittent Fasting Versus Extended Fasting
The answer to whether you can have broth also depends on the length and type of fast you are doing. In intermittent fasting, where you cycle between eating windows and fasting windows within a single day or across alternating days, the rules tend to be more flexible in practice. Some protocols allow a small calorie budget on fasting days. One clinical pilot trial of weekly 24-hour fasting set the ceiling at 300 calories on fasting days, with participants abstaining from solid food but permitted to consume low-calorie liquids.3PubMed Central. A nonrandomized controlled clinical pilot trial on 8 wk of intermittent fasting (24 h/wk) Vegetable broth fits comfortably within that kind of framework.
For people doing time-restricted eating, like 16:8 or 18:6 schedules, the fasting window is shorter, and the question is usually whether any calories at all will “break” the fast. Here, the purist position is that anything other than water, plain black coffee, or unsweetened tea technically ends the fasted state. But the metabolic reality is less binary than that. A cup of broth with 12 calories is not going to trigger a significant insulin response or halt fat oxidation in any measurable way. Whether you consider it “breaking” the fast depends on how strictly you define the concept, not on what your body actually does with those calories.
For extended fasts lasting multiple days, vegetable broth is commonly recommended by physicians who oversee these protocols. The electrolytes in broth, especially sodium, help prevent the headaches, dizziness, and fatigue that come from electrolyte depletion during longer fasts. Drinking only plain water for days at a time can flush out sodium and potassium faster than the body can compensate, and broth is a straightforward way to replace them.
Vegetable Broth Versus Bone Broth
Bone broth is the more popular product in fasting circles, but it is a meaningfully different drink from vegetable broth. Bone broth is made by simmering animal bones, often with connective tissue, for extended periods. The result is a liquid that contains more protein (from dissolved collagen and gelatin), more fat, and more calories per cup than plain vegetable broth. A cup of bone broth can range from 30 to 80 calories depending on how it was prepared, and some commercial versions push even higher.
That does not automatically disqualify bone broth from fasting protocols, but it does mean you need to pay more attention to quantities. Three cups of a rich bone broth could deliver over 200 calories, which starts to become a more significant metabolic input. The protein content is also relevant. Protein triggers an insulin response, and amino acids like leucine can stimulate the cellular growth pathway mTOR, which is one of the signals that fasting is thought to suppress. If your reason for fasting is specifically to promote autophagy, the cellular cleanup process that gets activated when nutrient-sensing pathways go quiet, then vegetable broth is the safer choice. Its near-zero protein content means it is less likely to flip those switches.
That said, the practical difference for most people doing standard intermittent fasting for weight management is probably negligible. Both vegetable broth and bone broth are low enough in calories that they sit well within the boundaries used by clinical fasting studies. The autophagy distinction matters more to people doing extended fasts with specific cellular health goals.
What About Store-Bought Versions
Not all vegetable broths are created equal. The basic, stripped-down versions are fine for fasting: water, vegetables, salt, maybe some herbs. But some commercial products add ingredients that change the equation. Sugar or sweeteners are occasionally added for flavor. Some brands include oils. A few products marketed as “broth” are closer to soups in terms of calorie content, especially if they contain vegetable purees rather than just strained liquid.
Reading the nutrition label takes about ten seconds and clears up any ambiguity. Look for a product with:
- Calories per serving: ideally under 20 per cup
- Sugars: minimal, ideally under 2 grams
- No added oils or fats
- No protein concentrates: some products add yeast extract or protein isolates for flavor, which increases the calorie and amino acid load
Homemade broth gives you complete control. Simmer a mix of vegetables like onion, celery, carrots, garlic, and whatever herbs you like in water for 30 to 45 minutes, strain out the solids, and you have a fasting-friendly liquid with known ingredients. Making a large batch and freezing it in portions is a practical move if you fast regularly.
The Electrolyte Benefit
One reason vegetable broth keeps showing up in fasting protocols is that it solves a real physiological problem. When you stop eating, your insulin levels drop. Lower insulin causes the kidneys to excrete more sodium than usual. This is why people often feel lightheaded, develop headaches, or experience muscle cramps during the first day or two of a fast. It is not hunger doing that; it is sodium loss.
A cup of vegetable broth typically contains 600 to 900 milligrams of sodium, depending on the brand or recipe. That goes a long way toward preventing the most common unpleasant side effects of fasting without adding meaningful calories. Potassium, magnesium, and other trace minerals leached from the vegetables during cooking also contribute, though in smaller amounts. For anyone who has tried water-only fasting and found the headaches unbearable, switching to broth during the fasting window often makes the difference between an experience that feels tolerable and one that feels miserable.
This is also why many fasting-focused physicians and dietitians actively recommend broth rather than just permitting it. The electrolyte replacement it provides can make fasting more sustainable over repeated cycles, which means people are more likely to stick with the practice long enough to see benefits. A technically “purer” fast that you abandon on day one because you feel terrible is less useful than a slightly less pure fast you can maintain consistently.
When Broth Might Not Be Allowed
There are specific situations where vegetable broth, or any caloric intake, genuinely needs to be zero. Pre-surgical fasting is the most common one. If your doctor tells you nothing by mouth before a procedure, that means nothing by mouth. Broth, even clear broth, contains solutes that can affect anesthesia safety. The same applies to fasting required before certain blood tests, particularly fasting glucose or lipid panels, where even a small amount of dietary carbohydrate or fat can skew the results.
Some religious fasts also have strict rules that exclude broth. Dry fasting, practiced in some traditions, prohibits all liquids including water. Other religious observances permit water but not flavored liquids. These are not questions that metabolic science can answer; they depend on the specific religious framework and often on individual interpretation within that tradition.
For medical water-only fasts conducted under supervision for specific therapeutic purposes, the protocol may exclude broth as well, though this varies by practitioner. If you are fasting under medical guidance, ask your supervising clinician rather than relying on general advice.
Common Misconceptions About Broth and Fasting
The biggest misconception is the idea that any calorie at all “breaks” a fast in some absolute physiological sense. Fasting is not an on-off switch with a single calorie threshold. It is a continuum of metabolic states that shift gradually as the body depletes glycogen, increases fat oxidation, ramps up ketone production, and eventually activates cellular maintenance processes. A cup of vegetable broth with 12 calories does not meaningfully reverse any of those processes. Your liver does not suddenly halt ketone production because it detected a trace of dissolved carrot.
Another common misunderstanding is that vegetable broth will spike your blood sugar. The glycemic load of clear vegetable broth is effectively zero. The small amount of sugar naturally present in vegetables (mainly from carrots and onions) dissolves into the broth in such minute quantities that it does not produce a measurable glucose or insulin spike in the blood. If you have diabetes and are monitoring blood sugar during fasting, vegetable broth is about as neutral a substance as you can consume other than plain water.
A third misconception goes in the other direction: that broth has special fasting-enhancing properties, like “healing the gut” or “detoxifying the liver.” Vegetable broth is warm, comforting, hydrating, and a decent source of sodium. Those are real benefits. But it does not have magical restorative powers. The gut-healing claims associated with bone broth (from collagen and gelatin) have limited clinical evidence, and they do not even apply to vegetable broth, which contains neither.
Flavoring Broth Without Adding Calories
If plain vegetable broth starts to taste monotonous during a fast, there are ways to vary the flavor without significantly changing the calorie profile. Adding fresh herbs like parsley, thyme, or dill during the simmering process gives each batch a different character. Ginger and turmeric, sliced and simmered in the broth, add warmth and mild spice. A squeeze of lemon juice after straining brightens the flavor and adds virtually no calories. A pinch of cayenne pepper provides heat if you want it.
What you want to avoid is adding ingredients that turn the broth into something closer to a meal. A tablespoon of miso paste adds about 25 calories and some protein, which is still modest but starts moving the needle. Coconut milk, cream, or butter (sometimes suggested in “keto fasting” communities) transforms the drink into something with real caloric density. Nutritional yeast, sometimes added for a savory boost, contains protein and B vitamins and pushes the calorie count up faster than most people realize. None of these additions are harmful in an absolute sense, but they move you further from the spirit of the fasting protocols that clinical research has actually tested.
The safest approach is to keep the broth simple: vegetables, water, salt, herbs, and spices. That combination stays firmly within the boundaries that fasting researchers and clinicians have used for decades, and it keeps the metabolic impact about as close to zero as a flavored liquid can get.