A disclosure before we go further: I develop soup cleanse products, which is a reason to read the evidence sections closely rather than take my word for it. Where the research is thin, I’ve said so.
What a broth fast is
A broth fast replaces all or most solid food with broth, often bone broth, for one to five days. The guides I looked at call for roughly 3 to 8 cups a day, plus water and tea. The best-known commercial plan, a 21-day bone broth diet, uses two broth-fasting days a week at about 300 to 500 calories on those days, which makes broth a pair of fast days inside a larger eating pattern.
What a cup holds
On one major brand’s labels, a cup of chicken bone broth lists 45 calories and 9 grams of protein. The same brand’s regular chicken broth lists 5 calories, 1 gram of protein, and 520 milligrams of sodium. If the label holds, 4 to 8 cups of the bone broth come to about 180 to 360 calories and 36 to 72 grams of protein.
The label gives one number for a product that varies. A 2019 analysis of commercial and homemade bone broths in the International Journal of Sport Nutrition and Exercise Metabolism found large variability in amino acid content and concluded that bone broth is unlikely to provide reliable amounts of collagen precursors compared with supplements. Collagen protein is also incomplete, since it contains little or no tryptophan.
Sodium needs a line of its own. At 520 milligrams a cup, 4 to 8 cups of a salted commercial broth supply roughly 2,100 to 4,200 milligrams, against a US Daily Value of 2,300. That sodium works against the dip behind the day-two headache, and it is a lot of salt for anyone watching blood pressure.
How to read a broth label
Two things on a label trip people up. The first is the serving. One major brand’s bone broth lists 45 calories and 9 grams of protein for a 240-gram serving, about a cup, while the same carton’s container holds 479 grams and lists 90 calories, which is two servings. Sip the container and you have taken double the headline figures. Six cups of that bone broth come to 270 calories and 54 grams of protein. Six cups of the same brand’s regular chicken broth come to 30 calories, 6 grams of protein, and 3,120 milligrams of sodium. A homemade vegetable broth strained of everything solid sits near zero on both energy and protein. The second is the protein itself, which varies from batch to batch in bone broth. Read the sodium line against the Daily Value of 2,300 milligrams before you count cups.
What the strainer takes out
The 3-day guide strains its broths, then reserves some of the cooked vegetables to puree into blended soups that leave nothing strained out. A broth fast stops at the strainer, so it has only the liquid. A soup cleanse carries the vegetables and their fiber, and some protein when legumes go in the pot. A broth made only from vegetables carries very little energy or protein.
The two can overlap. A soup cleanse built mostly on strained broth and thin purees looks a lot like a broth fast, and one with legumes or grains in it does not.
What the claims rest on
The usual claims for bone broth are collagen, joints, and a healed gut lining. The myths post covers the gut claim, and the bone broth post covers where the two broths came from. For fasting, there is one more: that broth adds autophagy to a fast. The autophagy post explains why protein and calories hold that signal back, so by that reasoning the 36 to 72 grams of protein a day in the example above works against it.
Hunger and fullness
Soup is among the better-studied foods for fullness. In a 2007 study in Appetite, 60 adults ate a low-energy-dense soup before lunch in four forms, from broth with vegetables served separately to fully pureed, and every form cut how much they ate at the meal that followed. A plain cup of broth is a lighter load than that soup: 5 calories for a regular chicken broth and 45 for a bone broth on one brand’s labels. Hunger on a broth fast follows the pattern in the hunger post, waves tied to your usual mealtimes, which is why guides space the cups two to three hours apart.
Coming off a broth fast
Broth fasts run one to five days, and the longer ones sit at the edge of the refeeding criteria. NICE counts little or no food for more than 5 days as a risk factor when it comes with another, such as a BMI under 18.5. The come-off post covers the criteria and the order of reintroduction. A three-day broth fast needs the same slow return as a soup cleanse.
Who should skip it
The skip list in the guide applies: pregnancy and breastfeeding, diabetes or medication that depends on food, kidney or liver disease, being underweight, a history of disordered eating, recovery from illness or surgery, heavy periods, and known low iron. A broth fast removes more food than a soup cleanse, so the list applies at least as strongly.
What hasn’t been tested
I haven’t found a trial of a broth-only fast, or of a soup cleanse. The nearest well-documented program is a clinic fast in Germany that allows about 250 calories a day from a small juice and a cup of vegetable soup, with daily monitoring. A broth fast resembles that program without the supervision, and I found no study of it.
Common questions
- What is the difference between a soup cleanse and a broth fast?
- A broth fast uses only broth. A soup cleanse adds blended soups that keep the vegetables and their fiber, so it carries more energy, and some protein when legumes go in.
- Is bone broth better than vegetable broth for fasting?
- Bone broth carries more protein and calories, about 45 calories and 9 grams on one label against 5 and 1 for a regular chicken broth, and its protein varies from batch to batch. Neither has been shown to improve a fast.
- How much sodium is in a broth fast?
- A salted commercial broth like one labeled at 520 milligrams a cup supplies about 2,100 to 4,200 milligrams over 4 to 8 cups, against a US Daily Value of 2,300.