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.
The hormone with a schedule
Ghrelin is made mainly in the stomach. Its level rises before meals and falls after eating, which is why it is called the hunger hormone. In a study of ten healthy women eating normally, it dropped 17.9% within an hour of a meal. A 2001 study in Diabetes found a rise in ghrelin before meals in people, which pointed to a role in starting a meal.
What it does without food
Take the meals away and the schedule keeps running. In a 2005 study, six healthy volunteers fasted for 24 hours with blood drawn every 20 minutes. Their ghrelin came in about eight pulses over the day and followed a pattern like that of people eating three meals. In a second study, 33 young adults were sampled every 3 hours from 12 to 84 hours of fasting. Ghrelin bottomed out around 8 in the morning, peaked in the afternoon, and fell through the night, and that rhythm held for the whole fast. In the same study, ghrelin ran opposite to cortisol, the stress hormone that peaks in the morning, with a correlation of -0.79, which fits the morning low.
The authors of the first study read this as evidence that the brain plays the main part in deciding when a meal begins. The hour of the peak varies between studies: a 4-day fast in ten women found ghrelin lowest in the afternoon with an evening peak. What the studies share is a daily rhythm without meals, and the exact hours differ.
Why it doesn’t keep climbing
Hunger can feel as if it builds with every skipped meal. The data on average ghrelin point the other way. In the 84-hour study, the mean 24-hour level declined slightly over the fast. A 2022 paper in the Journal of Clinical Endocrinology & Metabolism notes that total ghrelin rises after 48 to 72 hours of fasting in rodents, while multiple human studies have failed to show a rise after 24 to 72 hours.
In a study of ten healthy women on a 4-day complete fast, ghrelin fell, and the more it fell, the more their hunger was blunted. A clinic study of 1,422 people fasting for 4 to 21 days on about 250 calories a day found about 93% reporting no feeling of hunger. Those were fasts, or close to it, and a soup cleanse is a different plan.
Beyond ghrelin
Ghrelin is one signal among several. Leptin, made by fat tissue, falls during fasting, and gut hormones that signal fullness rise and fall with meals. In the 4-day fasting study, the change in ghrelin tracked the change in hunger even after the researchers adjusted for leptin and glucose, which is why ghrelin gets the attention. The brain adds habit and context on top, such as the time on the clock and the place you eat most meals.
What soup adds
Soup is one of 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. Soup in each form reduced how much they ate at the meal that followed, and counting the soup, total intake fell by about 20%, or 134 calories.
That was a lunch study with soup as a first course. It shows soup fills, and it says little about hunger on a plan built from soup alone.
Sleep changes the wave
Sleep sets the baseline. In a 2004 study in Annals of Internal Medicine, 12 healthy men slept 4 hours a night for two nights and 10 hours a night for two nights. After the short nights, leptin was 18 percent lower, ghrelin 28 percent higher, and hunger ratings about a quarter higher.
Later studies outside the lab have not always reproduced the hormone changes. A review of that work notes that energy restriction strengthens the appetite-hormone response, which describes a cleanse. The guide’s journal tracks sleep alongside hunger, which puts the two side by side.
Riding a wave
The 3-day guide’s daily framework puts broth, tea, or soup at the usual gaps: morning, mid-morning, midday, afternoon, evening, and before bed. That places something warm in the stomach at the times hunger arrives. Move the cup to the wave. If your hunger lands at 12:30 and 6:30, put the warm cup at 12:15 and 6:15. That is reasoning from the rhythm, and no study has tested it.
The guide’s advice is to expect hunger, and its limit is clear: if you are too hungry to continue, stop and eat a proper meal. Dizziness, weakness, or a racing heart means the cleanse is over. Lightheadedness on day two is often sodium, as the day-two headache post explains.
A test you can run on yourself
The prediction is checkable on a single cleanse. Write down the hours hunger arrives on day one, in the guide’s journal. If the rhythm holds, day two’s waves land at the same hours, and the what-to-expect post shows how the days feel from there. A pattern that tracks your usual mealtimes supports the fasting data. A pattern that wanders says the rhythm doesn’t carry over to a soup plan, which is a finding too.
What hasn’t been measured
I haven’t found a study that tracked hunger or ghrelin during a soup cleanse. The rhythm data come from fasts of 24 to 84 hours in small groups, so waves at your usual mealtimes are a prediction from fasting studies. They have not been measured on a soup plan.
Common questions
- Why do I get hungry at the same times every day?
- Ghrelin follows a daily rhythm that continued through 84 hours of fasting in one study, so hunger can arrive on schedule even when no meal is coming.
- Does hunger get worse each day of a soup cleanse?
- In studies of complete fasts, average ghrelin did not climb, and hunger blunted as it fell. Nobody has measured it during a soup cleanse.
- What should you do when a hunger wave hits?
- Sip warm broth or tea, which is what the guide’s daily framework schedules. If you are too hungry to continue, the guide says to stop and eat a proper meal.
- Does poor sleep make hunger worse on a cleanse?
- In a 2004 study, two nights of 4-hour sleep raised ghrelin by 28 percent and hunger ratings by about a quarter. Nobody has measured the effect during a cleanse.