One Day, Not Three: What the Latest Colonoscopy Diet Guidelines Actually Say
Current U.S. and European guidelines say most people at low risk of a poor prep (more on who that is below) only need to change what they eat the day before a colonoscopy. Many prep sheets still ask for three to five days.
Some of those longer instructions are deliberate, since people at higher risk of an incomplete prep may still need a longer, stricter diet. Your own care team’s instructions always come first, so ask before you change anything.
The three phases of the prep diet: low residue, clear liquids, then nothing
Most colonoscopy prep instructions move through three phases, and the laxative prep itself is taken during the second one.
Low-residue (or “low fiber”) eating. Solid foods that leave little behind in the colon, such as white bread, white rice, plain pasta, eggs and skinless chicken. Whole grains, nuts, seeds, and most fruit and vegetables are usually off the list. European guidelines tend to say “low fiber,” while U.S. guidelines tend to say “low residue.”
Clear liquids. Liquids you can see through, with no solid food, such as clear broth, black coffee or tea, and light-colored juices and sports drinks without pulp. Many instructions also rule out red and purple drinks and gelatin. This is when you take the laxative prep.
Nothing by mouth. A final window before the procedure, often several hours and set by your practice, when nothing at all is allowed, including water, coffee, gum or candy (https://www.marywashingtonhealthcare.com/our-services/medical-group/gastroenterology/colonoscopy-prep-faq/).
The guideline changes in this post are about the first phase: how many days of restricted eating most people need, and when clear liquids should begin.
What changed in the 2025 U.S. guidelines
In March 2025, the U.S. Multi-Society Task Force on Colorectal Cancer updated its bowel prep recommendations. The task force represents the three major U.S. gastroenterology societies, and its guidance was published in each of their journals.
The goal of the update was better prep quality, because an inadequate prep can mean a canceled or repeated exam. One of the authors said that outcome “creates tremendous frustration for patients.” On diet, the evidence showed that longer, stricter diets did not improve prep quality, while patients found a one-day restriction easier to follow (https://www.ccjm.org/content/93/3/169).
On diet, the guidance makes two points, and only the first is new:
New: one day is enough for most people. If you are at low risk of a poor prep, diet changes now only need to start the day before your colonoscopy.
Carried over: you can still eat that morning. Breakfast and lunch the day before can be light, low-fiber foods such as white toast or eggs, or full liquids. Your instructions will tell you when to switch to clear liquids.
The second point dates back to the task force’s 2014 guidance, which already allowed low-residue food the day before for patients using a split-dose prep, meaning half the prep is taken the evening before and half the morning of the procedure. What 2025 added was an explicit cap, limiting diet changes to one day for low-risk patients, along with a separate, longer approach for those at higher risk.
A review in the Cleveland Clinic Journal of Medicine summed it up plainly: clear-liquid-only diets are “unnecessary for most outpatients at low risk for inadequate preparation.”
For many patients, that is a real shift. Multi-day diets have long been common in practice, to the point that four of the five trials in a 2025 review compared one day of low-residue eating against three days. As the next section shows, some widely read patient instructions still recommend three to five days.
Europe got there first
Europe set the one-day standard six years earlier, when the European Society of Gastrointestinal Endoscopy (ESGE) issued a recommendation in 2019: “ESGE recommends a low fiber diet on the day preceding colonoscopy.” The British Society of Gastroenterology endorses that guideline. Research in Spain points the same way. A study of more than 800 people in a Catalan colorectal cancer screening program found that one day of a low-residue diet was as effective as the three-day diet that had been standard there.
Why your instructions may still say three days
If your prep sheet asks for several days of diet changes, that is still common. Patient instructions vary widely, even among respected sources:
| Source | Published | What patients are told |
|---|---|---|
| American Cancer Society patient article | March 2025 | Low-fiber foods “around 3 to 5 days before,” then clear liquids the day before |
| NHS hospital trust leaflet (UK) | April 2024 | Low-residue diet starting three days before, then clear fluids the day before |
Instructions differ partly because each practice sets its own protocol, and some also set a fixed afternoon cut-off for solid food on the day before. For some patients, a longer diet is exactly right.
Who may still need a longer diet
The one-day approach is meant for people at low risk of an incomplete prep. For people at higher risk, the 2025 U.S. guidance describes a longer path: a low-residue diet starting two to three days before, then clear liquids the day before.
Factors that can slow the gut and raise that risk include (https://www.ccjm.org/content/93/3/169):
Diabetes
Chronic constipation
Opioid pain medications and certain antidepressants
A previous colonoscopy with an incomplete prep
Previous colorectal surgery
Parkinson’s disease, cirrhosis or gastroparesis
Age over 65
Some weight-loss and diabetes medications, such as GLP-1 drugs, can also affect how well a prep works. An earlier post on this blog covers that in detail. If any of these apply to you, your longer instructions are likely deliberate. Always follow your doctor’s instructions, and if you have questions about which approach fits you, ask your care team before changing anything.
What patients in the studies said
The research behind the change is fairly consistent. The clearest evidence on timing comes from a 2025 review of five randomized trials with 2,248 patients, most of which compared one day of low-residue eating with three days. Prep quality was similar either way, while patients on the one-day diet found it easier to tolerate and were more willing to do it again.
A related question is what you can eat on that final day. Many instructions still call for clear liquids for the entire day before, while the current U.S. guidance allows light, low-residue meals for breakfast and lunch. Studies comparing the two found similar prep quality and fewer complaints when patients could eat:
In a review of nine trials, 77.8% of patients found low-residue meals on the day before manageable, compared with 68.1% on clear liquids all day, and 79.9% were willing to repeat it, compared with 68.5%.
A 2021 review of 16 studies found that patients on clear liquids all day reported more hunger, nausea and vomiting.
Willingness to repeat matters because screening is repeated over the years, and a prep people are willing to do again makes the next appointment easier to keep.
Your final day: common questions
For most people, the new guidance puts everything into a single day, and most of that day is clear liquids, which is where the practical questions come up. These answers apply only to that clear liquid phase.
Most instructions end with a final window before the procedure, often several hours and varying by practice, when you should have nothing at all by mouth, including water, coffee, gum or candy (https://www.marywashingtonhealthcare.com/our-services/medical-group/gastroenterology/colonoscopy-prep-faq/). Your own instructions set that window, and they take priority over anything here.
Can I drink coffee during a clear liquid diet?
Usually yes, if it is black and before your nothing-by-mouth window begins. Many instructions allow coffee or tea without milk, cream or creamer, though sugar or honey is often fine.
Can I have broth?
Clear broth, such as chicken, beef or vegetable, is commonly allowed. Other soups are not.
What color gelatin is OK?
Most instructions say to avoid red and purple gelatin, popsicles and drinks. Plain gelatin without fruit is usually fine.
Can I chew gum or suck on hard candy?
Some instructions allow hard candies, such as lemon drops, during the clear liquid phase. Like everything else, they stop once your nothing-by-mouth window begins. Gum rules vary, so check your own instructions.
Can I have sports drinks?
Usually yes, in light colors only. Skip red and purple flavors.
Can I drink alcohol?
No. Alcoholic drinks are typically on the avoid list during a clear liquid diet.
A step patients still carry on their own
A shorter diet is real progress, but the planning, the shopping, the restricted eating and the prep itself still happen at home, mostly without medical supervision. Patients describe that experience in their own words here.
Almost everything else about colonoscopy has been modernized. Zera Medical is working to change where the prep step happens. ZeraFlow™ is a clinic-based, nurse-supervised bowel preparation system designed to move prep out of the home and into the clinic. It is currently under review for FDA clearance and is not available for commercial sale.
In the meantime, the best prep is the one you can complete. Know your instructions, ask about anything unclear, and keep your screening appointment.
This post is part of an ongoing educational series from Zera Medical on the colorectal cancer screening gap and the preparation experience that shapes it. This content is for educational purposes only and is not medical advice. Always consult your physician or gastroenterologist with questions about your specific bowel preparation, medications, or symptoms. Zera Medical is developing ZeraFlow™, an investigational clinic-based bowel preparation system currently under FDA regulatory review. ZeraFlow has not been cleared or approved by the U.S. Food and Drug Administration and is not available for commercial distribution or sale.