Fiber and staying regular on a GLP-1

Short answer: drink enough, add fiber from food gradually, keep moving, and eat at regular times. Those are the first-line measures in a 2025 joint advisory from four US medical societies, which describes constipation as common on GLP-1 medications and says it "should be managed proactively".¹ If several days pass without a bowel movement, or there is pain, tell your prescriber.

Fiber is one of five priorities in our guide to what to eat when you're eating less.

How common it is

Medication and dose	Reported constipation	Placebo group
Semaglutide 2.4 mg	24%	11%
Tirzepatide 15 mg	11%	5%

Figures from the main trials, as tabulated in the joint advisory.¹

Why it happens

• Slower stomach emptying. GLP-1 medications slow how quickly food leaves the stomach. That is part of how they work.
• Less food, less bulk. The bowel has less to move.
• Less fiber. Most adults already eat too little, and smaller portions cut it further.
• Less fluid. Fiber needs water to do its job.

How much fiber

The Daily Value is 28 g.² The Dietary Guidelines scale it to intake: 14 g per 1,000 calories.³ On 1,400 calories that is about 20 g. More than 90% of women and 97% of men do not reach the recommended amount to begin with.³

Fiber in small portions

Food	Portion	Fiber
Raspberries	1 cup	about 8 g
Lentils, cooked	half a cup	about 8 g
Black beans, cooked	half a cup	about 7 g
Pear, with skin	1 medium	about 5.5 g
Chia seeds	1 tablespoon	about 4 g
Oats, dry	half a cup	about 4 g
Prunes	5	about 3 g

Typical values from USDA FoodData Central.⁴ The advisory specifically mentions prunes and other dried fruit.¹

Add it slowly

Too much fiber too fast causes gas and bloating, and the advisory suggests going easy on high-fiber foods in the first days after starting or raising a dose.¹ Add one serving, hold for three or four days, then add another. Drink a glass of water with each. Daily fluid targets are in how much water to drink on a GLP-1.

Other things that move things along

• Walking. Ten to fifteen minutes after meals.
• Regular meals. Eating triggers the reflex that moves the bowel. The plate is in what to eat on a GLP-1.
• A routine. Same time each morning, unhurried.
• Warm drinks in the morning.

Fluid targets, specifically

Fibre without fluid makes constipation worse, not better, which is the most common way people get this wrong. The National Academies reference intake for beverages is about 3 litres a day for men and 2.2 litres for women — roughly 100 oz and 73 oz.⁶ On a day you are adding fibre, that is a floor rather than a target.

The practical version: a glass of water with the fibre itself, and another within the hour. A fibre supplement taken with a mouthful of water is the setup for the problem you were trying to solve.

Over-the-counter options, by type

If fibre, fluid and movement have not worked, these are the categories. All of them are worth running past a pharmacist first, because some interact with how other medicines are absorbed — including, potentially, your GLP-1.

Type	Common examples	How it works	Notes
Osmotic	Polyethylene glycol (PEG), lactulose, magnesium hydroxide	Draws water into the bowel to soften stool	Generally the first choice for ongoing use. Needs fluid alongside. Works over 1–3 days, not instantly.
Stool softener	Docusate	Lets water mix into the stool	Gentle; evidence for it is weaker than for osmotics.
Stimulant	Bisacodyl, senna	Prompts the bowel wall to contract	Short-term use only. Not a daily habit — ask before using repeatedly.
Bulk-forming	Psyllium, methylcellulose	A fibre supplement in another form	Needs plenty of fluid. Introduce slowly.

One point specific to this situation: some laxatives can affect how other oral medications are absorbed, and a bowel that is already emptying slowly changes the picture further. This is a real reason to ask rather than a cautious disclaimer.

Things other than fibre that move things along

Fibre gets all the attention, and for a slow bowel it is often not the limiting factor.

• Walking. Unexciting and genuinely effective. Ten to fifteen minutes after a meal does more than most supplements.
• Timing. The urge is strongest in the half hour after waking and after breakfast. Being somewhere you can act on it matters, and routinely ignoring it trains the signal away.
• Position. Feet on a low stool, knees above hips, straightens the angle the bowel has to work around.
• Regular eating. Eating prompts bowel movement through the gastrocolic reflex. If you have stopped eating regularly, you have also removed the prompt.
• Magnesium. Magnesium at higher doses draws water into the bowel — which is why loose stools are its main side effect, and why it is sometimes used deliberately.⁵
• Review your other medicines. Iron supplements, opioid painkillers, some antidepressants and some blood pressure drugs all slow the bowel, and they are easy to overlook when a new medication is the obvious suspect.

How to raise fibre without making it worse

Going from 10 g to 30 g in a day produces bloating, gas and discomfort, and most people conclude fibre does not agree with them. It is the pace, not the fibre.

• Add about 5 g a day, then hold for several days before adding more. Reaching 25–30 g over two to three weeks is a reasonable ramp.
• Raise fluid at the same time, not afterwards.
• Soluble fibre — oats, beans, psyllium, partially hydrolysed guar gum — is generally better tolerated than coarse insoluble fibre when the stomach is already slow.
• If a step up causes trouble, drop back to the previous amount for a few days rather than abandoning it.

Fiber supplements: the types

Type	Examples	Character
Gel-forming, soluble	Psyllium	Thickens in water; adds bulk. Must be taken with plenty of fluid.
Non-gelling, soluble	Partially hydrolyzed guar gum (PHGG), inulin	Dissolves clear; fermented by gut bacteria. PHGG is fermented slowly.
Insoluble	Wheat bran	Adds bulk; can feel harsh for some people.

In a randomized, placebo-controlled trial in 44 healthy adults, daily PHGG for three months improved stool form.⁵ That study was in healthy volunteers, not people on GLP-1 medications. PHGG is the fiber we use in Replenish; the detail is on our ingredients page.

The advisory lists fiber supplements among the options when food is not enough, along with other measures a clinician may suggest.¹ Fiber is also a core part of what the GLP-1 diet is, and one row in our overview of what supplements to take with a GLP-1.

A product we are working on

Ease, our planned regularity product, is in development and has a waitlist. It is not available yet.

When to call your prescriber

• No bowel movement for several days despite the steps above.
• Abdominal pain, swelling or vomiting.
• Blood in the stool.
• Constipation alternating with diarrhea. The advisory notes that prolonged constipation can lead to this.¹

Do not start laxatives for regular use without advice. Your prescriber can recommend what is appropriate or adjust your dose.