Your target
How is your appetite right now?
This is education, not medical advice
Fiber needs are individual, and some conditions call for less rather than more, including flares of inflammatory bowel disease and known strictures or gastroparesis. If constipation is severe, or comes with vomiting or serious belly pain, that is a call to your prescriber rather than a fiber question.
Daily fiber target
a day
Fiber in this day
Add food to the day
Why fiber is half the constipation fix
Constipation is common on these medications
The Wegovy label reports constipation in 24% of people on semaglutide against 11% on placebo. The medication slows the gut, you eat less food so there is less bulk, and many people drink less without noticing. All three push the same direction.
Fiber works, and it is measured
A meta-analysis of sixteen randomized trials in adults with chronic constipation found 66% responded to added fiber against 41% on control, with psyllium and pectin the types that showed a significant effect. That response held only at doses above 10 g a day, and stool frequency improved with at least four weeks of it.
Most people on a GLP-1 fall short
In a study of 52 people taking a GLP-1 for type 2 diabetes, average fiber intake was 16 g a day, or 11 g per 1,000 calories, and not one of them met the recommendation. Eating less food makes fiber one of the first things to slip, which is the usual direction of the problem.
More is not better here
The Academy of Nutrition and Dietetics' position on fiber advises increasing it gradually with adequate fluids. On a medication that already slows digestion, a sudden jump trades constipation for gas, bloating and early fullness, which crowds out the protein you need more.
Where this number comes from
Fiber guidance is general population guidance. There is no test that measures your own fiber requirement, and nobody has run a trial that sets a fiber target for people on a GLP-1 specifically. So this tool is doing arithmetic on published recommendations, not measuring anything about you. Here is exactly what it does, so you can decide how much weight to give the number.
The general recommendation
The Institute of Medicine set an adequate intake of 14 g of fiber per 1,000 calories, drawn from observational data on heart disease risk. Applied to typical calorie intakes, that is where the familiar headline figures come from: 25 g a day for women and 38 g for men under 51, and 21 g and 30 g after 50.
An adequate intake is not a measured requirement. It is the level the evidence associates with better outcomes across a population.
What the GLP-1 guidance says
A 2026 expert consensus written specifically for people on GLP-1 medications recommends at least 25 g a day for women, at least 30 g for men, and at least 35 g for people with diabetes. Those are floors, not ceilings, and the panel reached them from the same 14 g per 1,000 calorie rate.
That consensus does not lower the target for a smaller appetite. It expects the gap to be closed gradually, with fluids, and with a fiber supplement such as psyllium if food alone cannot get there.
How this tool estimates your calories
Almost nobody tracks calories, so the appetite question stands in for them. "Much smaller" assumes roughly 1,300 calories a day for women and 1,600 for men; "somewhat smaller" assumes about 1,700 and 2,100. It then applies the 14 g per 1,000 rate to that figure.
Those calorie assumptions are estimates, not measurements, and they are not themselves from a guideline. They are a reasonable middle for a reduced appetite. If you do track your intake, enter it — the number you type will always beat the band.
Why age barely moves this
The 14 g per 1,000 calorie rate is the same at every adult age. The reason the headline figures drop after 50, from 25 g to 21 g and from 38 g to 30 g, is that calorie intake typically drops, not that older bodies need less fiber per calorie.
So once the target is already scaled to your appetite or your entered calories, age has been counted. Adjusting for it again would count it twice. The age question here only does anything on the "about normal" setting, where there is no appetite figure to scale from. The GLP-1 consensus floors do not split by age at all.
Why the tool can fall below the guideline
Because the target is scaled to what you actually eat, a small appetite can produce a number under the 25 g and 30 g floors above. Read the lower figure as a realistic next step rather than a new goal. The guideline floor is still the destination, and the tool says so whenever your target falls beneath it.
Why not just start at the full number
Both the GLP-1 consensus and the Academy of Nutrition and Dietetics say to raise fiber gradually alongside fluids. On a medication that already slows the gut, a sudden jump tends to buy gas, bloating and early fullness. The pacing is the part that is well supported. Lowering the destination is not.
What this is not
It is not a personal prescription, and it does not know your history. Some conditions call for less fiber rather than more, including inflammatory bowel disease flares, known strictures and gastroparesis. A dietitian or your prescriber can set a number for you; this can only show you what the general guidance implies.
Sources
- Institute of Medicine. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. National Academies Press, 2005. doi:10.17226/10490. Source of the 14 g per 1,000 kcal adequate intake and the 25, 21, 38 and 30 g figures by sex and age.
- Sievenpiper JL, Ard J, Blüher M, Chen W, et al. Nutritional and lifestyle supportive care recommendations for management of obesity with GLP-1-based therapies: an expert consensus statement using a modified Delphi approach. Obesity Pillars. 2026;17:100228. doi:10.1016/j.obpill.2025.100228. The GLP-1-specific consensus behind the at-least 25 g, 30 g and 35 g floors, the guidance to close the gap gradually with fluids rather than to lower the target, and the note on psyllium when food alone falls short.
- Ponzo V, Vitale M, Bo S, et al. Exploring dietary intake in adults with type 2 diabetes using GLP-1 receptor agonists: a cross-sectional analysis. Nutrients. 2025;17(21):3318. doi:10.3390/nu17213318. Source of the 16 g a day and 11 g per 1,000 calorie figures in 52 GLP-1 users, and of the finding that none of them met the fiber recommendation.
- van der Schoot A, Drysdale C, Whelan K, Dimidi E. The effect of fiber supplementation on chronic constipation in adults: an updated systematic review and meta-analysis of randomized controlled trials. The American Journal of Clinical Nutrition. 2022;116(4):953–969. doi:10.1093/ajcn/nqac184. Source of the 66% versus 41% response figures, the psyllium and pectin finding, the over 10 g a day threshold, and the four-week duration for stool frequency.
- Dahl WJ, Stewart ML. Position of the Academy of Nutrition and Dietetics: health implications of dietary fiber. Journal of the Academy of Nutrition and Dietetics. 2015;115(11):1861–1870. doi:10.1016/j.jand.2015.09.003. Source for increasing fiber gradually with adequate fluid.
- Wegovy (semaglutide) Prescribing Information: Adverse Reactions. Novo Nordisk. Current label at DailyMed. Source of the 24% versus 11% constipation figures.
- Mozaffarian D, et al. Nutritional priorities to support GLP-1 therapy for obesity: a joint Advisory from the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association, and The Obesity Society. The American Journal of Clinical Nutrition. 2025;122(1):344–367. doi:10.1016/j.ajcnut.2025.04.023. A corrigendum was published in 2026. The clinical advisory behind the fluid and gastrointestinal guidance on this page.
- US Department of Agriculture, Agricultural Research Service. FoodData Central. fdc.nal.usda.gov. Source of every food fiber value, per 100 grams, converted to the portion shown, and linked from each card.