Fiber on GLP-1: How Much You Need and the Best Sources

On Mounjaro, Zepbound, Ozempic or Wegovy, aim for the same amount of fiber as anyone else: 25 g a day for women and 38 g for men up to age 50, and 21 g and 30 g over 50, in the US, or 30 g of fibre for every adult in the UK. Most people eat far less, about 16 g a day in the US and 20 g in the UK, and a smaller appetite makes the gap harder to close. On a GLP-1, how you add fiber matters as much as how much: build up slowly, drink more as you go, and pair it with protein.

How much fiber you need

Adults	US target	UK target
Women up to 50	25 g	30 g
Men up to 50	38 g	30 g
Women over 50	21 g	30 g
Men over 50	30 g	30 g

The US figures come from the National Academies, which based them on studies linking low-fiber diets to heart disease, and set lower targets after 50 because people eat less as they get older. The UK figure comes from government guidelines. Anywhere in that range is a sensible target, and the calculator works out yours.

Why fiber matters more on a GLP-1

Constipation is one of the most common side effects. It affected 24% of people on Wegovy, against 11% on placebo, and 11 to 17% on Zepbound, against 5%. An expert consensus on GLP-1 side effects notes that it lasts longer than the others, a median of 47 days in people with obesity, and that feeling full leads people to drink less, which makes it worse. It recommends more water, more fiber and more movement.

It protects your long-term health. A Lancet review of 185 cohort studies and 58 trials found that the people who ate the most fiber had a 15 to 30% lower risk of early death, heart disease, stroke, type 2 diabetes and bowel cancer, with the biggest benefits at 25 to 29 g a day. In the trials, more fiber also meant lower body weight, blood pressure and cholesterol.

It helps you keep the weight off. The 2025 joint advisory from four US obesity and nutrition societies notes that people who maintain their weight loss tend to eat more minimally processed food that's higher in nutrients, fiber and protein. See keeping the weight off.

It nudges your own GLP-1. Gut bacteria ferment some fiber into short-chain fatty acids, which trigger your body's own GLP-1 release. The effect is small next to your medication, as boosting GLP-1 naturally explains, but it's one more reason to eat it.

The GLP-1 catch: fiber slows your stomach too

Fiber, like protein and fat, slows how quickly your stomach empties, and so does your medication. The advisory turns that into two practical points:

• Go easy at the very start. It suggests smaller, more frequent meals and avoiding fatty or high-fiber foods in the first few days of treatment, when nausea is most likely.
• If more fiber makes constipation worse, ease back. It notes that for some people, high-fiber foods slow things further and worsen constipation, which may mean cutting back for a while. Wetter, lower-fiber fruit and vegetables leave the stomach faster.

So fiber is still the goal, added gradually and with fluid once you're past the first few days. If constipation doesn't improve, talk to your prescriber or a dietitian, and see constipation on a GLP-1.

How to add fiber without the bloating

Adding a lot of fiber at once can cause gas, bloating and cramps. MedlinePlus, from the US National Library of Medicine, advises building up over a few weeks, which gives your gut bacteria time to adjust, and drinking plenty, because water helps fiber pass through.

• Add one higher-fiber food at a time, and give it a few days before adding the next.
• Drink more as you add more. Feeling full makes it easy to drink too little. The water calculator gives you a daily target.
• Spread it across the day instead of having one big high-fiber meal.
• Swap rather than add. Wholemeal bread instead of white, brown rice or wholewheat pasta instead of white, potatoes with the skins on, and beans, lentils or chickpeas stirred into soups, stews and salads, as the NHS suggests. Swaps add fiber without adding volume, which matters when you can only manage small portions.
• Check labels. The NHS counts a food as high in fibre if it has 6 g or more per 100 g.

Pair fiber with protein

With a small appetite, the most useful meals bring protein and fiber together, so every bite counts. These recipes from the site do both:

Recipe	Fiber	Protein
High-Protein Red Lentil Soup	11 g	24 g
Apple Cinnamon Overnight Oats	10 g	28 g
Tuna and Chickpea Protein Salad	10 g	25 g
Chicken Burrito Bowl	9 g	42 g
Tofu and Edamame Stir-Fry	8 g	27 g
High-Protein Greek Yogurt Bowl	8 g	26 g

The overnight oats for breakfast, the lentil soup for lunch and the tofu stir-fry for dinner come to 29 g of fiber and 79 g of protein for about 1,100 kcal.

Easy add-ons: a tablespoon of chia seeds adds about 4 g of fiber, half an avocado about 5 g, 100 g (3.5 oz) of cooked lentils or drained chickpeas about 8 g, and a small handful of berries about 3 g. The fiber calculator has a longer list.

Fiber supplements

Food comes first, because high-fiber foods bring vitamins and minerals with them. But if you can't eat enough, a supplement can help. For constipation, psyllium has the best evidence: in a 2022 review of 16 trials, 66% of people taking a fiber supplement improved, against 41% in the comparison groups. Psyllium and pectin were the fibers with a clear effect, which was strongest at the higher doses studied and over at least four weeks. Fiber supplements also caused more wind.

The advisory lists fiber supplements among the options for constipation on a GLP-1, and notes that fiber capsules or powders can also bulk up stools if you have diarrhea. Take any fiber supplement with plenty of water, build up slowly, and ask your pharmacist how to time it around your other medicines.

General nutrition information, not medical advice. If you have ongoing stomach symptoms, talk to your prescriber or a dietitian before making big changes to your diet.