Protein and fiber on a GLP-1 medication: what the 2025 advisory says

If you take semaglutide (Wegovy, Ozempic) or tirzepatide (Zepbound, Mounjaro), you've probably been told two things: get enough protein, and watch out for constipation. Both are true. What's less often said is that they can pull against each other, especially in the first weeks.

In 2025, four groups published a joint advisory on nutrition during GLP-1 treatment: the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association and The Obesity Society. This article walks through what it says about protein and fiber. Your prescriber or dietitian sets your actual plan. Use this to prepare questions for them, not to replace the conversation.

First, the name problem

GLP-1 is two things. It's a hormone your gut releases after you eat, and it's the name of a class of medicines that mimic that hormone at much higher, longer-lasting levels. Some food studies, including hemp studies, measure the hormone. That's not the same as the medicine. Nothing in this article suggests hemp protein, fiber or any food works like semaglutide or tirzepatide, or boosts what they do.

What changes on the medication

These medicines slow how quickly your stomach empties and act on the parts of the brain that control appetite. So you feel full sooner and stay full longer. That's how they work, and it's also why digestive side effects are the most common ones.

These rates come from each drug's FDA prescribing information, which pools the main placebo-controlled obesity trials:

Side effect Semaglutide 2.4mg Placebo Tirzepatide 15mg Placebo
Nausea 44% 16% 28% 8%
Diarrhea 30% 16% 23% 8%
Vomiting 24% 6% 13% 2%
Constipation 24% 11% 11% 5%
Abdominal pain 20% 10% 10% 5%

The semaglutide and tirzepatide figures come from different trials with different placebo groups, so don't compare the two drugs directly from this table. Sources: Wegovy and Zepbound prescribing information.

These side effects are most likely in the first weeks and after each dose increase, and they usually ease once the dose is stable.

Why protein gets so much attention

When you lose weight quickly, by any method, some of what you lose is lean mass, not just fat. In a body-scan substudy of the STEP 1 semaglutide trial (140 people), participants lost an average of 13.6kg of fat and lean tissue combined. Of that, 8.4kg (about 61%) was fat and 5.3kg (about 39%) was lean mass (figures from the trial's supplementary appendix). Lean mass includes organs and water as well as muscle. The advisory estimates that muscle was roughly 20% of the weight lost. Because fat fell faster, lean mass actually made up a slightly larger share of body weight at the end. The concern is the absolute amount of muscle lost, not the ratio.

Some lean-mass loss is expected with any large weight loss. The advisory names two things that help keep it: enough protein, and strength training. A smaller appetite makes the first one harder.

How much protein the advisory suggests

  • The general adult RDA is 0.8g per kg of body weight a day.
  • During active weight loss, 1.2–1.6g per kg a day has been proposed.
  • There's no agreement on which weight to use. Using your current weight can overestimate what you need if you have a lot of weight to lose. Some clinicians use an adjusted weight or your lean mass instead.
  • As a simpler target, 80–120g a day is suggested, which is 16–24% of calories on a 2,000-calorie diet.
  • Don't go below 0.4–0.5g per kg a day, and avoid staying at 2g per kg or more for long periods.

The practical problem is volume. At 80g a day, that's 20g at each of four small meals, and 20g of protein from food is a fair amount to eat when you're full after a few bites. The advisory suggests lower-volume, nutrient-dense protein foods such as fish, eggs, Greek yogurt, cottage cheese, and nuts and seeds or their butters. It also says some people can meet their targets with high-protein shakes, bars or other fortified products.

What it says about fiber, and the catch

On constipation, the advisory says it's common with weight loss and should be managed early, not after it's a problem. It recommends:

  • Enough fluids
  • Fiber from foods
  • A gradual increase in both soluble and insoluble fiber, such as prunes or other dried fruit
  • Water-rich, lower-calorie foods like many fruits and vegetables

If food isn't enough, it lists other options for your clinician to recommend, including fiber supplements.

Then come two cautions that are easy to miss:

  • Early nausea: during the first few days of treatment, smaller, more frequent meals and avoiding fatty or high-fiber foods can help with nausea.
  • Protein and fat slow things down too. Foods high in protein or fat slow stomach emptying even more, which can make constipation worse. Some people may need to cut back on them for a while.

So the advice isn't "load up on protein and fiber from day one." It's closer to this: eat small meals, drink enough, prioritize protein, add fiber gradually once the early nausea settles, and adjust with your care team as you go.

A pattern to discuss with your care team

This is drawn from the advisory, not a prescription:

  1. Eat small meals every 3–4 hours rather than going long stretches without food. The advisory notes that nausea is often worse in the morning or after long gaps.
  2. Put protein in every one of them, aiming for whatever daily total your clinician gives you.
  3. Drink through the day. Dehydration from vomiting or diarrhea can affect your kidneys.
  4. Add fiber in small steps once early nausea settles. About 5g at a time, with water, is the usual approach (here's a step plan).
  5. Do strength training if you're cleared for it. It's the main way to protect muscle, alongside protein.
  6. Track it for a couple of weeks. The advisory suggests food logs or photos so you and your clinician can see what's actually happening.

Where a shake fits, and which one

When you're full after a few bites, a drink can be easier than a plate of food. Here are our scoops side by side, per 35g:

Protein Fiber Calories Ingredients
Cantein Unflavored (original) 28g 2g 110 Organic hemp protein
Cantein Protein + Fiber Unflavored 26g 6g 110 Organic hemp protein, organic acacia fiber

Here's how I'd think about choosing, with your clinician's input:

  • Early weeks, or nauseous: the original is the simpler choice. More protein, less fiber, one ingredient. A half scoop is fine if a full one is too much.
  • Settled, and struggling to get fiber from food: Protein + Fiber gets you 26g of protein and 6g of fiber in one small drink. Count it as one of your fiber steps, not on top of them.
  • Constipated already: ask your clinician before adding any fiber product. Remember the advisory's point that protein can slow things down too.

To be straight with you: we haven't tested our products in people taking GLP-1 medicines. A scoop is a protein source, not a treatment for side effects. Hemp protein is also a fairly dense, earthy drink. Some people on these medicines find thinner drinks easier, so try a small amount blended with plenty of liquid.

When to call your prescriber

Don't wait it out if you have:

  • Severe or persistent abdominal pain, with or without vomiting
  • Vomiting or diarrhea that stops you keeping fluids down, or signs of dehydration such as dizziness, very dark urine or barely urinating
  • No bowel movement for several days along with pain, bloating or vomiting
  • Pain in the upper right of your abdomen, fever, or yellowing of your skin or eyes

Questions to bring to your next appointment

  • What daily protein target should I aim for, and based on which weight?
  • Should I hold off on extra fiber until my nausea settles?
  • How much fluid should I aim for?
  • If I get constipated, what should I try first, and when should I call you?
  • Is a protein shake a good idea for me, and does added fiber matter?
  • Can I start strength training, and can you refer me to a dietitian?

The short version

On a GLP-1 medication, protein helps protect muscle, and fiber and fluids help with constipation. But protein, fat and fiber all slow digestion, and in the first weeks less is sometimes more. The 2025 advisory suggests small, protein-forward meals, steady fluids, fiber added gradually, and strength training. Work out the numbers with your prescriber or a dietitian.

I run Cantein, a hemp protein company. I'm not a clinician, and this is not medical advice. It summarizes a published advisory to help you prepare questions for yours. Cantein products are not a treatment for obesity, diabetes, or medication side effects, and nothing here suggests they enhance GLP-1 medications. Talk to your prescriber before changing your diet on these medicines.

Sources

Also in the fiber series: How much fiber you need · Acacia fiber, honestly · Protein and fiber on a GLP-1 · Protein + Fiber vs the original · All Learn pages