Why nutrient gaps happen on a GLP-1
The 2025 joint advisory on nutrition during GLP-1 therapy notes that people using these medications for obesity reduce their calorie intake by 16% to 39%. It warns that a reduction that large and that fast can leave intake of essential vitamins and minerals short, especially when daily intake falls below about 1,200 calories for women or 1,800 for men.
Three things make it worse. Food aversions and nausea narrow the range of foods people eat, often toward whatever feels easiest. Long gaps between meals are common when hunger is low. And stomach side effects themselves, the advisory notes, may further compromise how well nutrients are absorbed.
What are the signs of a nutrient deficiency?
The advisory lists fatigue beyond what you would expect, excessive hair loss, flaky or itchy skin, muscle weakness, poor wound healing and unusual bruising as signs of frank deficiency. Several of those overlap with ordinary GLP-1 side effects and with rapid weight loss itself, which is exactly why guessing is unreliable. If you notice them, ask your clinician whether testing makes sense rather than starting supplements on a hunch.
What the 2025 joint advisory recommends
The most detailed guidance so far is a joint advisory from the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association and The Obesity Society, published on May 30, 2025. It was co-published in The American Journal of Clinical Nutrition, Obesity, Obesity Pillars and the American Journal of Lifestyle Medicine.
Its position on micronutrients is measured. Dietary guidance should focus on nutrient adequacy within a much lower-calorie diet. Supplements can be proactively considered for at-risk nutrients, tailored to the individual. And follow-up should include regular reassessment of diet and hydration, using tools such as food logs or food photos, plus reassessment of nutrient levels during therapy so that emerging deficiencies are caught early.
Which nutrients does the advisory flag?
It gives iron, calcium, magnesium, zinc, and vitamins A, D, E, K, B1 (thiamine), B12 and C as examples of nutrients of concern when intake drops. When it discusses supplementing, it names vitamin D, calcium and B12 specifically, or a multivitamin-mineral tablet. Separately, it treats protein and fiber as priorities of their own.
From the makers of this guide
See where your nutrition actually lands
The advisory recommends reassessing diet with food logs or photos. Pep AI makes that record easy to keep, so gaps show up before they become a problem.
- 01
Food logging built for small meals
Log meals by photo scan, barcode, restaurant menu scan, database search, recents or quick-add macros, even when a meal is only a few bites.
- 02
Protein, fiber and water against goals
Protein, fiber and water are tracked against your goals, the three shortfalls most people on a GLP-1 hit first.
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Side effects on one timeline
Log fatigue, hair thinning and digestive symptoms with severity, alongside your doses, to discuss with your clinician.
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Pep Bot for explanations
Ask Pep Bot, an AI assistant with a research-literature retrieval pipeline, to explain a nutrient or a study. It explains concepts and does not give dosing advice.
The nutrients most often flagged, and food sources first
Food first is not a slogan here. Whole foods bring several nutrients at once, plus fiber and fluid, which matters when every bite has to count. The table pairs the most frequently named nutrients with why they come up on a GLP-1 and where to find them.
| Nutrient | Why it comes up on a GLP-1 | Food sources to lean on |
|---|---|---|
| Protein | Falls short easily when volume is limited, and shortfall adds to muscle loss | Fish, eggs, Greek yogurt, cottage cheese, poultry, legumes, tofu |
| Fiber | Drops with smaller meals; low fiber and low fluid worsen constipation | Vegetables, fruit, beans and lentils, whole grains, dried fruit such as prunes |
| Calcium and vitamin D | Named for supplementation in the advisory; bone health matters during weight loss | Dairy or fortified alternatives, canned fish with bones, fortified foods |
| Vitamin B12 | Named in the advisory; found mainly in animal foods, and metformin may lower levels | Fish, meat, eggs, dairy, fortified cereals |
| Iron | Listed as a nutrient of concern when intake falls | Red meat, poultry, fish, beans, lentils, fortified cereals |
| Magnesium and zinc | Listed as nutrients of concern when intake drops | Nuts and seeds, beans, whole grains, leafy greens, seafood |
Should I eat more fiber on a GLP-1?
Generally yes, with timing in mind. The advisory encourages adequate fluids and fiber from foods to help with constipation, including a gradual increase in foods such as prunes or other dried fruit. It also notes that avoiding high-fiber and fatty foods for the first few days of treatment can help with nausea. Increase fiber gradually, and increase fluid with it.
Does metformin affect vitamin B12?
Its prescribing information says metformin may lower vitamin B12 levels and recommends periodic monitoring. Many people with type 2 diabetes take metformin alongside a GLP-1, so if that is you, it is a reasonable thing to raise at your next review.
When a multivitamin is worth discussing
The advisory does not tell everyone on a GLP-1 to take a multivitamin. It says supplements, including a multivitamin-mineral tablet, can be proactively considered for at-risk nutrients at appropriate doses and tailored to each person. In practice, that makes a multivitamin a reasonable conversation to have with your clinician or a registered dietitian in situations like these.
- Your daily intake has been very low for weeks, or you are regularly under the calorie levels the advisory flags.
- Nausea or food aversions have narrowed what you eat to a handful of foods.
- You follow a vegetarian or vegan diet, which already affects B12 intake.
- You have had bariatric surgery, or have a condition that affects absorption.
- Blood work has shown a low level of something.
- You notice the deficiency signs the advisory lists, such as unusual fatigue, hair loss or easy bruising.
Can I just take a multivitamin instead of eating well?
No. A multivitamin can fill specific gaps, but it does not supply protein, fiber, fluid or the energy your body needs, which are the gaps most people on a GLP-1 are actually at risk of. It works best as a backstop under a diet you are tracking, not as a substitute for one.
Is more always better?
No. MedlinePlus advises against taking a bigger dose than the label recommends. Some nutrients can build up to harmful levels, and stacking several products that contain the same ingredient is an easy way to get there without noticing. How much of anything to take is a question for your clinician or pharmacist.
Supplement cautions specific to GLP-1 users
A few risks are general to all supplements. Others matter more because of how these medications work.
Does the FDA approve supplements?
No. The FDA states that it does not have the authority to approve dietary supplements before they are marketed, and that the manufacturer is responsible for making sure its products are not adulterated or misbranded. The FDA also advises talking to a doctor, pharmacist or other health professional before using a supplement, partly because some supplements interact with medicines.
Are "natural GLP-1" or GLP-1 booster supplements safe?
Be wary of them. They are not GLP-1 medications, they have not been approved as treatments, and they are not a substitute for a prescribed medicine. A 2026 review in the Annals of Pharmacotherapy looked at 24 transdermal patches and one gel sold as natural GLP-1 supplements. It concluded that all of them were illegal as dietary supplements, found that none posted certificates of analysis, and reported that many used deceptive advertising. If a product promises the effects of a prescription GLP-1, treat that claim as a red flag.
Can a GLP-1 affect how pills and vitamins are absorbed?
It can affect oral medicines. The Wegovy and Zepbound labels both say that delayed gastric emptying may impact the absorption of oral medications taken at the same time, and advise closer monitoring for medicines where small changes matter, such as warfarin.
The most concrete example is birth control. The Zepbound and Mounjaro labels advise people using oral hormonal contraceptives to switch to a non-oral method, or add a barrier method, for 4 weeks after starting and for 4 weeks after each dose increase. Non-oral hormonal contraceptives should not be affected.
If you take Wegovy tablets, the label says to take the tablet on an empty stomach with a small amount of plain water and wait at least 30 minutes before eating, drinking or taking other oral medications. Ask your pharmacist how your vitamins and supplements fit around that.
What if I have kidney disease?
Talk to your clinician before starting anything. NIDDK advises people with kidney failure to take only the vitamin, mineral or dietary supplements their provider has recommended, because over-the-counter products may contain vitamins or minerals that are harmful to them. People with earlier kidney disease should still tell their pharmacist and provider about every supplement they use. This matters on a GLP-1 because the labels also warn that dehydration from stomach side effects can cause kidney injury.
What habits keep supplement use safe on a GLP-1?
None of these is complicated, and together they prevent most supplement problems.
- Tell your prescriber and pharmacist about every vitamin, mineral and herbal product you take. The Wegovy and Zepbound Medication Guides ask for exactly this.
- Add one supplement at a time, so that if something disagrees with you, you know which one.
- Keep a written list with product names, and bring it to appointments and before any surgery.
- Be skeptical of any product that claims to boost, replace or mimic a GLP-1 medication.
Key takeaways
- Calorie intake on a GLP-1 can fall by 16-39%, which makes vitamin and mineral gaps more likely, especially at very low intakes.
- The 2025 ACLM/ASN/OMA/TOS joint advisory recommends food first, with supplements for at-risk nutrients tailored to the individual.
- Nutrients it names include vitamin D, calcium, B12, iron, magnesium and zinc, with protein and fiber as separate priorities.
- The FDA does not approve supplements before sale, and "natural GLP-1" products are not a substitute for medication.
- GLP-1s can affect absorption of oral medicines, including oral contraceptives on tirzepatide, so check with your clinician or pharmacist before adding supplements.
Know what your smaller plate is missing.
Pep AI tracks protein, fiber and water against your goals and keeps a food record you can review with your clinician, so gaps show up early. Download Pep AI on iPhone or Android.
Frequently asked questions
Keep reading
Sources
- Mozaffarian D et al. Nutritional priorities to support GLP-1 therapy for obesity: a joint Advisory from ACLM, ASN, OMA and The Obesity Society. Obesity 2025;33(8):1475-1503
- Questions and Answers on Dietary Supplements, U.S. Food and Drug Administration
- Dietary Supplements, MedlinePlus, National Library of Medicine
- Zepbound (tirzepatide) prescribing information and Medication Guide, Eli Lilly / FDA (DailyMed)
- Wegovy (semaglutide) prescribing information and Medication Guide, Novo Nordisk / FDA (DailyMed)
- Metformin hydrochloride prescribing information, FDA (DailyMed)
- Eating Right for Kidney Failure, NIDDK
- White CM, Tai Z, Nuzi K. Transdermal "natural GLP-1" dietary supplements violate law and place patients at risk. Ann Pharmacother 2026
This guide is general information about GLP-1 medications and nutrition, based on prescribing information and published research. It is not medical advice and does not replace your prescriber, pharmacist or dietitian. Talk to your clinician before starting any supplement, especially if you have kidney disease or take other medicines. If a symptom is severe, getting worse, or worrying you, contact your healthcare provider. In an emergency, call 911.
Published by the Pep AI team · Updated September 2026