Can Ozempic, Wegovy, or Mounjaro Cause Vitamin Deficiencies? What to Watch For

This page is educational. It doesn't diagnose deficiencies or recommend supplement doses.

What the new study actually found (in kids and teens)

The figures shared widely on October 5, 2026, come from a study published September 17, 2026, in the journal Childhood Obesity (Kerr, Chang, Sulo, Stutts, Panchalingam, and Ryder).

Limits to keep in mind:

• It's a teen population. The figures shouldn't be applied directly to adults.
• Diagnosis codes aren't lab levels. A deficiency only shows up if someone was tested and coded. Teens who saw a nutrition professional had more recorded deficiencies (23.2% vs 14.8%), which may partly reflect more testing.
• No comparison group was reported in the abstract, so the study can't say how much of this the drug caused.
• The drug mix is older. Most patients took liraglutide, so the results may not reflect tirzepatide (Mounjaro, Zepbound) or current semaglutide use.
• Industry authorship. Five of the six authors are affiliated with Abbott, which sells nutrition products.

What about adults?

A separate adult study by the same research group found a similar pattern. This retrospective claims analysis covered 461,382 adults who started a GLP-1 between 2017 and 2021 (mostly people with type 2 diabetes, average age 53). Within 12 months, 22.4% had a recorded nutritional deficiency, and vitamin D deficiency was the most common at 13.6% (Butsch et al., Obesity Pillars, 2025). It has the same limits: diagnosis codes, a mostly diabetic population, and several Abbott-affiliated authors. Here too, people who saw a dietitian had more recorded deficiencies.

A 2026 narrative review of six adult studies reached a similar conclusion. Vitamin D deficiency was the most common problem, and iron stores were often lower. But the authors stress that the evidence is mostly observational and "causality ... cannot be definitively established" (Urbina et al., Clinical Obesity, 2026).

Why a GLP-1 can create nutrient gaps

The medicine itself isn't known to strip nutrients. The main problem is volume. The 2025 joint advisory on GLP-1 nutrition, from the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association, and The Obesity Society, notes calorie reductions of 16% to 39% on these drugs. It says vitamins and minerals are especially hard to get enough of below about 1,200 kcal/day for women and 1,800 kcal/day for men. It adds that stomach side effects "may further compromise nutrient absorption."

Intake can get very low. In a small 2026 online study of 387 adults on GLP-1 medicines who kept two-day food diaries, average intake was about 753 kcal/day, with 33 g of protein and 7 g of fiber. Fewer than 10% met protein recommendations (Korus et al., Journal of Translational Medicine). That was a self-selected social-media sample, so treat it as a warning sign, not a typical result.

Nutrients of concern

The joint advisory lists iron, calcium, magnesium, zinc, and vitamins A, D, E, K, B1, B12, and C as examples of nutrients of concern on GLP-1 therapy. It also stresses protein and fiber. Food sources below are from the NIH Office of Dietary Supplements.

Is protein enough on a GLP-1, or do I need fiber too?

You need both. Protein gets most of the attention on a GLP-1 because it helps protect muscle. But fiber matters too, and it's easy to miss on a small appetite. In the small 2026 food-diary study above, people averaged only 7 g of fiber a day.

Why fiber matters on a GLP-1:

• Constipation is common. In placebo-controlled weight-loss trials reported on the FDA labels, constipation affected 24% of people on Wegovy 2.4 mg injection vs 11% on placebo, 11% to 17% on Zepbound vs 5%, and 20% to 27% on Foundayo vs 9%. These are trial rates, not a prediction for you.
• Protein alone can make it worse. The 2025 joint advisory notes that foods high in protein or fat slow stomach emptying, which can worsen constipation. It recommends encouraging "adequate fluids and fiber from foods" and a gradual increase in foods with soluble and insoluble fiber, such as prunes or other dried fruits.
• Most people already fall short. The Dietary Guidelines for Americans, 2020–2025 list dietary fiber as a "dietary component of public health concern" because intakes are low. The 2025–2030 edition says to "prioritize fiber-rich whole grains." For reference, the FDA's Daily Value on food labels is 28 g of fiber a day, based on a 2,000-calorie diet. Your clinician or dietitian can help set a realistic goal at a lower calorie intake.

Food-first ways to add fiber:

• Pair protein with a fiber food at each meal, like Greek yogurt with berries, eggs with vegetables, or chicken with beans.
• Increase slowly over a few weeks, and drink more fluids as you go. The joint advisory notes that avoiding fatty or high-fiber foods during the first few days of treatment can help if nausea is a problem.
• Check the "Dietary Fiber" line and %DV on food labels.

We don't recommend fiber-supplement amounts here. If constipation doesn't improve, or you have severe stomach pain or vomiting, call your clinician. For more on stomach side effects, see our guide to what to eat for GLP-1 nausea. If you take a GLP-1 pill, our guide to eating on the Wegovy pill or Foundayo covers meal timing.

Signs worth raising with a clinician

The joint advisory lists these signs of frank nutrient deficiency:

• Fatigue beyond what you'd expect
• Excessive hair loss (see GLP-1s and hair loss)
• Flaky or itchy skin
• Muscle weakness
• Poor wound healing
• Unusual bruising

Also tell your prescriber if you're regularly eating very little, can't keep food or fluids down, or feel dizzy or weak. These symptoms have many possible causes, and only testing can confirm a deficiency.

Asking for labs

The joint advisory says lab testing before therapy may be warranted if you've had a very low-calorie diet, bariatric surgery, celiac disease, other inflammatory conditions that raise deficiency risk, or a past deficiency. If any of those apply, or you notice the signs above, it's reasonable to ask:

• "Should we check any vitamin or mineral levels before or during treatment?"
• "Given how little I'm eating, which nutrients are you most concerned about for me?"
• "Would seeing a registered dietitian help?" (Both claims studies found that few patients saw one early on.)

Your clinician decides which tests make sense. Don't self-diagnose from a symptom list.

Food-first: eating nutrient-dense on a low appetite

• Protein first, then color. Eat the protein part of a meal first, so it gets in before you feel full. Add a vegetable or fruit when you can.
• Small and often. For people struggling to eat, the advisory suggests small meals every 3 to 4 hours with adequate fluids.
• Pick foods that do double duty. Greek yogurt or milk (protein plus calcium, and vitamin D if fortified), eggs (protein, B12, some vitamin D), salmon or sardines (protein, vitamin D, and calcium if canned with bones), and beans or lentils (protein, iron, and fiber).
• Use fortified foods. Fortified cereals and milks can fill gaps in small portions.
• Supplements: ask first. The joint advisory says supplements "can be proactively considered for at-risk nutrients, such as vitamin D, calcium, B12, or a multivitamin-mineral tablet," at doses tailored to each person. That's a decision for your clinician, not a label on a bottle.

A note for parents

GLP-1 medicines for teens should be managed by a pediatric clinician. The study's senior author says vitamin D, iron, and calcium are "of particular concern during adolescence." Ask your teen's care team about nutrition counseling and monitoring early, not months in.

How Olive helps you plan and track

Olive is an AI health companion. It checks in daily so you can log small meals quickly, see whether protein, fiber, and nutrient-dense foods are showing up, and spot patterns, like skipping meals on low-appetite days. Bring that record to your clinician when you discuss labs. Olive doesn't diagnose deficiencies or recommend doses. Members who want clinical help can add the Olive Protocol, which includes a licensed-clinician consult; treatment only if the clinician decides it fits.

Who this guide is for (and who it isn't for)

Good fit:

• You're on semaglutide, tirzepatide, or another GLP-1 and eating far less than before.
• You saw the vitamin D headlines and want to know what they mean for you.
• You're a parent of a teen on a GLP-1 and want questions for the care team.

Not the right fit:

• You need dosing advice. Your clinician sets supplement plans.
• You have severe symptoms, such as fainting, chest pain, or confusion. Seek care promptly.
• You're pregnant, have had bariatric surgery, or have kidney disease. Your needs differ, so get individualized care.

Fill the gaps without overthinking it

Olive's companion checks in daily to help you plan small, nutrient-dense meals and keep a record to share with your clinician. It's free to try.

See how Olive can help →

Medical disclaimer

Medical disclaimer: This page is general education, not medical advice or a diagnosis. It gives no supplement doses. GLP-1 medicines are prescription-only and carry side effects and warnings, including stomach side effects, dehydration-related kidney injury, gallbladder disease, pancreatitis, and a boxed warning about thyroid C-cell tumors seen in rodents. Don't start supplements or change your diet or dose without your clinician, especially for children and teens, during pregnancy, or with kidney disease. Individual results vary.