GLP-1 Vitamin Deficiencies: What You Might Be Missing

Why GLP-1 Users Are at Risk for Nutrient Deficiencies

GLP-1 receptor agonists like semaglutide (Ozempic, Wegovy) and tirzepatide (Mounjaro, Zepbound) work by suppressing appetite and slowing gastric emptying. This leads to significant caloric reduction—often 500 to 1,000 fewer calories per day than pre-medication intake. While that caloric deficit drives weight loss, it also means you are consuming dramatically less of every vitamin and mineral your body needs.

The math is straightforward. If you were eating 2,200 calories per day before medication and now consume 1,300 calories, you have cut your total food intake by 41%. That means 41% fewer vitamins, 41% fewer minerals, and 41% less of every micronutrient that your body requires for hundreds of biological processes—unless you are deliberately choosing nutrient-dense foods at every meal.

A 2023 narrative review in Obesity Surgery drew parallels between the nutritional risks of GLP-1 medications and those of bariatric surgery, noting that any intervention producing rapid, significant weight loss through reduced food intake carries an inherent risk of micronutrient deficiency. The authors recommended proactive screening and supplementation for GLP-1 patients, particularly those on higher doses for extended periods.

Additionally, GLP-1 medications can cause GI side effects—nausea, vomiting, and decreased appetite—that further reduce food intake during dose titration periods. Some users report food aversions that eliminate entire food groups from their diet, compounding the risk. If you are dealing with nausea, see our guide on foods that help stop Ozempic nausea.

The 7 Most Common Deficiencies on GLP-1 Medications

1. Vitamin B12 (Cobalamin)

Why it matters: B12 is essential for nerve function, DNA synthesis, and red blood cell production. Deficiency can cause irreversible nerve damage if left untreated.

Why GLP-1 users are at risk: B12 is found almost exclusively in animal products, and reduced food intake means reduced B12 intake. Additionally, metformin—which many type 2 diabetes patients take alongside GLP-1 medications—is well documented to impair B12 absorption. A study in the Journal of Clinical Endocrinology & Metabolism found that long-term metformin use reduced B12 levels by an average of 19%.

Symptoms of deficiency: Fatigue, numbness and tingling in hands and feet, difficulty walking, memory problems, mood changes, and a smooth or swollen tongue.

Best food sources:

• Clams — 84 mcg per 85 g (3,500% of daily value)
• Beef liver — 70 mcg per 85 g
• Salmon — 4.8 mcg per 100 g
• Eggs — 1.1 mcg per large egg
• Greek yogurt — 1.3 mcg per 200 g
• Nutritional yeast (fortified) — 2.4 mcg per tbsp

Supplementation: 250–1,000 mcg of methylcobalamin daily. Sublingual forms may be better absorbed. If severely deficient, your doctor may recommend B12 injections.

2. Iron

Why it matters: Iron is required for oxygen transport via hemoglobin, energy production, and immune function. It is also critical for preventing hair loss—one of the most common concerns among GLP-1 users.

Why GLP-1 users are at risk: Iron is one of the hardest nutrients to get in adequate amounts when eating less food. Heme iron (from animal sources) has the best absorption rate at 15–35%, while non-heme iron (from plants) is absorbed at only 2–20%. Women who menstruate are at particularly high risk, as they lose iron monthly and need 18 mg per day compared to 8 mg for men.

Symptoms of deficiency: Fatigue, weakness, pale skin, cold hands and feet, brittle nails, hair loss, headaches, dizziness, and restless legs.

Best food sources:

• Chicken liver — 11 mg per 100 g
• Beef sirloin — 2.6 mg per 100 g
• Lentils — 3.3 mg per 100 g cooked
• Spinach — 2.7 mg per 100 g raw
• Pumpkin seeds — 8.8 mg per 100 g
• Fortified cereals — 8–18 mg per serving

Absorption tip: Pair iron-rich foods with vitamin C (citrus fruits, bell peppers, strawberries) to boost absorption by up to 6 times. Avoid consuming calcium supplements, coffee, or tea within one hour of iron-rich meals.

Supplementation: Only supplement if blood work confirms low ferritin (below 30 ng/mL) or iron deficiency anemia. Excess iron is toxic. Your doctor can recommend the appropriate dose.

3. Vitamin D

Why it matters: Vitamin D is essential for calcium absorption, bone health, immune function, and mood regulation. It also plays a role in hair follicle cycling and muscle function.

Why GLP-1 users are at risk: Few foods contain significant vitamin D, so most people rely on sun exposure and fortified foods. When food intake drops, the already-limited dietary sources become even scarcer. A 2022 cross-sectional study found that 42% of US adults are vitamin D deficient, and the rate is likely higher among people eating reduced-calorie diets.

Symptoms of deficiency: Bone pain, muscle weakness, fatigue, depression, frequent illness, and impaired wound healing.

Best food sources:

• Salmon (wild-caught) — 14.2 mcg per 100 g
• Sardines — 4.8 mcg per 100 g
• Egg yolks — 1.8 mcg per yolk
• Fortified milk or plant milk — 2.5–3.6 mcg per cup
• UV-exposed mushrooms — up to 10 mcg per 100 g
• Cod liver oil — 34 mcg per tbsp

Supplementation: 1,000–2,000 IU (25–50 mcg) of vitamin D3 daily for most adults. If your blood level is below 20 ng/mL, your doctor may prescribe a higher dose (50,000 IU weekly for 8–12 weeks). Take with a meal containing fat for best absorption.

4. Calcium

Why it matters: Calcium is essential for bone density, muscle contraction, nerve signaling, and heart function. Rapid weight loss itself is a risk factor for decreased bone mineral density, making calcium particularly important for GLP-1 users.

Why GLP-1 users are at risk: Dairy products are the primary calcium source in most diets. If GLP-1-related nausea causes dairy aversion (a common complaint), calcium intake can plummet. The body also needs adequate vitamin D to absorb calcium, creating a compounding effect if both are low.

Symptoms of deficiency: Muscle cramps, numbness in fingers, fatigue, poor appetite (ironically), abnormal heart rhythms, and over time, osteoporosis.

Best food sources:

• Greek yogurt — 200 mg per 200 g
• Milk — 300 mg per cup
• Sardines (with bones) — 382 mg per 100 g
• Collard greens — 266 mg per 100 g cooked
• Fortified plant milks — 300–450 mg per cup
• Tofu (calcium-set) — 350 mg per 100 g
• Almonds — 264 mg per 100 g

Supplementation: If dietary intake is below 1,000 mg per day (the RDA for most adults), supplement with calcium citrate, which does not require stomach acid for absorption. Split doses to no more than 500 mg at a time for optimal absorption. Take calcium and iron supplements at separate times.

5. Folate (Vitamin B9)

Why it matters: Folate is critical for cell division, DNA repair, and red blood cell formation. It is especially important for women of childbearing age due to its role in preventing neural tube defects.

Why GLP-1 users are at risk: Folate is found in green leafy vegetables, legumes, and fortified grains. If GLP-1-related appetite suppression leads to a diet low in these foods, folate levels can drop. This is compounded in women who may become pregnant after significant weight loss (as fertility often improves with weight reduction).

Symptoms of deficiency: Fatigue, mouth sores, gray hair, swollen tongue, and megaloblastic anemia.

Best food sources:

• Chicken liver — 578 mcg per 100 g
• Lentils — 181 mcg per 100 g cooked
• Spinach — 194 mcg per 100 g raw
• Black beans — 149 mcg per 100 g cooked
• Asparagus — 149 mcg per 100 g
• Fortified cereals — 100–400 mcg per serving

Supplementation: 400–800 mcg daily in the form of methylfolate (the active form) rather than folic acid. Most quality multivitamins contain adequate folate.

6. Zinc

Why it matters: Zinc supports immune function, wound healing, protein synthesis, and hair growth. It is involved in over 300 enzymatic reactions in the body.

Why GLP-1 users are at risk: The richest zinc sources are meat and shellfish. Reduced food intake on GLP-1 medications, especially among vegetarian users, increases the risk of deficiency. Phytates in whole grains and legumes further reduce zinc absorption.

Symptoms of deficiency: Hair loss, delayed wound healing, loss of taste or smell, frequent infections, diarrhea, and skin rashes.

Best food sources:

• Oysters — 74 mg per 100 g
• Beef — 4.8 mg per 100 g
• Pumpkin seeds — 7.8 mg per 100 g
• Chickpeas — 1.5 mg per 100 g cooked
• Cashews — 5.8 mg per 100 g
• Crab — 6.5 mg per 100 g

Supplementation: 15–30 mg daily, taken with food. Do not exceed 40 mg per day. Zinc competes with copper for absorption, so if supplementing long term, consider a zinc-copper combination.

7. Magnesium

Why it matters: Magnesium is required for muscle and nerve function, blood sugar regulation, blood pressure control, and bone health. It is one of the most common deficiencies in the general population, and GLP-1 users are at even higher risk.

Why GLP-1 users are at risk: Magnesium-rich foods include nuts, seeds, whole grains, and dark leafy greens—foods that many people eat less of when their appetite is reduced. GI side effects like vomiting and diarrhea can also deplete magnesium stores.

Symptoms of deficiency: Muscle cramps, twitching, fatigue, nausea, loss of appetite, numbness, tingling, and abnormal heart rhythms.

Best food sources:

• Pumpkin seeds — 550 mg per 100 g
• Dark chocolate (70%+) — 176 mg per 100 g
• Almonds — 270 mg per 100 g
• Spinach — 79 mg per 100 g raw
• Black beans — 70 mg per 100 g cooked
• Avocado — 29 mg per 100 g
• Quinoa — 64 mg per 100 g cooked

Supplementation: 200–400 mg daily. Magnesium glycinate or magnesium citrate are the best-absorbed forms. Magnesium oxide is poorly absorbed and more likely to cause GI discomfort—a significant consideration for GLP-1 users already dealing with GI side effects.

Blood Tests to Request From Your Doctor

Do not wait for symptoms to appear. Proactive screening can catch deficiencies before they cause harm. Request the following labs every 6 months while on GLP-1 medication:

1. Complete blood count (CBC) — Screens for anemia caused by iron, B12, or folate deficiency
2. Ferritin — The most sensitive marker for iron stores. Optimal range is 40–200 ng/mL (levels below 30 are associated with hair loss even without clinical anemia)
3. Vitamin B12 (serum) — Optimal range is above 400 pg/mL. Many labs flag "normal" at 200, but symptoms can appear at 200–400
4. 25-hydroxyvitamin D — Optimal range is 40–60 ng/mL. Below 20 is deficient; 20–30 is insufficient
5. Serum zinc — Normal range is 66–110 mcg/dL
6. RBC magnesium — More accurate than serum magnesium. Normal range is 4.2–6.8 mg/dL
7. Calcium (ionized) — More accurate than total calcium. Normal range is 4.5–5.6 mg/dL
8. Folate (serum or RBC) — Serum folate above 5.9 ng/mL is generally considered adequate

A Nutrient-Dense Daily Meal Plan

This sample day delivers maximum micronutrient coverage in approximately 1,450 calories and 115 g of protein. Each meal is designed to address multiple potential deficiencies simultaneously:

• Breakfast: Spinach and egg scramble (2 whole eggs + 2 egg whites) with 50 g sauteed spinach, 30 g feta cheese, 1 slice whole-grain toast — Provides: B12, iron, folate, calcium, zinc, vitamin D
• Lunch: Sardine and white bean salad — 100 g sardines (with bones), 100 g cannellini beans, mixed greens, cherry tomatoes, lemon-olive oil dressing, 15 g pumpkin seeds on top — Provides: B12, calcium, vitamin D, omega-3, iron, zinc, magnesium, folate
• Snack: 200 g Greek yogurt with 30 g almonds and 50 g mixed berries — Provides: B12, calcium, magnesium, zinc
• Dinner: 140 g baked salmon with 150 g roasted broccoli, 100 g cooked quinoa, drizzle of olive oil — Provides: B12, vitamin D, omega-3, magnesium, folate, iron, zinc
• Evening: 30 g dark chocolate (70%+) with herbal tea — Provides: magnesium, iron

For a full weekly meal plan optimized for GLP-1 users, see our complete GLP-1 meal plan guide.

Should You Take a Multivitamin?

For GLP-1 users eating less than 1,500 calories per day, a daily high-quality multivitamin serves as nutritional insurance. Look for one that contains:

• 100% daily value of B12 (as methylcobalamin)
• 100% daily value of folate (as methylfolate)
• 1,000 IU vitamin D3
• 15–18 mg iron (for menstruating women)
• 15 mg zinc
• At least 100 mg magnesium (you will likely need an additional standalone supplement to reach 300–400 mg total)

Take your multivitamin with a meal containing some fat to improve absorption of fat-soluble vitamins (A, D, E, K). If your multivitamin contains iron, take it at a different time than any calcium supplements.

How Nourie Protects Against Nutrient Deficiencies

Manually tracking seven different micronutrients across every meal is impractical for most people. Nourie generates personalized GLP-1 meal plans that are optimized not just for protein and calories, but for complete micronutrient coverage. The app cross-references your daily food intake against your requirements for each vitamin and mineral, flagging potential gaps before they become clinical deficiencies. When you enter your latest blood work results, Nourie can further personalize your meals to emphasize the specific nutrients you need most.

Key Takeaways

• Eating less food means less of every nutrient. Without deliberate planning, deficiencies are probable, not just possible.
• The seven most common deficiencies for GLP-1 users are B12, iron, vitamin D, calcium, folate, zinc, and magnesium.
• Request comprehensive blood work every 6 months, including ferritin, B12, vitamin D, zinc, and RBC magnesium.
• A daily multivitamin is reasonable nutritional insurance for anyone eating below 1,500 calories per day.
• Always pair iron-rich foods with vitamin C and take calcium and iron supplements at separate times.
• Choose nutrient-dense foods at every meal—every bite counts more when you are eating less.
• Do not self-diagnose or self-supplement iron; always confirm with blood work first.