Nutrient Deficiencies on GLP-1s: What to Test and How to Supplement
- Dr. Kate Kresge
- Jul 27
- 6 min read
GLP-1s have some evidence for supporting metabolic health, but new research shows that rapid or significant weight loss can increase the risk of developing nutrient deficiencies that may impact energy, immunity, and long-term wellbeing.
Common deficiencies include:
Zinc – associated with impaired immune response and poor wound healing
Iron – linked to fatigue, shortness of breath, and hair thinning
Fat-soluble vitamins (A, D, E, K) – which support blood clotting, skin and eye health, and bone integrity
Clinical guidelines recommend medical nutrition therapy for individuals taking GLP-1s to help them maintain adequate nutrient intake on a calorie-restricted diet. But without supplementation, adequate amounts of these nutrients are hard to obtain on a calorie restricted diet.
Here's what I recommend every person chat with their doctor about as a smart starting point when starting a GLP-1
Ensure you discuss any risk factors like pancreatic issues, gut issues, or history of an eating disorder to your doctor. Your doctor knowing your history is key to keeping you safe.
Run labs every 3-6 months to stay on top of potential deficiencies.
Use your test results to build a smart food and supplement plan with an RD or medical professional.
Strength train, if you’re able, to preserve muscle and prevent long-term weight regain.
Let’s walk through the lab tests I recommend and what you should know about each one.
Labs for People on GLP1-s
First up, let's talk about the lab panel I recommend you get before starting a GLP-1 and every 3-6 months after starting it. New evidence shows that people on GLP-1s are at risk of nutrient deficiencies, including vitamin A, B1, B12, C, D, E, K, and minerals like zinc and iron. But what's even more interesting is that obesity - often of the main indications for GLP-1s - itself increases the risk for nutrient deficiencies.
These nutrient deficiencies can cause some serious issues. I've put them in an easy list and complete panel for you to order yourself to be drawn at your local labcorp. Below, we'll go through each and why they matter so much for health.
CBC – Complete Blood Count
This test looks at red and white blood cells, hemoglobin, hematocrit, and platelets. Red call abnormalities can indicate anemia, which can develop if you're not getting enough iron, B12, or folate. It can also indicate issues with white blood cells and other immune system markers. If a CBC is abnormal, you might notice symptoms like fatigue, lightheadedness, shortness of breath, cold intolerance, or pale skin. Anemias can make working out enough to maintain lean muscle mass difficult and worse. People with anemia often report feeling so tired they can barely get through the day. Thankfully, finding and treating is super easy. You just have to make the effort to check. ( NIH Iron Fact Sheet, NIH B12 Fact Sheet). You can figure out exactly which type of anemia may be impacting your red blood cells by checking iron, B12 and folate (below). It's important to note that red blood cell marker's don't have to be abnormal for you to have low iron, B12 or folate.
Iron Panel – Ferritin, Serum Iron, TIBC
Iron is essential for oxygen transport and energy. GLP-1s can reduce your appetite for iron-rich foods (like red meat), and women are especially prone to low iron due to menstruation and blood loss each month. Low iron can give you the symptoms like fatigue, hair loss, brain fog, pale skin, or craving non-food items like ice. (Source: NIH Iron Fact Sheet).
B12 Panel (Serum B12, Homocysteine, Methylmalonic Acid)
This combo gives the clearest picture of your vitamin B12 status. B12 is crucial for energy, nerve health, and red blood cell production. Homocysteine and MMA are early warning signs that your B12 might not be working well, even if your levels look “normal.” Low B12 can result in symptoms like numbness, brain fog, mood changes, or fatigue (Source: NIH B12 Fact Sheet).
CMP – Comprehensive Metabolic Panel (with Calcium)
The CMP checks liver and kidney function, blood sugar, and electrolytes—including calcium. It's a good thing to measure regularly to if you are taking a GLP-1 to make sure it's not affecting your liver, kidneys or pancreas. It's also helpful for making sure key electrolytes like calcium are in range. GLP-1 users can be at risk for under-consuming, which over time can put them at risk for symptoms of deficiency like muscle cramps, numbness or tingling in fingers, or mood and energy changes. Because calcium helps to regulate how our hearts beat by controlling electrical signals, out-of-range calcium on a CMP is always a cause for follow up and correcting root cause contributors if they can be found. ( NIH Calcium Fact Sheet)
Zinc
Zinc plays a major role in immune function, healing, skin health, and even taste perception. Low zinc can happen when overall food intake drops or if digestion is impaired. Common signs of low zinc: Increased infections, slow wound healing, rash, or loss of taste/smell. (Source: NIH Zinc Fact Sheet)
Vitamin A (Retinol)
Vitamin A supports your vision, skin, immune system, and gut lining. It’s fat-soluble, which means you need enough dietary fat to absorb it properly. Deficiency signs can include: Dry eyes, trouble seeing at night, rough skin, or frequent colds. (Source: NIH Vitamin A Fact Sheet)
Vitamin D
Vitamin D helps with calcium absorption and supports immune and bone health. Low-fat diets and indoor lifestyles make deficiency more common than you’d think. You may notice: Low mood, fatigue, bone aches, or getting sick more often. (Source: NIH Vitamin D Fact Sheet)
Vitamin E
Vitamin E is another fat-soluble vitamin that acts as a powerful antioxidant. It protects cells and supports nerve health. Possible signs of low vitamin E: Muscle weakness, vision problems, or balance/coordination issues. (Source: NIH Vitamin E Fact Sheet)
Vitamin K
Vitamin K helps your blood clot properly and works with vitamin D to build and maintain strong bones. Low fat intake may reduce absorption. Low levels can show up as: Easy bruising, bleeding gums, or heavy menstrual cycles. (Source: NIH Vitamin K Fact Sheet)
Thiamin (Vitamin B1)
Thiamin helps turn food into energy and supports your nervous system. It’s especially vulnerable to depletion if you’re eating very little or have ongoing nausea. Symptoms can include: Fatigue, irritability, memory trouble, or tingling in the hands or feet. (Source: NIH Thiamin Fact Sheet)
Vitamin C
Vitamin C supports collagen production, immune defense, and helps absorb iron from plant foods. It’s easy to miss out on if you're eating less fruit and veg. Deficiency signs include: Gum bleeding, easy bruising, slow healing, or feeling worn down. (Source: NIH Vitamin C Fact Sheet)
Omega-3 Index
This test checks the levels of EPA and DHA—two anti-inflammatory fats that support brain, heart, and joint health. Most people don’t get enough, especially on low-calorie diets that exclude fish or nuts.
If your omega-3s are low, you might notice: Dry skin, joint stiffness, low mood, or poor focus. (Source: NIH Omega-3 Fact Sheet)
Supplements for People on GLP1-s
Covering your bases nutritionally actually isn't too hard. There are a number of multivitamin options that can give you most of the nutrients listed above, including vitamin A, B1, B12, C, D, E, K, zinc. What multivitamin don't often contain are the nutrients iron and omega 3s.
Iron - because not everyone needs it, it can cause GI upset, and too much iron can be dangerous
Omega 3s - because they're hard to fit in a multivitamin, can interfere with blood clotting medications
You can, however, take iron and omegas in addition to a multivitamin if your doctor recommends it. If you're looking for safe options for these supplements, this list is cGMP, third-party certified, and you can get 5% off.
Final Thoughts
If you’re on a GLP-1 medication and seeing great progress, that’s something to celebrate. But if your nutrient intake isn’t keeping up with your body’s needs, you may start to feel depleted, fatigued, or inflamed—even while the scale is moving in the right direction. That’s why I recommend testing these markers every few months, especially during active weight loss. Lab testing helps you catch issues early and create a smarter plan to stay strong, sharp, and healthy as your body changes. You deserve to feel amazing.
