Do GLP-1 Medications Cause Vitamin Deficiencies? Nutrition on Semaglutide (Ozempic®, Wegovy®) and Tirzepatide
- Joshua Silva, MD
- 3 days ago
- 7 min read
Medically authored by Joshua Silva, MD | Evidence-Based Weight Loss at Potere Health MD, serving patients across Utah
GLP-1 medications such as semaglutide (Ozempic®, Wegovy®) and tirzepatide (Zepbound®, Mounjaro®) reduce appetite and calorie intake. Many patients therefore wonder whether eating less could lead to vitamin or nutrient deficiencies during treatment.
In most people, nutritional deficiencies are not caused directly by the medication itself, but reduced food intake during weight loss can affect nutrient intake if meals are not balanced.¹–³
Do GLP-1 medications like semaglutide and tirzepatide cause vitamin deficiencies?
GLP-1 medications such as semaglutide and tirzepatide do not appear to directly cause vitamin malabsorption. Their primary physiological effects are slowing gastric emptying and reducing appetite.
However, because patients often consume fewer calories, nutrient intake can decline if meals are not nutrient-dense during weight loss.¹–⁴
Why GLP-1 medications usually do NOT cause true nutrient deficiencies
Unlike bariatric surgery, GLP-1 receptor agonists do not cause the intestinal malabsorption physiology seen after metabolic surgery. Their main effects are appetite suppression and delayed gastric emptying.
When nutritional deficiencies occur during treatment, they are usually related to reduced food intake rather than impaired nutrient absorption.³,⁴
How eating less on GLP-1 medications can affect nutrient intake
GLP-1 medications often reduce total calorie intake. When people eat less food overall, they may also consume fewer vitamins, minerals, and protein unless meals are intentionally nutrient-dense.
Over time, this can increase the risk of low nutrient intake during weight loss.¹,²,⁵
What vitamin deficiencies have been reported with GLP-1 medications?
Observational studies of GLP-1 receptor agonist therapy have identified nutrient deficiencies in some patients, most commonly vitamin D, with occasional reports of iron, vitamin B12, and folate.
These findings are inconsistent across studies and may reflect baseline deficiencies or reduced dietary intake during weight loss, rather than a direct drug effect.¹–³
Vitamin D
Vitamin D deficiency is common in people with obesity and has also been reported in some studies of patients treated with GLP-1 receptor agonists. Because deficiency frequently exists before treatment begins, most experts believe this reflects baseline deficiency and reduced intake rather than medication-induced malabsorption.¹,²
Iron
Iron deficiency has occasionally been identified in nutritional assessments of patients using GLP-1 receptor agonists. This may occur when calorie restriction reduces intake of iron-rich foods, particularly in menstruating women or individuals who reduce red meat intake during dieting.¹
Vitamin B12 and folate
Low vitamin B12 or folate levels have been reported in some observational analyses of patients treated with GLP-1 medications. In clinical trials, however, vitamin deficiency–related adverse events were uncommon and occurred at rates similar to placebo.⁶
Common nutritional deficiencies during calorie deficit and weight loss
When people lose weight, nutrient intake may decline simply because they consume fewer calories overall. This occurs with many weight-loss approaches and is not specific to GLP-1 medications.
Nutrients that may be affected during calorie restriction include protein, vitamin D, calcium, iron, and other micronutrients depending on diet quality.¹,⁵
Protein and lean body mass
Protein intake is one of the most important nutritional considerations during weight loss. When calorie intake drops but protein intake remains adequate, individuals are more likely to preserve lean muscle mass while losing body fat.⁵
Calcium
Calcium intake can decline during dieting because people often reduce dairy foods or overall food intake. Maintaining adequate calcium supports bone health and neuromuscular function, particularly during prolonged weight loss.¹
Iron
Iron intake may fall during calorie restriction when total food intake decreases or diets become lower in red meat and iron-rich foods. This pattern is commonly seen during prolonged dieting and is not unique to GLP-1 medications.¹
Zinc and hair-related nutrients
Rapid weight loss and reduced protein intake can contribute to telogen effluvium, a temporary hair shedding condition associated with physiologic stress and nutritional factors such as low iron or zinc levels.
Ensuring adequate protein and iron intake is often more clinically relevant than isolated biotin supplementation when addressing diet-related hair shedding.⁸
Fluids and electrolytes
Reduced appetite may also lead to lower fluid intake. Maintaining adequate hydration helps prevent dehydration and supports normal metabolic function during weight loss.⁷
Why reduced appetite on semaglutide or tirzepatide can affect nutrition
GLP-1 receptor agonists promote weight loss partly by reducing hunger and slowing gastric emptying, helping people feel full sooner and eat fewer calories.⁴
While beneficial for weight loss, this means that nutrition depends heavily on the quality of smaller meals.
Scientific explanation — calorie restriction and nutrient intake
When calorie intake decreases, total intake of protein, vitamins, and minerals may also decline unless meals are nutrient-dense.
Reviews of GLP-1 receptor agonist therapy emphasize that reduced energy intake is the primary driver of weight loss and can influence nutritional intake.⁵
Plain-English explanation — eating less food means fewer nutrients
If someone eats half as much food, they may also consume fewer nutrients unless they choose foods that provide more protein, vitamins, and minerals per bite.
Who is more likely to develop nutritional deficiencies on GLP-1 medications?
Most patients maintain normal vitamin levels during treatment. However, certain factors increase the risk of nutritional deficiencies.
Risk factors include:
Prolonged very low-calorie intake
Frequent meal skipping or fasting
Highly restrictive diets
Rapid or uncontrolled weight loss
Limited food variety
Pre-existing nutrient deficiencies¹,²
Do you need supplements when taking GLP-1 medications like Ozempic® or Zepbound®?
Most patients taking GLP-1 medications do not require extensive supplementation if they consume a balanced diet.
A simple multivitamin may be reasonable in some cases, but targeted testing and individualized guidance are often more appropriate than routine high-dose supplementation.¹,²
When a simple multivitamin may be reasonable
A multivitamin may be considered when:
Daily calorie intake is significantly reduced
Diet variety is limited
Rapid weight loss is occurring
Protein intake is consistently low
Multivitamins can help fill minor nutritional gaps but do not replace balanced meals.
Why excessive supplementation can be harmful
Taking high-dose vitamin or mineral supplements without medical guidance can cause side effects, interfere with nutrient absorption, or alter important lab tests.
Supplement | Potential Issue |
Zinc | High doses can reduce copper absorption, potentially leading to anemia or nerve symptoms.⁹ |
Calcium | Large doses can worsen constipation and reduce iron absorption when taken together.¹⁰ |
Iron | Iron supplements can cause nausea or stomach discomfort and are usually recommended only when deficiency is present.¹¹ |
Biotin | High-dose biotin can interfere with certain lab tests, including thyroid and cardiac markers.¹³ |
Fat-soluble vitamins (A, D) | These vitamins are stored in the body, and excessive doses can accumulate and lead to toxicity.¹² |
Most patients benefit more from balanced meals and targeted supplementation when needed than routine high-dose vitamin regimens.¹,²
How to prevent nutrient deficiencies while taking GLP-1 medications
Simple nutrition habits can help maintain adequate intake during weight loss.
Goal | Nutrition Strategy |
Preserve muscle mass | Prioritize lean protein at the start of every meal.⁵ |
Maximize nutrition | Choose nutrient-dense whole foods rather than empty calories. |
Maintain intake | Eat smaller meals consistently rather than skipping meals. |
Prevent dehydration | Sip fluids consistently throughout the day.⁷ |
Monitor health | Discuss symptoms such as fatigue or hair loss with your clinician. |
When nutritional symptoms on GLP-1 medications should be evaluated by a clinician
Patients should contact their clinician if they experience:
Persistent fatigue or weakness
Dizziness or dehydration
Significant hair shedding
Ongoing nausea preventing food intake
Rapid or excessive weight loss¹,²,⁸
Bottom line: nutrition while taking GLP-1 medications
GLP-1 medications such as semaglutide and tirzepatide do not directly cause nutrient malabsorption, but appetite suppression can reduce nutrient intake during weight loss.
Most patients maintain adequate nutrition with balanced meals, adequate protein intake, and attention to hydration. Individual evaluation may be appropriate if intake becomes very low or symptoms develop.¹–⁵
Disclaimer:
This article is for educational purposes only and is not a substitute for medical advice.
About the Author
Dr. Joshua Silva, MD, is a licensed physician and Medical Director of Potere Health MD. He earned his medical degree from the University of Hawaiʻi John A. Burns School of Medicine and completed residency training in Occupational and Environmental Medicine at the University of Utah, where he also earned a master’s degree in Occupational Health. He later completed a Master of Business Administration with an emphasis in health care administration at Ohio University.
Dr. Silva specializes in evidence-based weight management, including GLP-1 and GIP therapies such as semaglutide and tirzepatide. He works closely with patients to monitor nutritional health, manage medication tolerance, and guide safe, nutrient-dense dietary adjustments during both active weight loss and maintenance phases. He provides in-person and virtual care for patients in Salt Lake City, St. George, and Cedar City, Utah.
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Novo Nordisk A/S. Ozempic (semaglutide) injection, for subcutaneous use: prescribing information. Novo Nordisk; 2024. https://www.accessdata.fda.gov/drugsatfda_docs/label/2025/209637s025lbl.pdf
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Almandoz JP, Pickett-Blakely O, Tewksbury C, et al. Nutritional status with tirzepatide in obesity: a post hoc analysis of the SURMOUNT-1-4 randomized clinical trials. Obes Pillars. 2026;17:100248. doi:10.1016/j.obpill.2026.100248. https://pubmed.ncbi.nlm.nih.gov/41640675/
National Institutes of Health Office of Dietary Supplements. Zinc—Fact Sheet for Health Professionals. Updated Jan 6, 2026. Accessed March 4, 2026. https://ods.od.nih.gov/factsheets/Zinc-HealthProfessional/
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