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title: "Nutrient Deficiencies on GLP‑1 Medications: The Hidden Risks of Rapid Weight Loss"
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Many people taking GLP‑1 medications (like semaglutide , liraglutide , tirzepatide ) are not meeting their needs for key micronutrients, especially vitamin D, iron, several B vitamins (including thiamine and B12), calcium, protein, and trace minerals such as zinc and selenium.

## Why GLP‑1 Users Are at Risk

GLP‑1 receptor agonists reduce appetite, slow gastric emptying, and often lead to rapid, significant weight loss. In people already living with obesity or type 2 diabetes, diet quality is often suboptimal and baseline micronutrient deficiencies are common before treatment starts. When food intake drops further on GLP‑1s, total nutrient intake can fall below requirements even if weight loss is “on track.”

In a large US database study of 461,382 adults on GLP‑1 medications, 12.7% were newly diagnosed with a nutritional deficiency by 6 months and 22% by 12 months, with vitamin D deficiency most common. These findings suggest that micronutrient issues are a frequent, clinically relevant consequence of GLP‑1 therapy rather than rare side effects.

## The Top Nutrients GLP‑1 Users May Be Lacking

### Vitamin D3

Vitamin D deficiency stood out as the most frequently diagnosed problem in GLP‑1 users across several studies. In one claims‑based cohort, GLP‑1 users had a 49% higher risk of vitamin D deficiency than people on SGLT2 inhibitors and a 32% higher risk than those on DPP‑4 inhibitors. Average vitamin D intake in dietary surveys of GLP‑1 users reached only about 20% of recommended levels. [

Low vitamin D matters because it impairs calcium absorption, accelerates bone loss during rapid weight reduction, and may worsen muscle weakness and fatigue. Many people will require a vitamin D supplement in addition to limited food sources such as fatty fish, eggs, mushrooms, and fortified milk alternatives.

### Iron

Several datasets link GLP‑1 therapy with lower iron stores and a higher risk of iron deficiency. In one registry analysis of adults with type 2 diabetes, GLP‑1 users had a 54% greater risk of low ferritin (a marker of iron stores) than SGLT2 inhibitor users. A prospective pilot study in 51 adults found that intestinal iron absorption dropped markedly after 10 weeks of semaglutide. 

Iron deficiency can develop even without obvious anemia at first and may show up as fatigue, shortness of breath with exertion, hair shedding, or restless legs. People with hereditary hemochromatosis on GLP‑1s also showed 26–30% lower ferritin compared with SGLT2 users, underscoring how powerfully these drugs can shift iron balance. I like to see my patient's ferritin levels in the 65-75 ug/L range as a minimum.

Liposomal iron is a great tool when iron levels are low and IV iron is not easily accessible due to cost or access restrictions. Liposomal iron has very little if any side effects compared to regular iron such as ferrous fumarate (e.g. Ferramax, Palafer, Euro-fer ). I have found my patients absorb Liposomal iron and have seen good results in their blood work. The one I recommend is [Ferasom](https://www.ferosomcanada.com/) iron capsules or sachets.

### B Vitamins (Vitamin B1 -Thiamine, Vitamin B12, Folate/Folic Acid)

B vitamins are particularly vulnerable when calorie intake and animal protein consumption fall.

Thiamine (Vitamin B1) : Case reports have linked GLP‑1 use to severe thiamine deficiency, including Wernicke encephalopathy and beriberi in the context of rapid weight loss and prolonged low intake. Thiamine demands rise with carbohydrate metabolism, so even modest intakes may be inadequate when overall nutrition is compromised. 

Vitamin B12 : Delayed gastric emptying and lower intake of animal protein can reduce B12 absorption and intake, and lower levels have been documented in GLP‑1 users over time. B12 deficiency can contribute to fatigue, neuropathy, and cognitive changes. 

Folic Acid/Folate and other B vitamins: Observational analyses found a higher likelihood of being diagnosed with “other B‑vitamin” deficiencies in people on combined GLP‑1 plus metformin compared with metformin alone. 

Because neurological symptoms from B‑vitamin deficiency can be irreversible if missed, unexplained neurologic changes, gait disturbances, or cognitive decline in GLP‑1 users should prompt urgent assessment. 

## Calcium and Bone‑Related Nutrients

Rapid weight loss is associated with [bone loss as well as reduced bone mineral density](/blog/bone-health-and-preventing-osteoporosis) and many adults with overweight or obesity already fall short of calcium recommendations. In dietary analyses of GLP‑1 users, more than 60% consumed less than estimated requirements for calcium and iron. The recommended calcium intake for most adults is 1000–1200 mg per day, yet up to half of people with obesity do not reach this level even before starting GLP‑1 therapy. 

Vitamin D3 and calcium work together so poor vitamin D3 status makes it harder to maintain bone density during GLP‑1‑associated weight loss, particularly in midlife and older adults or those at risk of osteoporosis.

## Protein and Lean Muscle Mass

Reduced appetite and early satiety often lead GLP‑1 users to eat less protein than required for preserving lean mass. Studies included in the recent narrative review found that [protein insufficiency contributed to loss of muscle mass (sarcopenia)](/blog/obesity-inflammation-and-organ-health-why-it-s-about-more-than-just-weight)during therapy. This can show up as weakness, slower gait, or difficulty performing usual daily tasks even as the scale looks “successful.”

A target of roughly 1.0–1.2 g of protein per kilogram of ideal body weight per day is a common clinical starting point in weight‑loss settings to support muscle maintenance, with higher targets for older adults or those who are more active.

However much of the research has shown a higher goal of 0.5-1.0 g of protein per pound of body weight - which is much higher then the recommendations previously suggested. This is due to the higher muscle and bone demand on muscle and bone health especially for women in midlife during the menopause transition. You can learn more with my free protein ebook [here](/protein-handout/hormone-health).

## Trace Minerals: Zinc, Selenium, and Others

Diagnoses of mineral deficiencies, including zinc and selenium, rose over time among GLP‑1 users in large cohort studies. Obesity itself is associated with low intakes and suboptimal levels of zinc, magnesium, and other trace elements even before any medication is started. When appetite falls and portions shrink further, the risk of clinically relevant deficits increases. 

These micronutrients play roles in immune function, thyroid hormone metabolism, antioxidant defence, and taste sensation; deficiency may manifest as poor wound healing, altered taste, brittle hair or nails, or increased susceptibility to infections.

## What the Research Actually Shows (and What It Doesn’t)

Recent studies showed that looking at 480,825 adults treated with semaglutide, liraglutide, or tirzepatide for obesity and/or type 2 diabetes. The largest datasets come from two big database cohorts published in 2025, totalling over 480,000 individuals; the rest are mechanistic studies, dietary analyses, and case reports. 

- Nutritional deficiency diagnoses increased steadily over the first year of GLP‑1 therapy, especially vitamin D deficiency and anemia due to nutrient deficits.
- GLP‑1 users showed higher risks of vitamin D deficiency and lower ferritin levels than people treated with other diabetes medications such as SGLT2 and DPP‑4 inhibitors.
- Prospective data demonstrate reduced intestinal iron absorption with semaglutide, suggesting a plausible biological mechanism for iron depletion. 
- Case reports document severe thiamine deficiency syndromes in the setting of substantial weight loss on GLP‑1 drugs.

However, most of the current evidence is observational, and many individuals likely had micronutrient deficits before starting GLP‑1s. Vitamin levels were not always measured prior to treatment, so causality cannot yet be definitively established, and testing patterns may differ between groups. Even so, experts emphasize that micronutrient deficiencies during GLP‑1 therapy appear common enough to warrant proactive screening and prevention. 

## How GLP‑1 Users Can Protect Their Nutritional Status

For anyone on a GLP‑1 receptor agonist for obesity or type 2 diabetes, practical steps to protect nutritional status include:

- Regular lab work : Consider testing 25‑hydroxyvitamin D, ferritin and a full iron panel, B12, folate, and, when indicated, thiamine and serum zinc, especially during the first 6–12 months or when symptoms arise. I often run blood work for my patients and recommend at a minimum annual testing.
- Primary care provider referral to nutrition expert such as a Naturopathic Doctor, nutritionist or dietician : People who saw an expert in nutrition within six months of starting GLP‑1 therapy were more likely to have deficiencies detected and addressed, highlighting the value of structured nutrition support. 
- Protein‑first meal structure: Prioritize high‑quality protein (fish, poultry, eggs, Greek yogurt, tofu, legumes) at each eating occasion to support muscle and maintain micronutrient density even when portions are small.
- Daily sources of vitamin D and calcium: Include fatty fish, eggs, mushrooms, and fortified milks while also considering individually tailored vitamin D and calcium supplements as needed. 
- Iron‑rich foods: Focus on iron‑dense options (lean red meat, poultry thighs, legumes, lentils, pumpkin seeds) paired with vitamin‑C‑rich foods to enhance absorption, with supplements added when ferritin remains low (optimal ferritin I like to see for my patients is around 70ug/L).
- Targeted supplementation: For those with restricted diets (e.g., very low calorie, vegetarian/vegan, or post‑bariatric surgery), a high‑quality multivitamin plus condition‑specific add‑ons (vitamin D3, iron, B12, thiamine) may be appropriate under your clinician's guidance. 

If you are currently on a GLP-1 medication, discuss potential micronutrient deficiencies with your primary care provider. Particularly when unexplained fatigue, neuropathy, functional decline, or cognitive changes, especially during periods of marked caloric restriction. Early recognition and correction can help preserve muscle mass, protect bone health, and support long‑term metabolic outcomes especially while on any of the  GLP‑1 medications.

To your best health,

Dr. Amy J. Tung, ND

Naturopathic Doctor | Menopause Society Certified Practitioner

References:

Karam L, Mabilleau G, Paccou J. Effects of Glucagon-Like Peptide-1 receptor agonists on bone health in people living with obesity. Osteoporos Int. 2025 Nov;36(11):2115-2126. doi: 10.1007/s00198-025-07664-1. Epub 2025 Sep 8. PMID: 40920189; PMCID: PMC12628458.

Sibal R, Balamurugan G, Langley J, Graham Y, Mahawar K. Macronutrient, Micronutrient Supplementation and Monitoring for Patients on GLP-1 Agonists: Can We Learn from Metabolic and Bariatric Surgery? Nutrients. 2025 Nov 23;17(23):3659. doi: 10.3390/nu17233659. PMID: 41373949; PMCID: PMC12693348.

Urbina J, Salinas-Ruiz LE, Valenciano C, Clapp B. Micronutrient and Nutritional Deficiencies Associated With GLP-1 Receptor Agonist Therapy: A Narrative Review. Clin Obes. 2026 Feb;16(1):e70070. doi: 10.1111/cob.70070. PMID: 41549912.

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