GLP-1 Weight-Loss Drugs May Increase the Risk of Nutrient Deficiencies: What You Need to Know
GLP-1 medications have become increasingly popular for managing type 2 diabetes and supporting weight loss. These treatments can help people control their appetite, feel full for longer, and reduce their food intake. However, as their use expands, researchers are raising questions about another important aspect of health: getting enough essential nutrients while taking these medicines.
Recent research suggests that some people using GLP-1 medications may not consume adequate amounts of important vitamins, protein, and dietary fiber. These nutrients are essential for maintaining muscle strength, supporting digestion, protecting bones, and keeping the body functioning properly.
Although these findings do not mean everyone taking GLP-1 medication will develop a deficiency, they highlight why balanced nutrition and appropriate medical supervision should remain important parts of weight-management treatment.
What Are GLP-1 Medications?
GLP-1 medications work by mimicking the action of glucagon-like peptide-1, a hormone involved in regulating blood sugar and appetite. These medicines can slow stomach emptying, increase feelings of fullness, and help regulate glucose levels.
Examples include semaglutide and liraglutide. Some medicines in this category are prescribed for type 2 diabetes, while specific formulations are approved for chronic weight management. Tirzepatide acts on both GIP and GLP-1 receptors and is also used for diabetes and weight management, depending on the product and its approved indication.
For many patients, these treatments can offer meaningful health benefits. However, because they may reduce hunger and the amount of food someone eats, maintaining adequate nutrition can become more challenging.
Eating less does not automatically mean eating better. When food intake decreases significantly, people may need to pay closer attention to the nutritional quality of their meals.
1. Vitamin B12: Supporting Nerves and Red Blood Cells
Vitamin B12 is essential for healthy nerve function, red blood cell production, and DNA synthesis. A deficiency can develop when the body does not receive enough vitamin B12 or cannot absorb it effectively.
Research highlighted in an August review by researchers associated with the Harvard T.H. Chan School of Public Health and the University of Copenhagen identified vitamin B12 as one of the nutrients that may be inadequately consumed by some people using GLP-1 medications.
Vitamin B12 is naturally present in foods such as fish, meat, eggs, dairy products, and shellfish. People following vegan diets may be particularly vulnerable if they do not regularly consume fortified foods or take an appropriate supplement.
Potential symptoms of vitamin B12 deficiency include fatigue, weakness, numbness, tingling, and difficulties with memory or concentration. Some people may develop symptoms gradually, making the problem difficult to recognise.
People taking GLP-1 medications should discuss their dietary habits and individual risk factors with a healthcare professional. Testing or supplementation may be appropriate in certain circumstances, but individual needs vary.
2. Protein: Important for Muscle Strength and Recovery
Protein plays a vital role in maintaining muscle mass, repairing tissues, supporting immune function, and producing enzymes and hormones.
When appetite decreases during weight-loss treatment, people may unintentionally consume less protein than their bodies require. The August research review reported that approximately 43 per cent of GLP-1 users examined in the relevant research had inadequate protein intake.
This finding is important because weight loss can involve reductions in both fat and lean body mass. Preserving muscle is particularly valuable for maintaining strength, mobility, and physical function.
Protein-rich foods include eggs, fish, poultry, dairy products, tofu, beans, lentils, and other legumes. Depending on individual dietary requirements, incorporating protein into regular meals may help people meet their nutritional needs even when their overall appetite is reduced.
However, protein requirements differ according to age, activity level, medical conditions, and other factors. People with kidney disease or other health concerns may need individualised advice before making significant changes to their protein intake.
3. Fibre: Helping Maintain Digestive Health
Dietary fibre supports normal bowel function, helps regulate digestion, and can contribute to healthy blood sugar and cholesterol levels.
Some people taking GLP-1 medications experience constipation, nausea, bloating, or other digestive symptoms. Reduced food intake and inadequate fibre consumption may contribute to these problems.
The relationship can become frustrating. Someone experiencing nausea or bloating may eat less, making it harder to obtain enough fibre and other nutrients. Inadequate hydration can also contribute to constipation.
Fibre-rich foods include vegetables, fruits, whole grains, oats, beans, lentils, nuts, and seeds. Increasing fibre gradually, drinking sufficient fluids when medically appropriate, and maintaining regular physical activity may support digestive health.
Nevertheless, individual tolerance varies, particularly during treatment initiation or dose increases. Anyone experiencing persistent or severe digestive symptoms should contact their healthcare professional rather than assuming the symptoms are simply part of weight loss.
4. Vitamin D: Protecting Bones and Supporting Immunity
Vitamin D helps the body absorb calcium and maintain healthy bones and muscles. It also contributes to normal immune function.
A January review discussed in the supplied report found that vitamin D deficiency affected 13.6 per cent of more than 480,000 adults receiving GLP-1 medications after one year of treatment. Separately, a September study from Northwestern University reported that nearly one in six children aged 10 to 17 who had used these medications for a year were diagnosed with nutrient deficiencies.
Vitamin D deficiency was a prominent concern in the paediatric findings.
These results deserve attention, particularly because adolescence is an important period for bone development. Adults can also be affected, especially those with limited sun exposure, certain medical conditions, or diets that provide insufficient vitamin D.
Sources include oily fish, egg yolks, and fortified foods. In the UK, vitamin D supplementation may be recommended during autumn and winter, with additional advice for people at increased risk of deficiency.
However, taking high doses without medical guidance is not advisable. A healthcare professional can help determine whether supplementation or testing is appropriate.
Can Nutrient Deficiencies Affect Children and Adults Differently?
Nutritional needs change throughout life. Children and teenagers require sufficient nutrients to support growth, development, and bone formation. Adults need to maintain muscle, protect bone health, and support normal metabolic functions.
The reported research suggests that nutritional concerns deserve attention across different age groups. However, the findings should not be interpreted as proof that GLP-1 medications directly cause every deficiency identified.
Changes in appetite, pre-existing nutritional problems, underlying health conditions, and dietary patterns may all influence the results.
Children receiving weight-management treatment require particular care because their nutritional needs differ from those of adults. Decisions about medication should be made with qualified healthcare professionals who can assess growth, development, and the potential benefits and risks of treatment.
Warning Signs That Should Not Be Ignored
Nutrient deficiencies can sometimes develop without obvious symptoms. When symptoms occur, they may include:
- Persistent tiredness or unusual weakness.
- Hair thinning or increased hair shedding.
- Difficulty concentrating or changes in memory.
- Dry skin or certain skin changes.
- Frequent infections.
- Numbness or tingling associated with some deficiencies.
- Muscle weakness or discomfort.
- Symptoms associated with weakened bones.
These symptoms are not specific to nutritional deficiencies and can have many other causes. Anyone experiencing persistent or concerning changes should seek medical advice rather than self-diagnosing or starting multiple supplements.
How to Support Better Nutrition During GLP-1 Treatment
A few practical measures can help people pay closer attention to their nutritional health.
Prioritise nutrient-rich meals. Choose foods that provide protein, vitamins, minerals, and fibre rather than focusing exclusively on reducing calories.
Eat manageable portions. If appetite is low, smaller meals may be easier to tolerate. A healthcare professional or registered dietitian can help develop a suitable eating plan.
Stay hydrated. Adequate fluid intake supports normal bodily functions and may help prevent constipation, although people with fluid restrictions should follow their clinician's advice.
Discuss supplements before taking them. Supplements may be useful when a deficiency exists or intake is inadequate, but not everyone needs the same products or doses.
Attend follow-up appointments. Discuss changes in appetite, digestive symptoms, energy levels, and any difficulties maintaining a balanced diet. Your healthcare team can determine whether nutritional assessment or blood tests are appropriate.
Conclusion
GLP-1 medications can be valuable tools for managing diabetes and supporting weight loss, but successful treatment involves more than the number on the scales.
Emerging research highlights potential nutritional concerns involving vitamin B12, protein, fibre, and vitamin D among some people using these medicines. Reduced appetite can make it harder to consume sufficient nutrients, while inadequate intake may affect energy, digestion, muscle maintenance, and bone health.
The evidence does not suggest that everyone taking GLP-1 medication will develop deficiencies. Instead, it reinforces the importance of personalised nutritional guidance, appropriate monitoring, and balanced eating throughout treatment.
By working with a qualified healthcare professional and paying attention to nutritional needs, patients can take a more comprehensive approach to weight management and long-term wellbeing.
Sources
- The Independent, 27 October 2026.
- Harvard T.H. Chan School of Public Health and University of Copenhagen. August review on nutritional adequacy and GLP-1 medication use, as described in the supplied report.
- Northwestern University. September study examining nutrient deficiencies among children and teenagers using GLP-1 medications, as described in the supplied report.
- Mayo Clinic. Patient information on protein, dietary fibre, and their roles in maintaining health.
- Cleveland Clinic. Patient information on nutrient deficiencies and their potential effects on the body.
Medical Disclaimer: This article is intended for general informational and educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Research findings may vary, and the associations described do not establish that GLP-1 medications directly cause every reported deficiency. Do not stop, change, or adjust prescribed medication without consulting your healthcare professional. Speak with a qualified clinician or registered dietitian about your individual nutritional needs, symptoms, and whether testing or supplementation is appropriate.