When someone on a GLP-1 medication drops from 2,200 calories per day to 1,200, they have not just cut their energy intake by 45%. They have cut their micronutrient intake by a similar proportion. Unless dietary quality increases dramatically to compensate, deficiencies in essential vitamins and minerals develop over weeks and months, often without obvious symptoms until they are well established.
The Micronutrient Gap
The human body requires a consistent supply of vitamins and minerals for thousands of metabolic processes. Many of these nutrients cannot be stored in large quantities, meaning daily intake matters. When food volume decreases by 40 to 50%, maintaining adequate micronutrient status requires either a significant increase in the nutrient density of every food consumed, targeted supplementation, or both.
The most common deficiencies we see in clients on GLP-1 medications include B vitamins, iron, zinc, magnesium, and vitamin D.
B Vitamins
The B vitamin complex is involved in energy metabolism, neurotransmitter production, red blood cell formation, and DNA synthesis. B12 and folate deficiencies are particularly concerning because they can cause fatigue, cognitive fog, and anaemia that may be mistakenly attributed to the caloric deficit itself.
Food sources rich in B vitamins include meat, fish, eggs, dairy, and leafy greens. For clients with significantly reduced intake, a B-complex supplement provides insurance against deficiency.
Iron
Iron deficiency is the most common micronutrient deficiency globally, and it is exacerbated by reduced food intake. Women of reproductive age are at particularly high risk. Symptoms include fatigue, weakness, pale skin, and reduced exercise tolerance.
Haem iron from red meat, poultry, and fish is more bioavailable than non-haem iron from plant sources. For clients eating smaller quantities of meat, pairing non-haem iron sources with vitamin C-rich foods improves absorption. Iron status should be monitored through blood work, as both deficiency and excess carry health risks.
Zinc
Zinc plays critical roles in immune function, wound healing, protein synthesis, and taste perception. The irony is that reduced zinc status can further decrease appetite, compounding the appetite suppression from the medication itself.
Oysters, red meat, poultry, and pumpkin seeds are the richest food sources. Supplementation at 15 to 30mg daily may be appropriate for clients with confirmed deficiency or very low food intake.
Magnesium
Magnesium is involved in over 300 enzymatic reactions and is critical for muscle function, sleep quality, blood sugar regulation, and nervous system health. Deficiency can cause muscle cramps, poor sleep, anxiety, and irregular heartbeat.
Most people are already marginally deficient in magnesium before starting GLP-1 medications. Reduced food intake makes this worse. Green vegetables, nuts, seeds, and whole grains are good sources, but supplementation with magnesium glycinate or magnesium threonate at 200 to 400mg daily is often warranted.
Vitamin D
Vitamin D is unique because it is primarily synthesised through sun exposure rather than diet. However, dietary sources become more important during periods of reduced outdoor activity or in regions with less sun exposure. In New Zealand, vitamin D status varies seasonally, and clients in caloric deficit may not be consuming enough fortified foods or fatty fish to maintain adequate levels.
Supplementation at 1,000 to 2,000 IU daily is a reasonable baseline, with higher doses guided by blood test results.
Monitoring and Prevention
The most reliable approach to preventing micronutrient deficiency is a combination of high-quality, nutrient-dense food choices at every meal, targeted supplementation based on individual risk factors, and periodic blood work to check key markers including ferritin, B12, folate, vitamin D, zinc, and magnesium.
Our coaching programmes include personalised supplementation recommendations based on your body composition data, dietary intake analysis, and, where available, blood work results. We do not prescribe blanket supplement stacks. Every recommendation is justified by your individual data.
Frequently Asked Questions
Should I take a multivitamin while on GLP-1 medications? A high-quality multivitamin provides a safety net, but it should not replace dietary quality. Some nutrients in multivitamins are poorly absorbed or provided at insufficient doses. Targeted supplementation based on your specific risk factors is more effective.
How do I know if I am deficient? Many deficiencies develop without obvious symptoms initially. Regular blood work is the most reliable method. Discuss testing with your GP, particularly for iron, B12, vitamin D, and magnesium.
Can supplements interfere with GLP-1 medications? Most vitamin and mineral supplements do not interact with GLP-1 medications. However, taking supplements with food, even a small amount, improves absorption and reduces any potential nausea.
Our supplementation recommendations are personalised to your data, not generic. Explore our coaching packages and learn more about nutrition timing to maximise nutrient absorption.
