When someone on a GLP-1 medication drops from 2,200 calories per day to 1,200, they have not just cut energy intake by 45%. They have cut micronutrient intake by a similar proportion. Unless dietary quality rises sharply 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 body needs a steady supply of vitamins and minerals for thousands of metabolic processes. Many of these are not stored in large quantities, so daily intake matters. When food volume drops by 40 to 50%, maintaining adequate micronutrient status takes either much higher nutrient density per meal, targeted supplementation, or both.

The most common deficiencies we see in clients on GLP-1 medications are B vitamins, iron, zinc, magnesium, and vitamin D.

B vitamins

The B vitamin complex drives energy metabolism, neurotransmitter production, red blood cell formation, and DNA synthesis. B12 and folate deficiencies cause fatigue, cognitive fog, and anaemia that often gets blamed on the caloric deficit itself.

Food sources include meat, fish, eggs, dairy, and leafy greens. For clients with sharply reduced intake, a B-complex supplement is insurance.

Iron

Iron deficiency is the most common micronutrient deficiency globally, and it gets worse on reduced food intake. Women of reproductive age sit at highest 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 less meat, pairing non-haem iron sources with vitamin C-rich foods improves absorption. Monitor iron through blood work. Both deficiency and excess carry risks.

Zinc

Zinc supports immune function, wound healing, protein synthesis, and taste perception. Low zinc further decreases appetite, compounding the appetite suppression from the medication.

Oysters, red meat, poultry, and pumpkin seeds are the richest food sources. Supplementation at 15 to 30mg daily fits clients with confirmed deficiency or very low food intake.

Magnesium

Magnesium runs over 300 enzymatic reactions and matters for muscle function, sleep quality, blood sugar regulation, and nervous system health. Deficiency causes 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 it worse. Green vegetables, nuts, seeds, and whole grains are good sources. Supplementation with magnesium glycinate or magnesium threonate at 200 to 400mg daily is often warranted.

Vitamin D

Vitamin D is mostly made through sun exposure, not diet. Dietary sources matter more during periods of reduced outdoor activity or in regions with less sun. In New Zealand, vitamin D status varies seasonally, and clients in caloric deficit may not be eating enough fortified foods or fatty fish to maintain adequate levels.

A baseline of 1,000 to 2,000 IU daily is reasonable, with higher doses guided by blood test results.

Monitoring and prevention

Prevent micronutrient deficiency through a combination of nutrient-dense food choices at every meal, targeted supplementation based on individual risk factors, and periodic blood work for ferritin, B12, folate, vitamin D, zinc, and magnesium.

Our coaching programmes include personalised supplementation 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 anchored to your individual data.

Frequently asked questions

Should I take a multivitamin while on GLP-1 medications? A quality multivitamin is a safety net, not a replacement for dietary quality. Some nutrients in multivitamins are poorly absorbed or under-dosed. Targeted supplementation based on your specific risk factors works better.

How do I know if I am deficient? Many deficiencies develop without obvious symptoms early on. Regular blood work is the 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. Taking them with a small amount of food improves absorption and reduces 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.