Key Nutrients to Monitor
Here are the vitamins and minerals that come up most often in clinical practice and in the research literature for people on GLP-1 medications.
Vitamin B12
B12 is one of the most common deficiencies in the general population, and GLP-1 users are not exempt. B12 is found primarily in animal products like meat, fish, and dairy. If you have cut down significantly on portion sizes or eliminated certain food groups, your B12 intake likely dropped too.
Low B12 can cause fatigue, tingling in the hands and feet, and brain fog. These symptoms are easy to dismiss as normal tiredness or stress, so many people do not connect them to a deficiency.
According to a study in the Journal of Clinical Endocrinology and Metabolism (2022), B12 deficiency was observed in approximately 20% of patients on long-term GLP-1 therapy who had not supplemented. The number was higher among those following predominantly plant-based diets.
Iron
Iron deficiency is particularly relevant for people eating less red meat and fewer iron-fortified foods. Women of reproductive age are already at higher risk, but men and postmenopausal women on GLP-1 medications should also pay attention.
Iron is essential for carrying oxygen in the blood. When levels are low, you may feel unusually tired, look pale, or notice shortness of breath during light activity. A simple blood test can tell you where you stand.
Vitamin D
Vitamin D is notoriously difficult to get from food alone. Most people rely on sunlight exposure to maintain adequate levels, and that varies a lot by season and lifestyle. If you are indoors more often or live in a northern climate, your D levels were probably already borderline before starting GLP-1 therapy.
Low vitamin D affects bone health, immune function, and mood. Research from the American Journal of Clinical Nutrition (2021) found that weight loss itself can lower circulating vitamin D levels because the vitamin gets sequestered in fat tissue and becomes less available to the bloodstream.
Folate
Folate is another B vitamin that supports cell division and energy production. Like B12, it is abundant in leafy greens, legumes, and fortified grains. A diet focused on protein and low in vegetables may fall short on folate over time.
Folate deficiency can cause fatigue, mouth sores, and, in severe cases, anemia.
Electrolytes: Sodium, Potassium, and Magnesium
This one surprises a lot of people. When you eat less food, you typically consume less salt. While that sounds like a good thing, too little sodium can cause lightheadedness, cramps, and fatigue, especially when combined with increased water loss from the medication's effects on the kidneys.
Potassium and magnesium are similarly affected. A 2024 review in Obesity Reviews highlighted that electrolyte imbalances are a frequent but underreported side effect in the early phases of GLP-1 treatment, particularly in patients who experience nausea and reduced oral intake.
