GLP-1 drugs such as Ozempic, Wegovy, and Mounjaro have exploded in popularity in the U.K. and the U.S. About 12% of U.S. adults (roughly 41 million people) and about 1.6 million adults in the U.K. have taken medications for weight loss.
A Cleveland Clinic study of 460,000 adults found that nearly 1 in 5 patients who were prescribed them developed nutrient deficiencies within a year — often without obvious symptoms.
Another large Mexican study of 480,000 patients found that 13.6% had a significant vitamin D deficiency after one year, and about 60% did not get enough iron or calcium from their diets.
Additional research links taking weight-loss drugs to deficiencies in magnesium, potassium, and vitamins A, C, D, and E, and also to inadequate intake of protein and dietary fiber.
Why GLP-1 drugs create nutrient shortfalls
Professor Giles Yeo, an expert in neuroendocrinology and obesity at the University of Cambridge, explains that GLP-1 drugs mimic the body’s natural satiety hormone, so people feel full faster and eat less. That drop in food intake causes substantial weight loss, but it also reduces the chances of getting a full range of essential micronutrients.
“These are micronutrients — you need very small amounts of them, but they are crucial to how the body works,” Yeo says. If someone eats a diet low in vitamins before starting treatment (for example, few fresh vegetables and fruits, a one-sided diet, or too many ultra-processed foods), the appetite reduction increases the risk of deficiency.
Beyond eating less, side effects also play a role: almost a third of GLP-1 users experience diarrhea, and nearly a quarter experience nausea and vomiting. Steven Heymsfield, director of the Metabolism and Body Composition Laboratory at Louisiana State University and the senior author of the Cleveland Clinic study, explains: “If you have diarrhea, you lose nutrients before the body can absorb them.”
Why these deficiencies often go unnoticed
Despite how common they are, many deficiencies are rarely checked in patients on GLP-1 drugs. A 2025 paper in the International Journal of Obesity called the lack of nutritional monitoring “a critical oversight.”
“Obesity is a chronic disease and should be treated like other chronic diseases,” Heymsfield emphasizes. He adds that if a doctor prescribes these drugs, they should test the patient’s blood for nutrient levels — just as clinicians do for other illnesses.
How deficiencies can harm your health
In the most severe cases, deficiencies can lead to medical emergencies. There are isolated reports of serious neurological problems — including speech difficulties, disorientation, and weakness — that were linked to B-vitamin deficiencies after GLP-1 use.
Even the most common deficiency — vitamin D — has real consequences: low vitamin D raises the risk of osteoporosis and worsens weakness in older adults. The risk becomes especially dangerous when low vitamin D combines with inadequate protein intake, because weight loss can then include loss of muscle mass (sarcopenia), which increases the risk of falls and fractures.
“There are older adults with obesity who start taking these drugs, and that can pave the way to sarcopenia and frailty in later life,” Heymsfield warns.
Yeo agrees with those concerns but points out that most current GLP-1 users are relatively privileged people who buy the drugs privately and can afford reasonably healthy food. He warns that once pill forms appear and prices drop, a wider population with poorer diets — often for reasons beyond their control — will gain access to the drugs. Yeo says that scenario could become a serious public-health problem.
What experts recommend
- Treat GLP-1 drugs as powerful medications; they require medical oversight.
- Test blood levels of key nutrients (iron, vitamin D, B vitamins, calcium, and others) before starting and during treatment, and adjust the diet or add supplements under a doctor’s supervision if needed.
- Monitor for side effects such as prolonged diarrhea, vomiting, severe fatigue, memory problems, or loss of muscle strength, and report them to your doctor.
Yeo stresses: “We don’t want to overhype things. These drugs are a powerful tool. But monitor the micronutrients we already know are commonly deficient. When people eat less, those problems only get worse.”
GLP-1 drugs are changing how we treat obesity. At the same time, the medical community must not forget a basic duty: to monitor patients’ nutritional status so that rapid weight loss does not turn into hidden but significant nutrient deficiencies. That responsibility involves not just weight outcomes but long-term health.
Based on material from BBC Science Focus
Photo: Openverse
