Little wonder these treatments are ferociously popular. In the US, approximately 12 per cent of adults<\/a> say they\u2019ve tried GLP-1s \u2013 that\u2019s 41 million people. Across the Atlantic, an estimated 1.6 million adults<\/a> in the UK took a weight-loss drug in the last year.<\/p>\n The surge in GLP-1 use might look like a clear win for our waistlines. But beneath the excitement, a less visible problem could be taking shape.<\/p>\n Emerging research suggests that within months of starting these drugs, many people begin to fall short on essential nutrients their bodies need to function properly.<\/p>\n For instance, in a Cleveland Clinic study<\/a> of 460,000 adults prescribed a GLP-1 drug, nearly 1 in 5 developed a nutrient deficiency within a year \u2013 many without realising it.<\/p>\n A separate study<\/a> of 480,000 GLP-1 users by researchers in Mexico points to a similar pattern: 13.6 per cent developed a significant vitamin D deficiency within a year of starting the drugs, while around 60 per cent weren\u2019t getting enough iron or calcium from their diets.<\/p>\n The problem runs deeper still. Other research<\/a> suggests GLP-1 drug use can deplete a wide range of essentials \u2013 magnesium, potassium, and vitamins A, C, D and E among them.<\/p>\n \u201cYou don\u2019t actually need large quantities of these nutrients in a healthy diet,\u201d says Prof Giles Yeo<\/a>, a neuroendocrinology and obesity expert at the University of Cambridge.<\/p>\n \u201cThey\u2019re micronutrients \u2013 you need really small amounts of them. It\u2019s just that these small amounts are absolutely crucial for the running of the body.\u201d<\/p>\n And it\u2019s not just micronutrients \u2013 meaning vitamins and minerals \u2013 that are an issue here. Adults on GLP-1s may also struggle to consume enough protein and fibre.<\/p>\n But, despite their prevalence, these deficiencies are unlikely to be spotted by a medical professional. Many people take GLP-1 drugs without their nutrition being monitored \u2013 something described as a \u201ccritical oversight\u201d by a 2025 article<\/a> in the International Journal of Obesity.<\/p>\n Dr Steven Heymsfield<\/a> \u2013 director of the Metabolism and Body Composition Laboratory at Louisiana State University, in the US, and senior author of the Cleveland Clinic study \u2013 agrees.<\/p>\n \u201cObesity is a chronic disease and it should be managed like one,\u201d he says. \u201cIf your doctor prescribes these drugs for you, that doctor should assess you with nutrient blood tests \u2013 just like they do for other diseases.\u201d<\/p>\n Read more:<\/strong><\/p>\n Smaller portions, bigger problems<\/strong><\/p>\n So why do these deficiencies form in the first place? It largely comes down to how these drugs reshape how much you eat.<\/p>\n GLP-1 drugs mimic a natural fullness hormone, helping you feel satisfied on smaller portions. That\u2019s what drives the weight loss.<\/p>\n But it also means fewer opportunities to consume the full range of nutrients your body needs each day.<\/p>\n \u201cFor many people on these drugs, their diets may not have been great to begin with,\u201d says Yeo, noting that they\u2019re often low in fresh fruit and veg, limited in variety, or heavy in ultra-processed foods that lack essential nutrients.<\/p>\n \u201cIf you just take the drugs and don\u2019t make any behavioural changes, then you\u2019re going to eat less of a not-great diet,\u201d he continues.<\/p>\n \u201cUnless you improve your diet, you might end up with nutritional deficiencies.\u201d<\/p>\n That\u2019s why the deficiencies that crop up among GLP-1 users often mirror those that doctors routinely spot in the general population \u2013 vitamin B12 and iodine in vegetarians and vegans, iron in women due to menstruation, and vitamin D in anyone living somewhere short on sunshine.<\/p>\n \u201cThose are the deficiencies we already see relatively commonly,\u201d says Yeo. \u201cThose are only going to be worse [with GLP-1s].\u201d<\/p>\n But these drugs don\u2019t just increase our risk of deficiencies by shrinking our meals. Other side effects can play a part too.<\/p>\n \u201cWhen people are treated with GLP-1s, they reduce their food intake \u2013 but they also get gastrointestinal symptoms, like vomiting or diarrhoea,\u201d says Heymsfield.<\/p>\n \u201cIf you have diarrhoea, you\u2019re going to lose nutrients through that pathway.\u201d<\/p>\n In other words, some of the nutrients you do eat while on this medication might leave your body before they\u2019re absorbed.<\/p>\n These side effects aren\u2019t rare. Nearly a third of GLP-1 users experience diarrhoea, and almost a quarter<\/a> report nausea and vomiting.<\/p>\n Tipping the scales<\/strong><\/p>\n For experts, the size of the problem is alarming. With millions now using GLP-1 drugs, huge swathes of the population could be developing nutrient gaps without realising.<\/p>\n \u201cI think this will become very important,\u201d says Heymsfield. \u201cI\u2019ve been telling people, don\u2019t write off GLP-1s as completely safe. You\u2019ve got to wait and see how the deficiencies play into long-term impacts.\u201d<\/p>\n![\"Someone](\"https:\/\/www.europesays.com\/uk\/wp-content\/uploads\/2026\/05\/GLP-1-nutrients-1.jpg\")
Micronutrients include vitamins and minerals, whereas macronutrients refer to carbohydrates, fats, protein and fibre. All these are essential for the healthy functioning of the body – Credit: Getty<\/p>\n![\"A](\"https:\/\/www.europesays.com\/uk\/wp-content\/uploads\/2026\/05\/GLP-1-nutrients-2.jpg\")
The nutrient deficiencies that tend to crop up among GLP-1 users are the same ones commonly seen in the general population, including vitamin D, calcium and iron. – Credit: Getty<\/p>\n
![\"A](\"https:\/\/www.europesays.com\/uk\/wp-content\/uploads\/2026\/05\/GLP-1-nutrients-3.jpg\")
In the absence of rigorous nutritional monitoring, taking daily supplements may help keep deficiencies at bay – Credit: Getty<\/p>\n