People using popular weight loss injections such as Mounjaro and Wegovy may be at risk of serious nutritional deficiencies due to a lack of adequate dietary guidance, researchers have cautioned.
Around 1.5 million people in the UK are currently taking GLP-1 weight loss drugs, but experts say many could be “replacing one set of health problems with another” because of preventable nutrient shortfalls. A new review suggests that as much as 40 per cent of the weight lost while using these medications is lean body mass, including muscle.
The findings, published in the journal Obesity Reviews by academics from the University of Cambridge and University College London (UCL), highlight a “real risk” of health complications linked to poor nutrition, such as fatigue, hair loss and osteoporosis. The loss of muscle mass, researchers warned, can also increase the likelihood of weakness, injuries and falls.
GLP-1 receptor agonists work by mimicking a naturally occurring hormone that helps regulate appetite. They suppress hunger, increase feelings of fullness and reduce food cravings, leading to a 16 to 39 per cent reduction in calorie intake. However, the researchers said there has been little investigation into how these drugs affect diet quality.
The team analysed 12 studies involving adults taking GLP-1 medications and found that only three included input from nutrition professionals. One observational study revealed widespread nutrient inadequacies among users, alongside limited access to dietetic support.
Dr Marie Spreckley, the study’s lead researcher from the University of Cambridge, said the rapid rise in the use of weight loss injections has not been matched by appropriate nutritional care.
“Many people receive little or no structured guidance on diet quality, protein intake or micronutrient adequacy while experiencing marked appetite suppression,” she said. “If nutritional care is not integrated alongside treatment, there’s a risk of replacing one set of health problems with another, through preventable nutritional deficiencies and largely avoidable loss of muscle mass.”
The warning comes as private prescriptions for weight loss drugs surge. Of the estimated 1.5 million users in the UK, around 95 per cent are believed to be accessing the medication privately.
Dr Adrian Brown, an NIHR Advanced Fellow at UCL and the study’s corresponding author, said the injections can be “highly beneficial” for people living with obesity, but stressed the importance of professional guidance.
“Without appropriate nutritional support, there is a real risk that reduced food intake could compromise dietary quality,” he said. “People may not get enough protein, fibre, vitamins and minerals essential for maintaining overall health.”
Previous research has also suggested that users of weight loss jabs could experience muscle loss comparable to “10 years of ageing” if they do not engage in strength training.
The study aligns with recent warnings from the Royal College of Physicians (RCP), which said medication alone will not be enough to tackle the obesity epidemic. In a new position statement, the RCP called on the government to address the “social and environmental drivers of obesity” alongside expanding access to treatment.
Dr Kath McCullough, the RCP’s special adviser on obesity, said weight loss drugs can be “part of the solution for some patients” but added that preventing people from developing obesity and overweight in the first place should remain the priority.
