Weight Loss Jabs Pose Risks of Nutritional Deficiencies and Muscle Loss, Study Reveals
Users of weight loss injections, commonly known as fat jabs, are up to twice as likely to skip meals, leaving them vulnerable to nutritional deficiencies and muscle loss, according to a new study. The research indicates that this change in eating habits reduces opportunities for adequate protein intake, with a staggering 88 per cent of users now failing to consume enough protein. These findings underscore an urgent need for patients prescribed medications such as Wegovy and Mounjaro to receive close monitoring and personalised dietary guidelines to ensure safe and sustainable weight loss.
How GLP-1 Receptor Agonists Work and Their Impact on Diet
Weight loss jabs belong to a class of drugs called GLP-1 receptor agonists, which mimic the hormone GLP-1 to regulate blood sugar levels and suppress appetite. They have been proven to reduce calorie intake by between 16 to 39 per cent, making them a powerful tool in the fight against obesity. However, prior research has largely overlooked their effects on diet quality and the intake of essential macro- and micronutrients, including protein, fibre, vitamins, iron, and calcium, all crucial for maintaining good health.
Inadequate micronutrient intake can lead to a range of health issues, from hair loss, fatigue, and slow wound healing to a weakened immune system and osteoporosis. To investigate these risks, nutritionists from IRCCS San Raffaele Hospital and Vita-Salute San Raffaele University in Milan, Italy, analysed 5,741 days of data from 332 overweight or obese patients. Participants tracked their food consumption using an AI-powered mobile app, providing real-time estimates of intake through features like image recognition, barcode scanning, and voice logging.
Key Findings from the Study
The study compared 116 fat jab users with 216 non-users, examining total calorie intake, macronutrient intake, protein adequacy, meal patterns, and weight loss. Lead author Dr Valentina Vinelli noted, 'While GLP-1 RAs produce impressive weight loss, the question of whether meaningful muscle loss accompanies fat loss with these therapies is still hotly debated. What remains universally agreed, however, is that protecting muscle mass should be a central goal of any weight-loss programme.'
Muscle health depends on sufficient protein intake and regular physical activity, especially resistance exercise. Dr Vinelli added, 'For people using GLP-1 RAs, reduced appetite can make it harder to meet protein needs, making what you eat matter more than ever, especially given that protein requirements tend to be higher in people with obesity and during active weight loss. Protein requirements should always be personalised, expressed as grams per kilogram of adjusted body weight, rather than treated as a one-size-fits-all target.'
The results showed that participants using GLP-1 receptor agonists reported significantly lower calorie intake than non-users, with an average of 1,102 versus 1,281 calories per day. They also had lower intakes of macronutrients, including protein (53.8 vs 62.0 g/day), carbohydrates (128 vs 143 g/day), and fat (39.7 vs 45.7 g/day). Despite these reductions, the percentage of daily calories from protein, carbohydrates, and fat remained nearly identical, indicating a proportional decrease in food intake rather than a decline in diet quality.
Moreover, GLP-1 RA users were much more likely to skip meals: 31 per cent of days for breakfast (vs 16 per cent for non-users), 31 per cent for lunch (vs 18 per cent), and 40 per cent for dinner (vs 30 per cent), further limiting nutrient intake opportunities.
Weight Loss Outcomes and Clinical Implications
Among 177 participants who submitted regular weight measurements, those using fat jabs experienced significantly greater weight loss than non-users. They lost an average of 2.2kg or 2.5 per cent of body weight, compared to just 0.2kg or 0.2 per cent for non-users. Nearly a quarter (24 per cent) of fat jab users achieved clinically meaningful weight loss of at least 5 per cent of body weight, versus only 3 per cent of non-users.
Dr Vinelli emphasised that while weight-loss drugs are transforming obesity care, many users receive 'little or no systematic guidance on diet quality, protein intake, or micronutrient adequacy.' She stated, 'Real-world GLP-1 RA use in adults with overweight or obesity is associated with widespread protein inadequacy and increased meal skipping, underscoring the urgent need for proactive nutritional monitoring and personalised dietary guidance to be integrated alongside obesity treatment to support long-term health beyond weight loss.'
The study's modest weight loss results reflect real-world conditions, as it did not independently verify drug adherence and relied on self-reported medication use. Most users tracked their weight for only a few weeks and were likely still adjusting to their doses rather than being on full maintenance regimens. This research will be presented at the European Congress on Obesity in Istanbul, Turkey, next month, with future work planned to explore the impact on other key nutrients and the role of mobile apps in supporting healthy habits.
