FAT JAB USERS AT RISK OF NUTRITIONAL DEFICIENCIES AND MUSCLE LOSS AS THEY SKIP MEALS, STUDY SHOWS

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Fat jabs leave users vulnerable to nutritional deficiencies and muscle loss as they are up to twice as likely to skip meals, a study suggests.

The change in eating habits reduces opportunities for adequate protein intake, with 88 per cent now failing to consume enough, researchers warn.

The findings highlight an urgent need for patients prescribed the likes of Wegovy and Mounjaro to be monitored and given personalised dietary guidelines to support 'safe and sustainable' weight loss, they add.

Weight loss jabs are a class of drugs known as GLP-1 receptor agonists, which work by mimicking the hormone GLP-1 to regulate blood sugar levels and suppress appetite.

They have been shown to reduce calorie intake by between 16 to 39 per cent, making them a powerful tool for the treatment of obesity.

However, little research has previously examined their impact on diet quality or the intake of key macro- and micronutrients, such as protein, fibre, vitamins, iron and calcium, needed to maintain good health.

Inadequate micronutrient intake can put people at risk of a range of conditions, from hair loss, fatigue, and slow wound healing to an impaired immune system and osteoporosis.

Now nutritionists from IRCCS San Raffaele Hospital and Vita-Salute San Raffaele University, in Milan, Italy, have analysed 5,741 days of data from 332 overweight or obese patients who tracked what they ate using an AI-powered mobile app.

They compared total calorie intake, macronutrient intake, protein adequacy, meal patterns, and weight loss between 116 fat jab users and 216 non-users.

Lead author Dr Valentina Vinelli said: '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.

'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.'

Participants using GLP-1 RAs reported a significantly lower calorie intake than non-users (average 1,102 vs 1,281 per day) as well as significantly lower intake 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).

However, despite these lower absolute intakes, the percentage of daily calories derived from protein, carbohydrates and fat were nearly identical, indicating a proportional reduction in food intake rather than changes in diet quality.

Moreover, GLP-1 RA users were much more likely than non-users to skip breakfast (31 per cent of days vs 16 per cent of days), lunch (31 per cent vs 18 per cent) and dinner (40 per cent vs 30 per cent), reducing opportunities for nutrient intake.

Among the subset of 177 participants who submitted regular weight measurements, those using fat jabs experienced significantly greater weight loss than non-users, losing an average 2.2kg or 2.5 per cent of body weight, versus 0.2kg or 0.2 per cent of body weight.

Nearly a quarter (24 per cent) using fat jab achieved clinically meaningful weight loss of at least 5 per cent of body weight loss compared with just 3 per cent of non-users.

Dr Vinelli said weight-loss drugs are 'transforming obesity care' but many people using them receive 'little or no systematic guidance on diet quality, protein intake, or micronutrient adequacy'.

She added: '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.

'In our future work, we will look beyond protein to explore how GLP-1 RAs affect the intake of other key nutrients and examine how real-time mobile apps could help people stay on track with healthy eating and lifestyle habits throughout their journey.'

Studies traditionally ask participants to complete food questionaries or keep diaries, which are reliant on their memory and adequate record keeping.

But the AI app included image recognition, which allowed it to analyse ingredients and calculate nutrients from a photo, and barcode scanning alongside text and voice logging, providing real-time estimates of intake.

The authors explain that the modest weight loss seen in the GLP-1 group reflects the real-world conditions of the study.

It did not independently verify or control drug adherence and medication use was self-reported. Most users only tracked their weight for a few weeks and appeared to still be gradually increasing their dose, rather than on full maintenance doses.

The study will be presented at the European Congress on Obesity in Istanbul, Turkey, next month.

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2026-04-09T22:24:01Z