GLP-1 receptor agonists (RAs) are transforming how type 2 diabetes and obesity are managed, offering significant improvements in glycaemic control, cardiovascular risk factors, and of course, weight loss.

But alongside the impressive results, questions remain: weight loss at what cost? Can patients sustain healthy eating patterns, preserve muscle mass, and maintain long-term wellbeing while on treatment?

Nutrient deficiencies: an under-recognised risk

Many people eligible for GLP-1 therapy already have poor baseline diet quality. GLP-1 RAs can further reduce overall food intake, sometimes by as much as 40% of usual dietary volume, because of their appetite-suppressing effects. While this reduction is central to weight loss, it also increases the risk that nutritional inadequacies that were present before treatment may emerge or worsen during therapy.

A 2025 US study of adults using GLP-1 RAs for more than one month highlighted several concerns. Average fibre intake was only 50–60% of daily requirements. Protein intake averaged around 77 g/day, which falls well below the 1.2–1.6 g/kg body weight typically recommended for those losing weight. In addition, calcium, iron, vitamin D, zinc, potassium, and magnesium intakes were frequently below 75% of recommended levels.

Similarly to those who undergo bariatric surgery, patients taking GLP-1 RAs also need ongoing monitoring of vitamins, minerals and overall dietary intake.

Impact of gastrointestinal symptoms

On top of reduced nutritional intake, gastrointestinal side effects such as nausea, constipation, diarrhoea, reflux, and heartburn are common early complaints. For many patients, these issues are the first barrier to sustaining good nutrition, as they influence both how much and what people eat. Although commonly dose-related, temporary, and manageable, they can still have a marked impact on diet quality.

Patients with gastrointestinal issues often choose bland foods such as toast, crackers, or instant noodles to ease the discomfort, further increasing the risk of dietary inadequacy.

For GPs, a brief dietary recall during a consultation can flag risk. Where fatigue, reduced exercise tolerance, weakness, hair loss, impaired immune function or other red flags appear, a micronutrient screen may be appropriate to check iron, B12/folate, zinc, magnesium etc. Encouraging patients to include protein with every meal, through lean meats, fish, legumes, eggs or dairy, can help bridge the most common gaps.

In this context, early dietary advice can reduce symptom-related attrition and set the tone for better food quality.

Practice tips:

• Encourage smaller, more frequent meals rather than large portions.
• Cold proteins may be better tolerated (e.g. dairy, tinned fish, cooked and refrigerated meat/chicken and eggs).
• Suggest patients avoid greasy, spicy, or very rich foods during dose escalation.
• Recommend hydration and fibre for constipation, but with a gentle introduction to avoid bloating.
• Flag that persistent or severe GI symptoms warrant review, as they can undermine nutritional intake and adherence.

Body composition: more than just the scales

While patients are understandably thrilled with weight loss results, the quality of weight lost is critical. Research suggests that between 20% and 40% of the weight lost with GLP-1 therapy may come from lean mass, including skeletal muscle and bone. For example, findings from the SURMOUNT-1 trial suggest that around 25% of total weight lost on GLP-1 RAs came from lean muscle mass and the remainder from fat mass. The loss of lean mass can have serious implications for metabolism, physical functioning, and risk of sarcopenic obesity.

In clinical trials, participants typically had frequent input from dietitians and exercise specialists but these resources aren’t always available in the community, making GPs the primary source of nutrition advice and support for many patients. This underscores the importance of patient education regarding lifestyle changes to reduce muscle loss.

Practice tips:

• Emphasise the importance of protein intake during weight loss, aiming for 1.2–1.6 g/kg body weight, using an obesity adjusted weight where appropriate.
• Reinforce the value of resistance training at least two days per week, in addition to at least 150 minutes of aerobic activity per week.
• Frame exercise not simply as “burning calories” but as a way to preserve muscle and bone during weight loss.
• GPs can assess muscle strength and function preservation by measuring grip strength, the five-times sit to stand or the 3-m timed up and go test.

Psychological and social considerations

Although less studied, some patients report reduced enjoyment of food, discomfort eating socially, or changes in taste preferences. These experiences may affect social engagement and mental wellbeing, and they are worth acknowledging during routine consultations. Normalising these changes and checking in on quality of life can be reassuring for patients and may prevent premature discontinuation of therapy.

Diabetes-specific nutritional formulas

One increasingly discussed adjunct is the use of diabetes-specific nutritional formulas (DSNFs). These specialised supplement drinks, available in pharmacies, are designed to support people with diabetes or pre-diabetes.

Typically, DSNFs are calorie controlled, high in protein, based on low GI carbohydrates with fibre, and contain predominantly unsaturated fats. They are also fortified with micronutrients that support metabolic health, including magnesium, calcium, zinc, B vitamins, vitamin D, chromium, and potassium. They can be used to replace a meal or snack, or to boost overall nutrient intake when appetite is low.

For patients on GLP-1 therapy, DSNFs can be particularly helpful. Early in treatment, some people tolerate liquids better than solids. Others may be skipping meals altogether or falling back on nutrient-poor foods. A DSNF offers a nutrient-dense, convenient alternative or supplement to a meal or snack. Clinical evidence suggests they not only improve glycaemic control and support weight loss, but also help preserve muscle mass during weight reduction.

For example, a 2017 trial by Chee and colleagues showed that patients with type 2 diabetes using DSNFs once or twice daily achieved a 1.1% HbA1c reduction over six months, compared with only 0.2% in the usual care group. This is important because each 1% reduction in HbA1c is associated with a 37% reduction in the risk of microvascular complications and a 14% reduction in the risk of myocardial infarction.

More recently, a 12-week trial by Tey et al in 2024 found that patients using DSNFs not only lost about twice as much weight as those receiving usual care, but most of this loss came from visceral fat while muscle mass was preserved or even increased, highlighting their potential role alongside GLP-1 therapy.

In practice, GPs might recommend DSNFs as:

• a breakfast alternative or accompaniment for patients who are either skipping that meal or having a nutrient poor meal
• a higher-quality snack than biscuits or crackers
• a way to fill gaps in protein, fibre, and micronutrient intake.

A wholefood diet is always the preferred approach, but where it’s not feasible to meet all nutritional requirements through diet alone, DSNFs can be helpful.

DSNFs vs VLEDs: what’s the difference?

Very low energy diets (VLEDs) like Optifast are designed for total meal replacement under medical supervision. DSNFs differ in that they are not intended for total diet replacement, can be used flexibly regardless of BMI, and are specifically formulated with lower GI and diabetes-supportive nutrient profiles. In short, VLEDs are designed for intensive, medically supervised short-term weight loss, while DSNFs are aimed at managing post prandial glycaemia, achieving a healthy body weight, nutritional adequacy and metabolic health.

Key takeaways

• Appetite suppression, smaller meal volumes, and GI side effects can lead to reduced intake of protein and other important nutrients.
• This can increase risk of accelerated muscle loss and sarcopenic obesity, and/or nutritional deficiencies and associated side effects
• Prioritise protein with every meal (1.2–1.6 g/kg body weight, using an obesity adjusted weight where appropriate).
• DSNFs are one tool GPs can recommend to patients with diabetes or pre-diabetes when adherence to a wholefood first approach is not feasible.
• Promote resistance training in addition to aerobic activity.
• Check in on overall diet quality, not just calories consumed.
• Diabetes-specific nutritional formulas can help supplement dietary gaps.
• Where possible, refer to dietitians and exercise physiologists under chronic condition disease management plans.

Samantha Stuk is an accredited practising dietitian and director of The Nutrition Code.