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.