Focus on protein-rich foods at every meal — clinical guidance recommends around 1.2–1.6g of protein per kilogram of body weight per day while losing weight on a GLP-1 medicine, notably higher than the standard 0.8g/kg general recommendation, because protein needs increase as calorie intake falls in order to protect muscle. Stay well hydrated, introduce fibre gradually to manage constipation, and go easier on high-fat, greasy or very rich meals, particularly around dose increases, since these can worsen nausea by further slowing digestion. Because appetite suppression is so effective, the real risk with these medicines isn't overeating — it's under-eating to the point of inadequate nutrition, so prioritising nutrient-dense food over restriction is the right approach.
Mounjaro and Wegovy work by mimicking gut hormones that increase feelings of fullness and slow how quickly your stomach empties, which is what produces such a significant reduction in appetite — clinical research indicates GLP-1 treatments can reduce overall energy intake by up to 40%. That's a substantial change, and a growing body of clinical literature has raised a genuine concern: without deliberate attention to food quality, this reduced intake can lead to inadequate protein, fibre, fluid and micronutrient intake, contributing to muscle loss (sarcopenia) and nutritional deficiencies over time.
This isn't a reason to be alarmed, but it is a reason to shift how you think about food on these medicines. Rather than "eating less of everything," the more useful frame is "eating well within a smaller appetite" — making each meal count nutritionally, since you're likely to have fewer opportunities across the day to get the nutrients your body needs.
Protein: The Priority NutrientProtein is consistently identified in clinical literature as the single most important nutritional priority during GLP-1 treatment, because it provides the building blocks your body needs to preserve muscle tissue during weight loss — and muscle loss is a well-documented risk of rapid weight loss by any method, including these medicines.
Many experts recommend 1.2–1.6g of protein per kilogram of body weight per day while actively losing weight on a GLP-1 medicine, compared with the standard general recommendation of around 0.8g/kg. In practice, this usually means consciously prioritising a protein source at each meal, since your reduced appetite leaves less room to make it up later in the day.
- Lean meat and poultry, fish and eggs are all concentrated protein sources that don't require large portion sizes
- Dairy — particularly Greek yoghurt, cottage cheese and milk — offers protein alongside calcium, which is also worth prioritising
- Plant-based options like lentils, beans, tofu and edamame are useful, particularly for anyone eating less meat or wanting variety
- If appetite is very limited at a given meal, a protein shake or nutritionally complete drink can be a practical way to hit your target without needing to eat a large volume of food
Beyond protein, clinical research has flagged several specific micronutrients that are more likely to become deficient when overall food intake drops significantly, particularly if variety in the diet also narrows.
| Nutrient | Good food sources |
|---|---|
| Iron | Red meat, dark poultry, lentils, spinach, fortified cereals |
| Vitamin B12 | Meat, fish, eggs, dairy, fortified plant milks |
| Vitamin D | Oily fish, eggs, fortified foods (sunlight also contributes) |
| Calcium | Dairy, fortified plant milks, leafy greens, tinned fish with bones |
| Thiamine (B1) | Wholegrains, pork, legumes, fortified cereals |
Important
Don't start high-dose supplements, particularly iron, without medical advice — excess iron intake can be harmful. If you're concerned about your intake of any of these nutrients, or you're in a higher-risk group (older adults, those with existing health conditions, or anyone eating a very restricted diet), speak to your GP or ask about a referral to a registered dietitian. A food-first approach is the priority, with supplementation considered only where genuinely needed.
Nausea, feeling overly full, and general GI discomfort are common, particularly in the first few weeks after starting or increasing a dose. What and how you eat can meaningfully affect how noticeable these side effects are.
- Eat smaller meals, more frequently, rather than three large meals — a full stomach on top of medicine that already slows gastric emptying is a common trigger for nausea
- Go easy on high-fat, fried, greasy or very rich foods, especially in the days after a dose increase, since fat slows stomach emptying further and can intensify nausea
- Eat slowly and stop when you feel comfortably full, rather than finishing a portion sized for your old appetite
- Avoid lying down immediately after eating, which can worsen reflux and nausea
- Plain, bland foods (toast, rice, bananas, ginger tea) are often better tolerated than spicy or strongly flavoured meals during a rough patch
- Alcohol can worsen nausea and dehydration on top of these medicines — see our dedicated guides on alcohol and Mounjaro or Wegovy for more detail
Constipation is another frequently reported side effect, often linked to both reduced overall food intake and slower gut transit. Fibre and fluids are the two most useful levers here, but both work best introduced gradually rather than all at once.
- Build fibre up slowly through fruits, vegetables, wholegrains and legumes — a sudden large increase can worsen bloating and discomfort rather than help
- Aim to drink water consistently through the day. These medicines can reduce your sense of thirst alongside appetite, so it's easy to under-drink without noticing, which can worsen both constipation and general fatigue
- Gentle regular movement, even short walks, can help support digestion alongside dietary changes
Prioritise nutritional value in a smaller volume
Since you're likely eating less overall, foods that are high in calories but low in nutritional value — sugary drinks, ultra-processed snacks, refined carbohydrates — leave even less room for the protein, fibre and micronutrients your body needs. This isn't about eliminating treats entirely, but about being more deliberate, since the margin for "empty" calories is smaller than it used to be.
A practical way to structure meals, particularly when appetite is limited, is to prioritise in this order: protein first, then vegetables or fibre-rich foods, then whatever appetite remains for starches or extras. This helps ensure the nutrients that matter most — protein and fibre — are less likely to get crowded out by a stomach that fills up quickly. Little and often tends to work better than trying to force three conventional-sized meals, and it's entirely normal for appetite and food preferences to fluctuate week to week, particularly around dose changes.
Ongoing Support, Not Just a Prescription
Every Happy Pharmacy patient has access to our GPhC-registered pharmacy team throughout treatment — including questions about nutrition, side effects, and how to eat well while your appetite changes.
Start Your Free Online Consultation → Use code SWITCH10 if you're switching from another providerHappy Pharmacy is a GPhC-registered pharmacy (No. 9012585) — Superintendent Pharmacist: Palvinder Deol — Rated 4.8★ Excellent on Trustpilot
- Bridging the nutrition guidance gap for GLP-1 receptor agonist therapy assisted weight loss. Int J Obes. 2025.
- Avoiding Malnutrition in the Era of GLP-1 Medications: Emerging Evidence and Opportunities for Integrated Nutrition Care. 2026.
- Optimizing GLP-1 therapies for obesity and diabetes management: protein and lean mass preservation strategies.
- GLP-1 Receptor Agonists – Good for Body Weight, Bad for Micronutrient Status? Systematic review, 2025.
- Medical nutrition in the glucagon-like peptide-1 (GLP-1) era: Protein strategies, micronutrient monitoring, and lean mass preservation. 2026.