guide
What to eat on a GLP-1 treatment: protein, fibre, fluids, and what to avoid
Appetite drops on a GLP-1 treatment, and eating less can mean eating less well. Protein at each meal, fibre, fluids, what is often poorly tolerated, and why medical and dietary follow-up matters.
Short answer
On a treatment from the GLP-1 family, appetite drops and you eat less. The risk is eating less well: too little protein, fibre, fluid, vitamins and minerals. The 2025 joint advisory from four American professional societies (American College of Lifestyle Medicine, American Society for Nutrition, Obesity Medicine Association, The Obesity Society) makes this a priority: varied, minimally processed foods, protein at each meal, regular small meals, enough fluids and muscle-strengthening exercise. Everything about the treatment itself (dose, rhythm, a pause) belongs to the doctor who follows you. This article is about the plate, not about prescribing.
Why appetite drops, and why muscle is at stake
These treatments act on the gut and on brain areas that regulate hunger, fullness and the wish to eat. According to the 2025 joint advisory, they reduce energy intake by 16% to 39% compared with placebo: less hunger, more fullness, less "food noise", those thoughts of food that keep coming back. Eating little raises two problems. Intakes of vitamins and minerals can become tight. And when weight falls fast, the body loses fat but also muscle: in a trial cited by the advisory, about 38% of the average weight lost was lean mass, muscle included. The authors add that protein alone is probably not enough without structured strength training: they cite at least three sessions a week, plus 150 minutes of moderate aerobic activity, adapted to each person with the care team.
The table: what to aim for, and why
Here is, by nutrient or habit, what the 2025 joint advisory points to and why. Personal targets are set with a doctor or a dietitian.
| Marker | What to aim for | Why |
|---|---|---|
| Protein | At each meal, eaten first: eggs, fish, Greek yoghurt, cottage cheese, legumes, poultry | Keep muscle and bone when appetite is low |
| Fibre | Fruit, vegetables, legumes, whole grains, increased gradually | Constipation is common when weight falls |
| Fluids | Drink regularly, water or sugar-free drinks | Avoid dehydration, which can strain the kidneys |
| Meal rhythm | A small meal every 3 to 4 hours, without going too long unfed | Nausea rises on an empty stomach, and late hunger pulls towards sugars |
| Vitamins and minerals | Varied, minimally processed foods; supplements only on medical advice | Fewer calories leave less margin against deficiencies |
| To limit | Sugary drinks, ultra-processed foods, processed meats, alcohol | Few useful nutrients, and alcohol worsens nausea and reflux |
To understand why protein fills you up, read protein and fullness: eating less without counting.
What is often poorly tolerated
Digestive problems are the most frequent side effects, especially at the start and at each dose increase. Nausea comes first; vomiting is more likely after a large meal. Guy's and St Thomas' NHS Foundation Trust (2025) notes that they usually ease within three to four weeks. What often weighs on the stomach: large meals, fatty or fried dishes, strong smells, sugary drinks, ultra-processed foods and alcohol, which the joint advisory says to keep to a minimum because it can worsen nausea and reflux. Against nausea, the advisory cites small meals and ginger or peppermint tea. Against constipation: enough fluids and fibre from food, increased gradually (prunes, dried fruit, kiwi, legumes). If nausea dominates the first days, the advisory suggests avoiding very fatty or very high-fibre foods for a while. Tell your doctor if you vomit repeatedly, cannot keep fluids down, notice dark urine or feel dizzy.
Medical and dietary follow-up
A treatment of this family is not managed alone. The WHO (December 2025) recommends it conditionally, within care that includes a healthy diet, physical activity and support from health professionals, and recalls that medication alone will not solve the problem. In France, the ANSM (2024, updated 2025) reserves these obesity treatments for second-line use, after nutritional care, with a first prescription by a doctor specialised in nutrition. The 2025 joint advisory recommends a dietary assessment before starting, then regular follow-up of intake, hydration and possible deficiencies, with the help of a dietitian. Supplements (vitamin D, calcium, B12) are discussed with the doctor. For the wider picture, read obesity and diet: what the studies show. Sehtin is preparing a complete guide on this subject: you can ask to be notified when it comes out, just below this article.
Frequently asked questions
How much protein is needed on a GLP-1 treatment? There is no single figure. The 2025 joint advisory recalls the reference intake for adults (0.8 g per kilo per day) and notes that targets of 1.2 to 1.6 g have been proposed during active weight loss, with no consensus for people living with obesity. The calculation is made with the doctor or the dietitian. Should I drink more water? Fluids are one of the advisory's priorities, especially with nausea, vomiting or diarrhoea. A British hospital gives 2 litres a day of water or sugar-free drinks as a marker. What about Ramadan? This article does not rule on it. The joint advisory recommends avoiding long periods without eating, and the question of fasting is first one for the doctor who follows the treatment. For the religious side, ask a scholar or an imam.
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This article relays the public teachings of Dr. Diaa Al-Awadi for educational and informative purposes. It is not medical advice. Consult your physician before any dietary change. Legal notice.