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What foods should you avoid while on a GLP-1?
Choosing what to eat when using GLP1-s might not always be as simple as avoiding ‘unhealthy’ foods and only eating ‘healthy’ ones — it’s more a case of knowing how your body will respond to your food choices and how they can affect you.
Medically reviewed by
Alexandra Cristina Cowell, Writer & Clinical Content Reviewer
- While using weight loss injections, some dietary choices can worsen gastrointestinal (digestion based) side effects.
- Food choices aren’t quite as simple as ‘healthy’ and ‘unhealthy’ — it’s about knowing how your body responds to what you eat while taking your treatment.
- Cutting down on alcohol, sugar, and high fat and processed foods can reduce symptoms like bloating, as well as helping to create a calorie deficit.
- Monitoring your reactions to foods will help you learn which ones to avoid.
No foods are strictly off limits while you’re using weight loss injections. But being mindful of your dietary choices might mean you reach your weight loss target faster, as well as developing lasting eating habits you can stick to once your treatment ends.
Weight loss injections work by reducing your appetite and making you feel fuller, which often means you eat less calories than you normally would. They also slow down the speed at which food leaves your stomach. This can sometimes cause unwanted gastrointestinal side effects, which certain foods might trigger or make worse.
How do GLP-1s change your digestion?
GLP-1s slow down the rate at which your stomach digests food and moves it to your small intestine, a process known as ‘gastric emptying’. Because this delayed digestion means food sits for longer in your stomach, it can sometimes cause side effects like heartburn, bloating and nausea.
These side effects can also be caused or worsened by what you eat. Spicy foods, for example, tend to cause acid reflux, whereas high-fat foods sitting in your stomach can trigger nausea.
Reactions to specific foods might differ person-to-person, and depend on which injection you’re using. Your dose might also be a factor. But having an idea of why specific foods cause certain side effects means you’ll know why to avoid them, or what to expect when you do have them.
Which foods are most likely to trigger side effects?
Here are some foods that you might want to avoid while you’re using weight loss injections. As well as hindering your weight loss, these kinds of foods might also increase your risk of side effects.
Fatty foods
Fat is the slowest macronutrient to digest, and the added time weight loss injections cause it to linger in your stomach can cause side effects like bloating, nausea, and acid reflux.
If you’re trying to lose weight, it’s best to avoid trans and saturated fats where you can. In particular, it’s artificial trans fats that you should keep to a minimum.
While small amounts of trans fats occur naturally in foods like red meat and dairy products, artificial trans fats are made by adding hydrogen to vegetable oil. These have largely been removed from UK foods due to voluntary industry action and reformulation, so it’s usually easy to keep your artificial trans fat intake low, but they can still be found in food cooked at high temperatures, like fried and fast food, or some imported baked goods. So avoiding takeaways, or frying your food at home instead, could mean you’re less likely to feel sluggish and get uncomfortable side effects. It’s also an easy way of keeping your calories down.
But a balanced diet should still contain some fat, so you don’t need to avoid it completely. Fat is a source of essential fatty acids, and it also helps your body absorb important vitamins. But choosing which fats you eat can help you reduce your calories while getting the nutrients you need, all while reducing your chances of gastrointestinal issues.
Oily fish, nuts, avocados, and seeds can provide you with heart healthy omega-3 fatty acids, as well as protein and monounsaturated fats, which can reduce ‘bad’ cholesterol.
Sugary foods and drinks
Sugary drinks offer little in the way of nutrition, and can cause blood sugar spikes (which interfere with your energy and concentration levels). After the initial ‘boost’ from the sugar, you’ll experience a crash that can leave you feeling depleted, making you more likely to reach for more sugar.
And because sugary drinks are often carbonated (fizzy), adding gas to your stomach might cause side effects like bloating, nausea, and general discomfort. And lastly, they add unnecessary empty calories to your diet when you’re actively trying to reduce your daily intake.
Instead, try to stay hydrated by drinking water, herbal teas, or black coffee (in moderation).
Ultra-processed foods
Ultra-processed foods, or UPFs, are foods made using industrial ingredients and additives. They rarely contain ‘whole’ foods, and instead are full of preservatives that help ensure they have a long shelf life. Shop-bought cakes, biscuits, and ready-meals are some examples of UPFs; they’re usually foods that need little preparation and are readily available.
UPFs usually contain small amounts of fibre, protein, and essential nutrients. As a result, they can mostly be considered ‘empty’ calories, and won’t satisfy hunger cravings for very long.
Alcohol
Alcoholic drinks are often carbonated, so like sugary drinks, they can cause bloating. Bloating is a known common side effect of GLP-1s like Wegovy and Mounjaro, so drinking it will likely prolong or worsen any bloating you get.
And the effects of a hangover can closely mirror gastrointestinal side effects caused by your injection, such as stomach pain, diarrhoea and vomiting.
Alcohol won’t affect every weight loss injection user the same way, but you might find that eating less reduces your tolerance. This is something to be mindful of – if you are going to consume alcohol, drink it in small amounts and keep an eye on whether it worsens any side effects caused by your medication.
Healthy foods that might surprise you
Making the distinction between healthy and unhealthy foods should become easier once you’re in the habit of making your own meals and eating a diet built around your weight loss needs. Weight Loss HQ contains lots of recipes tailored to help you reach your target, and provides detailed information about each meal’s nutritional value.
But some foods, despite being nutritious, might need to be avoided if they’re hard to digest, or make your side effects worse. These can include:
Raw vegetables – Eating raw vegetables like carrots and kale is an easy way of getting a hit of essential vitamins. But eating them without cooking them means they can be hard to break down, which can cause discomfort. If you plan on eating raw vegetables, start with a small amount to see how your body reacts.
High-fibre foods – Fibre is an important part of a healthy diet; it can help improve digestion and balance your blood sugar. But like raw vegetables, high-fibre foods can be hard to digest while using GLP1-s, and might cause bloating. Try to mix up your fibre sources, and include easily digestible kinds, like fruit and legumes.
Spicy foods – Lots of recipes involve cooking with spices, but meals that are too spicy and could make side effects like heartburn worse. The capsaicin found in chillies can irritate your stomach lining, so you might want to stick to mild seasoning while you adjust to your treatment.
What should I eat?
Choosing what to eat while using weight loss injections isn’t just about avoiding side effects. Eating a balanced, nutrient-rich diet can help you keep your daily calories low while providing you with the energy you need.
The following table breaks down the five food groups you should aim to include in your diet, as well as options that might be better suited to anyone using a weight loss injection.
| Food group | Options to consider when using weight loss injections |
|---|---|
| Fruit & Vegetables | Fruit and veg are often low-calorie and packed full of essential vitamins and nutrients. But some fruits like pears and apples might be hard to break down, so try softer options like bananas, mangos, and berries, which are easier on your digestive tract. Limit your intake of raw vegetables if they cause discomfort. Instead, try steaming carrots, celery and broccoli until they’re soft, or adding them to soups. |
| Carbohydrates | Try to eat complex carbs that provide energy steadily, but which are also gentle on your stomach. Couscous, porridge oats and sweet potatoes are some examples which should be easy to break down. |
| Protein | Protein is possibly the most important macronutrient while using GLP-1s. It can keep you feeling full on a reduced calorie diet. Aim to eat lean meat like chicken or turkey, and 0% greek yoghurt for added probiotics. |
| Dairy or alternatives | Dairy products provide protein as well as essential vitamins for muscle bone health. Alternatives like soya milk or yoghurt often have vitamins added to them. Avoid full fat versions of either, and always check the sugar content of products labelled as ‘low-fat’ as they can sometimes be surprisingly high-calorie. |
| Fats and spreads | Don’t avoid fat completely — it’s essential for your body to absorb vitamins. Choose omega-3 rich fats like salmon and walnuts, and try to include seeds like flax and chia in your diet for added fibre. Limit your saturated fat intake, and avoid artificial trans fats completely. |
Easy ways to reduce GLP-1 side effects
Learning which foods to avoid means you can tailor your diet to meet all your nutritional needs while keeping side effects to a minimum. But there are also some practical lifestyle choices you can make during your treatment plan that might also help.
Weight loss injections will reduce your appetite, but you’ll still need to judge when you’re full, which might take some getting used to. Overeating while using GLP-1s can worsen nausea and even cause vomiting, so it’s important to know when you’ve had enough to eat. The odd indulgence won’t derail your weight loss plans, but slower digestion means any excess food you eat will sit in your stomach for longer and likely cause symptoms like sulphur burps, bloating and nausea.
Drinking water between meals can help to ease digestive side effects like nausea and constipation, and is a good way of making sure you’re properly hydrated. GLP-1s dull your hunger cues, which means they can also reduce your natural sense of thirst.
And if you experience side effects like bloating or acid reflux after meals, avoid lying down or even slumping on the sofa once you’ve eaten. As tempting as it can be, slouching or lying flat means gravity can’t do its job and keep stomach acid down. You might even find that a gentle walk after meals can get your digestion moving and help you avoid these kinds of side effects.
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When we present you with stats, data, opinion or a consensus, we’ll tell you where this came from. And we’ll only present data as clinically reliable if it’s come from a reputable source, such as a state or government-funded health body, a peer-reviewed medical journal, or a recognised analytics or data body. Read more in our editorial policy.
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Karrar, H.R., et al (2023).
'Tirzepatide-induced gastrointestinal manifestations: a systematic review and meta-analysis', Cureus.
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