Managing nausea, constipation and reflux with food

Nausea, constipation, reflux and diarrhoea are the most common problems of fast weight loss, whatever is causing it. Most of the time they can be eased by changing what, how much and how quickly you eat. This page covers the food side, and the signs that mean something more serious is going on.

Why fast weight loss upsets the gut

Eating much less changes how the gut works: less bulk going through, slower emptying of the stomach, different bacteria, and sometimes the direct effect of a medicine or surgery. GLP-1-class medicines slow gastric emptying, which is part of how they reduce appetite but also why nausea, bloating and reflux are their most common side effects.^[1] The side-effects section has the trial figures. Whatever the cause, the same food strategies apply.

On bad days: bland, small, low-fat

When nausea is bad, the advisory's advice is to keep food plain and low in fat for a few days: toast, crackers, rice, potatoes, plain chicken or fish, eggs, yoghurt, bananas.^[1] Fat slows the stomach further and makes nausea worse; so, at first, do very high-fibre foods. Eat a small breakfast even if you do not feel like it, then something small every three to four hours, because an empty stomach makes nausea worse and some people end up not eating because they feel sick, then feeling sicker because they have not eaten.^[1]

Cold or room-temperature food often smells less and goes down more easily than hot food. Someone else doing the cooking helps more than it sounds.

Portions, pace and "comfortably full"

Three habits do most of the work:

1. Smaller portions. Use a side plate. You can always have more in an hour. Vomiting is far more likely after a large meal than after two small ones.^[1]
2. Eat slowly. Put the fork down between mouthfuls. Chew properly. A meal should take 20 minutes, not five.
3. Stop at "comfortably full". When the stomach empties slowly, the "full" signal arrives late, so by the time you feel full you have overshot. Stop when you could eat more but do not need to.

Avoid large, fatty meals late in the evening. Food that is still in the stomach when you lie down is the main cause of night-time reflux and of waking up feeling sick.^[4]

Fluids between meals, not with them

If you fill up after a few mouthfuls, drinking with meals takes up space that food needs. Try drinking in the half hour before and after a meal instead of during it, and sip through the day rather than drinking large amounts at once. Keep total fluids up: aim for pale yellow urine, and more if it is hot or you have had diarrhoea.^[5]

Ginger, peppermint and other things people try

The advisory mentions ginger or peppermint tea and acupressure wristbands as things that some people find helpful for nausea.^[1] The evidence behind them is thin: small studies, mixed results, and for GLP-1-related nausea specifically, essentially none. They are cheap and safe, so there is no harm in trying ginger tea, ginger biscuits or peppermint tea, and a wristband if you like. Do not expect much, and do not let them replace the portion and pacing changes above, which are what actually work.

Constipation

Constipation is common with any drop in food intake and is worth managing early rather than waiting for it to become painful.^[1] The NHS advice is to eat more fibre, drink plenty of fluids, and move more; and to see a pharmacist if that is not enough, because over-the-counter laxatives are safe and effective for short-term use.^[2]

Practical points:

• Build fibre up gradually over a couple of weeks towards the NHS target of about 30 g a day. A sudden jump causes bloating.^[6]
• Drink more as you add fibre. Fibre without fluid makes things worse.^[2]
• Prunes, other dried fruit, kiwi fruit, oats, beans and lentils help many people. The advisory specifically mentions a gradual increase in foods with soluble and insoluble fibre such as prunes.^[1]
• Walk daily. Movement moves the bowel.
• Do not ignore the urge. Go when you need to, and use a footstool to raise your knees.^[2]
• High-protein, low-carbohydrate eating can worsen constipation because it is low in fibre. Keep the vegetables, fruit and wholegrains alongside the protein.

If nothing has moved for more than a few days, or constipation alternates with watery diarrhoea (which can be overflow from a blockage), see a pharmacist or GP.^[2]

Reflux and heartburn

Slow stomach emptying and lying down with a full stomach are the usual causes. The NHS advice for heartburn: eat smaller, more frequent meals; avoid eating in the three to four hours before bed; raise the head end of your bed by 10 to 20 cm; lose weight if you are overweight (which you are already doing); and cut down on fatty, spicy or acidic foods, coffee and alcohol if they set it off.^[4] A pharmacist can suggest an antacid or an acid-reducing medicine for short-term use. Reflux that is happening most days for more than three weeks, or with difficulty swallowing, needs a GP.^[4]

Diarrhoea

Large and high-fat meals are the commonest trigger, so the same small, low-fat approach helps.^[1] The main risk of diarrhoea is dehydration: replace fluids and salts with oral rehydration sachets from a pharmacy, not just water.^[5] Diarrhoea that lasts more than a week, or that has you passing water many times a day, needs medical advice, because severe fluid loss can damage the kidneys.

When it is not just a side effect

Food changes help with ordinary nausea and constipation. They do not help with, and can dangerously delay treatment for, a small number of conditions that can look similar at first. Pancreatitis, an inflamed pancreas, causes severe tummy pain that often spreads to the back and gets worse after eating, with nausea and vomiting and sometimes a high temperature; the NHS says to get urgent medical help if you have sudden severe abdominal pain.^[3] Gallstones, bowel obstruction, liver injury and severe dehydration can all present with symptoms that people put down to "just side effects".

If you are using a product sold as retatrutide, there is an added reason to take symptoms seriously: nobody knows what is in it, and the liver injury cluster in Australia involved symptoms, such as tiredness, tummy pain, dark urine and jaundice, that were easy to mistake for ordinary side effects. The when to seek help page sets out the full list.