13 January 2021

Section 11: Dietary advice for weeks 1 and 2 post surgery – liquids only


A liquid diet must be followed for the first 2 weeks after surgery to ensure optimum healing occurs. If you eat solid food too soon, it can cause the staple line to rupture. This could cause your stomach contents to leak into your abdomen, which can be extremely dangerous.


What constitutes a ‘liquid’?


‘Liquid’ defines any fluids that can be poured in a steady stream/flow. This can range from water to a custard consistency. Avoid any liquids with lumps – choose smooth varieties, or use a blender where needed. Thin down any thicker fluids to ensure it is at a pouring consistency.


How much should I drink?


Aim for a total fluid intake, including any meal replacement drinks/soups, of at least 2 litres (approximately 4 pints) per day. Everyone has different fluid requirements, so the best way to monitor your hydration is to check the colour of your urine. It should be pale straw coloured approximately 4-5 hours after waking. If it is dark and concentrated, this is an indication that you need to drink more.


How should I drink?


The early days after a gastric bypass or sleeve gastrectomy can be a steep learning curve. You may not feel much like having much, if anything, but your body needs nutrition to heal after your surgery. It is important to take things slowly, though – it isn’t a race. Do things at your own pace, and try not to feel anxious about drinking.


There are four very important things to remember:


  1. Don’t serve yourself too much in one sitting. The recommended portion size is around 200ml (~⅓ pint).
  2. Take small sips/mouthfuls, not large gulps. Using a child’s spoon to take fluids rather than drinking directly from a cup or glass can be useful. 
  3. Drink very slowly. After each mouthful, wait for 20 to 40 seconds before taking your next sip. This means that it is likely to take at least 20-30 minutes to drink 200ml (~⅓ pint) of fluid, especially initially post-surgery. If it takes longer than this, that’s fine.
  4. Don’t leave long gaps between drinks. Aim to sip continuously throughout the day. This will mean your digestive system is kept stimulated and so it will be easier to drink. It will also help to ensure you consume enough fluid, as it can be difficult to meet your fluid requirements early post-surgery.


It’s important to remember that everyone is different, and you may feel comfortable enough to drink at a faster pace than described – do not worry if this is the case. The main thing is to avoid discomfort and/or regurgitation.


What should I drink?


The main focus should be on liquids containing protein.


Your liquid diet will need to be high in protein rather than just water/squash/tea/coffee. At least 60g of protein is needed daily to ensure optimum healing. We recommend you aim for at least 6 x 200 ml (~⅓ of a pint) servings of liquids that contain at least 10g protein per serving. These could include:


  • Fortified milk (semi-skimmed, 1% fat or skimmed milk with 1 tablespoon (15g) of skimmed milk powder (e.g. Marvel) added)
  • Soya milk with 1 dessertspoon (10g) pea, rice or soy-based protein powder added
  • Meal replacement shakes (e.g. Asda Great Shape, Celebrity Slim, Lighterlife fast, SlimFast, SlimFast Advanced Vitality and Tesco Slim)
  • Meal replacement soups (e.g. Celebrity Slim, Lighterlife fast)
  • Lentil / pea & ham / bean soups with 1 tablespoon of skimmed milk powder, blended and thinned down if needed to ensure they are the correct consistency. Try to use milk rather than water or stock, as this will help to ensure they still contain enough protein
  • Any other type of soup (blended consistency) with 2 tablespoons of skimmed milk powder added to increase the protein content


There are many high protein drinks available to purchase that can help meet your requirements; often, these contain more than 10g of protein in 200ml. Some examples are:



Product size

Protein content

Ready-made milk/yogurt-based protein drinks


310ml bottle


U:Fit 50g

500ml bottle


For Goodness Shakes Protein

425ml bottle


For Goodness Shakes Ultimate Protein

425ml bottle


For Goodness Shakes Plant Protein (Vegan)

330ml bottle


Grenade Carb Killa shake

330ml bottle


Arla Protein shake

225ml bottle


Skyr Yogurt drink

350ml bottle


Ready-made protein waters / smoothies

Up Beat

500ml bottle


Asda Sports Nutrition protein water

500ml bottle


Vieve protein water

500ml bottle


Coco Pro (protein coconut water)

330ml bottle


Wow Hydrate protein water

500ml bottle


MyProtein protein water

500ml bottle



Other liquids


The following fluids are also allowed on the liquid diet. These can be used to top up your total fluid intake to 2 litres per day, but your primary focus should be on those with protein listed above.


  • Water
  • No added sugar squash/cordial
  • No added sugar still flavoured water
  • Regular/herbal/fruit tea
  • Coffee
  • Light hot chocolate e.g. Cadburys Highlights, Options or malted drink
  • Light malted drinks e.g. Horlicks, Ovaltine
  • Sugar free ice lollies


Thin yoghurts, jelly and custard


Smooth thin yogurts (pourable consistency) with no lumps/bits, sugar-free jelly and thin, pourable, low-fat custard can be taken once as long as you’re managing thinner liquids with no problems. You must ensure that you take a mouthful no larger than a 20p piece (using a child’s spoon is helpful) and eat very slowly (rest for 20-40 seconds between mouthfuls). If you experience any discomfort or regurgitation with these, remove them from your diet and try them again a few days later


Drinks to avoid or limit:


Avoid or limit sugary drinks such as:


  • Flavoured water or squash/cordial, unless ‘no added sugar’ or ‘sugar-free’ varieties
  • Still ready-mixed fruit drinks e.g. Oasis, Ribena, unless ‘no added sugar’ or ‘sugar-free’ varieties
  • Whole (full fat) milk – the fat content may cause unpleasant side-effects such as diarrhoea, as well as being higher in calories
  • Milkshakes that are not designed as meal replacements e.g. Frijj, Nesquick
  • Fruit juice – limit to 100ml per day and dilute 50:50 with water
  • Smoothies
  • ‘Still’ energy drinks e.g. Lucozade.
  • Hot chocolate and malted drinks (e.g. Horlicks, Ovaltine) – even the “light” varieties are high in sugar


The high sugar content of these drinks can mean that they increase the risk of you experiencing Dumping Syndrome.


You may notice on the labels of meal replacement milkshakes (e.g. Slimfast) that they are quite high in sugar. However, they are high in fibre and so are a better option than ‘regular’ milkshakes. The added fibre helps to slow the release of sugar into your bloodstream, reducing the chance of Dumping Syndrome.


Tip: Check the nutritional information on the label – anything containing less than 5g of sugar per 100g is considered “low sugar”. Anything above 22.5g per 100g is considered “high sugar”.


Avoid alcohol during this phase. As you are not consuming solid food, your tolerance levels will be greatly reduced and its dehydrating effects will be magnified. You also tend to absorb alcohol into your bloodstream a lot quicker when you have had a gastric bypass.


Vitamin and mineral supplementation


See separate section


Problems during this stage


Nausea with milky drinks


Some people find that milky drinks such as milkshakes can make them feel nauseous (feeling sick). If this happens, switch to meal replacement soups or choose hearty soups such as lentil, bean and pea & ham. Regular vegetable-based soups can have skimmed milk powder added to them to boost the protein content.


Discomfort/pain when drinking and or regurgitation/vomiting


If drinking is uncomfortable or you are struggling to swallow and/or you are regurgitating fluid after drinking it, firstly think about whether you are taking small mouthfuls and resting between mouthfuls as described at the start of this section. Try again taking very small sips and allowing at least a 20 second rest between sips


Stress and anxiety can also be associated with pain/discomfort on drinking and regurgitation. Try to ensure you are calm and relaxed before you start drinking anything. Relaxation techniques are useful in this respect, as are the use of herbal teas such as camomile.


If you are still struggling, contact us immediately for advice as you may need to a review with your dietitian or we may need to contact your surgeon. Furthermore, excessive vomiting can lead to thiamine deficiency. If vomiting continues for more than 5 days, you will need to see your GP to obtain a thiamine supplement of 200-300mg to be taken daily and 1 tablet of vitamin B co strong three times a day – your dietitian can discuss this with you if you have any queries



Sample Meal Plans

Remember: although we have shown your food intake split into specific meals/snacks, remember you should aim to sip continuously throughout the day.  Don’t forget to have additional fluids (water, sugar-free squash, tea, coffee) so your total fluid intake is around 2 litres.

Sample meal plan 1 (thin liquids only):

Breakfast: 200ml meal replacement shake – try a vanilla one blended with a teaspoon of coffee powder and lots of ice

Mid-morning: 200ml glass of fortified milk

Lunch: 200ml roasted pepper and tomato soup

Mid-afternoon: 200ml pouring yoghurt

Evening meal: any tinned soup (blended until smooth) fortified with skimmed milk powder

Supper: triple berry milkshake  


Find some of our recipes on our website



Sample meal plan 2 (slightly thicker consistency once thin fluids are well-tolerated)

Breakfast: A small handful of raspberries blended with 200ml fortified milk

Mid-morning: 200g natural low-fat yogurt (smooth pourable consistency)

Lunch: 200mls of sweet potato, lentil and spinach soup

Mid-afternoon: Pot of low-fat custard fortified with skimmed milk powder, thinned with a splash of milk if needed

Evening meal: 200ml meal replacement shake – try a vanilla one and blend with lots of ice

Supper: decaf latte made with 200ml of fortified milk


Liquid phase – check list (Marketing – add infographic)


  • Aim to have around 2 litres of fluid daily in total
  • Smooth, pourable liquids only – no lumps
  • Take small mouthfuls and wait at least 20 seconds before the next sip
  • Avoid using a straw
  • Have at least 6 protein-containing drinks daily – around a 200ml serving size
  • Avoid alcohol and fizzy drinks
  • Take all of your vitamin and mineral supplements daily


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