I recently underwent a gastric bypass operation and one of the many questions I am asked is what food and drinks are you allowed? From joining various support groups and online forums, I’ve quickly come to realise that the rules are different in most places. Every hospital has different guidelines, timeframes and suggestions for what should and should not be eaten, how much and when.

This post will focus on Liquids immediately after a Gastric Bypass.


Days 1-5 The Liquid Phase

All drinks should be smooth (no bits or lumps). Some hospitals say to drink through a straw, others say don’t do this as it can add gas to the stomach, which you really don’t want after a major operation as the stomach is already filled with gas.

The most important thing is to NOT take huge gulps but to drink small sips. Start with small sips and if this feels comfortable you can gradually increase the amount you take in one go. Be careful not to gulp your drinks as this may result in vomiting.

Aim to have a minimum of 2½ litres (4 pints) each day to avoid becoming dehydrated. At least 1-1.5 litres of this should be nutritious liquids.

Avoid all fizzy drinks. Fizzy Drinks can cause gas in the stomach pouch which could result in stretching. That would not be good and would defeat the whole purpose of the gastric bypass.


Nutritious liquids

Some Nutritious liquid options are:

Skimmed or semi-skimmed milk fortified with skimmed milk powder (1-2 tablespoons per 200ml)

Slimfast powder added to skimmed milk.


Smooth soup (homemade or tinned) fortified with 1-2 tablespoons skimmed milk powder.

Homemade Smoothies. Smoothies. (Fruit blended with milk) These need to be homemade as Shop-bought varieties will be too high in sugar.

Unsweetened fruit juice (limit to 1 small glasses per day)


Example Meal Plan

Example meal plan Breakfast Fruit smoothie (200ml)

Mid morning Fruit juice (200ml) Lunch Complan or Nestle Build-Up milkshake or a glass semi-skimmed milk including 2 tbsp skimmed milk powder (200ml)

Mid afternoon Slimfast (200ml) Dinner Thin soup with 1-2 tbsp of skimmed milk powder (200ml)

Supper Nestle Build-Up milkshake or Complan (200ml)

(Plus water/tea/coffee/sugar-free squash etc in between) When you feel ready, move on to Stage 2 The Puree/blended Stage

I hope this is useful. I am not a doctor and recommend anyone who has a GASTRIC BYPASS, follows the plan given them by their dietician/surgery team. This is simply me sharing one diet plan. To read about the next phase the pureed Diet phase please read here.