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Gastric Bypass Diet – What To Eat Before, and After The Surgery?

gastric bypass diet

Once you make the decision to undergo bariatric surgery, it is very important to keep in mind that your lifestyle will change a lot. This change will begin even before the operation, as you will have to make some modifications to your usual diet according to the medical indications received by the surgeon, doctors, and nutritionists.

If patients want to guarantee long-term results, they must follow the dietary guidelines religiously. Some of the general instructions is to eat food in small bites, chewing well, and drink slowly, as well as staying hydrated throughout the day (drink at least 1.5 liters per day).

Gastric bypass pre surgery diet

In general, any type of weight loss surgery requires a strict, low-calorie diet for approximately 2 to 4 weeks. The duration of the diet before gastric bypass varies depending on the degree of obesity of the patient and whether it is central – abdominal (apple type) or peripheral – gynoid (pear type) obesity.

With this diet you are expected to lose between 7 and 20 kg. This weight loss will favor the decrease in the volume of the liver, the fat that surrounds the intestines and the fat of the abdominal wall. All this will make you have a softer abdomen so that the intervention is easier.

Before the operation, in order to clean the stomach and intestine of waste,stimulant drinks such as caffeine, theine, isotonic, alcohol, etc. cannot be taken.

gastric bypass before and after diet

Now, let’s look at some diet examples prior a gastric bypass:

Patients usually follow a regimen that provides around 800 to 1,000 kilocalories, in which they consume healthy foods and plenty of fluids. With this type of diet, the size of the liver will be reduced before surgery, as this organ is close to the stomach and is generally larger when you suffer from obesity; making surgery difficult.

Another type of diet that is usually recommended in these cases is a liquid diet, as it helps prepare the digestive system for the operation and decreases the chance of complications. It is recommended to implement this diet one week before surgery. In it you can consume foods such as:

  • Fat-free broths.
  • Natural fruit juices without the added sugar.
  • Low-fat diet or skim milk and yogurt.

So that you too can have good results due to a good preoperative diet, it is important that you keep the following rule in mind; this information on diets prior to weight loss surgery is merely indicative. You should consult your bariatric surgeon to give you the necessary and personalized diet, attending to your health needs and requirements.

Diet after gastric bypass

1st week after the procedure

Patients start with only drinking liquids and increase to pureed and porridge-like food. Only at the end of the fourth week after the operation, if everything has gone well, patients will be able to approach solid food.

time nutrition
1st day after the operation – Drink only water or unsweetened tea (up to 1,000 milliliters)
2nd day after the operation – Drink water or unsweetened tea (quantity open) – one yogurt in the morning, 1 yogurt in the evening
From the 3rd day after the operation – Drink (quantity open) – Soups such as: clear broth, cream soup, pureed vegetable soup – Yoghurt: best little to no sugar, if possible low-fat yoghurt) – No sweeteners

With the passage of time, patients will be able to incorporate solid foods until they’ve reached a normal diet after 3 to 4 months. According to nutrition experts at the American Orange Coast Memorial, there are three stages of eating after gastric bypass during which liquids and solids are gradually introduced into the diet.

2nd to 4th week after the procedure

Even in the second to fourth week after the operation, you are still not allowed to eat solid foods, but your diet consists of liquid, pureed or porridge-like food.

Eat low-fat and low-sugar foods so as not to burden your digestion system. For this reason, patients must not drink carbonated beverages or beverages that are rich in carbohydrates.

The following foods, for example, are allowed in this phase: 

  • Skimmed yogurt (plain or with fruit puree)
  • Soft-boiled vegetables mashed with a fork
  • Porridge or semolina without sugar
  • Soft bananas
  • Soft eggs
  • Baby food
  • Low fat cheese
  • Pureed meat and poultry

Patients only start slowly with solid food at the end of the fourth week. You should bear in mind that you should only eat short-fiber, protein-rich white meat such as chicken or fish.

At this stage you only take medication as tablets, drops or suppositories. Metamizol drops (Novalgin) or paracetamol help against pain.

Good to know: Avoid acetylsalicylic acid (aspirin), anti-rheumatic drugs, ibuprofen, diclofenac and voltaren. These agents attack your stomach and can lead to ulcers or bowel perforations.

4th week after the procedure

In this phase you slowly switch to a normal diet, and nutrition. Remember that your stomach is now very small and you can eat very little at a time.

You should therefore avoid eating and drinking at the same time, as this takes up too much volume in the stomach.

Tip: Note in a food diary if you have intolerance to certain foods. Try not to eat these foods again at a later time.

You should absolutely avoid products with a high sugar content, otherwise dumping syndrome can lead to circulatory problems, sweating and diarrhea.

You should not drink alcohol either, because your body absorbs it too quickly and there is a risk of cirrhosis of the liver.

Try low-fat meats, eggs, low-fat cheeses, and cooked fruits. Low-fat yoghurt, unsweetened cornflakes and toast are ideal for breakfast. As soon as you feel full, you should stop eating.

Don’t forget: Drinking is important! Take about 150 to 300 milliliters of fluids per hour to keep your body hydrated.

gastric bypass pre surgery diet

Diet rules after a gastric bypass surgery

In general, it should always be clear to you: After gastric bypass surgery, you can only eat very little food at once. If you eat too much, you may experience pain and vomiting.

Therefore, try to have only three meals a day and avoid snacks in between. Your diet should consist of healthy and balanced mixed foods.

Tip: Use as little fat, mayonnaise and oils as possible. Also, avoid sugary drinks.

From now on, you need to adhere to the following rules: 

  • As soon as you feel full, stop eating.
  • Eat slowly and chew well.
  • Do not eat and drink at the same time.
  • Drink up to 300 milliliters of water and other unsweetened beverages per hour.
  • Avoid alcohol and sugar.
  • You only eat citrus fruits cooked as compote, otherwise there is a risk of an intestinal obstruction. 

Compensate for possible deficiencies

Because a large part of your small intestine is bypassed in the digestive process, important nutrients cannot be absorbed. You now have to take these nutritional components as nutritional supplements, otherwise there is a risk of deficiency symptoms.

Your doctor will advise you on the supplements to take.

The nutrients and vitamins that you must consume as dietary supplements include the following: 

  • Vitamin B12
  • Vitamin D
  • protein
  • calcium 

Regular blood tests will check whether you have any deficiency symptoms.

In the first two years after gastric bypass surgery, the examinations are carried out every three months, later they are only necessary every six or twelve months.

Gallstones due to weight loss

Patients lose a lot of weight relatively quickly with gastric bypass, which leads to the formation of gallstones in some patients. If you have any of these symptoms, tell your doctor right away:

  • Severe, cramp-like abdominal pain, especially on the right costal arch
  • At the same time nausea and a feeling of illness  


Unfortunately gastric bypass surgery is not enough. After the procedure, you will face major changes in the area of nutrition that require a lot of discipline and self-motivation.

You have to play an active part and support the success of the operation through your eating habits. This also means that you first take and follow your doctor’s recommendations regarding your diet.

This article is intended for general informational purposes only. Please consult with a licensed physician for medical advice. If you take whatever action based on the material presented is solely at your own risk, and responsibility (disclaimer).

  1. The gastric bypass diet outlines what you can eat and how much after gastric bypass surgery. Source
  2. Gastric bypass diet plan by MHC – Source
  3. Gastric bypass diet, and dumping syndrome. Source
  4.  Bariatric nutrition and lifestyle plan. Source


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