These notes are particularly intended for those who are committed to elective gastric bypass surgery as a remedy for severe obesity, but some sections relate to other surgical procedures or events that create onerous nutritional requirements.

The pre-operative preparation.

You will be undergoing an elective procedure, and should therefore have considerable advance notice of the actual date of the procedure. This allows you to prepare nutritionally, physiologically and psychologically for the procedure, and be in optimal state when the day arrives. At the same time, an added bonus is that you may even lose some weight while preparing, though this is not the main objective!

The detailed rationale for the preoperative preparation, with references, is given elsewhere on this site, so please consult it if you want to know why you need to follow this plan.

Firstly, at least a month before the planned procedure, you need to make a change in your eating habits. You must follow a diet that provides at least 30% of calories from fat, but the fat may not contain any trans fatty acids, so avoid all foods where "partially hydrogenated vegetable oil" shows in the ingredient listing, and it should contain as little as possible arachidonic acid, so avoid all red meat (beef, for example). Ideally, avoid meat altogether and rely on fish and plant products. If you cannot drop meat altogether, then chicken or pork is better than beef, but still not so good as fish (the lean tissues of animals contain arachidonic acid; the tissues of fish contain mainly an analogue known by the lengthy name of eicosapentaenoic acid. See the section on Essential Fatty Acids for detail). At the same time, it will help if you diligently use an essential fatty acid preparation, but it must contain the omega-6 and omega-3 essential fatty acids in the correct proportions, such as Bari-EFA®, and it must be used according to the directions or instructions from your doctor. Lastly, only about one third of the fat you consume should be saturated. The factor here is what you consume over a day, not the individual fats or oils you consume.

In practice, replacing all visible fats in your diet with soya bean oil or canola oil will give you a fairly balanced fat intake.

At the same time, you can start using the protein supplements; take two or three a day, and reduce the amount of carbohydrate foods you are eating in proportion. You can use protein bars as one or more of your daily protein supplements. If you can, a little exercise helps, but not very much, maybe a few extra minutes walking. You must not forget to drink plenty of liquids (water or low-calorie drinks) during this entire period.

Your weight should remain fairly stable during this stage, though you might drop a couple of pounds over a week or two.

Why are you doing this?

As you will have read elsewhere on this site, your body stores fat, and since you have a weight problem serious enough to drive you to surgery, you have stored a lot of fat! The composition of the stored fat depends to a considerable extent on what you have been eating, and if you have consumed foods containing trans fatty acids or arachidonic acid then your stored fat will contain these. So you need to flush them out. Fortunately, your fat stores are quite active physiologically, in the sense that there is constant movement of fatty acids into the fat stores, as well as constant movement out of the fat stores. It takes 7 - 15 days for half of the stored fat to be exchanged, so if all your fat intake over a two-week period is non-hydrogenated vegetable oil, you will have flushed out more than half the bad fat from your fat stores.

You need to "flush your fat stores", because after your surgery you will be losing weight quite rapidly and those bad fats will be released into the rest of your body, where they will have the same harmful effects as if you were eating them in your food. Taking the essential fatty acid supplement would mitigate the potential bad effects to some extent, and one of the reasons you should take it during the "flushing out" process is in fact to ensure you do not suffer any consequences from the presence of the bad fats in your body during that process.

The "fat flushing" and essential fatty acid intake also serves another important purpose; you will actually be storing a "reserve" of essential fatty acids in your fat stores. Since you will not be able to consume oils or the essential fatty acid supplement for a few days after your surgery, you need to rely on this "reserve" for your essential fatty acid requirements during that period.

Increasing the protein content of your diet during the pre-operative preparation is required for a number of reasons. Firstly, it will increase your metabolic rate and make the process of flushing the fats more efficient, secondly it will help increase your lean body mass by storing a little extra protein, thirdly, it will replace the protein that you will not be getting from red meat, and fourthly, it will allow you to become accustomed to what will be a mainstay of your diet post-operatively.

The peri-operative period.

As you get closer to the date of your surgery, your surgeon will have more and more to say about what you need to do, and there will probably be a bowel preparation required!

Nutritionally, about 7 days before the procedure, you should increase the number of protein supplements you are taking each day to four or five, and cease consuming solid foods with the exception of green leafy vegetables (cucumbers cut to remove seeds are also permitted, and you may also consume melons, likewise removing the seeds). Resign yourself to lots of salads for 3 days. You can make your own salad dressings using canola or soya bean oil, because continuing with the "fat flushing" remains of value. During this period you have a free choice of protein supplements (shakes, soups, bouillons, drinks, puddings, gelatines), except that you may not use the bars. Continue drinking plenty of liquids and taking your vitamin, mineral and essential fatty acid supplements.

For the period 96 - 72 hours before the surgery, abandon solid food, and just use the protein supplements. You can have up to six during this 24 hour period, and continue, of course, with the vitamin, mineral and essential fatty acid supplements.

During the period 72 - 24 hours before the surgery, change all your protein supplements to the clear gelatine drinks. Any other drinks consumed must also be clear liquid, and at this stage, you should also change to a chewable or liquid vitamin and mineral supplement. You can take your essential fatty acid supplement during this period.

During this last few days, you may lose a little of your stored fat. Good. The anaesthetics used during the surgery are fat-soluble, and even a small reduction in body fat content will make your immediate post-operative recovery quicker and more comfortable.

That's it! You have had the best nutritional preparation possible, and are now under the care of the surgeon.

The surgery.

In gastric bypass surgery, the stomach is divided into two unequal parts and the small intestine is connected to the uppermost part of the stomach. This new small "stomach" limits the amount of food a person can eat at any one time by reducing the holding capacity of the stomach. It also interferes with the complete absorption of nutrients by shortening the length of the small intestine. Once you have fully recovered from the surgery itself, it will be important for you to eat foods of good nutritional quality.

The post-operative period.

In general, any major surgery or trauma has physiological consequences which in turn create special nutritional considerations. Similar situations may occur in severe illnesses with continued fever or prolonged sepsis. You have just had a surgical procedure which, as any such procedure, will result in an initial depression of metabolic parameters which may be of short duration. After this, you will enter a hypermetabolic state which commences with a catabolic period and is then followed by an anabolic period, during which the metabolism gradually returns to normal. During the initial catabolic stage of the hypermetabolic period, there are significant requirements for energy substrates and the body will go into negative nitrogen balance. Since those who have undergone gastric bypass surgery have done so to reduce body mass, the increased requirement for energy substrates should not be met, but steps must be taken to mitigate the loss of lean body mass, and to ensure adequate intake of vitamins, minerals and essential fatty acids. Such steps guarantee that the nutritional rehabilitation of the patient will be facilitated, and that optimal results will be obtained from the gastric bypass procedure.

The nutritional approach therefore requires an increased protein intake and appropriate supplementation. Since the procedure itself may reduce digestive functionality, at least for an initial period, the protein must be given in liquid form and in small but frequent amounts in order not to overburden the digestive system.

The important thing is to develop your diet gradually and progressively and still obtain adequate nutrition. Do not expect to eat large amounts of food immediately following surgery. A total of 3 oz. (less than ½ cup) is all your stomach will hold. Eventually, you will be able to eat child-sized portions. As mentioned, since you will only be able to eat small quantities of food, it is important that the foods you choose are nutritious and meet the requirements which are dictated by your physiology!

You will receive ongoing guidance and advice from your health care team on what and how you should be eating, based on individual tolerance. Some people experience no discomfort in eating. Others may have problems tolerating certain foods. If you have a problem, try to figure out what caused it so that you may be able to prevent it from happening again. Vomiting usually means that you have swallowed too much too fast, eaten too large a bite, not chewed food well enough, or the food does not agree with you. Try diluting your protein supplement if you feel nauseated. Listen to your stomach!

For the first 2 days postoperatively.

You will not be eating or drinking any food during this period. You will be getting the fluids you need through your intravenous drip. You may have a nasogastrointestinal (NG) tube in for a day or so to help drain fluids from your new stomach. You will start drinking small sips of water, when your surgeon feels you are ready and after a barium swallow test shows no leak. You may sip 1 - 2 oz. water (less than ¼ cup) per hour.

For the 3rd day postoperatively.

You may be able to increase the amount of water you drink to 2 - 3 oz. per hour plus you will start receiving 3 meals a day. Your meal will be a standard clear liquid tray, which consists of a clear protein bouillon (broth), a clear gelatine protein drink (sugar-free), fruit juice (should be diluted by mixing ½ water, ½ juice), and plain decaffeinated coffee or tea. You do not have to finish everything; there will be too much on your tray for you to do so. You must remember to eat and sip very slowly, making each meal last at least 30 minutes.

From 4 - 10 days post-operatively.

You will probably be at home by now, provided that you have convinced the surgeon to discharge you! Continue to sip water throughout the day as you did in the hospital, no more than 4 oz. per hour and not within 30 minutes of a meal. If you are drinking enough fluid, you will urinate at least 3-4 times daily.

An additional fluid option is mix 2 packets of any of the clear gelatine protein drinks with 6 oz. water and freeze in an ice cube tray. Each cube is approx. 1 oz, and can be sucked to provide both protein and fluid in a pleasant form.

You will be taking your 3 meals a day, and these will still consist of standard clear liquids, namely the clear protein bouillon (broth), a clear gelatine protein drink (sugar-free), fruit juice (should be diluted by mixing ½ water, ½ juice), and plain decaffeinated coffee or tea. Portion size will still be 4 oz. of clear liquids. Small, high protein meals will help your new stomach pouch heal.

About this time you should also start taking chewable or liquid vitamin and mineral supplements, but don't worry if you can't quite do it, because if you took your vitamins and minerals diligently during your pre-operative preparation, you will have stored enough reserve to last you a few days.

From 10 days to 3 weeks post-operatively.

Try to increase your fluids to 4-6 oz. per hour in small sips. Separate fluids from meals by 30 minutes. The meals will remain the same, but now you can also use the gelatine-based drinks and puddings between meals.

Additionally, you can try small amounts of the other protein-based products, such as the puddings, the shakes and the cream soups, as well as the protein gels and the RTD ("ready to drink") protein supplements. Start with 2 tablespoons at a time and increase the amount to ½ cup, as tolerated. You will be consuming about 300 to 800 calories per day and moving toward your protein goal of 75 - 100 grams daily, which you should try to meet by week 5.

You will definitely need to start vitamin and mineral supplements now. These should be in the form of liquid or chewable supplements, and your target is to achieve 100% of the RDA for all vitamins and minerals. That should be easy enough to do for most, but potassium will be the most difficult. The various protein supplements you are taking do contain potassium, but you may have to rely on fruit juices and vegetable juices to ensure an adequate intake. Your doctor can prescribe potassium supplements if your intake is not sufficient. You should also start taking your essential fatty acid (EFA) supplement again at this time; the soft-gel capsules dissolve readily, but if they are difficult to swallow or cause discomfort, they can be chewed if you can tolerate the fishy taste. In any case, even if you can swallow the capsules, only take one at a time, and spread your daily dosage well out over the course of each day.

From 3 weeks to 5 weeks post-operatively (the pureed food stage).

You may now gradually add high protein pureed foods to replace the liquid protein supplements at meals. Pureed foods require no chewing and are easy to swallow and digest. Start with 2 tablespoons of pureed meat (avoiding red meat if you can; chicken, turkey or pork are better, and if you can tolerate it, pureed fish) and gradually increase the amount to ½ cup per meal, as tolerated. Cooked meats can be pureed with the soup-type protein supplements added for moisture and to increase the protein content. You can also add up to a teaspoon of soya bean oil or canola oil which not only makes the puree smoother but also makes a contribution to your essential fatty acid requirement.

Commercial baby foods can also be used. Baby foods have a smooth consistency and offer convenient portion sizes. See the Table below for other high protein foods that you can work into your daily menu.

Remember to eat slowly and stop eating at the first signs of fullness, nausea, or abdominal discomfort.

Continue to slowly drink 6-8 oz. of fluid per hour; separate fluids from pureed solids by 30 minutes.

Continue to eat and drink protein supplements between meals and as a bedtime snack. The hot drinks work particularly well as evening snacks, and shakes are good during the day, but it is your preference.

Continue to take your vitamin, mineral and EFA supplements.

From 5 weeks to 8 weeks post-operatively (the soft food stage).

You will expand your food choices as tolerated, adding one or two new foods at a time. Your protein needs are the most important; then you can add fruits and vegetables to further meet your nutritional needs. Starchy foods (such as rice, potatoes, pasta, crackers, bread, cereal) are added last and should be limited because they tend to lead to weight gain.

Solid foods will not digest well unless they are very soft and chewed thoroughly to a pureed consistency. Avoid foods that may cause gas or bloating; these are generally foods high in fibre or containing carbohydrates of low digestibility. You will need to increase your fibre intake later, but at this stage it could cause discomfort.

During this time, you will be adjusting to your pouch and making the necessary dietary changes to your eating habits for weight loss. Eliminate your trigger foods and the high fat, high sugar foods that may have been sabotaging your efforts to lose weight. Your fat intake should typically be 20% -30% of calories, and should be based on a choice of fats and oils as indicated for the initial pre-operative preparation. Your caloric intake in this stage is typically 600 - 900 calories.

Continue to eat and drink protein supplements between meals and as a bedtime snack.

Continue to take your vitamin, mineral and EFA supplements.

From week 8 post-operatively onwards (the healthy eating stage).

Advance to regular foods when you are ready. Don't rush! Your diet will be based on your own tolerance.

You will still be eating 3 small meals and 3 snacks during the day. Each meal or snack will consist of ½ cup portions, which may gradually be increased to a maximum of 1 cup over the next 6 months.

Eat slowly and chew thoroughly. Meals and snacks should be consumed over the course of an hour.

Continue to sip (1 oz. or less every 5 minutes) liquids between meals, but not during the 30 minutes prior to meals or for 60 minutes after meals.

Avoid "liquid calories", such as fruit juice, milkshakes, ice cream, etc. They move quickly through your pouch and do not make you feel full. They may also cause "dumping syndrome" (see below).

You will always need to take vitamin and mineral supplements, but you may be able to tolerate regular pills now.

You may now also require the addition of vitamin B-12 supplements, either as injections or as sub-lingual (under the tongue) tablets. If your vitamin and mineral supplement does not contain at least 25 mg of iron, then menstruating women may need iron supplements in the form of ferrous fumarate or gluconate (not sulfate).

Enjoy your weight loss! The new eating habits you learn during these months will help you to continue to lose weight and maintain your weight loss for the rest of your life.

Some general information to help you:

Assuring an adequate intake of nutrients is important for everyone, but it is especially important after gastric bypass surgery. You need to assure adequate intakes of protein, essential fatty acids, vitamins and minerals. After surgery, protein helps wound healing, fighting infection, and reducing muscle loss. Not enough protein in your diet results in poor healing, hair and muscle loss, and a decrease in energy level. Poor essential fatty acid intake is also linked to poor healing, hair loss, dry skin and decreased energy levels. If you have prepared yourself before surgery according to these guidelines, then your supply of stored essential fatty acids will be adequate to get you through the initial period after surgery. With regard to protein, as soon as you are eating again, your initial goal is 60-75 g of protein daily. You may need more depending on your weight and body composition. Since your new stomach pouch limits portion sizes to ½ cup at meals, it's important to choose high protein foods. Meat and dairy foods are high in protein, but milk and other dairy products may not be well tolerated for several weeks after surgery due to a temporary lactose intolerance. To digest lactose, or milk sugar, an enzyme called lactase is required. After surgery, lactase is often in short supply in the lower small intestine. Milk and milk products may not be fully digested and cause gas, cramps, and diarrhea.

Some Key Points to Follow After Bariatric Surgery:

  • Put protein first at meals. For the first month after surgery, drink protein-rich fluid as much as possible. You have a wide choice of protein supplements available to you as clear drinks, shakes, soups, hot drinks, bouillons, gels and in RTD (Ready to Drink) forms.
  • Maintain a half-cup portion size at meals for the first 6 months after surgery. Overeating can cause nausea and vomiting and may stretch the stomach, hindering weight loss. Portions can be increased to one cup after 6 months.
  • Drink enough fluids. Consume at least 6 cups or forty eight ounces of fluid, primarily water, a day. Avoid high-calorie drinks, carbonated beverages, and alcohol. Remember to sip slowly and avoid gulping.
  • Eat slowly and stop eating or drinking when you are full. Pay attention to signs of fullness to prevent overeating. Overeating or binging can stretch the stomach and hinder weight loss or lead to problems with nausea and vomiting.
  • Chew foods thoroughly, especially meats, to avoid stomach obstruction.
  • Stick to sugar-free, low fat foods. Foods high in sugar and fat may cause diarrhea, abdominal discomfort, or "dumping syndrome". And they can slow weight loss.
  • Dumping syndrome results from a rapid passage of food from the stomach into the small intestine. Symptoms include nausea, faintness, cold sweats, faintness, and diarrhea after eating. You can prevent dumping syndrome by avoiding concentrated sweets and choosing foods that are sugar-free. It may also help to lie down after eating to slow the transit of food into the intestine. Avoid foods that have sugar as the main ingredient. Read food labels and do not eat or drink food items that list any of the following sugars as one of the first 3 ingredients: Sugar, Honey, Corn Syrup, Sucrose, Glucose, Dextrose, Fructose, Molasses.
  • Make exercise a priority. Walking is the best exercise after surgery. Start slowly and work up to 30 - 45 minutes each day.
  • Start a Diary. Record everything you eat and drink. This will make you more conscious of what you are doing and help identify foods that may be causing a problem.

Finally, for your convenience, the above follows in a tabular summary form.

.- = pre-operative
+ = post-operative

Protein Supplements (Bariatrix or SlimForme)


- 4 weeks
Shakes, cream soups, hot drinks, puddings, gels, RTD, bars, 2 or 3 per day. Normal, no hydrogenated fats, 30%+ calories
from plant oils (non-hydrogenated), reduce carbohydrates, avoid red meat, avoid other meat if possible.
Vitamins, minerals, EFAs
- 1 week
Shakes, soups, hot drinks, puddings, gels, RTD, 4 or 5 per day Green leafy vegetables, watery vegetable or fruit but no seeds. Plenty of fluids. Vitamins, minerals, EFAs.
- 4 days
Shakes, soups, hot drinks, puddings, gels, RTD, 6 per day. None, but drink plenty of clear fluids. Chewable or liquid vitamins and minerals, EFAs.
-3 days
Gelatine drinks only. Drink plenty of clear fluids. Chewable or liquid vitamins and minerals, EFAs.
-1 day
None. Clear fluids as directed by surgeon and health care team.
Surgery. You are under the orders of your surgeon and the health care team.
+ 3 days
Gelatine drinks and bouillons, 6 spread over 3 clear liquid meals. Diluted fruit juice, water, decaffeinated coffee or tea. None.
+ 4 days
Gelatine drinks and bouillons, 6 spread over 3 clear liquid meals. Ice cubes of frozen gelatine drinks. Diluted fruit juice, water, decaffeinated coffee or tea. Chewable or liquid vitamins and minerals.
+ 10 days
Gelatine-based protein supplements, other protein supplements (no bars) if tolerated, 6 to 8 per day. Diluted fruit juice, water, decaffeinated coffee or tea. Chewable or liquid vitamins and minerals, EFAs.

+ 3 weeks
Protein supplements (no bars) between meals, 2 - 4 per day. Pureed foods, commercial baby foods, liquids as above. Chewable or liquid vitamins and minerals, EFAs.
+ 5 weeks
Protein supplements between meals, 2 - 4 per day, may include one soft chewy bar. Soft foods as tolerated, baby foods, liquids as above. Chewable or liquid vitamins and minerals, EFAs.

+ 8 weeks
Protein supplements between meals, 2 - 4 per day, may include bars. Advance slowly to regular foods, liquids as above. Regular vitamins and minerals, EFAs.

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