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Nutritional Considerations Following Gastric Bypass

The Gastric Bypass restricts the amount of food which you can eat, but it does not seriously affect the absorption of foods which you eat.  It is important to recognize that, because you can eat very small amounts, there is a risk of becoming deficient in certain nutrients, such as protein, vitamins and minerals.  In order to protect yourself, you may need to use special supplements, particularly supplemental vitamins and minerals.  

Vitamins and Minerals

Vitamins and minerals are chemicals which are necessary to the efficient function of your body.  Ordinarily, the body can store only a small amount of these substances, and if you do not regularly eat enough of them in your diet, you can reach a point where the cells in the body do not function properly, and you can become sick.  The best strategy is to take a daily multi-vitamin and mineral supplement, to keep the body's supply topped off, so that you do not rely upon getting enough vitamins in your food.   Use of a vitamin supplement is not optional -- it is essential to your continued good health, and the success of the operation.  If, for any reason (e.g., nausea), you are not taking your vitamins, you should contact us for advice, before you develop a serious problem.  

The cost of these supplements will be much less than the amount you save on food, and you should think of them as food in another form (not as pills or medicine).  The cost of vitamin replacement, and treating a deficiency disorder can be very substantial, and some problems may not be completely reversible (e.g., bone calcium loss).


There are many hundreds of vitamin products on the market.  The following products are well-formulated, and not extraordinarily expensive:  

Many wild claims for special vitamin formulations are made.  There is no scientific evidence that vitamins from a particular source or plant, like "natural vitamins" are any more effective than those which are chemically synthesized.  Vitamins are a chemical, and carry ID cards to tell where they came from.  Certain herbal vitamin formulations may contain substances which are not assayed, the effects of which are unknown, and are at least potentially dangerous.  

Vitamin B-12

Absorption of Vitamin B-12 normally requires a substance which is attached to it in the stomach.  Since your stomach is mostly bypassed, that substance may not be available in sufficient amounts, and deficiency of Vitamin B-12 can result, causing anemia, enlarged red blood cells, and potential nerve damage.  

We recommend you use a special supplement of  Vitamin B-12, either as a sub-lingual preparation, or by periodic injection.  The cost of empiric Vitamin B-12 supplements is far less than that of regular testing of levels, let alone repair of a deficiency.  Supplements:


Most trace minerals are present in a high-potency multi-vitamin preparation, and no other supplements are needed.  The exceptions are Calcium and Iron.  Neither of these minerals are well-absorbed after Gastric Bypass, and daily supplementation is essential.


Calcium intake is likely to be inadequate in the bypassed patient, due to reduced food intake, and the need to avoid milk ingestion. Calcium absorption is not impaired.   Patients should take 1000 - 1500 mgm of Calcium daily. Suitable preparations are numerous:

Your physician may want to monitor bone densitometry, in post-menopausal females.  We have not observed significant abnormalities of bone metabolism with the Gastric Bypass, and scrupulous use of calcium supplements will protect most individuals.  As in those who have not had such surgery, certain individuals may experience serious bone disease.


Iron absorption occurs primarily in the duodenum, and is significantly impaired following Gastric Bypass. Iron supplementation is recommended in all menstruating females. The preferred formulation is Ferrous fumarate, with Vitamin C, in a non-enteric coated tablet.  Chelated iron, in a non-enteric-coated form, may also be absorbed adequately. 

 Normally, iron stores can be maintained on oral iron supplements, and decreasing iron levels or anemia should alert one to alternative explanations, such as gastrointestinal ulceration, or colonic abnormalities.


We recommend that each meal contain approximately one-half of its volume as protein-containing foods, such as eggs, chicken, turkey or fish, and we do not require any detailed calculation of required protein intake. Other potential sources include soy protein (tofu), beans, cottage cheese. For those who prefer it, protein intake should approximate 1 - 1.5 gram per kgm of ideal body weight -- adipose tissue is predominantly stored fat, and does not require protein repletion.  During the early phase of weight loss, we estimate that some protein needs are met by catabolism of protein in fatty tissues.

Protein intake should be adequate with each meal, since the body's ability to store protein or amino acids is very limited, and they are constantly required for synthesis. Even more significant to the weight-loss process is the very important inhibitory effect which protein has on the desire to continue eating.  We recommend that protein be eaten first, to ensure that it is eaten, and to enhance the very important satiety response of the Gastric Bypass, which seems to be most effectively stimulated by protein contact with proximal jejunum.

We do not ordinarily recommend the use of protein supplements, such as high-protein drinks, unless we judge that your protein intake is insufficient, based upon what you tell us you are able to eat.  


We recommend that you cook most vegetables, particularly in the early phase after surgery, to aid in their absorption.  You should also become familiar with foods which have a high "glycemic index", which will make your blood sugar and insulin levels unstable, and cause you to experience an urge to eat between meals.  Snacking is the worst thing you can do, if you want to sustain your weight loss.

Certain vegetables, grains, white flour and breads will have a tendency to make you hungry again, soon after you eat them.  When you have a Gastric Bypass, the foods you eat pass quickly into the intestine, and if they can be quickly broken down to sugars, they will cause a spike in your blood sugar level.  Your body responds to this by pumping out insulin, to lower the blood sugar (the most dramatic example of this effect is what is called the dumping syndrome).  

When your blood sugar comes plummeting back down, it will cause you to become hungry, and may also make you drowsy, or even shaky and sweaty, about 3 hours after your last meal.  When this happens, you will quickly learn to recognize the impending problem, and to avoid it by eating a snack, typically something which will cause your blood sugar to yo-yo again.  However, if you had eaten the healthier food to start, the effect would never have happened, and you would have been able to avoid the snack, and the risk to your weight loss.

Many physicians, when informed of the small amounts of food ingested after gastric bypass, are moved to recommend frequent small feedings, to increase nutrient intake, and to "avert starvation". This is decidedly the wrong approach. The rapid weight loss which follows Gastric Bypass is almost entirely salutary, while long-term weight loss approximates 2 pounds per week, implying a caloric deficit of approximately 1000 calories per day. This is a healthful rate of loss, when accompanied by adequate intake of protein and essential vitamins. Frequent feedings frustrate weight loss, and more importantly. encourage the most self-defeating habitual behavior that the bypass patient can acquire: snacking and eating between meals.

Stool Softeners

Many patients experience no difficulty with bowel function after the Gastric Bypass, although bowel activity is usually less frequent (every 2-3 days), because your food intake is so substantially reduced.  In addition, the amount and proportion of dietary fiber which you consume may be markedly reduced, by the alteration in your dietary regimen.  

Some persons will find that, with reduced bowel activity, there is a tendency for the stools to become too dry and hard, causing difficulty with constipation.  A laxative may occasionally be required, but the best strategy is avoidance of the problem, by use of a stool softener, which supplements the fiber you need, to hold water in the bowel and prevent constipation.  

Stool Softeners

Buy the sugar-free versions of these products:

Stool softeners have another potential use, for patients who find they have regained the capacity to eat more food:  If taken just before your meal, they will reduce your capacity, and help you to eat less.

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