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Bariatric Nutrition Guidelines and Assessment ( Before and After Surgery)

Pre and Post Bariatric Surgery Diet

Bariatric Nutrition Guidelines and Assessment ( Before and After Surgery)

Bariatric Nutrition Guidelines aim to make the weight loss journey a success. It is important to fully assess the person before and after the surgery and identify nutritional deficiencies since metabolic and bariatric surgeries may result in the loss of some important vitamins especially vitamin B12 or cobalamine.

Patients are also at a high risk of developing dehydration because of post-meal fullness, nausea, and vomiting.

Bariatric Surgery Types, Advantages and Disadvantages


Obesity is one of the leading causes of many diseases and health problems, with the rapid increase it is now being named an epidemic.

Due to the increase in obesity incidences, bariatric surgery has now become a household word.

It is a surgical procedure to remove excess body fat and is one of the most effective methods of achieving long-term weight loss.

Although it is one of the most productive solutions to obesity yet, it requires careful multidisciplinary management. This surgery is done when diet and exercise have not worked and serious health problems exist due to excessive body fat.

Indications of Bariatric Surgery (Cardiometabolic Surgery):

After thorough studies, it was suggested that the surgery is an option for well-informed and highly motivated patients who have severe obesity with a Body Mass Index of >35, 40, or sometimes even 50 along with serious co-morbid conditions.

Some other factors that are implemented for the recommendation of surgery include age, ethnicity, and severity of the co-morbid conditions.

Bariatric Surgery Types (Commonly Used Surgical Procedures): 

Although, the field of cardiometabolic surgery is evolving, here is a list of some of the common procedures performed:


Global estimate
Roux-en-Y gastric bypass (RYGB) 40 – 55%
Laparoscopic adjustable gastric banding (LAGB) 30 – 45%
Vertical banding gastroplasty (VBG) < 5%
Biliopancreatic diversion (BPD) < 5%
Sleeve gastrectomy (SG) < 4% ( gaining popularity)

Bariatric Nutrition Guidelines:

Nutrition supervision is of significant value, like malnutrition, nutrient deficiencies may lead to deleterious effects on overall health.

Essential information on nutrition management, both before and after bariatric surgical procedures is mandatory.

Weight loss surgeries can greatly affect the stomach and small intestine which may affect the digestion and absorption of nutrients, it may also have an impact on the eating habits of the individual, hormones, or microorganisms in the gastrointestinal tract which may result in reduced appetite and improved metabolism of fat.

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Pre-operative Nutritional Assessment:

nutrition assessment before and after surgery

Nutrition assessment is an important component of the preoperative evaluation of the patient pursuing bariatric surgery.

Moreover, a careful nutritional assessment offers relevant information about a patient’s medical and emotional health, eating habits, health risks, weight history, and weight loss efforts that can help to assess the role of surgery on a patient’s health and his or her efforts of weight management.

Nutrition assessment of the patient should be done by the obesity specialist and a registered dietitian.

During nutritional assessment following data is collected:

  • Food and Nutrition related history
  • Anthropometric measures
  • Biochemical data and medical tests
  • Drug history
  • Physical examination

Nutritional assessment in a tabulated form:

BMI Calculation (kg/m²)                                     30 – 35

35 – 40


Obesity-related co-morbidities
  • T2DM
  • Hypertension
  • Hyperlipidemia
  • OSA/ hypoventilation syndrome
  • Asthma
Risk factors for preoperative morbidity
  • BMI > 50(kg/m²)
  • Physical inactivity
  • Smoking
  • Untreated OSA
  • Thromboembolism
  • DM2
Nutritional risk factors
  • Medications
  • H/O alcohol/substance abuse
  • Diet
  • GI disease and surgeries
Laboratory testing
  • CBC
  • Ferritin
  • Vitamin B12
  • 25 OH Vitamin D
  • Thiamine
  • FBG, Hgba1c
  • Lipid profile
  • Serum creatinine
  • TSH
  • Liver transaminases
  • Polysomnography
Dietary assessment
  • Weight history/weight loss efforts
  • Diet recall
  • Dietary restrictions
  • Dietary modification
  • Regular physical activity
  • Smoking cessation
  • Management of comorbidities

Why is Nutrition Guidelines Necessary?

  • Nutrition care plays a substantial role in preventing deficiencies that may result from decreased food intake, improper digestion, or malabsorption of nutrients.
  • It aids in weight loss.
  • Aids in preventing nausea, dizziness, vomiting, dehydration, hair loss, and other side effects.

Nutritional Management Before Surgery:

Before bariatric surgery, 5-10% weight loss is mostly suggested it is known to improve the surgical outcomes.

Excess of body weight and a fatty liver greatly increase surgical risk factors. Patients are advised to follow low-calorie and low-carbohydrate diets, two weeks prior to the surgery.

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Other nutritional changes prior to surgery include the following:

  • Eliminating caffeine:

    • Caffeine acts as a diuretic and may cause dehydration. But a sudden withdrawal of caffeine may cause dizziness and headache, that’s why a slow and gradual withdrawal is suggested.

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  • Physical activity:

    • All the patients must include mini-walks throughout the day. This will help to develop strength and stamina. Physical activity will help to prevent the risk of post-surgical venous thrombosis.

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  • Hydration:

    • Proper hydration must be encouraged in order to avoid post-operative dehydration.
  • Structuring meals and snacks:

    • Patients should be encouraged to have small meals throughout the day instead of large meals.

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  • Mindful eating:

    • The new pouch/sleeve will not grind food properly and the volume of digestive enzymes and acids will be significantly decreased, patients need to chew food thoroughly and breathe between bites.
    • These techniques will prepare them for the change in eating style after the surgery.

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Dietary Guidelines Before Surgery:

Diet changes before the surgery aid in weight loss and prevention of macro and micronutrient deficiencies.

The daily caloric intake should be 600-1000 kcal

  • Fluids:

    • Water intake should be increased and calorie-free fluids should be taken between meals. Caffeinated drinks should be avoided.
    • Total fluid intake must be gradually increased up to 2 liters (64 ounces or 8cups).

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  • Protein:

    • Protein-rich food consumption is necessary for the preservation of muscle tissue. Minimum 65-75% gram protein must be taken daily.

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  • Fats:

    • Food products high in fat will result in the addition of extra fat and a slowed rate of weight loss, it may even cause weight to regain.
    • To maintain the weight patients are advised to cut the extra calories and to have low fat dies with saturated fats <10%.
    • Foods that have 5% or less Daily Value should be included in the diet. Lean meat should be preferred to avoid excessive fat.

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  • Calcium Supplement:

    • 1,200 to 2,000 mg of calcium must be administered daily to prevent calcium deficiency and bone disease.

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  • Vitamin D Supplement:

    • Take a total of 800 to 1,000 International Units (IUs) of vitamin D each day. This total amount should be taken in divided doses.
  • Vitamin B12 Supplements:

    • Take 500 mcg of vitamin B daily.
  • Iron and Folic Acid:

    • Some patients may require supplementation of iron and folic acid.

Within 24 Hours of Surgery

  • One day before surgery Full Liquid Diet should be administered
  • After midnight the Patients should be given Clear Liquid Diet and this should be stopped 2 hours before the surgery.

Post-operative Nutrition Care:

sugar free juices after surgery

After the surgery, patients are advised to take the following diets according to the condition and time.


After the surgery has been performed the patient is given a Clear liquid diet and then Full Liquid Diet is administered for one week. Recommended Liquid and Semi-liquids:

  • Broth
  • Sugar-free fruit juices
  • Water
  • Decaffeinated tea or coffee
  • Skim milk
  • Low-fat yogurt
  • Low fat, sugar-free pudding

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Blended and Pureed Diet:

Two weeks following surgery, the patient may progress to blended/puréed foods. This diet will be high protein (>20gram protein) and low calorie (< 200 kcal). Along with the administration of protein supplements.

The patient needs to know that their stomach size has been reduced and the opening of the stomach has also been narrowed.

For this reason, it is important to take small sips and bites, chew the food properly, and add significant gaps between meals.


  • Foods allowed in blend diet include:
  • Yogurt
  • Cottage cheese
  • Lean Meat
  • Lean fish
  • Mashed Potatoes
  • Cereals
  • Noodles
  • Well Cooked/Blended vegetables
  • Scrambled egg whites
  • Spicy foods, canned fruits and vegetables, Bakery products, and junk food must be avoided
  • Taking fluids just after the meal should be avoided.

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Regular diet- beginning at 9th week after the surgery:

After the surgery, the patient switches back to a regular diet at 9th week. This diet includes 900-1000 calories with 60-80 grams of protein.

Here is a sample menu:

Breakfast 2 scrambled egg whites + 2 slices of bread
Snack 1 medium-sized apple
Lunch Boiled rice with lentils
Snack 1 cup Green tea
Dinner 2-40 oz baked fish + baked sweet potato
Bedtime Skim milk

Advancing to a regular diet should be thoroughly administered by a Registered Dietitian.

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Post-Operative Nutritional Guidelines:

  • Hydration:
    • It may be difficult for some patients to reach the recommended goal of 48-60 oz fluid per day. Patients taking diuretics must be monitored closely for hydration status.
    • Salty liquids must be administered to patients with dehydration
  • Dietary protein:
    • Bariatric surgery patients are recommended to include a comparatively greater amount of protein in their diets.
    • A balanced distribution of protein at each meal protects the skeletal muscle during weight loss. Protein shakes with zero carbohydrates and >30g protein per serving should be avoided.

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  • Dietary Carbohydrates:
    • The recommended amount of carbohydrates by WHO (World Health Organization) is 50g of carbohydrates per day to maintain normal brain function.
    • Postoperative patients must exclude highly processed and refined forms of carbohydrates. Consumption of whole grains must be encouraged.
  • Calorie Goals:
    • Bariatric patients must focus on incorporating a healthy and balanced diet with a higher proportion of nutrient-dense foods as compared to energy-dense foods.
    • Patients must be counseled to make smarter food choices to maintain a healthy weight and to avoid weight regain

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  • Micronutrient and macronutrient deficiencies:
    • Nutrient deficiencies are common in bariatric surgery patients, these deficiencies must be covered by proper diet and supplementation of these nutrients.

Standard Supplementations:

Supplement Dosage
Multivitamins 1-2 daily
Calcium citrate divided doses 1,200–1,500 mg/day.
Vitamin D 3,000 IU of D titrate to >30 ng/ml
Folic acid 400 µg/day in a multivitamin
Elemental iron
  • 18–27 mg/day elemental
  • Not to be taken with calcium; taken with vitamin C will increase iron absorption
  • 40–65 mg/day menstruating females
Vitamin B12 350–500 µg/day orally/sublingual, nasal, or 1,000 µg/month intramuscularly

Possible Nutrition-Related Problems that may occur after surgery:

  • Dehydration:

    • One of the common problems seen after surgery is dehydration caused due to inadequate intake of fluid. Its signs include dark urine, dizziness, headache, and nausea.
  • Decreased appetite:

    • It is very common to not feel hungry right after surgery. Patients are advised to eat according to the schedule and not on physical symptoms of hunger.
  • Nausea or vomiting:

    • This is usually caused by eating fast or eating too much, drinking with meals, or not chewing properly.
  • Bad taste in the mouth and taste changes:

    • This is commonly observed just after surgery and may resolve on its own in a couple of weeks.
  • Constipation:

    • May occur within the first few weeks after surgery due to medication, low-fiber diets, and decreased fluid intake. Stool softeners, physical activity, and taking whole grains may help in regular bowel movements.
  • Increased gas:

    • This is common during the first week, the patient may feel bloated. This can be caused due to lactose intolerance.
  • Hair loss:

    • Excessive hair loss after surgery is due to nutrient deficiencies and weight loss. It may gradually resolve on its own.
  • Pregnancy:

    • This should be avoided for the first 18 months. During this time pregnancy could cause complications and may result in birth defects.

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In Summary:

It is important to assess the patient before and after surgery, identify nutritional deficiencies, and avoid them or replace them in time. It is also important to avoid high-caloric diets so as to lose weight and achieve the targets of reversing diabetes and hypertension.

What do you think?

Written by Diabetes Doctor

I am an Internist practicing medicine for the last fifteen years. Over the years, I have learned that medicine is not about prescribing pills. True medical practice is helping people.
I do prescribe pills as well but the best results I get are when I motivate people to overcome their problems with little changes in their lifestyles.
Since most of my patients are obese, have diabetes, hypertension, high cholesterol levels, I am writing at when free.
Dibesity, I know the correct word is diabesity. Ignore this! Be with us.

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