The role of a dietitian


Bariatric/metabolic surgery has proven benefits for weight loss, improvement in metabolic/inflammatory state and resolution of medical co-morbidities related to obesity.

With anatomical and neuro-endocrine changes, after surgery there is a combinations of reduction in hunger, increased satiation and alteration in gut microbiota as well as changes in eating behaviour and food preferences.

The Bariatric Analysis and Reporting Outcome System (BAROS) assess health related quality of life, co-morbidities and complications after surgery.

The Bariatric Surgery Registry (BSR) (by volunteering surgeons/hospitals) is a registry/audit of all the bariatric/metabolic surgical procedures performed in Australia and New Zealand to assess weight loss, resolution of T2DM and complications after surgery.

But often these reporting systems does not properly evaluate food tolerances, post op eating habits, diet and lifestyle choices of the patients. A separate food tolerance test questionnaire is needed to assess the tolerance to different food groups and satisfaction with the diet.

There may be a change in taste and smell perception that affect food preferences after bariatric surgery. On the positive side some studies have shown a decreased intake of high fat, high carbohydrate and high sugar foods.

But food intolerances if severe or persist may lead to loss of muscle mass and nutritional deficiencies.

Working with the patients who has undergone restrictive/hypoabsorptive/malabsorptive bariatric procedures (sleeve, one anastomosis, Roux Y gastric bypass, SADI-S or others) it is the role of the dietitian to focus the patient’s attention on:

  • Healthy eating (good portion size, good food choices, good eating habits)
  • Food tolerances, energy and protein intake
  • Adequate vitamin/mineral intake and avoiding micronutrient deficiencies
  • Changes in body composition

Successful outcome after bariatric/metabolic surgery should be reported as adequate total body weight loss (%TBWL), resolution of medical co-morbidities, improvement in health related quality of life, reduction in premature cardio-vascular or cancer related mortality, etc plus positive impact on a patient’s dietary changes, eating behaviour and body composition.

Bioelectrical impedance tests can also be done to assess fat free mass, fat mass, muscle mass and FM/FFM ratio.


Exercise is an essential part of the effective weight loss and long-term weight maintenance. Even though morbidly obese post op patients can often safely participate in an exercise program or physical training, most don’t do half as much of the recommended exercise or accumulate over 150 minutes of exercise a week.

Individuals who successfully maintained weight loss over the long term (5 years or more) often report a significant reduction in sedentary activities and active participation in physical activity.

Exercise is necessary to:

  • Maintain lean body or skeletal muscle mass
  • Positively influence the metabolic rate
  • Help to maintain active bone metabolism and bone mineral content
  • Improve cardio-vascular function and improved health outcomes
  • Exercise also been associated with better eating habits and improved adherence to dietary guidelines
  • Positively affects eating behavior, cognitive function and motivation levels

Monitoring for micronutrient deficiencies

After hypoabsorptive/malabsorption surgery, it is recommended that lifelong multivitamin replacements be prescribed and blood test monitoring is necessary at regular intervals.

This is an example, more blood test may be needed for some other patients.

  • Iron studies may be tested every 3-6 months in the first year, then once or twice annually.
  • Folic acid levels may be tested every 3-6 months in the first year, then once or twice annually.
  • Vitamin B12 may be tested every 3-6 months in the first year, then once or twice annually.
  • Vitamin D may be tested every 3-6 months in the first year, then once or twice annually.
  • Thiamine may be tested every 3-6 months in the first year. It should be tested if the patient has been vomiting.

Annual blood tests should be done for vitamin A, B6, copper, magnesium, selenium and zinc

If there are micronutrient deficiencies detected, replacement doses above daily recommended may be needed and more frequent blood test is mandatory.

Special mention for pregnant ladies after bariatric surgery

Higher doses of folic acid may be needed such as 4-5g a day

Iron and vitamin B12 replacement is almost routinely given

Calcium and vitamin D supplements >50nmol/L is recommended

Caution with vitamin A supplement because it is potentially teratogenic

Fetal growth monitoring with ultrasound at 28, 32 and 36 weeks is a minimum

Blood tests such as HbA1C is performed instead of OGTT

Table 1. Vitamins replacements and deficiencies

Vitamins and RDIFood sourcesDeficiencies
A (retinol) 1500-3000mcgGreen leafy vegetable, carrots, pumpkins Orange, squash, liverNight blindness, hyperkeratosis
B1 (thiamine) 12mgEggs, pork, liver Brown rice, vegetables, oat meals, potatoesCardiovascular problems (wet Beri-Beri) Nervous system (dry Beri-Beri) Wernicke’s encephalopathy Korsakoff psychosis
B2 (riboflavin) 1.3mgDairy, bananas, green beans, asparagusSore mouth and tongue, ariboflavinosis
B3 (niacin) 16mgMeat, fish, eggs Vegetables, mushroom, nutsPellagra
B5 (panthothenic acid) 5mgMeat, broccoli, avocadoParasthesia
B6 (pyridoxine) 1.5 -5 mgMeat, vegetable, nuts, bananaDermatitis, glossitis Anaemia, peripheral neuropathy
B7 (biotin) 30mcgEgg yolk, liver Vegetables, peanutsDermatitis, enteritis
B9 (folic acid) 400-800mcgGreen leafy vegetables, spinach, peanuts Pasta, cereal, bread, beans, liverMegaloblastic anaemia Neural tube defects
B12 (cobalamin) 350- 500mcgMeatMegaloblastic anaemia
C (ascorbic acid) 90mgFresh fruits, vegetables, liverGingivitis, scurvy
D3 (cholecalciferol) 75mcg or 3000 IUFish, eggs, liver, mushroom Sunlight exposureRickets, osteomalacia
E (tocopherol) 15-20mgFruits, vegetables, grains, nuts, seedsReduced balance and reflexes
K (phylloquinone) 1mgGreen vegetables, gut bacteriaBleeding disorder
  • Please note: high levels of vitamin B6 may be associated with peripheral neuropathy (numbness, parasthesia, burning sensation in peripheries)

Table 2. Mineral supplements and function

SodiumSalt, milk, spinachFor fluid and electrolyte balance, blood pressure control
ChlorideSaltFor electrolyte balance, gastric acid secretion
PotassiumLegumes, bananas, tomatoes, grains, beans, spinachFor electrolyte balance
CalciumDairy products, eggs, nuts, seeds, green leafy vegetablesFor bone structure integrity
PhosphorusRed meat, dairy products, fish, rice, breadFor bone structure integrity
MagnesiumNuts, soy, vegetables, tomatoesFor cell energy and bones
Iron 18mg (45-60mg for young females)Meat, eggs, grains, beans, vegetable, lentilFor red blood cell synthesis and function
IodineIodinized salt, cheese, eggs, strawberry, yoghurtFor thyroid function and immune system
Copper 2mgGreen vegetables, mushroom, seeds, nutsFor cell enzyme function
ManganeseGrains, beans, rice, berryFor cell enzyme function
SeleniumFish, nuts, mushroomAnti-oxidant
MolybdenumTomato, carrot, onionFor cell function
Zinc 8-22mgOyster, seafood, meatFor skin, hair and nail function, wound healing

Table 3. Calcium deficiency and osteoporosis

Osteomalacia is defective bone mineralization due to vitamin D deficiency

Osteoporosis is defective bone formation

Bone mineral density (BMD) is measured with a nuclear medicine DEXA scan

NormalBMD within 1 SD adult mean (T score > -1)
OsteopeniaBMD -1 to -2.5SD below adult mean (T score -1 to -2.5)
OsteoporosisBMD >2.5SD below adult mean (T score below -2.5)
Severe osteoporosisBMD >2.5SD below adult mean with pathological fractures