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Identifying nutritional deficiency in clinical practice

Individuals who have undergone surgery for the treatment of obesity may be at increased risk developing nutritional problems. Deficiencies can be found to be pre-existing in obesity, and after surgery may arise because of decreased food intake, change in the types of nutrients obtained through diet, and/or alterations in how nutrients are digested and absorbed.

Part of the routine follow-up care of bariatric surgery patients should include screening for and the presence of nutrient deficiency. Guideline documents for screening have been issued by the American Society of Metabolic and Bariatric Surgery, The Obesity Society, European Society of Endocrinology, and by some regional organisations. Typically, screening will include the following features:

  1. Dietary history – to assess nutritional intake via food sources
  2. Clinical interview and examination – to elucidate any signs and/symptoms that could be indicative of deficiency
  3. Laboratory testing – to screen for common nutrient deficiencies and any additional of concern.

Dietary History

Following bariatric surgery, overall dietary intake decreases, and food selection may vary greatly from the pre-operative diet. Eating less food, which is common to all bariatric surgery procedures, means an overall increased likelihood for reduced nutrient intake in all areas.

It is also very common that dietary composition changes following bariatric surgery. This can be through instruction such as the common recommendation to increase protein intake and reduce carbohydrate intake, or due to the relatively common development of food aversions or intolerances. 

If possible with patient scheduling and time allowances, a three-day food record is an excellent tool for reviewing dietary intake. There are numerous formats used for this type of recording, but if not being used for research, a simple log that record foods eaten, estimated serving size, and eating occasions is generally adequate.

During an office visit, a 24-hour dietary recall (either the previous 24 hours or a “typical” 24 hour period) can be conducted. In either case, it is good to also include intake of any dietary supplements so a total picture of nutrient intake can be evaluated.

This is also a good time to assess specific eating challenges such as nausea, vomiting, hunger, cravings, dumping, post-prandial hypoglycemia and other issues that might have an overall impact on total nutrition.

Clinical Interview and Examination

In addition to the above-mentioned dietary recall, a clinical interview may be very helpful in the clinical evaluation of potential nutritional problems. It is important to ask about intake of dietary supplements and, if possible, to have patients bring these to the office visit for review.

A brief review of symptoms should be conducted with an emphasis on new, unusual or persistent symptoms. It can also be valuable to ask about medication intake (to elucidate drug-nutrient interactions). 

In addition to a current weight, a physical exam should generally look at body fat stores, muscle mass/wasting, quality of skin and hair, and other outward signs of nutrient deficiencies.

Any symptoms of concern elucidated from the interview should be examined if at all possible or referred to an appropriated clinician for follow up. For example, if a patient is reporting intermittent numbness and pain in the feet, a neurological exam should be conducted or the patient should be instructed to see a health care practitioner who is qualified to conduct this type of examination. (see Table 1 below for some common symptoms of select nutrient deficiencies).

Nutrient Common Symptoms Less Common
Thiamine (B1) Vomiting, weakness, calf and leg pain or cramps (more at night), burning feet, headache, blurred vision, confusion and memory changes, weakness, poor coordination Constipation, digestive problems, irritability, loss of appetite, nervousness, numbness of hands and feet, pain sensitivity, severe personality changes, inability to stand or walk
Folate Fatigue, headaches, weakness, anemia Apathy, diarrhea, insomnia, loss of appetite, neural tube defects in fetus, paranoia, shortness of breath,
B12 Anemia, dizziness, fatigue, loss of vibration sensation, numbness – especially numbness and tingling in feet and hands that starts at tips of fingers and toes and moves up. Constipation, depression, intestinal disturbances, headaches, irritability, low stomach acid, mental disturbances, moodiness, mouth lesions, spinal cord degeneration
Vitamin D Nothing, hip pain, hearing loss, osteomalacia Burning sensation in mouth, diarrhea, insomnia, myopia, nervousness, scalp sweating
Vitamin A Dry hair, dry eyes, immune impairment, night blindness, skin changes including acne Acne, fatigue, growth impairment, insomnia, hyperkeratosis (thickening and roughness of skin), weight loss, anemia (iron deficient that does not resolve)
Calcium None, leg cramps, periodontal disease and tooth decay Brittle nails, cramps, delusions, depression, insomnia, irritability, osteoporosis, palpitations
Iron Fatigue, hair loss (not hair loss that happen normally after surgery, but later or ongoing hair loss) pica (eating things that are not food like paper, sand, corn starch, paste, etc), ice eating, heart palpitations, dizziness Anemia, brittle nails, confusion, constipation, depression, fatigue, headaches, inflamed tongue, mouth lesions
Zinc Brittle nails, hair loss, loss of sense of taste, loss of appetite, white spots on nails, wound healing impairment, metallic taste in mouth Acne, amnesia, apathy, diarrhea, eczema, fatigue, immune impairment, impotence in men, irritability, lethargy, low stomach acid, male infertility, memory impairment, night blindness, paranoia

Table 1: Some common symptoms of select nutrient deficiencies

Some clinics also have the ability to include measurements of body composition via displacement (air or water), bio-impedance, dual-energy X-ray absorptiometry (DXA) or other means. If available, this kind of testing can be a useful addition especially in identifying excessive loss of lean body mass.

Laboratory Testing

Various guideline documents have addressed the need for regular, ongoing laboratory assessments to evaluate for the presence of nutritional deficiencies.

At a minimum, testing is often recommended to be done one to three times in the first year following surgery, one to two times in year two and then annually (assuming there are not deficiencies that need to be treated and re-evaluated).

Recommendations for specific nutrients to be tested tend to vary by procedure, as the risks are not entirely the same across the board. It would be advisable for clinicians caring for bariatric surgery patients to review the key guideline papers (ASMBS, Endocrine Society (2), AACE/TOS/ASMBS) and create a protocol suitable to their patients and clinical practice. Table 2 below gives a general summary from two of the guideline papers.

Nutrient Test(s) AGB RNY/VSG* BPD-DS Notes
B1 (thiamine) Serum or whole blood thiamine PRN Optional/PRN Optional/PRN Transketolase activity test can be useful if available, especially to track recovery. Many programs are screening at least once in the first 6 months for all procedures.
B6 PLP Need unknown With non-resolving anemia With non-resolving anemia May also be a useful screen for vitamin compliance
B12 Serum B12 Every 6 months in the first year then annually Ever 3-6 months x 2 years then annually Every 3-6 months for life Other tests can include MMA and homocysteine
Folate Serum or RBC folate Optional Optional Every 3-6 months for life Homocysteine can also be helpful. Important to consider in pregnancy. May be elevated in SIBO.
Iron Iron studies, Ferritin Every 6 months in the first year then annually Ever 3-6 months x 2 years then annually Every 3-6 months for life Remember that ferritin can be elevated with inflammation for any source or from pregnancy.
Zinc Plasma zinc Need unknown PRN Annually or PRN Can be a cause of PICA/hair loss, low testosterone. Plasma zinc may be unreliable with inflammation.
Copper Serum copper PRN PRN PRN With symptoms of B12 myeolneuropathy and normal B12/folate studies. With unresolved anemia especially with neutropenia.
Selenium Glutathione peroxidase activity Need unknown PRN Annually or PRN Meaning of deficiency in this population is somewhat controversial. Consider with unresolving anemias
Calcium 24-hr Urine or adjusted serum calcium See notes Ever 3-6 months x 2 years then annually Every 6-12 months Consider bone Alk Phos, N-telopeptide, DXA. N-telopeptide may be a very valuable test with AGB for assessing bone loss
Bone Metabolism iPTH PRN – see notes Ever 3-6 months x 2 years then annually Every 3-6 months for life Metabolic bone disease is an issue with all procedures. The AACE/TOS/ASMBS guidelines offer additional guidance on prevention and treatment that clinicians should be familiar with.
Vitamin D 25(OH)D Every 6 months in the first year then annually Ever 3-6 months x 2 years then annually Every 6-12 months for life Many programs now test pre-operatively. AACE/TOS/ASMBS Suggests it is best to maintain levels at least 30-60 ng/mL
Vitamin A Plasma retinol Need unknown PRN Every 6-12 months for life Consider with non-correcting microcytic anemia, eye symptoms
Vitamin E Plasma tocopherol Need Unknown PRN Every 6-12 months for life Very little data on deficiency in any procedures
Vitamin K K1 and INR Need unknown PRN Every 6-12 months for life  
Protein Albumen and Prealbumen PRN PRN Every 3-6 months for life  
Carnitine and EFAs By chromatography method Need unknown Need unknown PRN Little supportive data on utility of this testing

Table 2: Recommendations for Screening Labs and Frequency

Some words on adherence

While life long follow-up is clearly critical for supporting the nutritional health of individuals who have undergone surgical procedures for the treatment of obesity, it is clear from looking at follow-up numbers in clinical trials that adherence is an overall challenge in many areas.

Many patients simply get lost to follow up. However, others struggle with maintaining advised dietary changes, supplement recommendations and more. Ultimately, adherence may have a bigger impact on life-long nutrition in bariatric surgery patients than the surgeries themselves.

As prevention is generally easier than treatment, all programs providing care to bariatric surgery patients should consider the ways they can support patients (through education, reminders and other means) in adhering both to diet and lifestyle changes and also to the follow up care they need.


Nutrient deficiencies can arise in any patient who has had bariatric surgery. Deficiencies can generally be identified and treated with good follow-up care that includes dietary history, clinical and physical evaluation, and laboratory testing at regular intervals.

Emphasis should be given to adherence so that as much as possible deficiency can be prevented or discovered early when intervention tends to be most effective.