Nutritional Deficiencies

Low vitamin and mineral concentrations are common after weight-loss surgery; due to reduced food intake and the altered gut anatomy. Therefore, life-long nutritional monitoring and follow-up are essential components of bariatric surgical care. The British Obesity and Metabolic Surgery Society has updated the nutritional guideline in 2020 [1], and we advise you to follow this recommendation to prevent long-term nutritional deficiencies.


Let's see what will change once you had a weight loss surgery:

More detail:

Healthy individual:

Patient who had sleeve or gastric bypass:

Iron is important in making red blood cells, which carry oxygen in the body.

A lack of iron can lead to iron deficiency anaemia. The daily requirement is 8.7-14.8 mg.

You should be able to get all the iron you need from your daily diet.

Women who lose a lot of blood during their monthly period (heavy periods) are at higher risk of iron deficiency anaemia and may need to take iron supplements.


The majority of the iron absorbed from digested food or supplements is absorbed in the duodenum. Therefore the absorption after weight loss surgery is very limited. Following Sleeve gastrectomy and gastric bypass an additional elemental iron replacement is required. A daily intake of 45 mg iron recommended for males, and this can go up to 100 mg for females with heavy periods.

Folate (B9 vitamin) is found in many foods. 

Folate helps:

  • the body form healthy red blood cells

  • reduce the risk of birth defects called neural tube defects, such as spina bifida, in unborn babies

A lack of folate could lead to folate deficiency anaemia. Adults need 200 micrograms of folate a day, and during pregnancy it is recommended to double it. There are no long-term stores in the body, so you need to eat folate-containing foods frequently.


Folate is actively absorbed primarily from the upper third of the small intestine, therefore the absorption after gastric bypass is very limited.

At least 400 microgram daily intake is recommended, and and there are increased requirements before and during pregnancy and lactation

Thiamin (vitamin B1), helps:

  • the body break down and release energy from food

  • keep the nervous system healthy  

  • The amount of thiamin adults (aged 19 to 64) need is: 1mg a day for men, 0.8mg a day for women

​You should be able to get all the thiamin you need from your daily diet. Thiamin cannot be stored in the body, so you need it in your diet every day.


Vitamin B1

Thiamine is a water-soluble vitamin that is absorbed in the jejunum, so people are at high risk of developing thiamine deficiency post bariatric surgery. The “general” multivitamin and mineral supplement containing thiamine may not be sufficient to prevent deficiency. If people present with prolonged vomiting, dysphagia, poor nutritional intake, inability to tolerate vitamin and mineral supplements, high alcohol intake or fast weight loss, additional thiamine supplementation should be administered immediately to prevent the development of Wernicke's encephalopathy.

Vitamin B12 is involved in helping the body:

  • make red blood cells and keeping the nervous system healthy

  • release energy from food

  • use folate

A lack of vitamin B12 could lead to vitamin B12 deficiency anaemia. Adults (aged 19 to 64) need about 1.5 micrograms a day. If you eat meat, fish or dairy foods, you should be able to get enough vitamin B12 from your diet. But as vitamin B12 is not found naturally in foods such as fruit, vegetables and grains, vegans may not get enough of it.

Vitamin B12

Normally, vitamin B12 is readily absorbed in the last part of the small intestine (ileum). However, to be absorbed, the vitamin must combine with intrinsic factor, a protein produced in the stomach. Therefore after weight loss surgery the risk of developing vitamin B12 deficiency is very high, so supplementation is required for prevention. Untreated vitamin B12

deficiency may result in irreversible nerve damage or subacute combined degeneration of spinal cord, which may occur in the absence of megaloblastic anaemia. It is recommended to have a Vitamin B12 injection every day, or take high dose oral supplement daily.

Calcium has several important functions.

These include:

  • helping build strong bones and teeth

  • regulating muscle contractions, including your heartbeat

  • making sure blood clots normally

A lack of calcium could lead to a condition called rickets in children, and osteomalacia or osteoporosis in later life. Adults aged 19 to 64 need 700mg of calcium a day. You should be able to get all the calcium you need from your daily diet.


Calcium dissolves in the stomach and is absorbed through the lining of the small intestine into the bloodstream with the presence of vitamin D. Calcium absorption is adversely affected by bariatric surgery. It is recommended that  1200- to 1500-mg calcium per day from food and supplements following sleeve and gastric bypass, preferably in calcium-citrate form, which has more bioavailability.

Vitamin D helps regulate the amount of calcium and phosphate in the body.

These nutrients are needed to keep bones, teeth and muscles healthy.

A lack of vitamin D can lead to bone deformities such as rickets in children, and bone pain caused by a condition called osteomalacia in adults. Adults need 10 micrograms of vitamin D a day, this equals with 400 IU. This includes pregnant and breastfeeding women, and people at risk of vitamin D deficiency.

Vitamin D

Vitamin D (also referred to as “calciferol”) is a fat-soluble vitamin that is naturally present in a few foods, added to others, and available as a dietary supplement. It is also produced endogenously when ultraviolet (UV) rays from sunlight strike the skin and trigger vitamin D synthesis. It is absorbed from the small intestine.

Starting regimens of 2000–4000 IU of vitamin D3 per day are recommended to maintain serum 25OHD levels after surgery with adjustments being made dependent on results.

Copper helps:

  • produce red and white blood cells

  • trigger the release of iron to form haemoglobin, the substance that carries oxygen around the body

It's also thought to be important for infant growth, brain development, the immune system and strong bones. Adults aged 19 to 64 need 1.2 mg of copper a day. You should be able to get all the copper you need from your daily diet.


The site of maximal copper absorption is at the stomach and upper intestine. Therefore after bariatric surgery the copper absorption is impaired, and patients recommended to take at least 2 mg copper per day.

Zinc helps with:

  • making new cells and enzymes

  • processing carbohydrate, fat and protein in food

  • wound healing.

  • The amount of zinc you need is about:

    • 9.5mg a day for men (aged 19 to 64 years)

    • 7mg a day for women

    You should be able to get all the zinc you need from your daily diet.


Early during digestion, zinc ions present in food release and then are absorbed in the small intestine. After bariatric surgery the daily intake should reach the 15 mg per day.


[1]: British Obesity and Metabolic Surgery Society Guidelines on perioperative and postoperative biochemical monitoring and micronutrient replacement for patients undergoing bariatric surgery—2020 update

Mary O'Kane | Helen M. Parretti | Jonathan Pinkney | Richard Welbourn | Carly A. Hughes | Jessica Mok | Nerissa Walker |Denise Thomas | Jennifer Devin | Karen D. Coulman | Gail Pinnock | Rachel L. Batterham | Kamal K. Mahawar | Manisha Sharma| Alex I. Blakemore | Iris McMillan | Julian H. Barth

Obesity Reviews , 2020; 21:e13087, DOI: 10.1111/obr.13087