WLS Forte and other FitForMe supplements


The Sleeve Gastrectomy (SG) has become the most performed metabolic procedure worldwide1.  The procedure results in significant weight loss and improvement of comorbidities by reducing food intake and hormonal changes2-3. Unlike other procedures, the anatomy of the intestinal tract remains largely intact when performing an SG. For this reason, the risk of developing deficiencies and therefore the need of long-term supplementation was initially considered low4. However, an increasing number of studies have reported that in patients with an SG, deficiencies are as common as in RYGB patients5-8.

Deficiency prevalence

Pre-operative deficiencies

Even though metabolic surgery can worsen pre-existing nutrient deficiencies, pre-operative deficiency screening is often not performed9. Pre-operative screening is important since nutrient deficiencies are found in more than half of all patients prior to metabolic surgery10-11, due to a unilateral diet and impaired metabolism. Pre-operative deficiencies are most prevalent for vitamin D, folic acid, vitamin B12 and ferritin6,10-14.

Post-operative deficiencies

After SG, the same nutritional deficiencies remain prevalent. Furthermore, vitamin B1 and zinc deficiencies are often encountered4,14,16-18. Even when patients use a standard multivitamin, deficiencies often occur, possibly affecting long-term health. A recent study on the effectiveness of supplementation after SG found that 42% of patients develop one or more nutritional deficiencies in the first year after surgery15.


Conversely, after an SG, some patients have vitamin levels above the normal range. Several studies found this to be the case for vitamin A, vitamin B1 and vitamin B214-17, when taking multivitamins of ±150% recommended daily intake (RDI). The exact mechanism behind hypervitaminosis after SG might be linked to increased absorption due to a diminished production of gastric acid, but is yet to be determined in studies.


Factors leading to increased deficiency risk

SG patients have an increased risk of developing nutrient deficiencies postoperatively due to:

Decreased food intake

Several factors lower the food intake post-SG. The SG significantly reduces the volume of the stomach, making it impossible to eat large amounts of food. Additionally, the part of the stomach that produces ghrelin, the hormone that stimulates appetite, is removed. This decrease in food intake leads to weight loss, but also contributes to the risk of developing nutritional deficiencies. Since the sensation of appetite comes back after the first postoperative year, behavioral change within that first year is crucial.

Food tolerance is decreased after SG

This is mostly the case for red meat, dairy products, rice, pasta and bread19-21. Lowered intake of animal food sources leads to an insufficient intake of B-vitamins, including vitamin B12, which is not naturally found in foods of plant origin. Moreover, meat is a major source of protein and iron. The type of iron found in red meat (haem iron) is more easily absorbed and used by the body than the iron in plant food sources. In general, after SG, food tolerance improves with time19-21.

Faster passage of food along the digestive tract

Removal of the lower part of the stomach might result in faster gastric emptying, however studies on this topic are inconclusive22. Studies on bowel motility after SG are scarce, however it seems that, compared to an intact gastro-intestinal tract, the food moves faster through the section of the small intestine where most of the (passive) absorption takes place, leaving less time for absorption.


Vomiting is one of the possible complications after SG and affects approximately 8% of the patients, according to a study by Major et al23.  Vomiting might be a consequence of ‘dumping syndrome’. Dumping syndrome is commonly seen after RYGB, when a large amount of foods suddenly enters the intestines. Dumping syndrome can also occur after SG, possibly due to the rapid gastric emptying24. Vomiting is especially a risk factor for vitamin B1 deficiency, because vitamin B1 needed for the production of gastric acid25.

Decreased production of gastric acid

The production of gastric acid is stimulated by gastrin. Since this hormone is produced in the section of the stomach that is removed, the SG leads to a decrease of the production of gastrin and gastric acid in the stomach. Gastric acid is required  to release nutrients from the food to which they are bound, so they can be absorbed. Furthermore,  it is needed to convert non-haem iron from plant food sources, to haem iron. Only haem iron can be absorbed by the body. When gastric acid production is impaired, iron absorption is reduced substantially26.

Decreased production of Intrinsic Factor

The section of the stomach that produces gastric acid and intrinsic factor, both required for vitamin B12 absorption, is resected in SG27. Gastric acid is needed to release vitamin B12 from protein, to which it is attached in food. As vitamin B12 passes from the stomach to the small intestine, it binds with intrinsic factor. Bound together, the intrinsic factor-vitamin B12 complex travels to the end of the small intestine (ileum), where receptors recognize the complex. Vitamin B12 is gradually and actively absorbed into the bloodstream. Without intrinsic factor, vitamin B12 can only be diffused passively throughout the entire small intestine, accounting for only 1% of absorption28.

The need for specialized multivitamins

Composition of a specialized multivitamin for SG patients

The unique changes of the GI-tract after SG have a specific impact on nutrient absorption. The high prevalence of deficiencies and hypervitaminosis underscore the importance of lifelong use of a specialized multivitamin after surgery, tailored to the needs of SG patients.

Supplements should contain the best absorbable nutrient compounds in exactly the right balance, to avoid deficiencies or hypervitaminosis. For example, since only 1% of vitamin B12 is passively absorbed after SG, very high dosages are needed to reach the daily needed 2,5 µg. Taking multiple standard multivitamins is no option, since this would cause too high levels of for instance vitamin B6, risking nerve damage (peripheral neuropathy) as a possible result.

Why suppletion with WLS Optimum

FitForMe offers WLS Optimum: a specialized multivitamin for SG patients, tailored to their specific nutritional needs. WLS Optimum was first developed in 2009, based on scientific literature. Since that time, WLS Optimum was already optimized twice based on FitForMe (preliminary) study results and scientific literature.

Two separate studies evaluated the safety and efficacy of WLS Optimum, comparing WLS Optimum 1.0 to a standard multivitamin that contained 100% of the recommended daily allowance. Both studies confirm previous findings, that even with the non-malabsorptive nature of the procedure, nutritional deficiencies often occur after SG14-16.

Heusschen et al.14 found a relatively high deficiency prevalence for SG patients, regardless of which type of food supplement was used. Usage of WLS Optimum resulted in higher serum values for folic acid and vitamin B1, compared to patients taking a standard multivitamin. However, no significant differences in deficiency levels were found between the two groups, which is thought to be linked to the small sample sizes and low compliance.

Smelt et al.15 found higher mean serum concentrations of ferritin, folic acid, vitamin B1 and vitamin D and less deficiencies in vitamin B12, ferritin, folic acid and vitamin B1 in patients using WLS Optimum 1.0, compared to patients using standard multivitamins. However, anemia was diagnosed more often in WLS Optimum users, compared to patients using standard multivitamins. The results of this study have lead to an optimization of WLS Optimum in 2017, increasing the iron dosage from 21 mg to 28 mg in the current version of WLS Optimum (2.2).


Nutritional screening and adequate supplementation are imperative pre- and post-SG to ensure optimal nutritional status and health. Supplementation should be tailored to the need of patients with SG to prevent nutritional deficiencies as well as excessive rise in micronutrient levels.

WLS Optimum is proven to be effective in preventing nutritional deficiencies and hypervitaminosis when taken daily. Compliance is essential, but relatively low, as shown in several studies12,14,29.

To keep improving our products on a daily basis, FitForMe continuously conducts both internal  and external studies on product effectiveness and customer experience. Findings are implemented in product development, professional collaboration and customer education.


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13. S. Pellitero, E. Martinez, R. Puig, A. Leis, R. Zavala, M. L. Granada en et al., „Evaluation of Vitamin and Trace Element Requirements after Sleeve Gastrectomy at Long Term,” Obesity Surgery, vol. 27, nr. 7, pp. 1674-1682, 2017.

14. L. Heusschen, W. Schijns, N. Ploeger, L. N. Deden, E. J. Hazebroek, F. J. Berends en E. O. Aarts, „The True Story on Deficiencies After Sleeve Gastrectomy: Results of a Double-Blind RCT,” Obesity Surgery, 2019.

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