Researchers looked at data from nearly 3,000 American adults to understand how weight loss surgery affects vitamin and mineral levels in the body. They compared three groups: people with normal weight, people who had weight loss surgery, and people who needed the surgery but hadn’t had it yet. The surprising finding was that people who needed surgery but hadn’t gotten it yet had more vitamin deficiencies, while those who had the surgery and took supplements afterward had normal vitamin levels—just like people with normal weight. This suggests that proper care after surgery, including taking vitamins, can prevent the nutritional problems that sometimes happen with weight loss surgery.

The Quick Take

  • What they studied: Whether weight loss surgery affects how much vitamins and minerals people have in their bodies, and whether taking supplements after surgery helps prevent deficiencies.
  • Who participated: Nearly 3,000 American adults aged 18 and older, divided into three groups: people with healthy weight, people who had weight loss surgery, and people who were eligible for surgery but hadn’t had it yet.
  • Key finding: People who needed weight loss surgery but hadn’t had it yet had significantly more vitamin deficiencies (including low calcium, low vitamin D, and iron problems) compared to people with healthy weight. However, people who had the surgery and followed proper aftercare with supplements had normal vitamin levels, similar to healthy-weight people.
  • What it means for you: If you’re considering weight loss surgery, know that vitamin deficiencies are common before surgery, but proper supplementation after surgery can prevent these problems. This suggests that following your doctor’s supplement recommendations after surgery is really important.

The Research Details

This study used information from the National Health and Nutrition Examination Survey (NHANES), which is a large, ongoing program that collects health information from a representative sample of Americans. The researchers looked at data collected between 2015 and 2018 from nearly 3,000 adults. They divided participants into three groups based on their weight and surgery history: those with normal weight (BMI 18.5-24.9), those who had weight loss surgery, and those who were eligible for surgery but hadn’t had it yet. The researchers then compared blood test results showing vitamin and mineral levels between these groups using statistical methods that account for the survey’s design.

The study measured several important nutrients including iron levels, calcium, and vitamin D. These nutrients are especially important to track because weight loss surgery can sometimes make it harder for the body to absorb them from food. By comparing the three groups, the researchers could see whether surgery itself caused problems or whether the problems existed before surgery.

Understanding how weight loss surgery affects vitamin and mineral levels is crucial because these nutrients are essential for bone health, energy, immune function, and many other body processes. If people don’t have enough of these nutrients, they can develop serious health problems. This study helps doctors understand whether the vitamin problems sometimes seen in weight loss surgery patients are caused by the surgery itself or by the conditions that made surgery necessary in the first place.

This study used real-world data from a nationally representative survey, which means the results likely apply to the general American population. The large sample size (nearly 3,000 people) makes the findings more reliable. However, because this is a cross-sectional study (a snapshot in time rather than following people over years), we can’t be completely certain about cause and effect. The study also relied on blood tests that were already done for other purposes, so the researchers couldn’t control exactly how or when the tests were performed.

What the Results Show

The most important finding was that people who were eligible for weight loss surgery but hadn’t had it yet had much higher rates of vitamin and mineral deficiencies compared to people with normal weight. Specifically, they were 78% more likely to have high iron levels (hyperferritinemia), more than twice as likely to have high transferrin receptor levels (a sign of iron problems), 3.4 times more likely to have low calcium, and more than twice as likely to have vitamin D deficiency.

In striking contrast, people who had already undergone weight loss surgery and were presumably following their doctor’s recommendations for supplements showed no significant difference in vitamin and mineral levels compared to people with normal weight. This suggests that the surgery itself, when combined with proper supplementation and follow-up care, does not cause the nutritional problems that were previously thought to be inevitable.

The researchers also found that the vitamin deficiencies seen in the pre-surgery group were not simply due to having excess weight. Instead, these deficiencies appear to be related to the underlying metabolic conditions that make someone a candidate for weight loss surgery. This is an important distinction because it suggests that the surgery, combined with proper nutritional management, may actually help correct these pre-existing problems.

While the study focused on specific nutrients, the pattern of findings suggests that comprehensive nutritional management after weight loss surgery is effective. The fact that people who had surgery showed normal levels across multiple different nutrients (not just one or two) indicates that following post-surgery supplement recommendations helps maintain overall nutritional health. This supports the importance of the updated 2022 guidelines from major surgical organizations that emphasize the need for careful nutritional monitoring and supplementation after weight loss surgery.

Previous research has shown that weight loss surgery can sometimes lead to vitamin deficiencies, particularly with iron, calcium, and vitamin D. This study adds important new information by showing that these deficiencies may be more related to the conditions that make surgery necessary rather than the surgery itself. When patients follow proper supplementation protocols after surgery, they can maintain healthy nutrient levels. This finding aligns with and supports current medical guidelines that emphasize the importance of lifelong vitamin supplementation after weight loss surgery.

This study has several important limitations to consider. First, it’s a snapshot in time (cross-sectional), so we can’t prove that surgery caused the improvements in vitamin levels—only that people who had surgery had better levels. Second, the study didn’t have detailed information about how well people followed their supplement recommendations after surgery, so we can’t be certain that supplements alone explain the good results. Third, the study couldn’t account for all the differences between groups, such as diet quality or exercise habits. Finally, the study only included data from 2015-2018, so more recent practices and guidelines may have changed how doctors manage nutrition after surgery.

The Bottom Line

If you’re considering weight loss surgery: (1) Get your vitamin and mineral levels checked before surgery to understand your baseline status (moderate confidence); (2) Plan to take vitamin supplements for life after surgery as recommended by your surgical team (high confidence); (3) Have regular blood tests to monitor your nutrient levels after surgery (moderate confidence); (4) Work with a dietitian who specializes in bariatric surgery to ensure you’re eating enough nutrient-rich foods (moderate confidence). These recommendations are based on this study plus existing medical guidelines.

This research is most relevant for people considering weight loss surgery, people who have already had weight loss surgery, and their doctors. It’s also important for people with obesity-related health conditions to understand that vitamin deficiencies are common with their condition, not just with surgery. People with normal weight don’t need to worry about these specific findings, though the general message about the importance of vitamins applies to everyone.

If you have weight loss surgery and start taking supplements immediately afterward, you should expect to see improvements in vitamin and mineral levels within a few months, though this varies by individual. The key is consistency—taking supplements as prescribed and maintaining regular follow-up appointments with your surgical team. Long-term success requires lifelong commitment to supplementation and monitoring.

Want to Apply This Research?

  • Track daily vitamin and mineral supplement intake (specific supplements: multivitamin, calcium, vitamin D, iron if recommended) with checkmarks or logging, aiming for 100% compliance. Set reminders for supplement times and log any missed doses to identify patterns.
  • Set up a daily supplement routine by taking vitamins at the same time each day (e.g., with breakfast) and use the app to send reminders. Create a checklist of your prescribed supplements and check them off as you take them each day.
  • Log supplement adherence daily, schedule reminders for blood work appointments (typically every 6-12 months after surgery), and track any symptoms of deficiency (fatigue, bone pain, weakness). Review monthly compliance reports to identify barriers to taking supplements consistently.

This research is informational only and should not replace professional medical advice. If you’re considering weight loss surgery or have had weight loss surgery, consult with your doctor or a registered dietitian about your specific nutritional needs and supplementation plan. Blood test results and nutritional status vary by individual, and your healthcare provider should monitor your specific situation. This study shows associations, not definitive proof of cause and effect. Always follow your surgical team’s recommendations for supplements and follow-up care.