Researchers followed 54 people who had two different types of weight loss surgery for two years. One surgery (called sleeve gastrectomy) makes your stomach smaller by removing part of it. The other surgery (called gastric bypass) makes your stomach smaller and reroutes your digestive system. Both surgeries helped people lose weight in the first year, but the gastric bypass kept the weight off better at two years. However, gastric bypass patients were more likely to develop nutritional deficiencies. This study helps doctors and patients understand the trade-offs between these two popular weight loss surgeries.

The Quick Take

  • What they studied: How well two different weight loss surgeries work over two years, including weight loss, metabolism changes, and nutritional health
  • Who participated: 54 people in Poland who had weight loss surgery between 2018 and 2022. Half had sleeve gastrectomy (27 people) and half had gastric bypass (27 people)
  • Key finding: Both surgeries worked well for the first year, but gastric bypass kept weight off better at two years. However, gastric bypass patients had more nutritional problems, especially with iron and vitamin B12
  • What it means for you: If you’re considering weight loss surgery, gastric bypass may keep weight off longer, but you’ll need careful monitoring for nutritional deficiencies. Sleeve gastrectomy is simpler with fewer nutritional risks, though some weight may return. Talk to your doctor about which is best for your situation

The Research Details

This was a retrospective study, meaning researchers looked back at medical records of patients who had already had surgery. They examined 54 patients from Poland—27 who had sleeve gastrectomy and 27 who had gastric bypass. The researchers measured their weight, blood sugar levels, cholesterol, and important nutrients (like iron and vitamin B12) at four time points: one month, six months, one year, and two years after surgery.

Sleve gastrectomy works by removing about 75% of the stomach, leaving a tube-shaped pouch. Gastric bypass is more complex—doctors make a small pouch from the stomach and connect it directly to the small intestine, bypassing most of the stomach and part of the intestines. Both procedures reduce how much food you can eat and change how your body processes food.

Comparing these two surgeries head-to-head over two years is important because most studies only follow patients for one year. The longer timeframe shows what happens when the initial weight loss slows down and whether people regain weight. Understanding the nutritional side effects helps doctors prepare patients for what they need to monitor after surgery.

This study has some strengths: it followed patients for a full two years and measured multiple health markers. However, it has limitations: it’s a relatively small group (54 people), it only looked at Polish patients so results might differ in other populations, and it’s a retrospective study which means researchers relied on existing medical records rather than carefully controlling the study conditions. The study didn’t randomly assign people to surgery types—they chose their own, which could affect results

What the Results Show

In the first year after surgery, both groups lost significant weight. People who had sleeve gastrectomy lost an average of about 30-35% of their excess body weight, and gastric bypass patients lost about 35-40%. Their BMI (a measure of weight relative to height) dropped dramatically in both groups.

At the two-year mark, something important happened: the gastric bypass group maintained their weight loss very well, but the sleeve gastrectomy group started gaining some weight back. This difference was statistically significant, meaning it wasn’t just random variation—it was a real pattern.

Both surgeries improved metabolic health markers. Blood sugar levels improved, cholesterol improved, and liver function improved in both groups. These improvements were similar between the two surgery types.

The nutritional deficiency findings were striking. Gastric bypass patients had significantly lower levels of iron, ferritin (stored iron), and vitamin B12 compared to sleeve gastrectomy patients. This makes sense because gastric bypass bypasses the part of the intestine that absorbs these nutrients. Sleeve gastrectomy patients had much fewer nutritional problems because their digestive system still works normally—the stomach is just smaller. These nutritional deficiencies can cause problems like anemia (low red blood cells) and nerve damage if not managed with supplements

This study adds to existing research by providing a direct two-year comparison in a European population. Previous studies have shown similar patterns—gastric bypass tends to produce more weight loss long-term, but at the cost of nutritional complications. This research confirms those findings and emphasizes that the nutritional issues with gastric bypass are real and require ongoing management

The study is relatively small with only 54 participants, which limits how much we can generalize the findings. It only included Polish patients, so results might be different in other countries with different populations. The study was retrospective, meaning researchers looked at past records rather than carefully controlling conditions. People chose which surgery to have rather than being randomly assigned, so there might be differences between the groups that affected outcomes. The study didn’t report how many people dropped out or were lost to follow-up, which could affect the results

The Bottom Line

If you’re considering weight loss surgery: (1) Gastric bypass appears more effective for long-term weight stability, but requires lifelong vitamin and mineral supplementation and careful monitoring. Confidence level: Moderate. (2) Sleeve gastrectomy is simpler, less invasive, and has fewer nutritional risks, though some weight regain may occur. Confidence level: Moderate. (3) Whichever surgery you choose, plan for regular blood work and nutritional monitoring for at least two years. Confidence level: High. (4) Work with a bariatric surgery team that includes nutritionists to manage your diet after surgery. Confidence level: High

This research is most relevant for people with severe obesity (BMI over 40, or BMI over 35 with obesity-related health problems) who are considering weight loss surgery. It’s also important for their doctors and nutritionists. People with existing nutritional deficiencies should be especially cautious about gastric bypass. This research is less relevant for people managing weight through diet and exercise alone

Most weight loss happens in the first 6-12 months after either surgery. By two years, you should see stabilization of weight (with gastric bypass) or possible slight weight regain (with sleeve gastrectomy). Nutritional deficiencies can develop gradually over months to years, so ongoing monitoring is essential. Benefits to metabolism and blood sugar control often appear within the first few months

Want to Apply This Research?

  • Track weekly weight measurements, monthly nutritional supplement intake (iron, B12, multivitamins), and quarterly blood work results for iron, ferritin, and B12 levels. Set reminders for supplement doses and doctor appointments
  • If using a health app post-surgery: (1) Log all food intake to ensure adequate protein (critical after surgery), (2) Track supplement adherence daily, (3) Record energy levels and any symptoms of nutritional deficiency (fatigue, weakness, numbness), (4) Monitor water intake to prevent dehydration
  • Create a dashboard showing: weight trend over time, supplement compliance percentage, upcoming lab work dates, and a checklist of nutritional symptoms to watch for. Set monthly reminders to review trends and quarterly reminders for blood work scheduling

This research summary is for educational purposes only and should not replace professional medical advice. Weight loss surgery is a serious procedure with significant risks and benefits. If you’re considering bariatric surgery, consult with a qualified bariatric surgeon, your primary care doctor, and a registered dietitian who specializes in bariatric nutrition. This study represents one research group’s findings and should be considered alongside other medical evidence and your individual health situation. Always discuss the specific risks and benefits of each surgery type with your healthcare team before making a decision.