Researchers studied 198 people with type 2 diabetes who had weight loss surgery. Before surgery, patients followed a very strict diet with only 600 calories per day. Scientists measured their blood sugar levels during this diet period. They found that patients whose blood sugar dropped below 143 mg/dL on the second day of the diet were much more likely to have their diabetes completely go away after surgery—over 70% success rate. This simple early test could help doctors predict which patients will benefit most from weight loss surgery for diabetes.

The Quick Take

  • What they studied: Can a simple blood sugar measurement before weight loss surgery predict whether someone’s type 2 diabetes will go away after the operation?
  • Who participated: 198 adults with type 2 diabetes who were preparing for gastric bypass surgery (a common weight loss surgery). All participants followed a very strict 600-calorie-per-day diet before their surgery.
  • Key finding: Patients whose blood sugar was below 143 mg/dL on day two of the pre-surgery diet had more than a 70% chance of their diabetes completely disappearing within two years after surgery. Overall, about two-thirds of all patients achieved complete diabetes remission.
  • What it means for you: If you’re considering weight loss surgery for diabetes, your doctor might use this simple blood sugar test to estimate your chances of success. However, this is just one predictor—many other factors affect outcomes, and you should discuss your individual situation with your healthcare team.

The Research Details

This was a forward-looking study where researchers followed 198 people preparing for gastric bypass surgery (a procedure that makes the stomach smaller and rearranges the digestive system). Before surgery, all participants ate a very restricted diet of only 600 calories per day—much less than normal. Doctors measured their blood sugar levels, particularly on the second day of this diet. The researchers then tracked these patients for two years after surgery to see whose diabetes completely went away.

The study focused on a specific measurement: capillary blood glucose, which is blood sugar measured from a small finger prick (the same test many people with diabetes do at home). This is a practical, inexpensive test that doctors can do in any office. The researchers wanted to know if this early measurement could predict long-term success.

By comparing the pre-surgery blood sugar readings with the actual outcomes two years later, the scientists could identify which blood sugar level was most predictive of diabetes remission.

This research approach is important because it looks for a simple, practical way to predict surgery success before it happens. If doctors can identify which patients are most likely to benefit, they can better counsel patients about realistic expectations and plan appropriate follow-up care. The study uses a real-world test (finger-stick blood sugar) that’s already available in every doctor’s office, making it practical to implement.

This study followed real patients over a two-year period, which is a solid timeframe for seeing lasting results. The sample size of 198 is reasonably large for this type of research. However, the study was conducted at a single center in Brazil, so results might vary in different populations. The researchers measured a specific, objective outcome (blood sugar levels), which is reliable. One limitation is that the study doesn’t explain why this particular blood sugar level is predictive—it just shows the association. Additionally, this study doesn’t compare different types of surgery or different diet approaches.

What the Results Show

The main finding was striking: about two-thirds (66.7%) of all patients achieved complete remission of their type 2 diabetes within two years after surgery. This is an excellent outcome and shows that weight loss surgery is very effective for diabetes.

The key predictor was the blood sugar level measured on the second day of the pre-surgery diet. Patients whose blood sugar dropped below 143 mg/dL had more than a 70% chance of complete diabetes remission. This is important because it’s higher than the overall remission rate, meaning this test can identify patients with especially good chances of success.

The blood sugar measurement was particularly good at identifying patients who would NOT achieve remission (high specificity, in medical terms). This means if a patient’s blood sugar didn’t drop below 143 mg/dL, doctors could be fairly confident that diabetes remission was less likely. This helps avoid false hope for patients who might not benefit as much.

The study showed that the body’s response to the very strict pre-surgery diet—specifically how much blood sugar drops—reflects something important about how the body will respond to surgery. This suggests that the diet period isn’t just about weight loss; it’s also a test of how well the body can regulate blood sugar when calories are severely restricted. Patients whose bodies responded well to this challenge tended to have better outcomes after surgery.

Previous research has shown that weight loss surgery is very effective for type 2 diabetes, but doctors haven’t had a reliable way to predict which individual patients will achieve complete remission. This study adds to that knowledge by identifying a specific, measurable predictor. The finding aligns with what we know about diabetes: it’s related to how the body handles blood sugar regulation, and surgery appears to reset this system in many people. This research suggests that a patient’s ability to improve blood sugar control during the pre-surgery diet is a window into how well their body will respond to the surgery itself.

The study was conducted in one hospital in Brazil, so results might be different in other countries or populations with different genetics or healthcare systems. The research doesn’t explain the biological reason why this blood sugar level is predictive—it just shows the connection. The study only looked at one type of surgery (gastric bypass), so these findings might not apply to other weight loss surgeries. Additionally, the study didn’t account for all factors that might affect outcomes, such as medications patients were taking, how much weight they lost, or their diet after surgery. Finally, while 70% success is excellent, it means 30% of patients in the favorable group still didn’t achieve complete remission, so this test isn’t perfect.

The Bottom Line

If you have type 2 diabetes and are considering weight loss surgery, ask your doctor about this blood sugar test during your pre-surgery diet period. A result below 143 mg/dL suggests you have a good chance (over 70%) of achieving complete diabetes remission. However, this is just one piece of information—your overall health, other medical conditions, and your commitment to lifestyle changes after surgery also matter significantly. Even if your blood sugar doesn’t drop below 143 mg/dL, surgery may still help your diabetes; this test just identifies those with especially high success rates. Confidence level: Moderate—this is promising research, but it comes from one center and needs confirmation in other populations.

This research is most relevant for adults with type 2 diabetes who are considering gastric bypass surgery. It’s also important for bariatric surgeons and diabetes doctors who counsel patients about surgery. If you have type 1 diabetes, this research doesn’t apply to you. If you’re managing diabetes with diet and medication alone and not considering surgery, this information is less directly relevant, though it does show how powerful weight loss can be for diabetes control.

The study followed patients for two years after surgery, which is when most diabetes remission occurs. Some patients may see improvements in blood sugar within weeks of surgery, but complete remission typically takes several months. You should expect to see significant changes within the first year, with the full picture becoming clear by two years post-surgery. However, maintaining these results requires ongoing lifestyle changes, including healthy eating and physical activity.

Want to Apply This Research?

  • If you’re preparing for weight loss surgery, track your fasting blood sugar levels daily during your pre-surgery diet period. Record the specific reading from day two of your very low-calorie diet, as this is the most predictive timepoint. Compare this to the 143 mg/dL threshold to understand your predicted success rate.
  • Use the app to log your daily blood sugar readings during the pre-surgery diet phase and set a goal of achieving a reading below 143 mg/dL by day two. This creates accountability and helps you understand how your body responds to the strict diet. After surgery, continue tracking blood sugar to monitor your progress toward remission.
  • Set up monthly blood sugar tracking for the first two years after surgery to document your diabetes remission progress. Create a comparison chart showing your pre-surgery baseline, pre-surgery diet response, and post-surgery trajectory. This visual record helps you and your doctor assess whether you’re on track for complete remission and identifies any concerning trends that need attention.

This research describes findings from a single-center study and should not be used as a substitute for personalized medical advice. If you have type 2 diabetes or are considering weight loss surgery, consult with your doctor or endocrinologist to discuss whether these findings apply to your situation. Blood sugar predictions are not guarantees—individual results vary based on many factors including genetics, medications, lifestyle changes, and overall health. This information is educational and does not constitute medical advice. Always work with your healthcare team to make decisions about diabetes treatment and surgery.