Doctors wanted to know if people with obesity could safely lose weight quickly before colon cancer surgery. They studied 26 patients—13 who worked with a nutrition expert on a special low-calorie diet plan and 13 who didn’t. The group that followed the diet plan lost about 10 pounds on average in just a month, and two-thirds of them lost at least 3% of their body weight. Importantly, no one had serious problems from the diet. The diet group also had fewer surgery complications than the control group. This suggests that working with a nutrition expert on a short-term diet before colon cancer surgery might help patients and could be a safe option.

The Quick Take

  • What they studied: Whether people with obesity could safely lose weight quickly before colon cancer surgery by following a very low-calorie diet plan with help from a nutrition expert.
  • Who participated: 26 adults (average age 63 years, mostly men) who were scheduled for colon cancer surgery. Half followed a special diet plan, and half didn’t. Both groups were similar in age, health conditions, and the type of surgery they needed.
  • Key finding: People who followed the diet plan lost an average of 10.5 pounds (4.75 kg) in about a month, with two-thirds losing at least 3% of their body weight. No one experienced serious problems from the diet, and this group had fewer surgery complications (8 complications) compared to the group that didn’t diet (15 complications).
  • What it means for you: If you’re facing colon cancer surgery and have obesity, working with a nutrition expert on a short-term, supervised diet plan before surgery may help you lose weight safely and could reduce your risk of surgery complications. However, this is a small study, so talk with your doctor about whether this approach is right for your situation.

The Research Details

This was a retrospective cohort study, which means researchers looked back at medical records from 2017 to 2023 to compare two groups of patients. One group (13 patients) had worked with a dietitian (nutrition expert) on a very low-calorie diet before their colon cancer surgery. The other group (13 patients) had surgery without following this special diet plan. The researchers matched the groups carefully so they were as similar as possible in age, health conditions, and type of surgery planned.

The very low-calorie diet was a supervised program where patients ate significantly fewer calories than normal for a short period (about 18 to 47 days) before surgery. A dietitian guided them through this process. The researchers then compared how much weight each group lost and tracked any health problems that occurred during the diet period or after surgery.

This type of study is useful for understanding real-world outcomes because it uses actual patient data from medical records rather than a controlled laboratory setting. However, because researchers looked backward at existing data rather than randomly assigning people to groups, it’s not as strong as some other study types.

This research matters because obesity can make colon cancer surgery riskier—patients may experience more complications during and after surgery. If a safe, short-term diet plan can help patients lose weight before surgery, it could improve their surgical outcomes. This is the first study to look at this specific approach for colon cancer surgery, so it provides new information that doctors didn’t have before.

Strengths: The groups were well-matched in important ways (age, health conditions, surgery type), no one dropped out of the study, and the researchers carefully tracked complications. The diet was supervised by professionals, which is important for safety. Weaknesses: This is a small study with only 26 patients total, which limits how much we can trust the results. The study looked backward at medical records rather than following patients forward in time. The researchers didn’t randomly assign people to groups, so there could be unmeasured differences between groups that affected the results. More research with larger groups is needed to confirm these findings.

What the Results Show

The main goal was to see if the diet plan helped people lose weight. The results were positive: people in the diet group lost a median of 4.75 kg (about 10.5 pounds) before surgery, which represented 3.8% of their body weight. This loss happened over about 18 to 47 days. Two-thirds of the diet group (67%) achieved the target of losing at least 3% of their body weight, which is considered meaningful for health.

It’s worth noting that the diet group started out heavier than the control group (about 20 pounds heavier on average), so they had more weight to lose. Despite starting heavier, they successfully lost weight in a short timeframe.

The second main goal was to check if the diet was safe. The good news: no one in the diet group experienced serious problems related to the diet itself during the intervention period. This suggests that when supervised by nutrition professionals, this type of diet can be done safely for short periods before surgery.

An interesting secondary finding was the difference in surgery complications between groups. The diet group experienced 8 surgical complications total, while the control group experienced 15 complications. This suggests that the weight loss achieved through the diet may have helped reduce surgery-related problems. However, because this is a small study, we can’t be completely certain this difference was caused by the diet rather than other factors. The study didn’t provide details about what specific complications occurred in each group.

This is the first study to examine very low-calorie diets specifically for people preparing for colon cancer surgery. However, similar diet approaches have been studied for other types of surgery (like weight loss surgery and hip/knee replacement surgery) and have shown promise for reducing complications. This study adds to that body of evidence by showing the approach may also work for cancer surgery. The safety profile found here is consistent with what researchers have observed in other surgical populations when the diet is properly supervised.

Several important limitations should be considered: First, this is a small study with only 26 patients, so the results may not apply to larger populations. Second, the groups weren’t randomly assigned—researchers matched existing patients, which means unmeasured differences could have influenced results. Third, the study looked backward at medical records, which can sometimes have incomplete information. Fourth, the study didn’t track patients long-term after surgery to see if weight loss benefits lasted. Fifth, all patients were treated at one hospital, so results might differ in other settings. Finally, the study didn’t compare this diet approach to other weight loss methods, so we don’t know if this is better than other options.

The Bottom Line

For adults with obesity facing colon cancer surgery: Discussing a supervised, short-term diet plan with your healthcare team and a registered dietitian may be worth considering, as this small study suggests it could be safe and might help reduce surgery complications. However, this should only be done under professional supervision and with your surgeon’s approval. Confidence level: Moderate—this is promising but based on a small study, so more research is needed. For healthcare providers: This study suggests that dietitian-led preoperative weight loss interventions may be a safe option to discuss with eligible patients, though larger studies are needed before making it standard practice.

This research is most relevant for: Adults with obesity who are scheduled for colon cancer surgery and want to optimize their health before the procedure. Colorectal surgeons and their teams who care for patients with obesity. Registered dietitians who work with cancer patients. This research is less relevant for: People with normal weight who are having colon cancer surgery. People with obesity having other types of surgery (though similar approaches may apply). People who cannot safely follow a very low-calorie diet due to other health conditions.

In this study, weight loss occurred relatively quickly—over about 18 to 47 days (roughly 3 to 7 weeks) before surgery. Most patients lost weight within the first few weeks. If you were to pursue this approach, you could expect to see weight loss results within weeks rather than months. However, the long-term benefits (whether weight loss is maintained after surgery) were not studied, so we don’t know how long the benefits last.

Want to Apply This Research?

  • Track daily weight (same time each morning) and weekly body weight percentage change. Set a goal of 3% body weight loss over 4-8 weeks before surgery. Log this in your app with a target date aligned with your surgery date.
  • If working with a dietitian on a preoperative diet plan, use the app to: (1) Log all food and drinks consumed daily to stay accountable to your calorie goals, (2) Record how you’re feeling physically and emotionally during the diet period, (3) Set reminders for meal times and water intake, (4) Track any symptoms or concerns to discuss with your dietitian.
  • Create a pre-surgery optimization dashboard that tracks: weekly weight trend, percentage of daily calorie goals met, energy levels (1-10 scale), and any symptoms. Share weekly summaries with your healthcare team. After surgery, continue tracking weight and recovery milestones to see if the preoperative weight loss correlated with better recovery outcomes.

This research describes a specialized medical intervention (very low-calorie diet before colon cancer surgery) that should only be pursued under direct medical supervision. If you have colon cancer and obesity, do not attempt any restrictive diet without first consulting your oncologist and a registered dietitian. Very low-calorie diets are not appropriate for everyone and may interact with cancer treatments or other health conditions. This study is small and preliminary—it should not be considered definitive medical guidance. Always work with your healthcare team to develop a personalized preoperative plan that is safe for your specific situation. This information is educational and not a substitute for professional medical advice.