Is There Such Thing as an Ideal Body Mass Index After Bariatric Surgery?

At a bariatric surgery consultation with a new patient, ideal or goal weight and BMI are almost always discussed. Even if the patient doesn’t explicitly ask about their weight results, we know to address it because, after all, beyond the primary goal of improving or eliminating obesity and its related diseases, losing weight is top of mind for us all. Weight loss is also a primary measure of success (for better or worse) and a marker for hitting different phases of the postoperative process. But is there an ideal weight or BMI, and how important is that?

The Body Mass Index or BMI

To best understand the concept of ideal weight, we must learn more about the body mass index or BMI. Yes, it is ubiquitous in the weight loss world, and no, it is not the definitive measure for ideal weight. BMI can be wildly incorrect, and our major bariatric societies (ASMBS and IFSO) have recommended changes in BMI thresholds as of 2023. On one hand, BMI does not consider the full range of body type variances, including muscle tone, body frame, and even gender. While modifiers have been tried, the BMI remains inaccurate. Beyond that, however, the BMI is also arbitrary. How did we ultimately decide on a BMI of 30 as the threshold for obesity? It’s nothing more than an educated guess, knowing that patients above this threshold are at greater risk of complications and symptoms associated with obesity.

Getting back to the ideal weight, we must discuss expectations and goals to understand precisely what constitutes an ideal final number. You may have seen data showing the average weight loss among patients for each procedure. This can vary from about 65% of excess body weight loss for the gastric sleeve to upwards of 90% for the duodenal switch. This does not mean that this is the best you can do or is the number to strive for. Some patients can lose all their excess body weight, while others may fall short and below average. Again, every individual is different, as are their motivations and abilities related to their health and weight loss. Our conversation on expectations, therefore, becomes even more crucial.

What We Consider Success

It’s also important to remember what success means to your surgeon versus your idea of success versus failure. If we see that significant comorbidities have been minimized or eliminated, we’re thrilled, regardless of weight loss. If you no longer have to take medication for various issues, including high cholesterol, high blood pressure, and other concerns, if you are no longer using a CPAP machine for sleep apnea, as an example, we are happy and consider this a great success.

Your Goals

Back to the BMI. If you have very specific muscle-building goals, your BMI will be skewed, as will your weight. You have undoubtedly learned that muscle mass is heavier than the same volume of fat. As such, if you’re working hard in the gym, you should expect to be more muscular and carry additional (good) weight. The important measure here is your body shape and musculature, not the BMI. This will be very particular to you, and only you can decide if you have succeeded. Measuring waist size and following blood markers as co-primary measures of success is very important.

The Bottom Line

As you can see, there’s no one-size-fits-all measure of success after bariatric surgery. We preach individuality in postop life in that what you do will naturally vary from what your friends, family members, or support group partners may have done in their journey. As such, keep an open mind about what success looks like, and don’t limit yourself to BMI and weight as your only measures. In the meantime, if you have any questions or are struggling with your progress, we encourage you to contact our office and speak to one of us about the next steps.