Studies have investigated the metabolic effect of bariatric surgery and the impact it can have on a patient's long term weight loss success. Bariatric surgery is most commonly classified as restrictive, meaning the procedure restricts how much food you can eat, and malabsorptive, the procedure alters how your body absorbs nutrients. Through these two effects, patients are able to lose a significant amount of weight after their bariatric procedure. But there is another classification of bariatric surgery that impacts the degree of weight loss, and that is the metabolic nature of these operations. 

Although restricting the amount of food a patient can intake is one method of losing weight, it is not sustainable. Let's face it, you don't need surgery to restrict how much you can eat; you can do that on your own with enough willpower. 

If I told a patient, "I am going to make your stomach so small, or restrict your intake so much, that you will lose 200 pounds", that would be starvation which is not healthy weight loss. Similarly, with this mentality, a patient wouldn't be able to regain weight because they would be eating so few calories, and we know that your stomach won't stretch out again to the size it once was. Yet we see that weight regain can occur in patients who revert to old habits. 

The Challenge of Weight Loss

Through more research over the last ten years, we have learned that certain operations will allow patients to lose weight by resetting their set point for the amount of body fat they have. The set point is the certain weight the body wants/needs for proper functioning. This number varies by the individual based on genetics, previous diet history, age, and hormones. 

Before weight loss surgery, you likely tried to lose weight through traditional means, such as diet and exercise. You may notice that you lose weight for some time, the weight loss seems to stall, and then over time, your weight floats back up to where you started. As frustrating as this can be, that is how your body weight is supposed to work. 

Despite what we want to believe, we don't have ultimate long-term control over the amount of body tissue we have. Body fat keeps us alive when there's no food around; it is our reserve energy source. The primary purpose of adipose tissue is to store energy in the form of lipids (fat), but it is also used for thermal insulation, organ cushioning, and endocrine functioning. 

Our bodies learned long ago that adding extra body fat would increase our survival. But in today's world, where we are swimming in a world of excess calories, our bodies have been trained to consume and create more body fat. Every time we add extra body fat, our bodies reset that as our new baseline normal because our bodies see this body fat as protection against potential starvation. This explains the yo-yo weight loss effect. 

How to Permanently Lose Weight

For patients to permanently lose weight, they have to decrease the amount of body fat they have and ultimately reduce their body's set point. Understanding weight set point and body fat led researchers and physicians to dig deeper into finding methods for sustained weight loss. 

It was understood that various factors contributed to significant weight loss after surgery, including changes in nutrient detection, pancreatic function, mechanisms in the brain, and gastrointestinal hormones. 

We have been doing bariatric surgery for 60 to 70 years, thinking we can help patients lose weight by restricting their intake. We have only recently discovered that operations like a sleeve gastrectomy, gastric bypass, or duodenal switch work to reset the amount of body fat your body thinks you have, resulting in a metabolic effect of bariatric surgery. 

The Metabolic Effect of Bariatric Surgery

The moment you wake up from your surgery, your body recognizes that there is too much body fat and will begin working on getting it down to a healthy level. Particularly, your metabolism revs up, and your hunger hormones will go quiet. Sometimes we even have to remind our patients to intake enough calories to support their metabolism.

For some patients, this process can go on for a year or two as the body resets to a lower weight. Yet, once the body senses that it is at a “normal” weight, your metabolism will settle down as your weight begins to plateau. If you eat a healthy diet and incorporate movement into your everyday life, you will likely maintain weight loss through the years.

And this is explains the metabolic effect of bariatric surgery. 

Non-Metabolic Weight Loss Surgery

There are other forms of weight loss surgery that do not alter your metabolism and ultimately reset your set point. These operations include the gastric band, gastric balloon, and endoscopic sleeve gastrectomy. These procedures use mechanical means to restrict intake but do not change the GI tract’s anatomy. 

Therefore, these operations do not have the same effect in changing nutrient detection, metabolism, and gastrointestinal hormones. In many cases, patients who have a non-metabolic operation will not have as significant or permanent weight loss as they otherwise would with a metabolic procedure (gastric bypass, gastric sleeve, duodenal switch, SADI-S). 

Similarly, non-metabolic operations are more likely to result in weight regain. A study found that the rate of revisions for patients 10+ years out from surgery was 26% for the gastric band, 9.8% for the gastric sleeve, and 4.9% for the gastric bypass. 

In conclusion, there is a metabolic effect of bariatric surgery that works to reset your weight set point resulting in extreme and sustained weight loss, while the non-metabolic procedures will only restrict your intake, which almost always leads to less weight loss and a higher chance of weight regain.