October 3, 2019 by Dr. Kyle Varner in Bariatric Surgery

A lot of people think that bariatric surgery results in weight loss because it restricts the amount of food that a patient can eat and, in some cases, reduces the calories that they absorb from the food that they do eat. This may be partially true but is extremely misleading. 

The largest benefits of bariatric surgery are metabolic benefits. Not restrictive or malabsorptive benefits! 

The traditional understanding of obesity is that it is caused by excess calorie consumption. This is a gross oversimplification of this complex hormonal disease, and it leads to misguided and self-defeating weight-loss strategies. 

Bariatric surgery is one of the very few weight-loss strategies that has been proven to result in long term weight loss. Sadly, it frequently doesn’t result in loss of as much weight as the patient would like. 

Ultimately, it makes the situation better but doesn’t fix the problem entirely.

In order to get the most out of bariatric surgery, we have to first understand why it is one of the few proven interventions to result in long term weight loss–and then figure out how we can capitalize on that to turbocharge the results. This is possible, but only by first understanding the basic science behind why the surgery works.

For reasons that are not entirely understood, patients experience changes in a variety of body-weight regulated hormone levels and their response to those hormones after having surgery; these are the drivers of long term post-bariatric success.

Increased insulin sensitivity

High levels of insulin in the blood is both a marker for metabolic disorder and a precursor to many diseases such as obesity, high blood pressure, heart disease, osteoporosis and even cancer.

High levels of insulin set in when someone has reduced insulin sensitivity. Also called insulin resistance, it means that he or she needs a higher than normal amount of insulin to bring down or control blood glucose level. 

Insulin resistance is a major driving force behind obesity. As insulin levels in the body rise, fat cells hold onto fat and go into overdrive, storing as much of it as they can. At the same time, other hormones that regulate appetite stop working properly.

Interestingly, bariatric surgeons have noticed that a substantial number of bariatric surgery patients who are diabetic no longer need insulin injections shortly after their surgery–prior to substantial weight loss that is known to often have this result. 

There are a variety of proposed mechanisms for this early reduction in insulin resistance, and scientists are still working to fully understand why this happens. 

From the perspective of the patient, though, it is important to realize: there’s a substantial metabolic benefit from the surgery that appears to be independent of the weight loss. And it is likely responsible for a significant portion of that weight loss.

Increased leptin sensitivity

Leptin is known as the satiety hormone. It is secreted by fat cells and travels to the hypothalamus–the part of the brain that regulates your body weight. When there are high levels of leptin in a properly functioning hormonal axis, this tells your brain to reduce your appetite and increase your metabolism. 

For those of us suffering from obesity, this is a Godsend. The only problem? More and more people are developing resistance to this hormone!

So what happens? As your fat cells grow, levels of insulin in your blood rise. But the hypothalamus doesn’t respond the way it should–it still thinks that your fat cells are too small! 

The result is a sustained increase in hunger and a sustained decrease in your metabolism. That’s a surefire recipe for weight gain, no matter how hard you try to eat less and move more.

We’re learning now that there’s a strong link between insulin resistance and leptin resistance. That means that the more insulin you have circulating through your veins, the less likely your brain is to respond appropriately to this satiety hormone.

Bariatric surgery, however, acts like a reset in some patients, resulting in a healthier, more normal response to leptin. This is most likely the primary mechanism behind the results of the much-discussed “Biggest Loser Study.” 

This study looked at the basal metabolic rates of participants on the popular television show “The Biggest Loser”. It found that the “eat less, move more” strategy devastated the metabolism of the participants, and almost all gained the vast majority of their weight back by the end of the study…except for one. One patient in the study had a Roux-N-Y Gastric bypass. 

One year after the competition, all of the other patients had basal metabolic rates markedly lower than they should have based on their body weight. The bariatric patient? He had a normal BMR for his body weight.

There’s a lot of debate about the exact reasons for this, but the smart money is on leptin: by undergoing bariatric surgery, the patient likely made himself substantially more sensitive to the hormone leptin, and his body responded by demonstrating a healthier innate weight regulating method.

This isn’t just a single case study, either!

In another study, 45 patients were evaluated to determine the impact of gastric bypass surgery on resting metabolic rate (RMR). They were divided into 4 groups, based on patterns of change in RMR after surgery. 

The study demonstrated that there is a clear correlation between weight loss and post-operative RMR. The increase in RMR is a major factor that is related to loss of excess weight after surgery.

The Effects Of Bariatric Surgery

It is becoming more and more obvious that bariatric surgery has metabolic benefits that go far beyond restriction and malabsorption that most people consider to be its primary mechanism of action.

However, this isn’t the end of the story–it’s just the beginning. There are three strategies that are known to induce similar metabolic changes–and all three strategies are possible for bariatric patients who are about a year or more out from their surgery. 

1. Reduction or elimination of processed carbohydrates from diet

If you continue binge eating on potato chips and other tasty processed carbohydrates after gastric bypass surgery, you are not likely to benefit from the surgery for a long period of time. In fact, studies have found that processed carbohydrates can build up insulin and leptin resistance.

Sadly, it is far too common for people to fall back into the Standard American Diet after bariatric surgery. They still try to count calories, but they include processed carbohydrates in their calorie goals. 

The problem is that processed carbohydrates are the most potent fuel possible for insulin and leptin resistance. 

If you’re eating processed carbohydrates, like bread, white rice, sugar and high fructose corn syrup, you’re doing damage to your weight regulating hormones even if you stay on track with your calorie goals.

As these processed foods lay waste to your body’s healthy mechanism of weight regulation, how long do you think you’ll be able to stick to your calorie goals? With more and more leptin resistance, your appetite goes up, your metabolism goes down and the pounds creep back. 

2. Intermittent fasting

Intermittent fasting is the practice of not eating for a period of time. Sometimes this is 16 hours, or sometimes it is 24 to 48 hours; there are a variety of ways that this is implemented. This has a remarkable effect on the body’s weight regulating hormones. 

Insulin and leptin sensitivity goes up, the basal metabolic rate goes up and even levels of growth hormone (which is known to promote fat loss and muscle gain) increase.

This tactic for managing weight has experienced a resurgence in popularity, and for good reason: it works!

3. Low carb, High-fat diets

High fat, low carb diets (often called ketogenic diets) are gaining tremendous popularity as a means of combating obesity. 

Again, this is for good reason: they work. They result in increased insulin and leptin sensitivity and have been shown to result in dramatic weight loss with improved metabolic profiles.

In a study conducted by the US Army and published in the Journal of Military Medicine in March of 2019, soldiers placed on a ketogenic diet and high-intensity interval training program lost an average of 7.7kg of body mass, 5.5% of body fat, and had a 48% increase in insulin sensitivity.

Advocates of ketogenic diets often point out that there is something very unique about this diet: it gets easier with time, and that’s because it results in improvements in the body’s weight regulating mechanism. 

So, instead of fighting their biology, they end up working with it to reach a more healthy weight!


Bariatric surgery works–but not as well as we would like it to. 

The reason that it works for the long term is its beneficial metabolic effect. However, too many patients don’t understand this and revert back to the Standard American Diet that counteracts the metabolic benefits of the surgery.

Instead of counteracting the surgery and obsessing over calories, it’s time that we take a new approach to the management of obesity after bariatric surgery: with dietary and lifestyle interventions designed to preserve and enhance the metabolic benefits of the surgery. 

It’s time to turbocharge our bariatric surgery results, and we can do that by cutting out processed carbs, intermittent fasting and adopting low carbohydrate diets.

References in the comments…

This information is intended to help readers be more informed about their health options when speaking with a professional, but it should not be used alone to diagnose, treat, prevent or cure any disease or condition. Be sure to speak to a qualified doctor before taking any action to make sure that your choices reflect your actual health situation.

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