Metabolism and Weight Loss Surgery 3

Your Metabolism & How It Works With WLS Pre-Op & Long-Term

January 17, 2018

The Obesity, Metabolism and Weight Loss Surgery Connection

Obesity is a chronic relapsing condition, which means short-term therapies have a very high likelihood of failure. So far, the only proven and effective long-term therapy has been bariatric/metabolic surgery. Obesity is a complex disease and we have recently started appreciating its complicated and intricate pathophysiology. The metabolic, chemical and neurohormonal changes are intricate and unique to each individual. It is through surgical alteration of these pathways that we get the beneficial and potent effects on metabolism and weight loss surgery.

Obesity and Metabolic Abnormalities

Metabolic derangements are one of the leading causes of multiple medical comorbidities and ailments, these derangements are more prevalent in the overweight and obese population. Having metabolic syndrome, which is more prevalent in the obese population, predisposes one to heart disease, diabetes, stroke, sleep apnea, certain cancers, gallbladder disease, and an overall lower quantity and quality of life.

Metabolic syndrome is a constellation of abnormal physical findings and blood tests, which is usually diagnosed by a physician. It is three or more of these abnormalities;

  • Obesity / central obesity
    • BMI >30 or
    • Men waist size 40 inches or greater
    • Women waist size 35 inches or greater
  • Blood pressure of 130/85 or greater
  • Triglycerides of 150 mg/dL or greater
  • Fasting glucose of 100 mg/dL or greater
  • HDL (good cholesterol)
    • Men - less than 40 mg/dL
    • Women - less than 50 mg/dL

Calorie Expenditure after WLS

Total metabolic expenditure (TME) is the number of calories you need every day to meet your overall energy requirement. This is composed of resting metabolic rate (RMR), which is the amount of energy needed for your body to perform its basic bodily functions such as breathing, thinking, repairing damaged tissue, maintain blood pressure, adequate blood sugar levels, etc. which accounts for about 75-90% of the total metabolic expenditure. The additional energy requirement is called physical energy expenditure (PEE), that’s additional energy the body needs to walk upstairs, sit, stand, carry objects to and from places, etc.

For example, if your TME is 2000 calories, your RMR is most likely going to be around 1750 calories and your PEE around 250 calories. Of course, this changes if you have a physically demanding job, exercise regularly or you are a professional athlete. In these cases, your physical energy expenditure will be significantly higher.

Increasing physical activity helps us lose more calories, and thus lose more weight. However, if we desire to lose weight and correct our metabolic state then we are better off increasing our RMR because it accounts for the largest portion of our caloric consumption.

Exercise has two effects on the energy expenditure, it directly increases PEE and more importantly, it elevates the RMR.

With these two effects of exercise, it translates into, much higher energy expenditure at rest and causing a negative energy balance which leads to weight loss and a better metabolic profile.

Surgical Therapy as a Treatment Option for Obesity

The aim of any intervention has to be two-fold; decrease our excess body weight and improve the metabolic and blood profile.

When your body maintains a certain weight for a prolonged period of time then your brain resets ‘normal’ to that weight. Let us examine that further from an interesting study that recently followed several contestants of the Biggest Loser program six years after completing the show. Almost all the contestants had gained significant weight back several years after the competition. More importantly, they had a much lower resting metabolic rate (RMR) than their matched counterparts did.

Despite consuming fewer calories, at the six-year interval, the Biggest Loser contestants were not able to lose weight or sustain their weight loss.

This complex process is due to metabolic and neurohormonal factors. The brain decided their new and much lower body weight is unhealthy and abnormal for them; subsequently, it will lower their resting metabolic rate to return their weight to levels prior to the show. This is called metabolic adaptation. Interestingly, one contestant had metabolic surgery during these six years and he had increased RMR after his surgery and started to lose weight!

Surgery is the only effective long-term therapy in reducing the excess body weight and improving the metabolic profile. Furthermore, it’s the only treatment modality that doesn’t allow the brain to develop metabolic adaptation. So, in the long run, weight loss maintenance is possible and weight regain is less likely.

I believe the term "weight loss surgery" is a misnomer, biased, and may be misleading. Weight loss is certainly a very important benefit of surgical therapy; the effects of bariatric surgery are predominately due to its neurohormonal and metabolic effects.

The Role of the Brain in Obesity

To better understand the way our body metabolizes food think of the THREE main players; BRAIN, GUT, and FAT cells.

The gut-brain axis has several hormones/peptides that play a role in stimulating the brain to feel hungry or full. These either travel through the bloodstream to the brain or transmit signals via nerves to the hunger control centers of the brain.

The gut releases these hormones when food stretches it and when its mucosa (inner lining) encounters food. The stomach releases ghrelin (the hunger hormone) when it’s empty, this hormone is released from the cells in the neck and upper portions of the stomach. When a vertical sleeve gastrectomy or a roux-en-y gastric bypass is performed, these cells are either removed or desensitized. The effect is a depression of hunger sensation by the brain and it’s tricked into thinking calories are plentiful and there is no need to go into starvation mode. Thus, the resting metabolic rate is kept the same.

This is not the case when we severely restrict our caloric intake, our brain will slow down our metabolism especially our resting metabolic rate. Therefore, we end up consuming fewer calories with no weight loss to show for it because we are not burning enough calories! This is the reason why calorie-restrictive diets work very well initially and once metabolic adaptation occurs the weight loss stops despite being on a very low-calorie diet.

Roux-en-y Gastric Bypass & Duodenal Switch

The Roux-en-Y Gastric Bypass and Biliopancreatic Diversion with Duodenal Switch (usually shortened and called Duodenal Switch) bypass the first portion of the small bowel. Digested food moves from the stomach into the middle third or the last third of the small bowel. This stimulates another set of hormones that induce satiety, by blocking the hunger center in the brain and, slowing the stomach from releasing digested food. This translates into feeling full longer.

Furthermore, the ingested food encounters bile and other digestive juices farther in the small intestine. This leads to decreased caloric absorption in the short and intermediate post-operative period. In addition, the smaller stomach limits the caloric intake in the long run by decreasing the volume of food consumed.

Initially, the impact of surgery is very pronounced, thus the weight loss is very fast over the first 3-6 months. As the body's metabolic and neurohormonal pathways slowly adapt, the weight loss will slow down. After about 18 months from surgery, the body would have reached a new equilibrium with a new ‘reset’ weight.

It’s normal for the body to gain a few pounds from 18 to 36 months out from surgery.

The Importance of Follow-up

It’s very important to keep seeing your surgeon, frequently in the first year and then every six months for two years. Once you are out two years from your surgery, it is important to see your surgeon or your primary care once a year to evaluate your progress and, perform comprehensive blood work to ensure your vitamin levels are within normal parameters.

Also, weigh yourself every 3-4 weeks, and keep a weight and food journal. If you notice you have started to gain weight and you are not able to lose it on your own, make sure you see your bariatric surgeon. There are many ways of trying to reverse the recidivism and help you lose weight again.

Remember, obesity is a chronic and relapsing condition and there are many moving parts to it. Don’t wait to seek professional help. The sooner obesity is treated the less likely you will develop the co-morbidities associated with the disease.


Dr. Husain Abbas of Memorial Advanced Surgery, is a Board Certified surgeon trained in Minimally Invasive Surgery. After his surgical residency at St. Mary's, a Yale University affiliated hospital, Dr. Abbas completed a fellowship in Minimally Invasive Gastroesophageal & Bariatric Surgery at the University of Florida, Gainesville. Dr. Abbas' expertise extends to a wide array of gastroesophageal disorders, anti-reflux surgery, complex hernia repairs, endocrine, oncology and bariatric procedures.

Read more articles from Dr. Abbas!