The Role Of The Vagus Nerve In Weight Loss Surgery


The vagus nerve has long been recognised as the internal sensory system, regulating breathing and heart rate among, as well as sensing and signalling that feeling of fullness to the brain. That same nerve also detects nutrients and controls digestion. Yet how it receives the information it uses to perform these tasks has been less well-known.

To trigger that feeling of fullness, does just one wire need to be activated, or are there several that need to be activated? How is this sensory system organised to distinguish proteins from carbohydrates or lipids, and then how does it send messages to secrete enzymes that will digest each of them?

Peering into the gut-brain connection in mice, Harvard Medical School researchers led by Stephen Liberles discovered two distinct types of sensory neurons that survey the status of the gastrointestinal tract: one senses stretch in the stomach and one responds to the presence of nutrients in the intestine.

The findings, ‘Sensory Neurons that Detect Stretch and Nutrients in the Digestive System’, published in the journal Cell, have potential relevance for understanding how bariatric surgery not only achieves weight loss but also diminishes Type 2 diabetes. In addition to weight loss, the work may be relevant for disorders of intestinal motility, such as dyspepsia.


“Using genetic tools, we were able to classify two major cell types that differentially innervate the GI tract,” said Liberles, HMS associate professor of cell biology and senior author of the paper. “One cell type broadly accounts for several classes of stretch receptors in the stomach and intestine. Another cell type is completely different, detecting nutrients.

The neurons that sense stretch in the stomach produce receptors for glucagon-like peptide 1 (GLP-1), a hormone released from the intestine in response to the arrival of nutrients. GLP-1 analogs are powerful anti-diabetic drugs. While it might seem likely that neurons containing the GLP-1 receptor would respond to nutrients, the team’s experiments instead showed they were sensitive to mechanical stretch of the stomach and the intestine.

These neurons, the researchers found, project to the muscular wall of the stomach but not to the inner surface of the intestine where nutrient detection occurs.

Nutrients are detected by GPR65 neurons, which express receptors for the hormone serotonin. Specific in purpose, these neurons sense nutrients that travel through the intestine through projections that end in the intestinal villi, tiny peninsulas that line the intestine and aid in food absorption.

The GPR65 neurons held another surprise: They respond to all sorts of chemical cues from food in the intestine, whether that cue is a sugar or fat or protein or salt or a change in pH balance.

“Here you have one neuron informing the brain on just about everything,” Liberles said, “which is a much less specific role than we were expecting going in.”

Also unexpected was the finding that the two nerve cell types project to different regions within the same nucleus in the brain stem.

“The two types form non-overlapping projection fields right next to each other, suggesting that each type sends information to different circuits in the brain,” said Erika Williams, an HMS graduate student in cell biology. “They are engaging different brain pathways and presumably then orchestrating different, multi-organ physiological responses.”

Liberles said there might be pharmaceutical targets for the regulation of food intake, perhaps the receptors that modulate responses to nutrients.

“The tools we used – optogenetics, imaging, and neural mapping – allowed us to paint a comprehensive picture of what these neurons do,” said Liberles. “That capability could in future studies help us understand how these neurons work at a molecular level: What are the key receptors that detect stretch of the stomach or nutrients in the intestine, or even other sensory cues outside the GI tract.”

Title of Paper: Sensory Neurons that Detect Stretch & Nutrients In The Digestive System

Paper Reference: DOI:10.1016/j.cell.2016.05.011

Published in the Journal Cell



Weight Regain? Put A Ring On It!

Weight Regain After A Gastric Bypass? Put A Band On It!

Low-pressure gastric band / adjustable
BioRing Adjustable Gastric Band

Dr Rudolf Steffen is a bariatric and metabolic surgeon at the Hirslanden Klinik Beau-Site in Bern, Switzerland, one of the leading centres in the country for bariatric and metabolic surgery. Since 2003, he has performed more than 3,000 banded bypass operations.


“The reasons why patients experience weight regain two years after a gastric bypass is because it is a restrictive operation and if the restriction fails, the patients regain weight,” began Professor Steffen. “In our experience, 29% of 404 patients in the fourth year after unbanded bypass required a pouch revision with a band for weight regain because of loss of restriction. Percentages increasing thereafter.

As a result, he recommends banded bypass to all his bypass patients who are suitable for the procedure, after explaining the advantages and disadvantages of the procedure and he informs them that in his opinion, there is good, but limited data. He also recommends a banded bypass for revision procedures, primarily for those patients who received a gastric band in the mid 90’s.


Gastric-Bypass (1)

“I explain that approximately 50% of patients will probably not need one but there is no way to know who these patients are,” he added. “In addition, I tell them that about half of all bypass patients will need a reoperation due to a loss of restriction. It is important to give our patients as much information as possible so they can make an informed decision. Some patients may not like the idea of having a foreign body inside them, so they just have a bypass.”

He said that he does not perform many sleeve gastrectomies (20 or so a year), as he do not want a restriction in the same location where a leak might occur and explained that he views the sleeve as a high-resistance tube, so in the first instance it does not require a band.

“However, a banded sleeve can be considered in a secondary case, but in such cases I usually convert the sleeve to a bypass.”




Professor Steffen said that it is important to understand the mechanisms of a banded bypass and many people are under the misapprehension that the goal of a banded bypass is to make people lose more weight. He clarified this by stating that the goal of the banded bypass is not to regain weight, which has been demonstrated in several multi-centres studies that showed after two or three years, the non-banded patients reported more weight regain.

“If a bariatric surgeon chooses not to place a ring, in my opinion, it is justified because we do not have the long-term data yet from prospective, randomised clinical trials,” he concluded. “However, in my experience it is of benefit to explain the procedure to gastric bypass patients. The ring can always be placed in a revision procedure if the patient has weight regain or presents with hyperglycaemia.

Why Are Children Becoming Overweight?

What Causes Obesity in Children?

Children become overweight and obese for a variety of reasons. The most common causes are genetic factors, lack of physical activity, unhealthy eating patterns, or a combination of these factors. Only in rare cases is being overweight caused by a medical condition such as a hormonal problem. A physical exam and some blood tests can rule out the possibility of a medical condition as the cause for obesity.

Although weight problems run in families, not all children with a family history of obesity will be overweight. Children whose parents or brothers or sisters are overweight may be at an increased risk of becoming overweight themselves, but this can be linked to shared family behaviours such as eating and activity habits.

A child’s total diet and activity level play an important role in determining a child’s weight. Today, many children spend a lot time being inactive. For example, the average child spends approximately four hours each day watching television. As computers and video games become increasingly popular, the number of hours of inactivity may increase.

Children TV

What Diseases Are Obese Children at Risk For?

Obese children are at risk for a number of conditions, including:

  • High cholesterol
  • High blood pressure
  • Early heart disease
  • Diabetes
  • Skin conditions such as heat rash, fungal infections, and acne
  • Bone problems


How Do I Know if My Child Is Overweight?

The best person to determine whether or not your child is overweight is your child’s doctor. In determining whether or not your child is overweight, the doctor will measure your child’s weight and height and compute his ”BMI,” or body mass index, to compare this value to standard values. The doctor will also consider your child’s age and growth patterns.

Girl being weighed by doctor.
GP Checking Child’s Weight & Height

How Can I Help My Overweight Child?

If you have an overweight child, it is very important that you allow him or her to know that you will be supportive. Children’s feelings about themselves often are based on their parents’ feelings about them, and if you accept your children at any weight, they will be more likely to feel good about themselves. It is also important to talk to your children about their weight, allowing them to share their concerns with you.

It is not recommended that parents set children apart because of their weight. Instead, parents should focus on gradually changing their family’s physical activity and eating habits. By involving the entire family, everyone is taught healthful habits and the overweight child does not feel singled out.

How Can I Involve My Family in Healthful Habits?

There are many ways to involve the entire family in healthy habits, but increasing the family’s physical activity is especially important. Some ways to accomplish this include:



  • Lead by example. If your children see that you are physically active and having fun, they are more likely to be active and stay active for the rest of their lives.
  • Plan family activities that provide everyone with exercise, like walking, biking, or swimming.
  • Be sensitive to your child’s needs. Overweight children may feel uncomfortable about participating in certain activities. It is important to help your child find physical activities that they enjoy and that aren’t embarrassing or too difficult.
  • Make an effort to reduce the amount of time you and your family spend in sedentary activities, such as watching TV or playing video games.

Whatever approach parents choose to take regarding an overweight child, the purpose is not to make physical activity and following a healthy diet a chore, but to make the most of the opportunities you and your family have to be active and healthy


The Centres for Disease Control

The National Institute of Diabetes and Digestive and Kidney Diseases