You may think that gastric bypass surgery aids weight loss simply because you cannot eat or digest as much food. That is certainly what most doctors assumed when the procedure was first developed. However, researchers have discovered that surgery to reduce the size of the stomach and intestine literally changes the way we think (or not think!) about food. It is all about the hormones.
After weight-loss / bariatric surgery, people tend to become very sensitive to food. It is common to go off sweet foods and drinks completely and many people feel nauseas when cooking meat. And it is not only appetite which is changed, many people suffer mental side-effects such as memory loss, auditory hallucinations (hearing voices) and even improved mental clarity. Several people have reported that a few months after weight loss surgery their minds become sharper and they can think more clearly. So, what is going on? Fortunately Samantha Murphy decided to investigate and report her findings in the May 2012 publication of New Scientist.
Types of Weight Loss Surgery
There are now several surgical methods that are used to promote weight loss. Gastric banding is considered the safest option as this involves restricting the size of the stomach by closing a part of it with a band. The band is usually applied by keyhole surgery and then tightened slowly to make a more gradual change to the size of the stomach.
A more aggressive method is to perform a full gastric bypass, which simply cuts off all (or most) of the stomach from the digestive system. This method is called a Roux-en-Y (Roux-en-Y anastomosis), and named after Dr. César Roux who developed the idea. The small intestine is joined to the top of the stomach so that food passes very briefly into the stomach before being sent to the intestine.
A mini gastric bypass turns the stomach into a tube, significantly reducing its volume. This method is sometimes called stomach stapling, as the stomach is literally stapled along its centre to close the larger part off. This is also know as loop reconstruction. In the New Scientist it is called a Vertical Sleeve Gastrectomy. The vertical sleeve is the tube that runs down the length of the stomach.
A final method discussed is the Duodenal Switch. This involves a vertical sleeve gastrectomy (loop) and a reduction in the length of the small intestine. It is in the small intestine that much of the digestion takes place and the digested food is then absorbed into the body (i.e. into the blood) through the intestine wall. By shortening the small intestine, there is less time and opportunity for food to be digested and absorbed. Some weight loss drugs have attempted to perform a similar action (fat blockers and carbohydrate blockers), however, these tend to have unwanted side-effects.
Changes to our Thinking is Key to Weight Loss Success
Samantha Murphy discovered that these changes to the way we think are not merely a side effect of weight loss surgery, they are actually fundamental to the success of the surgery.
Stephen Benoit, a behavioural neuroscientist at the University of Concinnati explained that after weight-loss surgery a person’s relationship with food is fundamentally changed. People not only feel less hungry, but they no longer desire sugar and fat. Foods that were once craved are suddenly undesirable. For patients who have the Roux-Y surgery (full stomach bypass) the change in attitudes tend to be permanent and healthy eating is preferred with more fresh fruits and vegetables and less fat and sugar.
Hormones drive much of our actions – just about every impulse is driven by a hormone. There are 4 main hormones which play a role in digestion and appetite:
- Ghrelin – this is released by the stomach and increases appetite.
- Glucagon0like peptide-1 (GLP-1) – this suppresses appetite and is released by the small intestine.
- Peptide-YY (PPY) – suppresses appetite and is also released by the small intestine.
- Leptin – this inhibits the desire to eat and is released by fat cells.
Immediate Changes to the Way We Think
Recent studies have found that some of these changes are immediate. The Imperial College London took MRI scans of patients before and after surgery to see if there were changes to the areas of the brain that control appetite. The results shocked.
Before a Roux-en-Y operation pictures of cakes and burgers resulted in the reward centres of the brain lit up but a few days after surgery the reward centres did not respond at all to images of cakes (sugar) and burgers (fat). All temptation to eat junk food had been removed.
Better Brain Function
In 2010 a research carried out by Gladys Strain at Cornell University found that brain function was improved 3 months after surgery and continued to improve after that. Tests were done at 3 months and at 1 year after surgery and subjects showed cognitive improvements during both tests (Surgery for Obesity and Related Disease, vol 4, p 465).
These findings raise an important question which will, no doubt, lead to a new research: If weight loss surgery works by inhibiting and boosting hormones, is there a chemical solution? Maybe surgery is not required at all, but instead a pill that can mimic the hormonal changes which result from the surgery. This would provide a ground breaking solution to the obesity crisis.
Unfortunately not all the changes that take place are positive. In January 2012 it was reported that weight-loss surgery can cause a significant increase in alcohol abuse. Studies showed that around 2 years after weight-loss surgery subjects were more likely to increase alcohol consumption and develop alcohol disorders.
“These findings show that there is much more to learn about bariatric surgery and how it influences a patient’s health and well-being” Dr. Griffin P. Rodgers, NIDDK Director.
The reason is thought to be due to the increased concentrations of ethanol (alcohol) in the body. Drinking alcohol after weight loss surgery is much like drinking on a completely empty stomach – the alcohol is immediately released into the intestine and absorbed into the body, affecting hormone levels and the reward centers of the brain.
As well as alcohol abuse some people have experienced cognitive problems, such as short-term memory loss, not being able to remember words and not being able to concentrate. MRI research by Keith Josephs, a neurologist at Mayo Clinic in Rochester, found that subjects who had reported cognitive problems after Roux-en-Y surgery had experienced a 25% reduction in the size of their thalamus. The thalamus controls sensory taste as well as memory, attention and concentration. It is also the area of the brain where the hormones GLP-1 and ghrelin bind together (hormones must bind to neurons to send signals to the brain).
So it seems that the stomach surgery has a long term effect – as hormone levels are reduced there is less need for receptors in the thalamus, so receptors die out. The side-effect is that other brain functions that rely on the thalamus also suffer. The damage is irreversible.
The science of weight loss continues to throw up new problems. While surgery may help to reduce the burden of obesity, it may also lead to an increase in cases of dementia, another growing health burden. Once again it seems that the best option is to encourage regular exercise and a healthy diet.
“The Subtle Knife” by Samantha Murphy. New Scientist, 19th May 2012. Published by Reed Business Information.
“Weight-loss surgery increases alcohol use disorders over time” - National Institutes of Health (NIH), Monday, June 18, 2012. Accessed on July, 2012.
Diagram of Surgical Options. Image credit: Walter Pories, M.D. FACS., from by U.S. National Institute of Diabetes and Digestive and Kidney Disease (NIDDK).- http://win.niddk.nih.gov/publications/gastric.htm