• Credits
  • Section Writer: Dr. Om J Lakhani
  • Section Editor: Dr. Om J Lakhani

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• Q. What is the essential argument of bariatric surgery in terms of weight loss strategy ?

  • The body has a metabolic set point and tries to maintain the same
  • Those on caloric restrictive diets- loose weight initially and acutely the set-point is lowered.
  • But as soon as their fast period stop → the set points goes to normal (even supranormal) and the patient starts to regain weight gain often overtaking the original weight
  • the problem with pharmacotherapy is that is only works on one physiological aspect which the body often overcomes
  • bariatric surgery surgery works because it changes local anatomy as well as physiology on several aspects leading to a multiprong apporach

• Q. Which are the areas bypassed in RYGB surgery ?

  • part of stomach
  • Whole of duodenum
  • Proximal Jejunum

• Q. Which neurotransmitters in brain promote food intake and which promote satiety ?

  • AgRP - Promotes food intake
  • POMC- Promotes satiety
  • 

• Q. Do patients change food preference after bariatric surgery ?

  • yes
  • they prefer less energy dense and sweet food
  • infact this occurs ealy on after surgery
  • 

• Pearls:

  • Functional neuroimaging studies have shown that the rewarding aspects of food is reduced after bariatric surgery especially RYGB
  • The rate of salivation depends on the taste of food
  • Orofacial response in animal models is good indicator of whether they find food tasty or not
  • There is changes in taste after bariatric surgery
  • In initially few weeks after surgery there is craving for increased sugar and fat but this goes away
    • Probably becauser the reward aspect of the food goes away
  • Dumping syndrome also contributes to this food selection
    • increased glycemic load of food increases dumping syndrome
    • This is lost following bariatric surgery
  • Taste changes occurs with RYGB and Sleeve gastrectomy but not with adjustable gastric banding
  • Brown adipose tissue and rest energy expenditure changes are not certain following surgery

• Q. Which are the two most important gut hormones involved in the bariatric surgery ?

  • GLP-1
  • PYY
  • Both are secreated by the L cells of the pancreas
  • Both are elevated post-prandially after surgery
  • Fasting concentration do not change
  • both are anorexiogenic hormones which act centrally by crossing the blood brain barrier
  • RYGB the food reaches jejunum and ileum directly - there the L cells are most abandunt and they are stimulated leading to the release of these hormones
  • However, mice models have shown that though these mechanisms are helpful- they do not work in isolation
  • 
  • 

• Q. Does Sleeve gastrectomy also have an impact on the L cells ?

  • yes
  • Sleeve gastrectomy produces rapid gastric emptying
  • Because of this more amount of nutrients get dumped into the jejunum and ileum more rapidly
  • However, the release of the hormones is less compared to RYGB

• Q. Which two new hormones are now considered to be playing an important role

  • Oxyntomodulin
    • This is a dual GLP-1 and glucagon agonist
    • Reduces food intake and produces satiety
    • 
  • Glicentin
    • Exact mechanism is not not
    • It is the most stable of the proglucagon peptides hence may prove to be a good biomarker for L cells function in future
  • Both are released by the L cells
  • Levels of both are increased post surgery

• Q. Give us a breakdown of the Proglucagon peptides

  • 

• Q. What happens to Ghrelin ?

  • Little changes after RYGB
  • Reduces after Sleeve gastrectomy

• Q. Are bile acid levels increased after obesity surgery ?

  • Yes

• Q. What is the impact of bile acid on weight loss ?

  • 

• Q. Are bile acids increased following weight loss following lifestyle measures?

  • Bile acids, FGF19 and GLP-1 and PYY are reduced following Lifestyle measure induced weight loss
  • Hence the weight loss does not sustain

• Q. What is the role of FXR in weight loss ?

  • FXR induces browing of adipose tissue
  • Bile acid stimulate FXR
  • 

• Q. What are the two types of FGR which increase following obesity surgery ?

  • FGF19 and FGF21
  • 

• Q. Which genetic cause of obesity responds well to bariatric surgery ?

  • MC4R mutation

• Q. Which 2 gut microbes are strongly associated with obesity ?

  • Firmicutes
  • Bacteroidetes

• Q. How soon after bariatirc surgery is the gut microbes changes ?

  • As soon as three months after the surgery

• Q. How do certain gut microbes produce weight loss ?

  • Gut microbes --> Short chain fatty acid --> Stimulate GLP-1 receptors

• Q. Summarize the Mechanisms of Weight loss after Obesity surgery ? ^[1]

  • 
  • 1. Mechanical effect
  • 2. Neurohormonal changes
    • A) Change in taste after bariatric surgery
      • Less craving for sugary and fatty food
      • Possible contributed by Dumping syndrome
  • 2. Gut hormonal changes
    • A) Changes in GLP-1 and PYY
      • RYGB the food reaches jejunum and ileum directly - there the L cells are most abandunt and they are stimulated leading to the release of these hormones
      • Rapid gastric emptying in Sleeve gastrectomy also produces same effect
    • B) role of Oxatomodulin and Glicentin
    • C) Reduction of Ghrelin after RYBG
  • 3. Role of bile acid
    • 
  • 4. Gut microbes