For those scientific folks out there... random question about malabsorption

So I tried to search for this, but to no avail... but I've been thinking about this, and I need some layman term explanations

malabsorption... 

So, of course, assuming RNY, because that's A. what I had, and B. the surgery I've heard about this the most with...

So we don't absorb all of our nutrients for the first +/- year... and we don't absorb all of our vitamins for life, so that's why it's so important to take your vitamins forever faithfully... got it.

But, why is it that our body learns to reabsorb all the calories, but not the vitamins? I mean, how does it know, "Oh look a yummy calorie! Better keep that,,, but, eh, that vitamin C that just passed by doesn't look important enough to absorb?" What's the deal on that?

Thanks much!

Random mind ramblings of the day... 

So we don't really malabsorb calories.  Calories are a measurement of energy (actually kcal is more accurate) that is created from certain macronutrients - specifically, fat, carbohydrate, and protein.  These substances are converted to energy via certain processes, the most common being the citric acid cycle and ketosis.  It is protein or fat that you cannot absorb - it has nothing to do with calories.

Bypass procedures have two effects: they alter the absorption of nutrients, and they alter the digestive hormones that affect fat storage, burning, and satiety/appetite.  There are like 20+ hormones other than ghrelin which do this.

Anyway!  Micronutrients and vitamins are absorbed in certain areas of the small intestine.  Macronutrients, fat and protein, are typically absorbed in the first part.  Carbohydrate is absorbed via passive diffusion throughout the length of the small intestine.  The reason the duodenal switch has such high malabsorption, is because the longer food is in contact with the small intestine, the more it is processed and absorbed, for instance.  Any carbs that don't get absorbed with the DS are not absorbed because the food does not have contact with the small intestine long enough for them to be processed; that is why they do not absorb all complex carbs, but also why they still typically absorb all simple carbs.  You need contact with the small intestine wall to be able to start breaking down macronutrients for energy.

The RNY has very low fat and protein malabsorption comparatively.  I don't know that it "goes away," so much as: after surgery we all 1) eat more and 2) typically eat higher carb meals.  Also, I suspect the villi (tiny wavy fingers that grab nutrients in the intestine) are damaged during the surgery around where the bypass is created, and that after a year they have definitely healed.  during that time they would be unable to absorb nutrients.

This is just my personal theory, mind.  I'm curious so I'll ask a surgeon for the reason.  However, since you are still having less food contact with the intestines due to the smaller bypass, there should still be a long-term energy deficit of some sort.  I think it's consumption habit that causes much of the "malabsorption going away."  Again, that's a theory.  I will try to find a study when I'm not at work.

I am not as familiar with the RNY pouch.  In a stomach with a pylorus, carbohydrate is emptied first, then protein, then fat last.  Fat actually contributes to satiety and fullness the most.  Carbohydrate is problematic because it is processed quickly and spikes insulin - insulin increases hunger, and also is how fat gets stored.  The lower your serum insulin, the less able you are to store fat.  That is why insulin resistance is so dangerous in terms of causing obesity.  

This is also why when we go back to higher carb diets we gain weight.  Those of us who were 200+ overweight are well served to always eat low carb/low sugar diets regardless of surgery for the above reasons.

Edited for a brief summary since I got way too wordy >.> : vitamins, protein, and fat are site-specific in terms of intestinal absorption, while carbs aren't.  You always absorb carbs fully, and you only malabsorb a very small amount of protein and fat compared to the DS.  Several vitamins and minerals are mostly absorbed in the part that surgeons bypass for the RNY, so that never returns. (Also I can't type today, ughhhh.)

We really need a button that allows us to like something a million times over or give a big HELL YEAH!   That is the best answer I have seen, ever!!!   I am 16 years out and this topic comes up a lot, for many of us and we always wonder.  

THANK YOU!!!!   

What a wonderful reply Donna, thank you very much! 

I love this site, there are so many knowledgeable people here and so many of you are willing to take the time for newbies and vets alike, looking for advice. 

Thank you! both the long, and short, versions were really informative and a great way to understand (and further explain to people that ask me since they know I have surgery) it all. I like your personal theories too, and I think there is probably a lot of truth in that.

I am glad me being a nerd came in handy for once, haha!

In reality I was super curious, because this is often (in my opinion) poorly explained to us.  I hate ignorance, especially when I have it, so I wanted to understand.

I actually would argue the reason the RNY and VSG have similar outcomes is because habits creep back post-op.  The RNY patients I've talked to who do not engage in this habits are typically more successful than VSG peeps - this is my anecdotal observation, of course.  The malabsorption isn't huge, necessarily, however if used well it will continue to give you an edge.

Short version:

Damaged villi take a about two years to completely grow back.

The part of the intestines where some vitamins are absorbed never grows back.

 

If the RNY bypass part is undone, the vitamin absorption returns almost immediately since food comes into contact with that part of the intestine again.  Those villi are mostly undamaged (aside from the area near the anastamosis); their contact with food is removed and they are dormant until it's reconnected.

So I do not know about the RNY-but the DS done by the Hess method has the following malaborbtion (this was based on an old poop study...yes someone dissected poo to figure this out):



Malaborbtion:

50 percent protein

80 percent fat

30 percent complex carbs

We absorb 100 percent simple carbs 0% malabsorbtion.



Most DSers are successful if they remain lower carb (not nessarily low carb), high fat, and high protein.



I eat pretty much anything I want. Since it's not Atkins, I'm not dependent on Ketosis to lose weight- so if I have an "off day" which I now at 11 years out, I have many....it's not a big deal.



Scott

Do you mean absorption?  I thought DS'ers absorbed simple carbs.