Mechanics of Protein Absorption

Earlier today I responded to a question posed by a new post-op patient on the ObesityHelp.com forums about how protein is absorbed in the body.  My response turned into a super long post with a bunch of information and resources.  I wanted to save it and refer back to it later... so I'm putting it here for safe keeping (and for the joyful reading pleasure of you all - nice of me, huh?). 

Here's the original questions asked on the message board.

I am very interested in the mechanics of when, where and how is protein absorbed. For example, is protein absorbed more/easily from liquids vs. solid food containing protein? Is protein absorbed more from our new pouch vs. small intestines? Is there any relationship between the amount of protein absobed and the rule of not drinking for at least 30 minutes after meals? 

I had my RNY on 1-6-10 and have been pleased with my protein intake. I average 75-95 g per day, which includes 30 g from a liquid protein shake and the rest from solid food.  However my liquid intake is not as strong and I only get between 40-50 oz of liquids in per day.


As I reflect on my challenges to get more water in, I find myself hesitant to drink sometimes because I have the mindset of not wanting to drink at times because it will prolong when I can eat again. So I have now learned that it is not as important to wait before eating but more important to wait to drink after eating.

I was told the main reason for not drinking afterwards was that it flushes the food through the pouch and you won't feel full as long. Is this the only reason? Would it impact the amout of protein that was absorbed if I drank before the 30 minutes and possibly "washed" the food out of my pouch?

I am fascinated with learning as much as I can about the mechanics and details of my new healthy lifestyle.

And here is my VERY long winded response:

This is gonna be long so grab a cup of tea.  First let's talk quickly about the difference between micronutrients and macronutrients.

Micronutrients are vitamins and minerals from food and supplements.... along the digestive tract there are specifically assigned spots of absorption for vitamins/minerals. Here's a diagram. Because of the bypass of about 4-5 feet of our small intestine we will always malabsorb micronutrients because those bypassed spots of absorption never grow back or generate themselves in a different part of the intestines. 

Macronutrients include protein, carbs and fats -- these are the nutrients that contain calories which provide energy for the body to function on a daily basis. There is no specific spot of absorption for macros... they are absorbed all along the small intestine and to a limited extent in the large intestine (not much actually happens in the large intestine except water absorption and prep of waste). All along our intestinal tract are little finger-like tentacles called villi. Here's a picture. As food passes by these villi they grab the macronutrients from the food and directs those nutrients into the bloodstream for use by the body's cells.

Because of our shortened intestines (originally about 25' but now only 20' or so) the body is not able to absorb as many macronutrients (calories) from food because food isn't in there for as long. This is where malabsorption of calories comes into play during the first few years post-op. But the body is very very smart and will do extraordinary things to ensure it's survival. Once your body figures out that we've screwed up our digestive tract it immediately begins to repair itself. This process is called adaptation (you can read a lot of about this process in research done on cancer patients who lose portions of ther GI tract). This adaptation includes two main things.

1) the pouch begins to grow. At the time of surgery the pouch is about 1oz in size and can hold about 2-3oz of food, but as the pouch matures and grows (not stretches, but physically grows) it will reach about 6-9oz in size holding about 8-12oz of food. It will stop growing at about this size and reaches maturity about 2 years post-op.

2) the intestinal tract will grow it's own villi --- it'll become longer, stronger and will create new tentacles. Because of our new super-villi we are better able to absorb all the macronutrients from the food that brushes by... therefore also absorbing 100% of the calories we put in our mouth. This portion of the adaptation process takes anywhere rom 2 to 4 years to complete. 

Ok, on to the stomach and pouch. Before surgery our stomachs absorbed very little stuff. In fact it's primary job was to churn the food we ate until it was ready for digestion. This was also the main spot for absorbing water and a few minor minerals (copper, iodine, etc.). The water absorption thing is key... what that means to use is that our stomachs no longer have the ability to absorb water and the only other main absorption spot for water is the large intestine. This is why it is SO essential we get all 64oz of water everyday... because just like vitamins/minerals, we are malabsorbing water and it now becomes easier for us to get dehydrated. 

So the churning of food in the stomach was an important part of the whole digestive process pre-op. Food could stay in our stomach for up to 6 hours or however long it needed to be in there to be broken down enough to be released to the intestines for macro/micronutrient absorption. But now we don't have a plyoric valve to keep food in the pouch to churn -- which means the only "churning" we get is from the chewing we do in our mouths. There is a small amount of churning in the pouch, it's minimal but it's sill happening, so we can't elminate this completely from the equation, it's just greatly reduced in the pouch vs. what used to happen in our bypassed stomachs. This also means that food particles will enter the intestines not as broken down as it was pre-op so poor chewing habits can contribute to gastric upset and constipation. Chew, chew, chew!

Liquid protein vs. solid protein. Protein contained in a whey protein supplement is already in a form that the body can use immediately -- in fact it's been shown that protein supplements are fully utilized by the body's cells within 45 minutes of drinking a shake. We're getting the full benefit of this form of protein... 100%. Protein from food is also well used by the body but it's got a lot more processing to go through before the body can use the nutrients. Remember, we need to chew the protein-based food well, then when it hits the intestines it'll brush by the villi so the protein macronutrients can be grabbed as it passes, then the body can use the protein it absorbs. But remember that we've got a shorter intestine and less villi in the first couple years so we'll be malabsorbing a certain percentage of the protein from food we eat (and no, there is no known percentage of malabsorption, it's different for each person and it's different from one month to the next as the body adapts). Also consider the thermic effect of protein usage from food. Basically that means that the body uses up energy (calories) to extract the new energy (calories) from food for new uses. We burn calories to use calories. Studies show that the thermic effect may account for up to 25% of the calories we eat. (i.e.: eat 100 calories and we burn 25 calories while abssorbing those 100 - not an exact number but just an example of how the math might work). 

SOOO... what does that mean for protein? It means that right after surgery when our body needs the most protein to heal the wounds of surgery and build new cells... we need to give it the highest quality protein we can for the best possible chance of healing and cell regeneration. Therefore, protein shakes are a good thing.

We're getting to the end... promise.

Ok, drinking after meals. As we just learned there is no absorption of nutrients happening in the stomach, so that's not the reason we want food to be in the pouch for as long as possible. The whole purpose of WLS is for us to feel full on less food. And the only way to feel full is if our tummies are actually full. Most surgeons recommend waiting 30 minutes after a meal to drink again ... but the further out you get and when hunger returns you'll want to wait longer. I wait 60-90 minutes. And we know that when we add liquid to our meals that the food becomes a sloshy mess and just flows straight through the pouch. (Watch this video, it's enlightening.) So we want food to stay in the pouch for a while, not just for the full factor but also for that little bit of churning we get to aid in digestion. Remember that there are enzymes in our saliva that aid in the breakdown of food in the pouch, so letting food and enzymes live together for a while helps with digestion too.

The other big issue is that when we drink with our meals or too soon afterward we are forcing food through the stoma before it's ready. (Stoma = opening between pouch and intestines that is normally the size around as a lady's index finger.) Abusing the stoma over time can cause it to stretch. A stretched stoma is a very bad thing. In fact, it's much worse than a stretched pouch because if your stoma becomes wide open and the same size as the pouch - you've basically created a 20' stomach to pack food into. Sometimes a stretched stoma is no fault of the patient and is a result of mechanical failure. But often it's a result of drinking with meals. I've got an essay on my blog that explains this in deeper detail.

Ok. Is that enough information to make your head spin?

~Pam