Balrogs and Disaccharides

Last February I lectured about SIBO at grand rounds at my alma mater NCNM.  I was pleased to see that the student evaluations were very positive considering the over-worked and under-slept state of the student body.  Apparently it had more to do with my Lord of the Rings example for disaccharide absorption then anything else!  Excellent- I’ll be keeping that in my future presentations. 

So here are some basics about digestion, disaccharides and Balrogs.

Digestion

Digestion is the the breaking down of food into it's smallest possible elements so that it may be absorbed.     
    Fats are broken down into fatty acids and glycerol   
    Protein is broken down into single amino acids   
    Carbohydrates are broken down into single sugars

Enzymes

Chewing physically breaks apart food and then enzymes do the rest.  Enzymes are in small amounts in the mouth and stomach, but mostly work in the small intestine (SI).  Enzymes usually have the suffix ase (exceptions: pepsin, trypsin, chymotrypsin).  They are secreted from the pancreas and embedded in the brush border, or lining, of the SI.

Pancreatic enzymes get all the press and we often forget about the brush border enzymes- peptidases and disaccharidases.
    Peptidases break petides (very small proteins) into single amino acids
    Disaccharidases break double sugars (disaccharides) into single sugars

Absorption

Very small molecules are all that can be absorbed across the brush border.  They absorb into and then pass out of a single layer of cells, called enterocytes, into the blood vessel underneath.

What can and can’t pass?
                    Amino acids (single proteins) pass the brush border
                    Di & Tri Peptides (very small proteins) pass the brush border
                    Single sugars pass the brush border
                    Disaccharides can’t pass brush border
                            (they need disaccharide enzyme digestion first) 

Problem

The problem in SIBO is that disaccharide enzymes are damaged and can't do their job.  Then the disaccharide sugars, such as lactose (milk sugar), sucrose (table sugar) and isomaltose (starch), sit unabsorbed.  This makes a perfect meal for the overgrown bacteria, who then rudely expel gas and acids into our SI, leading to all sorts of havoc such as bloating, constipation, diarrhea and brain symptoms.

Balrog

To illustrate, here's a picture of the “You Shall Not Pass” scene from the first Lord of the Rings movie (one of my favorite scenes).  Here, the heroes have already crossed the bridge but Gandalf stays to fight off the fiery Balrog that’s been chasing them.

The bridge is the brush border, Gandalf is the disaccharide enzyme and the Balrog is the disaccharide sugar.

Gandalf (enzyme) will not allow the Balrog (disaccharide) to pass as is (across the brush border).  It must be transformed first (obviously, who wants that coming across).  For our body, it's just too big and must be broken into smaller pieces. 

This is why the diets that treat SIBO avoid all but the single sugars (honey and ripe fruit) which can pass the brush border freely.

Conclusion

In the case of SIBO, disaccharides are like a Balrog.


For more on how disaccharides are problematic in SIBO, see The Gut/Brain/Food Connection, and/or Breaking the Vicious Cycle, both by Elaine Gottschall.