As far as I can see, the basic rationale for the
paleo diet (stone-age diet), the
specific carbohydrate diet (SCD), the
GAPS diet and the
FODMAP diet is essentially the same: these diets are all designed to
stop partially digested carbohydrates reaching the colon, where they can feed bad bacteria.
The idea in all these diets is that you only eat carbohydrates which can be instantly absorbed without needing any prior digestion via digestive enzymes: because these instantly assimilated carbohydrates get completely absorbed into the bloodstream as they pass along the small intestine, they will never reach the colon, so there is no chance that they will feed pathogenic bacteria in the colon.
That then narrows your carbohydrate eating choices down to glucose and fructose (the sugar found in fruit), because these are immediately absorbed in the small intestine. Other carbohydrates like sucrose, lactose, maltose (the disaccharides), as well as complex carbohydrates (polysaccharides) like grains, potatoes, rice and maize must first be broken down by digestive enzymes before they can be absorbed, and that is why there is a risk these carbohydrates can pass only partially digested into the colon, where they feed bad bacteria, and that in turn may worsen autoimmunity and other diseases (so the theory goes).
Normally there are no bacteria at all in the small intestine (except in cases of SIBO), so there is no concern about the carbohydrates feeding bacteria in the small intestine; the only concern is if undigested carbohydrates reach the colon.
So that appears to be the essence of all these diets. The paleo diet is actually a little bit less strict on carbohydrate restrictions, but the specific carbohydrate diet, which is a diet devised in 1924 for medical purposes, tells you exactly which carbohydrates to avoid, in order not to feed the bad bacteria in the colon. So the idea is that after many months (or even years) on these diets, you will starve off any pathogenic bacteria in your colon (especially I would think if you also take prebiotics, which are defined as foods which feed the good bacteria, but which bad bacteria cannot make much use of).
I have just been looking into these diets in recent days, and posted some info in
this post.
Because I don't like the idea of giving up all my favorite carbohydrates foods like grains, potatoes, rice and maize, I have been trying to come up with a
shortcut method that would provide the same benefits as these diets, but without needing to do the diet!
I think a good shortcut approach could be to take high doses of supplemental
brush border enzymes and
pancreatic enzymes with every meal, which include the digestive enzymes responsible for breaking down disaccharide and polysaccharide carbohydrates in your food. That way, you can eat any carbohydrate you like, and hopefully these supplemental enzymes will ensure that the carbohydrates are fully digested and absorbed in your small intestine, so that no carbohydrates whatsoever reach your colon.
Not all digestive enzyme supplements contain the brush border enzymes that digest carbohydrate (namely the brush border enzymes: glucoamylase, maltase, isomaltase, sucrase and lactase), but there are several brands that do, along with the important pancreatic enzyme for carbohydrate digestion: amylase.
I am planning to try these brush border enzyme supplements, as an easy shortcut to the full paleo / SCD / GAPS / FODMAPS diet.