Nope, if you are healthy (as per official medical standards) your stomach and small intestine should be sterile. Digestion and absorption happens mostly there and bacteria not only don't play a positive role but if you have it in small intestine or stomach then it's pathogenic (i.e. SIBO, ulcers, etc). Bacteria should be only in the colon, and when food reaches the colon ideally it should be digested as close to 100% as possible and expelled as quickly as possible to prevent the bacteria in the colon form digesting whatever leftovers there are from the food and making endotoxin. So from Peat's point of view, healthy means all three portions of the digestive tract should be sterile as opposed to official medical guidelines of having only the first two clean.
The colon bacteria can do some good for things like turning vitamin K1 into vitamin K2 or producing SCFA like butyrate. However, butyrate is actually pro-serotonergic as the study in my original post shows so even though it inhibits cancer it is actually irritating to the stomach as are the SCFA acetate and proprionate. Peat says the same thing in one of his recent interviews. He said butyrate is probably effective for cancer and many people are selling it for that purpose, but it is pro-inflammatory for the gut. Btw, it is fairly common knowledge that giving butyrate to dogs and cats with cancer effectively allows them to live disease free and die from other cause (aging). Just Google around for butyrate and cancer in pets. Why this is not hailed around the world as a breakthrough in cancer therapy is beyound me...