Any bacteria can overgrow, but with a good balance they are generally kept in check – so for those with relatively healthy microflora in their body bifidum may not be too bad (though some research indicates that when bifidum persists beyond childhood it can be a marker for certain cancers APPLIED AND ENVIRONMENTAL MICROBIOLOGY, Sept. 1995, p. 3202-3207 Vol. 61, No. 9 from http://www.breakingtheviciouscycle.info/knowledge_base/kb/bifidus.htm )
However, with SCD microbes are starved out. Bifidum bacteria seem to take advantage of this unique situation and the bacteria which normally is a good bacteria tends to overgrow. And when there is overgrowth of any bacteria their metabolites can cause problems.
Unfortunately there is no research on this specific aspect of bifidum bacteria because it seems to pertain only to SCDers.
Perhaps it is because the SCD clears out the harmful microbes and bifidum takes over, overgrowing into huge numbers. The by-products of bifidum bacteria could be what sends people into flares – especially those who have sensitive guts or those at the beginning of the diet, these people unfortunately have “fertile ground” for bifidum bacteriato overgrowth.”