What types of bacteria are essential for the human diet?

There are over 1000 different micro-organisms in the human bowel  all going about their own fight for survival and contributing in  different wells to our health, well being and sometimes disease. Most of  these organism have not been sufficiently studied and their role is  uncertain. But there is an increasing amount of data available for  certain types of bacteria which seem to have some beneficial effects on  our gut health, our immune system, on nutrition and even our  psychological state. These include ..........   Diet  can drastically change the composition of the gut microorganisms that  live within us. If you have a diet with fruit, vegetables and fibre then  a good proportion of this will be indigestible by ourselves but can be  broken down (or fermented) by the bacterial in our large bowel. We can  get between 10-20% of our nutrition this way and it can help to keep our  systems happy and healthy. However, a low fibre diet can starve the  bacteria of the nutrients they need which can lead to symptoms such as  constipation. Conversely, if the bacteria in the large bowel are too  effective in fermenting the undigested food then they can cause symptoms  of bloating and loose bowel movements. As with most health issues, the  first challenge is to see what’s right for you, what type of person you  are (loose bowel movements, tend towards constipation etc) and then try  and logically plan a  diet which would either increase fibre and  fermentable foods in your diet (constipation type patients) or reduce  them (bloating and alternating bowel habit). Recent research with  concepts such as the FODMAP diet have shown how effective these  interventions can be if the right patients are selected.   The  human-bacterial interface has evolved over millions of years and yet is  a relatively undiscovered country for researchers. The exciting thing  for me is that these are things that we can control ourselves to a great  extent often without the need for medical interventions. If tests are  needed then simple and minimally invasive procedures such as a hydrogen  breath test can put you on the right track.

None, humans can eat completely sterilized food and survive.  It is hypothesized that babies do need to colonize their stomachs with bacteria at some point, but knowing babies that will happen inevitably (they slobber all over all sorts of bacteria covered stuff). The bacteria that we have in our digestive system survives between meals, so we don't have to eat bacteria every meal.