It is generally known that healthy gut bacteria is great for weight loss, weight control and a healthy body. But fewer people know that specific food are required by healthy gut bacteria.
Gut bacteria (Probiotics) need specific non digestible food called Prebiotics. 
Prebiotics are in essence fiber rich foods that you do not digest but is digested by your healthy gut bacteria (food for your bacteria)
Much of the natural Probiotics (good bacteria) you may eat daily, are likely killed by stomach acid and digestive processes before reaching your gut. Certain types of natural Probiotics have protection, for example the Natural probiotics in yogurt uses the fat in yogurt to survive the digestive process without being killed. Prebiotics as essentially all non digestible fiber rich foods that promote growth of beneficial microorganisms (gut bacteria and fungi) 
a Healthy diet should include at least 5g of Prebiotics, daily.
Prebiotic rich foods:
- Bananas & Other fiber rich fruits
- Fiber rich veggies, nuts or beans
Read more about Probiotics:
 http://articles.mercola.com/sites/articles/archive/2013/04/10/gut-bacteria.aspx // http://articles.mercola.com/sites/articles/archive/2013/04/10/gut-bacteria.aspx