Healthy Gut Flora is one cornerstones of good health and wellbeing.

Before proceeding with the relationship of gut flora to health and disease, one should know what gut flora is. The essential meaning of gut flora is the same as the flora and fauna of the environment but in medical and scientific terms it doesn’t mean plants but the various bacteria which normally reside small and large intestine. These are the permanent residents of the intestine and are not involved in pathogenesis (that is they do not cause diseases) but if somehow they get systemic entry then they can cause sepsis (generalized infection of the al body organs).
The part of the gut which contains majority of gut flora is the caecum at the site of right iliac fossa. The small intestine contains fewer microbes than large intestine because it has comparatively low pH which makes it a bit unfertile for microbes. The gut contains approximately 750 trillion bacteria. Following organisms are the important members of the gut flora; Pseudomonas, coliforms such as E.coli, Lactobacillus species, Enterococcus faecalis, clostridium species, candida albicans, Fimicutes, bifidobacterium and bacteroides species. The human gut flora has important function in the normal physiology of the digestive tract.
1. It prevents pathogens from harboring in the gut hence prevent their colonization and infections. This is referred as colonization resistance and the mechanism is competition between microbes for nutrients necessary for their survival. In the absence of gut flora, many pathogens overgrow in the gut especially those which get attached to gut wall and sequentially get entry into the blood stream.
2. Gut flora controls the proliferation and differentiation of epithelial cells.
3. Gut flora causes fermentation of carbohydrates mainly polysaccharides. In herbivore animals it is responsible for break-down of starch. This role is important in lactose intolerant individuals as the body itself is incapable of metabolizing lactose while gut flora metabolizes it partially.
4. They are capable of synthesizing vitamin B and vitamin k which they provide to the human host. This nutritional function is quite important since human beings largely depend on the gut flora for the synthesis of vitamin K.
5. It also protects body from inflammatory bowel syndrome and autism.
6.  Gut flora also prevents some allergic reactions since it control the immune response to certain antigens and their absence can cause hypersensitive immune responses. This is believed to be due to cytokines modulation.
7. They cause the lymphoid tissue near the gut to grow hence giving a boost to the immune system.
They have certain disadvantages as well 
1. They are capable of causing disease in the host when immunity is quite low such as in immuno-compromised or AIDs patients. But these microbes cause diseases in areas other than the anatomic locations in which they normally reside.  
2. Even in uncompromised patients E.coli is the leading cause of urinary tract infections and Bacteroides fragilis causes peritonitis following trauma to the gut. That is why gut is sterilized before gastrointestinal surgeries by oral administration of neomycin so as to minimize the risk of systemic infections. The gut flora is usually reduced and returns to normal soon after the operation.
3. Certain members of gut flora are believed to increase the formation of tumors such as bacteroides and closridium while lactobacillus is believed to decrease the tumor growth rate.
The relationship of gut flora with antibiotics is also quite interesting. The growth of the gut flora is inhibited by antibiotics. Those organisms which are resistant to antibiotics can cause superinfection e.g clostridiun difficile which cause pseudomembranous colitis is resistant to most antibiotics and can cause super-infection when growth of gut flora is inhibited by some antibiotic. When mal-nourished people take antibiotics such as clindamycin to treat some infection they may be at risk of vitamins deficiencies. The antibiotics which inhibit gut flora disrupt the microbes and hence stop the synthesis of vitamins.
Another interesting relationship exists between the gut flora and obesity. A research study indicated that the balance between Fimicutes and bacteroides species can cause a person to become obese or lean with or without the genetic predisposition even when they are taking the same type of diet. Bacteroides species are found to be present in a decreased proportion in obese and in high proportion in lean people. Higher the level of bacteroides species higher is the ability of the body to oxidize fat and lower body weight. 
It is also established that lean people have diverse gut flora as compared to obese people. Gut flora inhibiting antibiotics when taken orally are associated with obesity. So a microbial theory of weight suggests that the quality and quantity of gut flora can change the phenotypic presentation of humans by altering the accumulation of the lipids.
It is speculated that autism which is a mental condition causing anti-social behavior is associated with poor or imbalanced gut flora. These children frequently suffer from gut problems and a study showed that they have higher incidence of clostridium species than the normal children. Hence the antibiotics which inhibit gut flora such as vancomycin has shown to possess slight efficacy against autism when used on short term basis. Abnormal gut flora has shown to be a cause of D-Lactic acidosis and oral therapy with vancomycin has been effective to control metabolic acidosis in patients gone through bowel resection. A healthy gut flora is the key to prevent various medical issues as well as obesity which is a predisposing risk factor to diseases associated with high mortality incidence. Diarrhea and constipation, though minor problems are also associated with the health of the gut flora. Due to this importance of gut flora in medicine, sometimes it is also considered a protective and separate organ.
The healthy gut flora diet consists of vegetarian diet which contains fibers. If the gut flora is deficient or imbalanced then pro-biotics are used which means “for life”. Probiotics are live bacteria which are believed to be beneficial to the host. These supplements can restore the normal gut flora and hence are used in diarrhea associated with antibiotics, colon cancer growth(which can be decreased by lactobacillus species and bifidobacterium), lactose intolerance, helicopylori infections which cause ulcers, inflammatory bowel disease, irritable bowel syndrome which is an autoimmune disorder and in various other inflammatory and allergic reaction associated with the gut. High lactose diet is also restricted in people with congenitally imbalanced gut flora, though this is still controversial. Those who get develop gut flora imbalance after some antibiotic therapy are encouraged to eat yogurt since it increases the growth rate of lactobacillus and bifidobacterium.
Gut flora complex is also a supplement which plays essential role in restoring gut flora or its maintenance. It promotes a healthy and fertile environment for the microflora of the gut so that a balanced growth may occur. It has a cleansing effect as well hence it cleans away the toxins normally present in food which can cause food poisoning. It is made of natural substances; herbs and essential oils including oregano essential oil (popular with the Italians), Anise (Aniseed) essential oil, Andrographis and Phellodendron.
These contain active compounds such as monoterpenes, gamma-terpenes, alkaloids (berbine which is an alkaloid of isoquinolone type), thymol and diterpenoid lactone. The normal formulation is enteric coated to provide resistance against stomach enzymes and consist of 10 mg of andrographolide and 36 mg of berberine .Its use has been contraindicated in pregnancy and lactation since the gut of the infants is sterilized and do not contain microflora. Normal healthy flora is associated with a healthy life so essential care should be taken to keep the gut flora healthy and flourishing. This is quite easy and just requires an adjustment of the diet but if not taken proper care, the consequences can be quite adverse.

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