The gastrointestinal (GI) microbiota (bacteria), or probiotics as they are more commonly known, are the collection of microbes that live in our gut. They are essential for digestion and healthy metabolism as well as playing a crucial role in the development of our immune system. Our probiotics function as a major immunological organ and along with the gastrointestinal tract constitute about seventy percent of the immune system.
If probiotic balance is disrupted, termed dysbiosis; harmful inflammation, autoimmunity and altered immune function occurs along with an increased risk of disease. In this state, the intestinal tract is particularly vulnerable to chronic conditions such as ulcerative colitis, Crohn’s disease, coeliac disease, and irritable bowel syndrome. Studies have also found links to systemic conditions such as obesity, type 1 and type 2 diabetes and many more highlighting the growing importance of GI microbiota to human health.
The traditional belief was that the composition of GI microbiota was relatively stable from early childhood. However, overwhelming new evidence shows that diet, environmental, and lifestyle factors such as stress can induce dysbiosis in GI microbiota. This was shown in studies on mice where diet was found to account for 57% of structural deviation in GI microbiota, with genetic difference only accounting for 12%.
These findings further highlight the dominating role of diet in shaping GI microbiota. For example, the “Western” diet has been shown to induce dysbiosis. Diets rich in high-fibre, complex carbohydrates (primarily from fibrous vegetables) show less growth of pathogenic species than diets higher in fat or protein. Refined sugars, on the other hand, mediate the overgrowth of opportunistic bacteria and mould species.
Best way to restore probiotic balance in the gut
Prebiotics are non-digestible food ingredients used as a second strategy that stimulate the growth and activity of the ‘friendly’ bacteria already in the gut. These have a more lasting effect than probiotics. A number of recent studies have shown a positive effect of prebiotic supplementation on immune health including: a reduced allergic response, prevention of respiratory disease and decreased frequency of diarrhoea, particularly in children. In fact researchers have found that breast milk naturally contains prebiotics, believed to stimulate bifidobacteria – so-called ‘friendly’ bacteria that help release energy and nutrients from food.
The potential beneficial mechanism of prebiotics to a developing immune system is the ability to remediate an imbalance between T helper type 1 and 2 cells. It is this imbalance that is thought to cause allergic diseases. T helper cells type 2 are associated with allergic diseases, and it is the T cells which then instruct the B cells to manufacture antibodies and develop an allergic reaction.
In humans, a number of randomised controlled trials have shown a preventative effect of prebiotic feeding on the development and severity of allergic disease and food hypersensitivity. Atopic dermatitis is usually the first manifestation of allergy during early infancy. Infants with early onset allergic disease are also at risk of other variations of allergic disease, described as the allergic march. In a study on infants in the first six months of life, 9.3% of the prebiotic group had atopic dermatitis compared to 23.1% of the placebo group. Similarly, a Meta-analysis of four studies investigating susceptible children found a reduction eczema of approximately 38% in the prebiotic group. They also reported a significant reduction in asthma and eczema from prebiotic supplementation in infants who were not a high allergy risk.
A number of studies have also shown that prebiotics can enhance immune responses to protect against infections. They have been shown to prevent intestinal infections, particularly for pathogens that affect the large bowel as well as reduce infections in infants, including fewer upper respiratory tract infections and fewer infections that required treatment with antibiotics. The incidence of any recurring infection was reduced by 9.6%, while the incidence of recurring respiratory infection was cut by 6.7% infections during the first six months of life.
The researchers reported the immune modulating effect of the prebiotic mixture was most likely via modification of intestinal microflora. In two animal studies mice fed prebiotics and then challenged with toxic chemicals, tumor cells and Candida albicans, or were infected systemically with Listeria or Salmonella all showed lower rates of infection and disease. In the first study they had around 50% lower rates of pre-cancerous cells and had 50% lower densities of Candida in the small intestine. None of the prebiotic mice died in the trial while nearly 30% of the mice in the control group died. In the second study more than 80% for control mice died after being infected with Salmonella, but only 60% of the prebiotic fed mice died.
Based on this and dozens of other studies the research overwhelmingly shows prebiotics have a powerful effect on developing and controlling our immune system.