The mammalian gastrointestinal tract contains considerable neuronal tissue and is capable of releasing many of the same hormones and neurotransmitters found in the brain. Recent research suggests that there may be bidirectional communication between the gut tissue and the central nervous system. This brain-gut-microflora axis has been suggested to allow direct communication between the colonic bacteria and the enterocytes of the gut through the two way release of signal molecules and hormones. The result is that major physiological changes can be affected by altering the microflora, through manipulation of their environmental conditions. Prebiotic supplements, for example. Have been shown to be able to increase the numbers of beneficial bacteria, decrease production of cytokines such as interleukin 6 (IL-6) and increase natural killer cell activity. Prebiotic supplementation has also proven effective at reducing the duration and severity of cold and flu and to improve stress induced gastrointestinal dysfunction.
For example, researchers1 used a randomised, double blind study design to investigate the effects of 0, 2 or 5g of galactooligosaccharides on levels of stress and cold and flu symptom intensity in university students over 8 weeks. Analysis showed that stress was positively associated with diarrhoea, indigestion, reflux symptoms and abdominal pain, as well as average daily cold or flu symptom severity and number of days with a cold or flu. However, following galactosaccharide supplementation scores for diarrhoea, constipation, abdominal pain and indigestion were lower. The oligosaccharide supplements were also associated with lower intensity of cold and flu symptoms. Interestingly the beneficial effects of the oligosaccharides on stress were related to body mass index of the individual. For example, a 40% reduction in the probability of having a sick day with 5g of galactooligosaccharides occurred in normal weight but not over-weight or obese subjects.
This study suggests that galactooligosaccharide supplements are effective in reducing gastrointestinal discomfort, at reducing stress and decreasing the severity of cold and flu symptoms. Interestingly, the 2.5g dose was more effective at reducing abdominal pain, and indigestion compared to the 5g dose, and this may related to greater gas production with the higher dose. Therefore, for gastrointestinal symptoms of stress, a ‘U’-shaped benefit curve may be associated with galactooligosaccharide use. Low intakes produce negligible benefits, intakes up to ≈2.5 g produce optimal effects, but at higher doses the gas production negates any advantage to supplementation. The general benefits from prebiotic supplements such as galactooligosaccharides may result from modulation of the immune system. However, galactooligosaccharides have also been shown to increase population numbers of bifidobacteria and lactobacilli and increase short-chain fatty acid synthesis, which may decrease epithelial permeability.
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