Gut microbiota is heavily influenced by the  environment - geography, medication use, stress and most importantly, diet, influences the gut microbiome. Diet has a greater impact than the human genome! For example, the gut can change its microbiota within 24 hours of eating a high fat/high sugar diet; and it takes one year for the gut to repair itself after one course of antibiotics.

Pregnancy, the gut, diet and epigenetic changes
There is clear evidence that expecting mothers who experience a viral or bacterial infection have an increased risk of their offspring developing autism or schizophrenia.  Probiotic use during pregnancy can minimise this risk by helping to keep the gut microbiota healthy.

Expecting mothers with an unhealthy diet are more likely to have offspring with increased externalising behaviours and poor cognitive function. Research suggests that unhealthy diets during pregnancy alters methylation and gene expression of dopaminergic and opioid genes, which leads to increased anxiety in females and aggression in males. A diet high in fat up-regulates inflammatory genes which increases oxidative stress and mitochondrial dysfunction.

The gut and brain interaction
The gut and brain interact with each other via the vagal nerve. In studies of germ-free mice (no gut microbiota), stress response and stress hormones were increased, and levels of neurotransmitters (such as serotonin and noradrenaline) were altered. Research has shown that probiotic use reverses these anxiety-like behaviours. Fermented milk products with a probioitc can modulate brain activity, with lactobacillus rhamnos shown to decrease anxiety and depression.

Studies indicate that within four months of a high fat/sugar diet, free radicals increase and neurological function within the hippocampus decreases. This causes cognitive defects and decreased performance with attention and speed of information retrieval. Adults with a healthy diet have a larger hippocampus and better memory. These declines are apparent after only one week of poor diet!

A poor diet can also lead to a 'leaky gut', whereby tight junctions within the gut do not work properly causing bacteria and toxins to enter the bloodstream. This leads to systemic inflammation and a myriad of health complications, including depression.

To decrease inflammation and thus improve the gut and brain interaction, and to prevent unwanted epigenetic changes (poor diet/lifestyle factors affecting offspring), researchers suggest to: