A long-term high-fat diet often results in obesity, which in turn builds up insulin resistance. It can also cause cognitive decline and microglial hyperactivity.
While probiotic and prebiotic intake have been shown to lower obese-insulin resistance by modifying gut microbiota, their impact — along with that of synbiotics — on cognitive function and microglial activity in obese-insulin resistant individuals have yet to be studied.
Researchers at Chiang Mai University sought to determine the effect of a probiotic (Lactobacillus paracasei HII01), prebiotic (Xyloolidosaccharide), or synbiotics on male obese-insulin resistant rats on a high-fat diet.
They fed male rats either a normal diet or high-fat diet for 12 weeks. In the 13th week, they divided the rats in both groups randomly into four subgroups: a control group, prebiotic group, probiotic group, and synbiotic group.
The rats remained on their respective diets for another 12 weeks, after which the cognitive function of each rat was assessed, using blood and brain samples respectively to measure metabolic parameters and examine brain pathology.
What's good for the gut is good for the…brain?
The researchers observed that in the treatment groups, gut and systemic inflammation and impaired peripheral insulin sensitivity caused by chronic high-fat diet intake were all alleviated.
The mice on a high-fat diet also displayed enhanced hippocampal plasticity and diminished brain mitochondrial dysfunction.
In addition, the rats on a high-fat diet in the treatment groups exhibited "significantly decreased" hippocampal oxidative stress and apoptosis, which in turn lowered microglial activation and resulted in restored cognitive function.
Less gut inflammation, more brain health
The researchers wrote that obese-insulin resistance brought on by a long-term high-fat diet leads to gut and systemic inflammation, peripheral insulin resistance, brain mitochondrial dysfunction, hippocampal apoptosis, dysplasticity and oxidative stress, and microglial morphological changes, all of which result in cognitive decline.
They added that the results of the study pointed to how the consumption of probiotics, prebiotics and synbiotics could restore cognitive function in obese-insulin resistant subjects via the gut-brain axis, "leading to improved hippocampal plasticity, brain mitochondrial function, and decreased microglial activation".
In conclusion, they wrote: "This is the first report to show the possible link between gut microbiota modification by prebiotics, probiotics, or synbiotics, and the improvement of cognitive function in obese-insulin resistant rats.
"These neuroprotective effects may possibly be mediated through the attenuation of inflammation, hippocampal oxidative stress, hippocampal apoptosis, mitochondrial dysfunction as well as microglial dysfunction."
Source: Journal of Neuroinflammation
https://doi.org/10.1186/s12974-018-1055-2
"Decreased microglial activation through gut-brain axis by prebiotics, probiotics, or synbiotics effectively restored cognitive function in obese-insulin resistant rats"
Authors: Titikorn Chunchai, et al.