The findings come from new animal data, which backs up previous suggestions that probiotic bacteria could play a role in the managing or preventing depression via the gut0brain axis.
Writing in Brain, Behavior, and Immunity, the team found that rats fed lactic acid bacteria alongside a fatty and fibreless diet remained neutral in their behaviours while those fed the fatty diet without the probiotic developed behaviours similar to depression.
Led by Dr Anders Abildgaard at Aarhus University the team said that in simple terms, the probiotics offset the consequences of the unhealthy diet.
“Specifically in this study, the rats offset the consequences of the fatty diet with the help of probiotics, so that they were on a par with their peers in the control group,” said Abildgaard. “This is a fascinating discovery which supports the conclusion that probiotics, which normally do good in the intestines, also affect the brain.”
“That makes the result interesting for the treatment of depression," he added.
The researchers noted that rats not fed probiotics were found to have an increased number of white blood cells in their brain tissues, which can be a sign of chronic inflammation and is also seen in the fatty tissues and liver of people who are overweight and in diabetics.
But they did not find elevated white blood cells in the brains of the rats with probiotics in their drinking water.
"This may indicate that one of the things the probiotics do is work to reprogram the immune system,” said Abildgaard.
Rats in the study were divided into four groups and fed on different compound feeds and diets. Two groups of rats were fed an extra fatty and fiberless diet – with one of the two groups also fed water with the probiotics. A further two control groups were fed with a higher fibre and less fatty diet – again one group was fed water with a probiotic alongside the control diet.
After twelve weeks, the found that the rats on the fatty compound feed without probiotics behaved more depressively when they were given a swimming test.
The Danish team noted that white blood cells in the brain – in the form of cerebral T lymphocyte CD4/8 ratios – closely mirrored the behavioural changes, while the proportions of Treg and Th17 subsets were unaltered.
The authors concluded that depression may have a metabolic component – and that this responds to probiotics.
AS such, they suggest the finding has wide implications due to the high occurrence of metabolic conditions alongside depression.
Indeed, Abildgaard things it is possible to imagine some of the people who suffer from depression benefiting from probiotics.
"There is an increasing amount of research which suggests that an unhealthy diet contributes towards triggering or maintaining a depression,” he commented. “We also know that patients suffering from depression generally live in a more unhealthy way compared to the average, probably because they do not have the necessary resources to lead a healthy lifestyle.”
“Though probiotics do not make food healthier and do not affect weight or blood sugar levels in the laboratory animals, probiotics can nevertheless help to lessen the depressive symptoms and give patients the resources to change their lifestyle, so the vicious circle is broken.”
Source: Brain, Behavior, and Immunity
Volume 65, Pages 33-42, doi: 10.1016/j.bbi.2017.04.017
“Probiotic treatment protects against the pro-depressant-like effect of high-fat diet in Flinders Sensitive Line rats”
Authors: Anders Abildgaard, et al