A high-fat diet could increase risk of mental illness even in the absence of obesity by driving changes in gut bacteria, say researchers.
While previous studies have suggested that mental illness, particularly depression and dementia, could increase in conjunction with obesity, the research published in Biological Psychiatry said that a high-fat diet could alter behaviour and produce signs of brain inflammation. This in turn, could increase the risk for depression and other psychiatric disorders, irrespective of obesity.
The study led by Dr Annadora Bruce-Keller said that the findings represented the first demonstration that high-fat diet-induced changes to the gut bacteria were sufficient to disrupt brain physiology and function.
Thus, conversely, the authors added that the data emphasised that the therapeutic manipulation of the gut bacteria could “dramatically mitigate the prevalence and severity of neuropsychiatric disorders”.
Clinical studies could therefore use the gut-brain axis as a target for future therapeutic intervention to reverse the effect, they added.
Fatty foods and brain inflammation
To reach the conclusion, the team of researchers tested whether obesity-related gut bacteria altered behaviour and cognition even in the absence of obesity using a mouse model.
Non-obese adult mice were conventionally housed and maintained on a normal diet, but received a transplant of gut bacteria from donor mice that had been fed either a high-fat diet (HFD) or control diet (CD).
The recipient mice were then evaluated for changes in behaviour and cognition. The animals who received the bacteria shaped by a high-fat diet showed increased anxiety, impaired memory, and repetitive behaviours, the study said. Signs of inflammation in the brain were also evident and may have contributed to the behavioural changes, it added.
Explaining the results, the authors said previous studies reported a shift in the balance of gut bacteria populations, particularly in Bacteroidetes and Firmicutes, suggesting that the balance between these two phyla might reflect the balance of unhealthy and healthy microbiota.
However, the new data showed that changes within the Firmicutes group rather than a change from Bacteroidetes to Firmicutes drove the changes.
It added that the overall data were in agreement with other research that described the sensitivity of the brain to diet-induced obesity and the growing number of studies linking gut bacteria to central nervous system health and behaviour.
“Conversely, recent studies link probiotics to positive changes in mood and behaviour,” it added.
Source: Biological Psychiatry
Vol: 77 doi: 10.1016/j.biopsych.2015.02.019
‘Obese-type Gut Microbiota Induce Neurobehavioral Changes in the Absence of Obesity’
Authors: A. J. Bruce-Keller, et al