12 January - 20 June 2016

Which diet is best for the ageing brain?

A mouse study published in the journal Frontiers in Molecular Neuroscience by researchers from the University of Groningen, Netherlands, suggests that a low fat diet with a restricted calorie intake may help protect the brain during age-associated decline.

A mouse study published in the journal Frontiers in Molecular Neuroscience by researchers from the University of Groningen, Netherlands, suggests that a low fat diet with a restricted calorie intake may help protect the brain during age-associated decline.

With an ageing population and obesity becoming ever more prominent, it is more important than ever to consider which diets are most beneficial to the ageing brain. Both ageing and obesity are linked to chronic low-grade inflammation that is associated with multi system diseases. In the current study, Eggen et al. monitored inflammation of the brain using different inflammatory genes as markers within microglia activity. Microglia act as the first form of active immune defense in the central nervous system (CNS) and are important for brain development, neural signaling, and homeostasis. Previous research however has found a link between ageing and parts of the brain becoming inflamed due to microglia activity, leaving questions around how this process responds to different diets.

Eggen et al. conducted the study by observing groups of 6-month-old and 2-year-old mice, studying the effects of a low-fat diet (LFD) with 6.5% total fat, and a high-fat diet (HFD) with 42% total fat, as well as comparing 2-year-old mice in restricted calorie LFD and HFD groups, who received 40% less calories. To explore the impact of varied lifestyle, a group of mice who had no opportunity to exercise were included in the study as well as a group of mice with constant access to a wheel. Eggen et al. compared the expression levels of genes that act as markers of immune response inflammation in the hypothalamus of the mice.

The study found that expression of phagocytic markers in the white matter microglia of the 2-year-old brain was dramatically decreased in calorie restricted LFD mice.  Phagoctyes are cells which protect the body by ingesting harmful particles, bacteria and dead or dying cells. Eggen et al. also found that the mice fed the HFD showed an increased number of microglia in the hypothalamus compared to the LFD mice of the same age and while they state that “the detrimental effect of HFD on the brain predominantly occurs in the hypothalamus” they also note that the expression of genes involved in pro-inflammatory signaling in the hypothalamus were not significantly different between the HFD and LFD mice. They also found no significant differences in inflammatory gene markers between the groups of mice that did and did not exercise, although the research into exercise and reducing age related diseases is heavily supported.

A noteworthy conclusion from the study is that inflammation in the hypothalamus promotes insulin and lepton resistance. Leptin is a satiety hormone secreted by fat tissue, essential for regulating body weight and a feeling of fullness when it enters the brain. Inflammation within the brain can prevent this pathway, thereby favouring an elevated body weight. A weakness within the study was that the mice maintained the same diet their whole lives, and so the effects of changes to a diet were not monitored.

In conclusion, Eggen et al.  reiterate that they found that a HFD increased the number of microglia in the hypothalamus and that a LFD caloric restriction prevented the increased expression of phagocytic markers in the older mice. They note that the protective effect of the caloric restriction was not seen in the HFD mice and so conclude that “dietary fat as well as caloric content may play an important role in the inflammatory process in brain ageing”

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