Mice fed fast food diet suffer ‘scary’ loss of synapses in the brain

A study published in the journal Brain, Behavior, and Immunity provides some of the first evidence that a fast food diet is bad for the brain — in test mice, at least.

The neuroscientists from the Medical College of Georgia found that a fast food-equivalent diet causes immune cells in the brains to damage the connections between neurons.

Tests carried out demonstrated that going on a low-fat diet for two months was enough to reverse the cognitive decline.

Dr Alexis Stranahan, the study’s corresponding author, said: ‘Microglia eating synapses is contributing to synapse loss and cognitive impairment in obesity. On the one hand, that is very scary, but it’s also reversible, meaning that if you go back on a low-fat diet that does not even completely wipe out the adiposity, you can completely reverse these cellular processes in the brain and maintain cognition.”

The researchers fed two groups of mice in a way that is roughly equivalent, in terms of fat content, to a healthy diet compared with a fast-food diet in humans. That is, one group gained 60 per cent of its calories from saturated fat, while for the healthy-eating mice this was 10 per cent.

Various tests revealed that cognitive function was essentially the same at four weeks, but by 12 weeks the fat-eating mice were obese and showing signs of cognitive decline.

‘When you get out to 12 weeks, you start seeing great increases in peripheral obesity. While you don’t see insulin resistance, you also start seeing loss of synapses and increases in inflammatory cytokines in the brain,’ Stranahan said.

The researchers say their observations have shown that having too much fat in the body produces chronic inflammation, which stimulates microglia (which make up between 10 and 15 per cent of cells in the brain) to have an autoimmune response.

Stranahan said: ‘Normally in the brain, microglia are constantly moving around. They are always moving around their little fingers and processes. What happens in obesity is they stop moving. They draw in all their processes; they basically just sit there and start eating synapses. When microglia start eating synapses, the mice don’t learn as effectively.’

The study’s authors say that their findings may have revealed potential new purposes for existing drugs used for conditions such as rheumatoid arthritis and Crohn’s disease.