A regular weekend indulgence of a pub schnitzel and chips could affect your memory and undo the good work of eating well, a new study has found.

Cycling between eating clean and cheating occasionally with junk food could impact on your spatial memory and do damage to the gut microbiome, causing people to gain weight, according to UNSW research published in Molecular Nutrition and Food Research.

During the study, adult male rats were given a healthy diet of rat food, while some were given a "cafeteria diet" of a highly processed and sugary foods.

Some of the rats were given unhealthy foods for shorter or longer binges.

Rats on unhealthy diets performed more poorly in "spatial memory" tests, requiring them to recall where objects had been placed.

The results became worse the more days in a row the rats had eaten the unhealthy food, or had longer binges of junk food, researchers said.

Poor diet also led to negative changes in their gut microbiome, boosting the levels of bad bacteria associated with obesity and increasing those linked with an ability to control your weight.

It is possible a number of factors may have caused the change in diet to have affected the rats' memories, including their gut microbiome, study researchers Mike Kendig and Margaret Morris say.

"We know the gut is very connected to our brain. Changes to the microbiome in response to our diet might impact our brain and behaviour," Dr Morris said.

Eating an unhealthy diet could lead to additional inflammation in the body, affecting brain function, she said.

The study builds on previous research which associated high fat, high sugar diets with poorer cognition, in rats and humans.