Eating junk food may shrink the part of your brain involved in learning, memory and mental health, a new study has claimed.
Older adults who eat more unhealthy foods, such as sweet drinks, salty snacks and processed meats, have smaller left hippocampi, researchers said.
The study also shows that older people with healthier diets have larger hippocampi, a region of the brain used for learning, memory and mental health.
As the negative impact of unhealthy foods on the waistline of the population grows, so does the evidence suggesting that our brain health is also affected, said lead author Felice Jacka, associate professor at the Deakin University in Australia.
"We've known for some time that components of diet, both healthy and unhealthy, have a rapid impact on aspects of the brain that affect hippocampal size and function, but up until now these studies have only been done in rats and mice," Jacka said.
"This is the first study to show that this also appears to be the case for humans," Jacka said.
The researchers used magnetic resonance imaging to measure the size of hippocampi in adults aged 60-64 years, participating in a large longitudinal study of ageing conducted at the Australian National University (ANU).
They also measured the participants' regular diets and took into account a range of other factors that could affect the hippocampus.
The study suggests that older adults who eat more unhealthy foods, such as sweet drinks, salty snacks and processed meats, have smaller left hippocampi.
It also shows that older adults who eat more nutrient-rich foods, such as vegetables, fruits and fish, have larger left hippocampi.
These relationships existed over and above other factors that may explain these associations, such as gender, levels of physical activity, smoking, education or depression itself.
These findings have relevance for both dementia and mental health, Jacka said.
"Mental disorders account for the leading cause of disability worldwide, while rates of dementia are increasing as the population ages," she said.
"This latest study sheds light on at least one of the pathways by which eating an unhealthy diet may influence the risk for dementia, cognitive decline and mental disorders such as depression and anxiety in older people," Jacka said.
"As the hippocampus is critical to learning and memory throughout life, as well as being a key part of the brain involved in mental health, this study underscores the importance of good nutrition for children, adolescents and adults of all ages," she said.
The study was published in the journal BMC Medicine.